Research ArticleMillimeter-Wave Microstrip Antenna ArrayDesign and an Adaptive Algorithm for Future5G Wireless Communication Systems

Cheng-Nan Hu1 Dau-Chyrh Chang1 Chung-Hang Yu2

Tsai-Wen Hsaio2 and Der-Phone Lin2

1Communication Engineering Department OIT New Taipei City 22061 Taiwan2National Chung-Shan Institute of Science and Technology PO Box 90008 Longtan Taoyuan City Taiwan

Correspondence should be addressed to Cheng-Nan Hu fo011mailoitedutw

Received 9 September 2016 Accepted 14 November 2016

Academic Editor Atiqur Rahman

Copyright copy 2016 Cheng-Nan Hu et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

This paper presents a high gain millimeter-wave (mmW) low-temperature cofired ceramic (LTCC)microstrip antenna array with acompact simple and low-profile structure Incorporating minimummean square error (MMSE) adaptive algorithms with the pro-posed 64-elementmicrostrip antenna array the numerical investigation reveals substantial improvements in interference reductionA prototype is presented with a simple design for mass production As an experiment HFSS was used to simulate an antenna witha width of 1mm and a length of 123mm resonating at 38GHz Two identical mmWLTCCmicrostrip antenna arrays were built formeasurement and the center element was excited The results demonstrated a return loss better than 15 dB and a peak gain higherthan 65 dBi at frequencies of interest which verified the feasibility of the design concept

1 Introduction

The growing demands on data traffic are propelling the evo-lution of wireless standards Soon after the first forzon releasein December 2008 commercial development of the 3rd-Generation Partnership Project (3GPP) Long-Term Evolu-tion (LTE) systembegan To increase capacity LTE-Advancedwas launched in March 2011 rendering LTE formally com-pliant with the International Telecommunication Unionrsquosdefinition of the fourth generation of wireless technologytermed IMT-Advanced [1 2] However new traffic typesand data services are emerging notablymachine-to-machinecommunications to support applications such as smart gridsmart homes and cities and e-health With the developmentof new applications as many as 50 billion devices may beconnected by 2020 according to one estimate [3]The growingannual traffic demands (conservative estimates range from40 to 70 [4ndash6]) imply that cellular networks may need todeliver as much as 1000 times their current capacity withinthe next decadeThe challenging task ofmeeting this demand

impels the development of future wireless networks calledbeyond fourth-generation (4G) and fifth-generation (5G)cellular systems offering peak throughputs of multigigabitsper second (Gbs) and cell edge rates in tens of megabits persecond (Mbs) [7]

In addition to offering greater performance than LTE-Advanced future networks must be much more energyefficient than current networks for 5G technology to besustainable in the long termMillimeter-wave (mmW) beam-forming technology is a key enabling factor for the datacapacity improvement that is essential for 5G networksto be commercially successful This technology employs amassive multi-input multioutput (MIMO) system operatingbetween 30 and 300GHz where the available bandwidths aremuch wider than current cellular networks [8ndash11] The newspectrum released by the Federal Communications Commis-sion features bandwidth up to 11 GHz including 38GHz oflicensed spectrum from 275 to 2835GHz and 37 to 40GHzand 7GHz of unlicensed spectrum from 64 to 71GHz Theavailable spectrum of the mmW band can achieve data rates

Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2016 Article ID 7202143 10 pageshttpdxdoiorg10115520167202143

2 International Journal of Antennas and Propagation

Transceiver(MCPA)1

2

d

x

M

(mmW antenna array)

S(t)

z

Ij

120579j

1205790 Mod

emp

roto

cols

Appl

icat

ions

Weighting (Wopt)calibrations

x1k

x2k

xMk

Transceiver(MCPA)

Transceiver(MCPA)

Front-end

Front-end

Front-end

Beam

form

er (d

igita

l)

Figure 1 The functional block diagram of an adaptive antenna array for massive MIMO systems

200 times greater than those realized by current cellularsystems under 3GHz [8 10] Furthermore the relatively shortwavelength of an mmW signal which incorporates leadingradiofrequency integrated circuit technologies renders theimplementation of an antennawith numerous (ge32) elementswith small dimension possible Consequently future wirelessnetworks can be equipped with massive MIMO systemsto provide an extremely high gain electrically steerablearray and adaptive beamforming arrays Furthermore thesesystems can be built in the base station on the terminaldevice or within a chip [8 12]

Despite the benefits of using the mmW band numeroussubstantial challenges must be addressed before the wirelesssystems in these bands can be realized especially for the arrayantenna design

(1) In the mmW region designing electromagnetic cir-cuit elements is difficult because of the sensitivityin fabrication requirements and the high insertionloss in wave propagation Slight misalignments ofparameters on the order of 01mm can change thecharacteristics of the circuit element and cause unex-pected consequences

(2) Greater antenna gain for the same physical antennasize is attained because of the smaller wavelength ofthe mmW signal However the reliance on highlydirectional transmissions necessitates design changesto current cellular systems [13]

(3) Fabricating structures and fixing connectors whentransitioning to the other transmission lines requirecare The fringing fields over the transition regionon the panel launch transmission line feed havecapacitive or inductive input impedance resulting indistortion and poor matching performance

This paper reports on the recent progress in design-ing a prototype mmW antenna array for massive MIMOapplications the array involves a 64-element microstripantenna array operating at 38GHz In Section 21 the system

configuration of the proposed mmW microstrip antennaarray is discussed in detail This section also outlinesthe minimum mean square error [14 15] and least meansquares (LMS) [14] adaptive algorithms which show greatimprovement in signal-to-noise ratio (SNR) by placing nullsin interference directions Section 22 presents the designof a prototype mmW antenna array using a microstrippatch antenna printed on a low-temperature cofired ceramic(LTCC) substrate Section 3 describes the experimental studyof the mmW microstrip antenna arrays namely 64-elementmicrostrip patch antennas and a reference antenna forself-calibration [16] Concluding remarks are provided inSection 4

2 Analysis and Design

21 System Configuration The functional block diagram ofan 119872-element massive MIMO system for future networksis depicted in Figure 1 During transmission the optimalweighting vector (Wopt) is computed to generate high gainradiation fields along the signal directions (1205790 1206010) and syn-thesize nulls on other unlined user equipment (UE) direc-tions (120579119895 120601119895) this minimizes channel interferenceThereforewhen the SNR increases a high-quality signal is achievedin the radio line between BS and UE for high-throughputperformance Similarly the incoming signal and interferencein the directions received by the array are amplified down-converted and transformed to the baseband signal fromanalog to digital format While the radiation pattern is syn-thesized with the high gain in the signal direction and nulls inthe interference directions a closed-loop adaptive processormodifies the received signals in a fading environment bycomputing the optimal weighting vector (Wopt) An equallyspaced 119889-space119872-element antenna array is subjected to thisprocess

Figure 2 illustrates the design concept of the proposedmmW active antenna array for massiveMIMO systems indi-cating that it comprises the following components (1) 64-elementmicrostrip patch antennas (2) 16 front-endmodules

International Journal of Antennas and Propagation 3

4

3

3

2

2

1

TRmodule

TRDBFPDN module

k-connector

Controlsignal IO

Controlsignal IO

Front-endmodule

Front-endmodule

Front-endmodule

Y

X

Z

5dx

dy

120601

120579

(a)

dividercombiner Phaseshifter

Rx

Tx

PWR6

PWR5

PWR4

PWR1PWR3

PWR2 PS2 LNASWITCH1

ANT

Power_AMPPS1

empty

empty

1 4 power

(b)

PWR1IF

SWITCH1

Rx

Tx

RF_AMP

IF_AMP1 RF_AMP1RF_BPF1IF_BPF1

Local_OSC

MIX1

MIXIF_AMP IF_BPF RF_BPF38GHz

38GHz

35GHz

3~35GHz

Lo

Lo

(c)

Figure 2 (a) Design concept of the mmW active antenna array for massive MIMO systems comprising (1) 64-element microstrip patchantennas (2) 16 front-end modules (3) eight T-R modules (4) an eight-channel digital beamforming network and power distributionnetwork and (5) a reference antenna integrated with a T-R module (b) Schematic of the front-end module on one channel (c) Schematic ofthe T-R module on one channel

(3) eight transmitter-receiver (T-R) modules (4) a powerdistribution network and (5) a reference antenna integratedwith a T-R module which is applied to the system self-calibration using the phase-match method [16]

The antenna array comprises a set of polarized elementsin the position vector (D = [d1 d2 dm dM])where dm denotes the location of the 119898th antenna elementFor plane waves that propagate in a locally homogeneousmedium the wave K is defined as

K = 2120587120582 [sin 120579 cos120601 sin 120579 sin120601 cos 120579]119879 (1)

where 120582 represents the wavelength at frequency 119891 120579 and 120601are the azimuthal angle and angle of elevation of the far-fieldsource respectively and 119879 denotes the matrix transpose

When the time phase factor 1198901198952120587119891119905 is omitted the far-fieldpattern of the simultaneously excited adaptive antenna arraybecomes

119891 (120579 120601) =W119867 sdot 119890minus119895K119879sdotD120585 (120579 120601) =W119867 sdot E (120579 120601) (2)

whereW = [1199081 1199082 119908119872]119879

E (120579 120601) = eminusjKT sdotD120585 (120579 120601)

(3)

4 International Journal of Antennas and Propagation

The polarized element pattern function for an individualelement is denoted by 120585(120579 120601) and 119908119894 (119908119894 = 119888119894119890119895120595119894) representsthe complex weighting coefficient with an amplitude of 119888119894and phase of Ψ119894 at the 119894th element of the weight vector Wwhich is generated by the adaptive algorithmThe Hermitiantranspose which combines transposition and conjugationis denoted by H and the radiation pattern of the array isdenoted by 119891(120579 120601) For a given radial vector (defined byangles 120601 and 120579) 119891(120579 120601) yields the magnitude of the arrayresponse in the and directions

The system performance enhancement of the massiveMIMO system was assessed using adaptive algorithms in anoisy environmentThe received signal of a single antenna inan additive white Gaussian noise channel is represented by119909(119905) = 119878(119905) + 119899(119905) where 119878(119905) denotes the received signal inthe direction (1205790 1206010) and 119899(119905) denotes the noiseThe adaptivebeamformerwith the selected algorithm is then derived usingthe conventional phased array approach at radiofrequency(RF) or intermediate frequency (IF) [14 15] The signalscollected from each of the antenna elements are processedand summed in the analog devices and downconverted tothe baseband The weighting process in the RF and IF analogdomains is relatively inflexible and can become complexas the number of space-division multiple-access channelsincreasesThedigital-domain or digital beamforming (DBF)approach has numerous advantages [17 18] but is alsodisadvantaged by its unavailability high cost increased signalbandwidth and the dynamic range of characteristics ofanalog-to-digital and digital-to-analog converters

In this paper themean squared error (MSE) isminimizedby using the LMS algorithm [14 19 20] as an example ofselected adaptive DBF In discrete time at time index 119896 andperiod119879119904 119905 = 119896119879119904 the input signal vector of an equally spaced119872-element array (Figure 1) is

X119896 = [1199091119896 1199092119896 119909119898119896 119909119872119896] (4)

where 119909119898119896 is the transmitted narrowband signal in a complexenvelope and 119898 is the number of antenna elements at 119896MoreoverW119896 is the weight vector at 119896 which can be appliedin the analog portion of the receiver using phase shiftersand attenuators or in the digital domain after digitizing andfiltering the signal For narrowband arrays the output is thelinear combination of the sampled inputs that are multipliedwith complex weights

119910119896 = X119896119867 sdotW119896 (5)

The optimal solution that minimizes MSE leads to theWienerndashHopf solution [14] and is given by

W119896 = R119909119909minus1 sdot r119909119889 (6)

whereR119909119909 denotes the input correlation or covariancematrixand r119909119889 is the cross-correlation vector between the receivedand training (or desired) signals

For stationary input data the process requires only thetime to yield adequate estimates of R119909119909 and r119909119889 R119909119909minus1 isthen computed and the optimal weight vector is determinedHowever because matrix inversion is nontrivial particularlywhen conducted using a digital signal processor iterativetechniques easily yield the optimal solution in a limitedtime The updated equation of these iterative approaches isgenerally expressed by the LMS algorithm [18] given by

Wk+1 =Wk minus Δ (Gk) (7)

where Δ represents the step-size value and is allowed tochange at every iteration and Gk denotes the gradient orderivative of the MSE with respect to the weight vector (W119896)

Gk = minus2rxd + 2RxxWk (8)

Stochastic gradient algorithms attempt to determine theoptimal solution by continually stepping in the negativedirection of the gradient Thus the weight vector is adjustedtoward the minimum optimal MSE surface Therefore theadaptive weighting vector can be computed with the DBFunit (Figure 1) by using (7) the adaptive weighting vector isthen fed into transceivers to adjust the amplitude and phaseof each patch antenna through the automatic gain controllerand phase shifter Consequently the far-field pattern ofthe simultaneously excited adaptive antenna array can beachieved and the SNR can be maximized to optimize thesystem performance under fading environments

Figure 3(a) indicates that the computed element gain ofa single patch antenna of 686 dBi which is achieved usingHFSS and the theoretical directivity gain improvement fora massive MIMO system with a 64-element array antennaand element spacing of 119889119909 = 55mm and 119889119910 = 85mm is18 dB according to (2) The beamwidth of the array patternis approximately 5∘ and 6∘ on the Az- and El-planes (119909-119911and 119910-119911 planes) respectively and plusmn25∘ beams are capableof electronic steering in the coverage region Furthermorewhen the MSE adaptive algorithms in (5) and (6) are appliedthe massive MIMO can synthesize the radiation pattern withnulls in the interference directions (ie (120579∘ 120601∘) = (13∘ 0∘)(30∘ 0∘) (50∘ 0∘)) to increase the system SNR (Figure 3(b))Figures 3(c) and 3(d) illustrate plots of the 3D and 2D contourradiation patterns of the array respectively

22Microstrip AntennaArrayDesign Considering the draw-backs of working at the Ka band frequencies discussed inSection 1 we employed the microstrip antennas for thisprototype study because the manufacturing process formicrostrip type antenna with the help of modem-printedcircuit technology adapted to testing and constructing pur-poses is simpler less expensive and faster than that of othertypes of antennas Moreover if manufactured carefully theproducts are almost identical implying that verification of thedesign microstrip prototype antenna will also be satisfactoryfor other copies of the antenna However the microstripantennas have notable disadvantages such as low powerhandling and narrow frequency bandwidth

International Journal of Antennas and Propagation 5

25

20

15

10

5

0

minus5

minus10

minus15

Theta (degrees)9070503010minus10minus30minus50minus70minus90

Sim

ulat

ed d

irect

ivity

(dBi

)E-plane (array)H-plane (array)H-plane (scan)E-plane (single)H-plane (single)

(a)

25

20

15

10

5

0

minus5

minus10

minus15

minus20

Sim

ulat

ed d

irect

ivity

gai

n (d

Bi)

Theta (degrees) x-zplane cut9075604530150minus15minus30minus45minus60minus75minus90

(b)

0

020

02

TxTy

0

minus20

minus40

minus60

minus02 minus02

Relat

ive p

ower

(dB)

(c)

Contour of sum pattern

0 01 02

0

005

01

015

02

minus02minus02

minus015

minus01

minus005

minus01

Ty -

sin(Th

)lowast

sin(P

hi)

Tx - sin(Th) lowast cos(Phi)

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40minus40

minus40

minus30

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus10

minus10

minus20

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus30minus30

minus30

minus10

minus10

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus20

minus30

minus30

(d)

Figure 3 (a) Comparison of the simulated radiation patterns of a single antenna using HFSS and a 64-element array antenna with elementspacing of 119889119909 = 55mm and 119889119910 = 8mm through (2) in E- andH-planes (119909-119911 and 119910-119911 planes) (b) Comparison of theH-plane radiation patternwith and without the adaptive algorithm demonstrating the nulls on the interference directions (120579∘ and 120601∘) of 13∘ and 0∘ 30∘ and 0∘ and 50∘and 0∘ respectively (c) 3D radiation pattern of the array (d) 2D contour of the radiation patterns

Many feeding design methods can be applied to excitemicrostrip patch antennas but a perpendicular coaxial tran-sition is the most suitable for mmW applications becausethis methodrsquos measurements indicate a return loss betterthan 14 dB and an insertion loss better than 04 dB fromDC to 40GHz [21 22] Therefore we proposed the mmWantenna array comprising 64-element perpendicular coax-fed microstrip patch antennas that resonate at 38GHz(Figure 4) The mmW microstrip patch array is integratedwith eight subarrays each comprising eight microstrippatches printed on the RF substrate with a thickness of 15milThe element spacing of the array is arranged in a triangularlattice (119889119909 = 55mm 119889119910 = 85mm) to obtain a beamscanning azimuth angle of plusmn25∘ whenmaintainingmaximumroom to allocate the modified k-connector

A key parasite of perpendicular transition is the induc-tance triggered by ground currents that must flow aroundthe circumference of the coax outer conductor to reach

the underside of the microstrip section Therefore in eachsubarray substrates with the printed microstrip patches weresoldered on amodified k-connector with four ground pins onthe four corners of the connector base to secure the antenna(Figure 5(a)) After all of the subarrays were integrated ninescrews were used to fix the RF substrate of each subarray ontothe back plane of the array (Figure 5(b)) Subsequently thearray was placed in a tin stove for wave soldering reflow Afterall subarrays were soldered on the back plane of the array allof the screws were removed

3 Numerical and Experimental Study

The design approach of the microstrip patch printed on theLTCC substrate with a dielectric constant of 59 and thicknessof 15mil was verified using HFSS (Figure 6) The transitioneffects of the coaxially fed launcher were considered in thesimulation

6 International Journal of Antennas and Propagation

k-connector

Figure 4 Design concept of the proposed mmWmicrostrip antenna array

1

23

31

21

33

34

(a)

Ground pads

Microstrippatch

(b)

Figure 5 (a) Design of a single microstrip patch (b) Close look of the assembled array

000

minus500

minus1000

minus1500

minus2000

minus2500

minus3000

Freq (GHz)

w = 10mmL = 123mmyo = 025mmdB

(S(11

))

m1

m1 373400

389600

m2

40003900380037003600

Name X Y

m2

minus102285

minus101687

Figure 6 Simulated 11987811 of a single microstrip antenna patch inset shows the simulation layout

The simulation results (Figure 6) showed a return loss ofless than 10 dB at the frequencies of interest ranging from3734 to 3889GHz To experimentally verify this designapproach two identical mmW microstrip patch antennaarrays were built for testing (Figure 7) The measurementsetup was established by connecting one patch with twommW microstrip patch arrays which were placed face-to-face 195 cm apart (Figure 8)

Two-port 119878-parameters were measured using the Rohdeamp Schwarz ZVA40 vector network analyzer (Figure 9) Thesimulated 11987811 (solid line in Figure 9) was computed usinga single microstrip patch to reduce computing time but themeasured 11987811 (the solid line with diamond shapes) and 11987822(the solid line with rectangular shapes) corresponded to thecenter element of two microstrip antenna arrays (Figure 8)Thus the discrepancy between the measured and simulated

International Journal of Antennas and Propagation 7

Figure 7 Photograph of two identical mmWmicrostrip arrays for testing

Figure 8 Measurement setup established by connecting one patch to two arrays placing two arrays face-to-face at a distance of 119877 = 195 cmand testing the 2-port S-parameters using the Rohde amp Schwarz ZVA40 vector network analyzer

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

minus45

S-pa

ram

eter

(dB)

Frequency (GHz)

Simulated_S11Measured_S11

Measured_S22Measured_S21

4039539385383753736536

Figure 9 Measured 119878-parameters of the test setup (Figure 8)

data (Figure 9) can be attributed to the reactive loading effectcaused by the mutual coupling

Next the Friis power transmission formula [23] was usedto calculate the maximum antenna power gain (in the centralforward direction of the antenna)

GrGt = G2 = (PrPt)(4120587R1205820 )

2

= 1003816100381610038161003816S2110038161003816100381610038162 (4120587R1205820 )2

(9)

where Gr and Gt are the power gains of the receiving andtransmitting antennas respectively and Pt and Pr are thetransmitted and received powers respectively Because the

two antennas are identicalGt = Gr = G and the power ratioPrPt is the measured direct transmission coefficient |S21|2which was obtained using the vector network analyzer Bysubstituting the measured |S21| into (9) the measured max-imum antenna power gain was plotted against frequenciesranging from 360 to 40GHz to compare with simulationdata (Figure 10) they indicated an acceptable agreementThemeasured gain of a singlemicrostrip patchwas approximately68 dBi at 38GHz

Finally the radiation pattern at the center element ofthe prototype mmW array (Figure 7) was measured at OIT

8 International Journal of Antennas and Propagation

10

9

8

7

6

5

4

3

2

1

0

Gai

n (d

Bi)

Frequency (GHz)

Measured_GainSimulated_Gain

4039539385383753736536

Figure 10 Comparison of the gain measured by (9) and the gain simulated using HFSS on a single microstrip patch antenna

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Amp45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(a) Amplitude

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Phase45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(b) Phase

Figure 11 Measured (a) amplitude and (b) phase of the aperture field of the mmWmicrostrip antenna array excited at the center element

near- and far-field test ranges The measured amplitude andphase of the aperture field are plotted in Figures 11(a) and11(b) respectively Meanwhile Figures 12(a) and 12(b) displayphotographs of the tested setup and Figure 12(c) illustratesplots of the measured Co-Pol and Cross-Pol for the 2Dradiation pattern cuts in the 119909-119910 and 119909-119911 planes at 3775GHz

4 Conclusion

Our design prototype for an mmW microstrip antennaarray operating at the Ka band frequency range for 5Gcommunication system applications is presented using 64-element microstrip patches printed on an LTCC substratewith a thickness of 15mil and a dielectric constant of 59

Our numerical and experimental study revealed acceptableagreement between themeasured and simulated return lossesand antenna power gain performance This confirms that amicrostrip patch antenna array with a high radiation gainperformance in an mmW range is feasible for future 5Gapplications

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors thank the Chung-Shan Institute of Science andTechnology (Taiwan) for financially supporting this research

International Journal of Antennas and Propagation 9

(a)

y

xz

(b)

0 Co-Pol90 Co-Pol

0 X-Pol90 X-Pol

Max 158

Co-Pol and X-Pol-Amp

Far-field patterns

Scan surface planar rectangularPoints per scan 51Points per scan 51

Frequency 377500

787 cm787 cm

Polarization linear AUT probe separation 394

Freq 37750ndash38250 GHz

Reference power minus4853 dBx-axisy-axis

(c)

Figure 12 (a) Amplitude and (b) phase photographs of the tested setup of the mmWmicrostrip antenna array (c) Measured 2D Co-Pol andCross-Pol radiation patterns

(CSIST-A7I-V1XX) and thank Kevin Peng for assisting in themanufacture and integration of the array

References

[1] J Thompson X Ge H-C Wu et al ldquo5G wireless communica-tion systems prospects and challenges [Guest Editorial]rdquo IEEECommunications Magazine vol 52 no 2 pp 62ndash64 2014

[2] M S Pandey M Kumar A Panwar and I Singh ldquoA surveywireless mobile technology generations with 5Grdquo InternationalJournal of Engineering Research and Technology vol 2 no 42013

[3] Ericsson ldquoMore than 50 billion connected devicesrdquo WhitePaper [Online] httpwwwakos-rssifilesTelekomunikacijeDigitalna agendaInternetni protokol Ipv6More-than-50-bil-lion-connected-devicespdf

[4] CiscoCiscoVisualNetwork Index GlobalMobile Traffic ForecastUpdate 2013

[5] Ericsson ldquoTraffic and market data reportrdquo 2011[6] UMTS Forum Mobile Traffic Forecasts 2010ndash2020 Report

UMTS Forum Zurich Switzerland 2011[7] P E Mogensen K Pajukoski B Raaf et al ldquoB4G local area

high level requirements and systemdesignrdquo inProceedings of the

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

2 International Journal of Antennas and Propagation

Transceiver(MCPA)1

2

d

x

M

(mmW antenna array)

S(t)

z

Ij

120579j

1205790 Mod

emp

roto

cols

Appl

icat

ions

Weighting (Wopt)calibrations

x1k

x2k

xMk

Transceiver(MCPA)

Transceiver(MCPA)

Front-end

Front-end

Front-end

Beam

form

er (d

igita

l)

Figure 1 The functional block diagram of an adaptive antenna array for massive MIMO systems

200 times greater than those realized by current cellularsystems under 3GHz [8 10] Furthermore the relatively shortwavelength of an mmW signal which incorporates leadingradiofrequency integrated circuit technologies renders theimplementation of an antennawith numerous (ge32) elementswith small dimension possible Consequently future wirelessnetworks can be equipped with massive MIMO systemsto provide an extremely high gain electrically steerablearray and adaptive beamforming arrays Furthermore thesesystems can be built in the base station on the terminaldevice or within a chip [8 12]

Despite the benefits of using the mmW band numeroussubstantial challenges must be addressed before the wirelesssystems in these bands can be realized especially for the arrayantenna design

(1) In the mmW region designing electromagnetic cir-cuit elements is difficult because of the sensitivityin fabrication requirements and the high insertionloss in wave propagation Slight misalignments ofparameters on the order of 01mm can change thecharacteristics of the circuit element and cause unex-pected consequences

(2) Greater antenna gain for the same physical antennasize is attained because of the smaller wavelength ofthe mmW signal However the reliance on highlydirectional transmissions necessitates design changesto current cellular systems [13]

(3) Fabricating structures and fixing connectors whentransitioning to the other transmission lines requirecare The fringing fields over the transition regionon the panel launch transmission line feed havecapacitive or inductive input impedance resulting indistortion and poor matching performance

This paper reports on the recent progress in design-ing a prototype mmW antenna array for massive MIMOapplications the array involves a 64-element microstripantenna array operating at 38GHz In Section 21 the system

configuration of the proposed mmW microstrip antennaarray is discussed in detail This section also outlinesthe minimum mean square error [14 15] and least meansquares (LMS) [14] adaptive algorithms which show greatimprovement in signal-to-noise ratio (SNR) by placing nullsin interference directions Section 22 presents the designof a prototype mmW antenna array using a microstrippatch antenna printed on a low-temperature cofired ceramic(LTCC) substrate Section 3 describes the experimental studyof the mmW microstrip antenna arrays namely 64-elementmicrostrip patch antennas and a reference antenna forself-calibration [16] Concluding remarks are provided inSection 4

2 Analysis and Design

21 System Configuration The functional block diagram ofan 119872-element massive MIMO system for future networksis depicted in Figure 1 During transmission the optimalweighting vector (Wopt) is computed to generate high gainradiation fields along the signal directions (1205790 1206010) and syn-thesize nulls on other unlined user equipment (UE) direc-tions (120579119895 120601119895) this minimizes channel interferenceThereforewhen the SNR increases a high-quality signal is achievedin the radio line between BS and UE for high-throughputperformance Similarly the incoming signal and interferencein the directions received by the array are amplified down-converted and transformed to the baseband signal fromanalog to digital format While the radiation pattern is syn-thesized with the high gain in the signal direction and nulls inthe interference directions a closed-loop adaptive processormodifies the received signals in a fading environment bycomputing the optimal weighting vector (Wopt) An equallyspaced 119889-space119872-element antenna array is subjected to thisprocess

Figure 2 illustrates the design concept of the proposedmmW active antenna array for massiveMIMO systems indi-cating that it comprises the following components (1) 64-elementmicrostrip patch antennas (2) 16 front-endmodules

International Journal of Antennas and Propagation 3

4

3

3

2

2

1

TRmodule

TRDBFPDN module

k-connector

Controlsignal IO

Controlsignal IO

Front-endmodule

Front-endmodule

Front-endmodule

Y

X

Z

5dx

dy

120601

120579

(a)

dividercombiner Phaseshifter

Rx

Tx

PWR6

PWR5

PWR4

PWR1PWR3

PWR2 PS2 LNASWITCH1

ANT

Power_AMPPS1

empty

empty

1 4 power

(b)

PWR1IF

SWITCH1

Rx

Tx

RF_AMP

IF_AMP1 RF_AMP1RF_BPF1IF_BPF1

Local_OSC

MIX1

MIXIF_AMP IF_BPF RF_BPF38GHz

38GHz

35GHz

3~35GHz

Lo

Lo

(c)

Figure 2 (a) Design concept of the mmW active antenna array for massive MIMO systems comprising (1) 64-element microstrip patchantennas (2) 16 front-end modules (3) eight T-R modules (4) an eight-channel digital beamforming network and power distributionnetwork and (5) a reference antenna integrated with a T-R module (b) Schematic of the front-end module on one channel (c) Schematic ofthe T-R module on one channel

(3) eight transmitter-receiver (T-R) modules (4) a powerdistribution network and (5) a reference antenna integratedwith a T-R module which is applied to the system self-calibration using the phase-match method [16]

The antenna array comprises a set of polarized elementsin the position vector (D = [d1 d2 dm dM])where dm denotes the location of the 119898th antenna elementFor plane waves that propagate in a locally homogeneousmedium the wave K is defined as

K = 2120587120582 [sin 120579 cos120601 sin 120579 sin120601 cos 120579]119879 (1)

where 120582 represents the wavelength at frequency 119891 120579 and 120601are the azimuthal angle and angle of elevation of the far-fieldsource respectively and 119879 denotes the matrix transpose

When the time phase factor 1198901198952120587119891119905 is omitted the far-fieldpattern of the simultaneously excited adaptive antenna arraybecomes

119891 (120579 120601) =W119867 sdot 119890minus119895K119879sdotD120585 (120579 120601) =W119867 sdot E (120579 120601) (2)

whereW = [1199081 1199082 119908119872]119879

E (120579 120601) = eminusjKT sdotD120585 (120579 120601)

(3)

4 International Journal of Antennas and Propagation

The polarized element pattern function for an individualelement is denoted by 120585(120579 120601) and 119908119894 (119908119894 = 119888119894119890119895120595119894) representsthe complex weighting coefficient with an amplitude of 119888119894and phase of Ψ119894 at the 119894th element of the weight vector Wwhich is generated by the adaptive algorithmThe Hermitiantranspose which combines transposition and conjugationis denoted by H and the radiation pattern of the array isdenoted by 119891(120579 120601) For a given radial vector (defined byangles 120601 and 120579) 119891(120579 120601) yields the magnitude of the arrayresponse in the and directions

The system performance enhancement of the massiveMIMO system was assessed using adaptive algorithms in anoisy environmentThe received signal of a single antenna inan additive white Gaussian noise channel is represented by119909(119905) = 119878(119905) + 119899(119905) where 119878(119905) denotes the received signal inthe direction (1205790 1206010) and 119899(119905) denotes the noiseThe adaptivebeamformerwith the selected algorithm is then derived usingthe conventional phased array approach at radiofrequency(RF) or intermediate frequency (IF) [14 15] The signalscollected from each of the antenna elements are processedand summed in the analog devices and downconverted tothe baseband The weighting process in the RF and IF analogdomains is relatively inflexible and can become complexas the number of space-division multiple-access channelsincreasesThedigital-domain or digital beamforming (DBF)approach has numerous advantages [17 18] but is alsodisadvantaged by its unavailability high cost increased signalbandwidth and the dynamic range of characteristics ofanalog-to-digital and digital-to-analog converters

In this paper themean squared error (MSE) isminimizedby using the LMS algorithm [14 19 20] as an example ofselected adaptive DBF In discrete time at time index 119896 andperiod119879119904 119905 = 119896119879119904 the input signal vector of an equally spaced119872-element array (Figure 1) is

X119896 = [1199091119896 1199092119896 119909119898119896 119909119872119896] (4)

where 119909119898119896 is the transmitted narrowband signal in a complexenvelope and 119898 is the number of antenna elements at 119896MoreoverW119896 is the weight vector at 119896 which can be appliedin the analog portion of the receiver using phase shiftersand attenuators or in the digital domain after digitizing andfiltering the signal For narrowband arrays the output is thelinear combination of the sampled inputs that are multipliedwith complex weights

119910119896 = X119896119867 sdotW119896 (5)

The optimal solution that minimizes MSE leads to theWienerndashHopf solution [14] and is given by

W119896 = R119909119909minus1 sdot r119909119889 (6)

whereR119909119909 denotes the input correlation or covariancematrixand r119909119889 is the cross-correlation vector between the receivedand training (or desired) signals

For stationary input data the process requires only thetime to yield adequate estimates of R119909119909 and r119909119889 R119909119909minus1 isthen computed and the optimal weight vector is determinedHowever because matrix inversion is nontrivial particularlywhen conducted using a digital signal processor iterativetechniques easily yield the optimal solution in a limitedtime The updated equation of these iterative approaches isgenerally expressed by the LMS algorithm [18] given by

Wk+1 =Wk minus Δ (Gk) (7)

where Δ represents the step-size value and is allowed tochange at every iteration and Gk denotes the gradient orderivative of the MSE with respect to the weight vector (W119896)

Gk = minus2rxd + 2RxxWk (8)

Stochastic gradient algorithms attempt to determine theoptimal solution by continually stepping in the negativedirection of the gradient Thus the weight vector is adjustedtoward the minimum optimal MSE surface Therefore theadaptive weighting vector can be computed with the DBFunit (Figure 1) by using (7) the adaptive weighting vector isthen fed into transceivers to adjust the amplitude and phaseof each patch antenna through the automatic gain controllerand phase shifter Consequently the far-field pattern ofthe simultaneously excited adaptive antenna array can beachieved and the SNR can be maximized to optimize thesystem performance under fading environments

Figure 3(a) indicates that the computed element gain ofa single patch antenna of 686 dBi which is achieved usingHFSS and the theoretical directivity gain improvement fora massive MIMO system with a 64-element array antennaand element spacing of 119889119909 = 55mm and 119889119910 = 85mm is18 dB according to (2) The beamwidth of the array patternis approximately 5∘ and 6∘ on the Az- and El-planes (119909-119911and 119910-119911 planes) respectively and plusmn25∘ beams are capableof electronic steering in the coverage region Furthermorewhen the MSE adaptive algorithms in (5) and (6) are appliedthe massive MIMO can synthesize the radiation pattern withnulls in the interference directions (ie (120579∘ 120601∘) = (13∘ 0∘)(30∘ 0∘) (50∘ 0∘)) to increase the system SNR (Figure 3(b))Figures 3(c) and 3(d) illustrate plots of the 3D and 2D contourradiation patterns of the array respectively

22Microstrip AntennaArrayDesign Considering the draw-backs of working at the Ka band frequencies discussed inSection 1 we employed the microstrip antennas for thisprototype study because the manufacturing process formicrostrip type antenna with the help of modem-printedcircuit technology adapted to testing and constructing pur-poses is simpler less expensive and faster than that of othertypes of antennas Moreover if manufactured carefully theproducts are almost identical implying that verification of thedesign microstrip prototype antenna will also be satisfactoryfor other copies of the antenna However the microstripantennas have notable disadvantages such as low powerhandling and narrow frequency bandwidth

International Journal of Antennas and Propagation 5

25

20

15

10

5

0

minus5

minus10

minus15

Theta (degrees)9070503010minus10minus30minus50minus70minus90

Sim

ulat

ed d

irect

ivity

(dBi

)E-plane (array)H-plane (array)H-plane (scan)E-plane (single)H-plane (single)

(a)

25

20

15

10

5

0

minus5

minus10

minus15

minus20

Sim

ulat

ed d

irect

ivity

gai

n (d

Bi)

Theta (degrees) x-zplane cut9075604530150minus15minus30minus45minus60minus75minus90

(b)

0

020

02

TxTy

0

minus20

minus40

minus60

minus02 minus02

Relat

ive p

ower

(dB)

(c)

Contour of sum pattern

0 01 02

0

005

01

015

02

minus02minus02

minus015

minus01

minus005

minus01

Ty -

sin(Th

)lowast

sin(P

hi)

Tx - sin(Th) lowast cos(Phi)

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40minus40

minus40

minus30

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus10

minus10

minus20

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus30minus30

minus30

minus10

minus10

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus20

minus30

minus30

(d)

Figure 3 (a) Comparison of the simulated radiation patterns of a single antenna using HFSS and a 64-element array antenna with elementspacing of 119889119909 = 55mm and 119889119910 = 8mm through (2) in E- andH-planes (119909-119911 and 119910-119911 planes) (b) Comparison of theH-plane radiation patternwith and without the adaptive algorithm demonstrating the nulls on the interference directions (120579∘ and 120601∘) of 13∘ and 0∘ 30∘ and 0∘ and 50∘and 0∘ respectively (c) 3D radiation pattern of the array (d) 2D contour of the radiation patterns

Many feeding design methods can be applied to excitemicrostrip patch antennas but a perpendicular coaxial tran-sition is the most suitable for mmW applications becausethis methodrsquos measurements indicate a return loss betterthan 14 dB and an insertion loss better than 04 dB fromDC to 40GHz [21 22] Therefore we proposed the mmWantenna array comprising 64-element perpendicular coax-fed microstrip patch antennas that resonate at 38GHz(Figure 4) The mmW microstrip patch array is integratedwith eight subarrays each comprising eight microstrippatches printed on the RF substrate with a thickness of 15milThe element spacing of the array is arranged in a triangularlattice (119889119909 = 55mm 119889119910 = 85mm) to obtain a beamscanning azimuth angle of plusmn25∘ whenmaintainingmaximumroom to allocate the modified k-connector

A key parasite of perpendicular transition is the induc-tance triggered by ground currents that must flow aroundthe circumference of the coax outer conductor to reach

the underside of the microstrip section Therefore in eachsubarray substrates with the printed microstrip patches weresoldered on amodified k-connector with four ground pins onthe four corners of the connector base to secure the antenna(Figure 5(a)) After all of the subarrays were integrated ninescrews were used to fix the RF substrate of each subarray ontothe back plane of the array (Figure 5(b)) Subsequently thearray was placed in a tin stove for wave soldering reflow Afterall subarrays were soldered on the back plane of the array allof the screws were removed

3 Numerical and Experimental Study

The design approach of the microstrip patch printed on theLTCC substrate with a dielectric constant of 59 and thicknessof 15mil was verified using HFSS (Figure 6) The transitioneffects of the coaxially fed launcher were considered in thesimulation

6 International Journal of Antennas and Propagation

k-connector

Figure 4 Design concept of the proposed mmWmicrostrip antenna array

1

23

31

21

33

34

(a)

Ground pads

Microstrippatch

(b)

Figure 5 (a) Design of a single microstrip patch (b) Close look of the assembled array

000

minus500

minus1000

minus1500

minus2000

minus2500

minus3000

Freq (GHz)

w = 10mmL = 123mmyo = 025mmdB

(S(11

))

m1

m1 373400

389600

m2

40003900380037003600

Name X Y

m2

minus102285

minus101687

Figure 6 Simulated 11987811 of a single microstrip antenna patch inset shows the simulation layout

The simulation results (Figure 6) showed a return loss ofless than 10 dB at the frequencies of interest ranging from3734 to 3889GHz To experimentally verify this designapproach two identical mmW microstrip patch antennaarrays were built for testing (Figure 7) The measurementsetup was established by connecting one patch with twommW microstrip patch arrays which were placed face-to-face 195 cm apart (Figure 8)

Two-port 119878-parameters were measured using the Rohdeamp Schwarz ZVA40 vector network analyzer (Figure 9) Thesimulated 11987811 (solid line in Figure 9) was computed usinga single microstrip patch to reduce computing time but themeasured 11987811 (the solid line with diamond shapes) and 11987822(the solid line with rectangular shapes) corresponded to thecenter element of two microstrip antenna arrays (Figure 8)Thus the discrepancy between the measured and simulated

International Journal of Antennas and Propagation 7

Figure 7 Photograph of two identical mmWmicrostrip arrays for testing

Figure 8 Measurement setup established by connecting one patch to two arrays placing two arrays face-to-face at a distance of 119877 = 195 cmand testing the 2-port S-parameters using the Rohde amp Schwarz ZVA40 vector network analyzer

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

minus45

S-pa

ram

eter

(dB)

Frequency (GHz)

Simulated_S11Measured_S11

Measured_S22Measured_S21

4039539385383753736536

Figure 9 Measured 119878-parameters of the test setup (Figure 8)

data (Figure 9) can be attributed to the reactive loading effectcaused by the mutual coupling

Next the Friis power transmission formula [23] was usedto calculate the maximum antenna power gain (in the centralforward direction of the antenna)

GrGt = G2 = (PrPt)(4120587R1205820 )

2

= 1003816100381610038161003816S2110038161003816100381610038162 (4120587R1205820 )2

(9)

where Gr and Gt are the power gains of the receiving andtransmitting antennas respectively and Pt and Pr are thetransmitted and received powers respectively Because the

two antennas are identicalGt = Gr = G and the power ratioPrPt is the measured direct transmission coefficient |S21|2which was obtained using the vector network analyzer Bysubstituting the measured |S21| into (9) the measured max-imum antenna power gain was plotted against frequenciesranging from 360 to 40GHz to compare with simulationdata (Figure 10) they indicated an acceptable agreementThemeasured gain of a singlemicrostrip patchwas approximately68 dBi at 38GHz

Finally the radiation pattern at the center element ofthe prototype mmW array (Figure 7) was measured at OIT

8 International Journal of Antennas and Propagation

10

9

8

7

6

5

4

3

2

1

0

Gai

n (d

Bi)

Frequency (GHz)

Measured_GainSimulated_Gain

4039539385383753736536

Figure 10 Comparison of the gain measured by (9) and the gain simulated using HFSS on a single microstrip patch antenna

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Amp45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(a) Amplitude

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Phase45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(b) Phase

Figure 11 Measured (a) amplitude and (b) phase of the aperture field of the mmWmicrostrip antenna array excited at the center element

near- and far-field test ranges The measured amplitude andphase of the aperture field are plotted in Figures 11(a) and11(b) respectively Meanwhile Figures 12(a) and 12(b) displayphotographs of the tested setup and Figure 12(c) illustratesplots of the measured Co-Pol and Cross-Pol for the 2Dradiation pattern cuts in the 119909-119910 and 119909-119911 planes at 3775GHz

4 Conclusion

Our design prototype for an mmW microstrip antennaarray operating at the Ka band frequency range for 5Gcommunication system applications is presented using 64-element microstrip patches printed on an LTCC substratewith a thickness of 15mil and a dielectric constant of 59

Our numerical and experimental study revealed acceptableagreement between themeasured and simulated return lossesand antenna power gain performance This confirms that amicrostrip patch antenna array with a high radiation gainperformance in an mmW range is feasible for future 5Gapplications

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors thank the Chung-Shan Institute of Science andTechnology (Taiwan) for financially supporting this research

International Journal of Antennas and Propagation 9

(a)

y

xz

(b)

0 Co-Pol90 Co-Pol

0 X-Pol90 X-Pol

Max 158

Co-Pol and X-Pol-Amp

Far-field patterns

Scan surface planar rectangularPoints per scan 51Points per scan 51

Frequency 377500

787 cm787 cm

Polarization linear AUT probe separation 394

Freq 37750ndash38250 GHz

Reference power minus4853 dBx-axisy-axis

(c)

Figure 12 (a) Amplitude and (b) phase photographs of the tested setup of the mmWmicrostrip antenna array (c) Measured 2D Co-Pol andCross-Pol radiation patterns

(CSIST-A7I-V1XX) and thank Kevin Peng for assisting in themanufacture and integration of the array

References

[1] J Thompson X Ge H-C Wu et al ldquo5G wireless communica-tion systems prospects and challenges [Guest Editorial]rdquo IEEECommunications Magazine vol 52 no 2 pp 62ndash64 2014

[2] M S Pandey M Kumar A Panwar and I Singh ldquoA surveywireless mobile technology generations with 5Grdquo InternationalJournal of Engineering Research and Technology vol 2 no 42013

[3] Ericsson ldquoMore than 50 billion connected devicesrdquo WhitePaper [Online] httpwwwakos-rssifilesTelekomunikacijeDigitalna agendaInternetni protokol Ipv6More-than-50-bil-lion-connected-devicespdf

[4] CiscoCiscoVisualNetwork Index GlobalMobile Traffic ForecastUpdate 2013

[5] Ericsson ldquoTraffic and market data reportrdquo 2011[6] UMTS Forum Mobile Traffic Forecasts 2010ndash2020 Report

UMTS Forum Zurich Switzerland 2011[7] P E Mogensen K Pajukoski B Raaf et al ldquoB4G local area

high level requirements and systemdesignrdquo inProceedings of the

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

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Submit your manuscripts athttpwwwhindawicom

VLSI Design

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Electrical and Computer Engineering

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Advances inOptoElectronics

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Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of Antennas and Propagation 3

4

3

3

2

2

1

TRmodule

TRDBFPDN module

k-connector

Controlsignal IO

Controlsignal IO

Front-endmodule

Front-endmodule

Front-endmodule

Y

X

Z

5dx

dy

120601

120579

(a)

dividercombiner Phaseshifter

Rx

Tx

PWR6

PWR5

PWR4

PWR1PWR3

PWR2 PS2 LNASWITCH1

ANT

Power_AMPPS1

empty

empty

1 4 power

(b)

PWR1IF

SWITCH1

Rx

Tx

RF_AMP

IF_AMP1 RF_AMP1RF_BPF1IF_BPF1

Local_OSC

MIX1

MIXIF_AMP IF_BPF RF_BPF38GHz

38GHz

35GHz

3~35GHz

Lo

Lo

(c)

Figure 2 (a) Design concept of the mmW active antenna array for massive MIMO systems comprising (1) 64-element microstrip patchantennas (2) 16 front-end modules (3) eight T-R modules (4) an eight-channel digital beamforming network and power distributionnetwork and (5) a reference antenna integrated with a T-R module (b) Schematic of the front-end module on one channel (c) Schematic ofthe T-R module on one channel

(3) eight transmitter-receiver (T-R) modules (4) a powerdistribution network and (5) a reference antenna integratedwith a T-R module which is applied to the system self-calibration using the phase-match method [16]

The antenna array comprises a set of polarized elementsin the position vector (D = [d1 d2 dm dM])where dm denotes the location of the 119898th antenna elementFor plane waves that propagate in a locally homogeneousmedium the wave K is defined as

K = 2120587120582 [sin 120579 cos120601 sin 120579 sin120601 cos 120579]119879 (1)

where 120582 represents the wavelength at frequency 119891 120579 and 120601are the azimuthal angle and angle of elevation of the far-fieldsource respectively and 119879 denotes the matrix transpose

When the time phase factor 1198901198952120587119891119905 is omitted the far-fieldpattern of the simultaneously excited adaptive antenna arraybecomes

119891 (120579 120601) =W119867 sdot 119890minus119895K119879sdotD120585 (120579 120601) =W119867 sdot E (120579 120601) (2)

whereW = [1199081 1199082 119908119872]119879

E (120579 120601) = eminusjKT sdotD120585 (120579 120601)

(3)

4 International Journal of Antennas and Propagation

The polarized element pattern function for an individualelement is denoted by 120585(120579 120601) and 119908119894 (119908119894 = 119888119894119890119895120595119894) representsthe complex weighting coefficient with an amplitude of 119888119894and phase of Ψ119894 at the 119894th element of the weight vector Wwhich is generated by the adaptive algorithmThe Hermitiantranspose which combines transposition and conjugationis denoted by H and the radiation pattern of the array isdenoted by 119891(120579 120601) For a given radial vector (defined byangles 120601 and 120579) 119891(120579 120601) yields the magnitude of the arrayresponse in the and directions

The system performance enhancement of the massiveMIMO system was assessed using adaptive algorithms in anoisy environmentThe received signal of a single antenna inan additive white Gaussian noise channel is represented by119909(119905) = 119878(119905) + 119899(119905) where 119878(119905) denotes the received signal inthe direction (1205790 1206010) and 119899(119905) denotes the noiseThe adaptivebeamformerwith the selected algorithm is then derived usingthe conventional phased array approach at radiofrequency(RF) or intermediate frequency (IF) [14 15] The signalscollected from each of the antenna elements are processedand summed in the analog devices and downconverted tothe baseband The weighting process in the RF and IF analogdomains is relatively inflexible and can become complexas the number of space-division multiple-access channelsincreasesThedigital-domain or digital beamforming (DBF)approach has numerous advantages [17 18] but is alsodisadvantaged by its unavailability high cost increased signalbandwidth and the dynamic range of characteristics ofanalog-to-digital and digital-to-analog converters

In this paper themean squared error (MSE) isminimizedby using the LMS algorithm [14 19 20] as an example ofselected adaptive DBF In discrete time at time index 119896 andperiod119879119904 119905 = 119896119879119904 the input signal vector of an equally spaced119872-element array (Figure 1) is

X119896 = [1199091119896 1199092119896 119909119898119896 119909119872119896] (4)

where 119909119898119896 is the transmitted narrowband signal in a complexenvelope and 119898 is the number of antenna elements at 119896MoreoverW119896 is the weight vector at 119896 which can be appliedin the analog portion of the receiver using phase shiftersand attenuators or in the digital domain after digitizing andfiltering the signal For narrowband arrays the output is thelinear combination of the sampled inputs that are multipliedwith complex weights

119910119896 = X119896119867 sdotW119896 (5)

The optimal solution that minimizes MSE leads to theWienerndashHopf solution [14] and is given by

W119896 = R119909119909minus1 sdot r119909119889 (6)

whereR119909119909 denotes the input correlation or covariancematrixand r119909119889 is the cross-correlation vector between the receivedand training (or desired) signals

For stationary input data the process requires only thetime to yield adequate estimates of R119909119909 and r119909119889 R119909119909minus1 isthen computed and the optimal weight vector is determinedHowever because matrix inversion is nontrivial particularlywhen conducted using a digital signal processor iterativetechniques easily yield the optimal solution in a limitedtime The updated equation of these iterative approaches isgenerally expressed by the LMS algorithm [18] given by

Wk+1 =Wk minus Δ (Gk) (7)

where Δ represents the step-size value and is allowed tochange at every iteration and Gk denotes the gradient orderivative of the MSE with respect to the weight vector (W119896)

Gk = minus2rxd + 2RxxWk (8)

Stochastic gradient algorithms attempt to determine theoptimal solution by continually stepping in the negativedirection of the gradient Thus the weight vector is adjustedtoward the minimum optimal MSE surface Therefore theadaptive weighting vector can be computed with the DBFunit (Figure 1) by using (7) the adaptive weighting vector isthen fed into transceivers to adjust the amplitude and phaseof each patch antenna through the automatic gain controllerand phase shifter Consequently the far-field pattern ofthe simultaneously excited adaptive antenna array can beachieved and the SNR can be maximized to optimize thesystem performance under fading environments

Figure 3(a) indicates that the computed element gain ofa single patch antenna of 686 dBi which is achieved usingHFSS and the theoretical directivity gain improvement fora massive MIMO system with a 64-element array antennaand element spacing of 119889119909 = 55mm and 119889119910 = 85mm is18 dB according to (2) The beamwidth of the array patternis approximately 5∘ and 6∘ on the Az- and El-planes (119909-119911and 119910-119911 planes) respectively and plusmn25∘ beams are capableof electronic steering in the coverage region Furthermorewhen the MSE adaptive algorithms in (5) and (6) are appliedthe massive MIMO can synthesize the radiation pattern withnulls in the interference directions (ie (120579∘ 120601∘) = (13∘ 0∘)(30∘ 0∘) (50∘ 0∘)) to increase the system SNR (Figure 3(b))Figures 3(c) and 3(d) illustrate plots of the 3D and 2D contourradiation patterns of the array respectively

22Microstrip AntennaArrayDesign Considering the draw-backs of working at the Ka band frequencies discussed inSection 1 we employed the microstrip antennas for thisprototype study because the manufacturing process formicrostrip type antenna with the help of modem-printedcircuit technology adapted to testing and constructing pur-poses is simpler less expensive and faster than that of othertypes of antennas Moreover if manufactured carefully theproducts are almost identical implying that verification of thedesign microstrip prototype antenna will also be satisfactoryfor other copies of the antenna However the microstripantennas have notable disadvantages such as low powerhandling and narrow frequency bandwidth

International Journal of Antennas and Propagation 5

25

20

15

10

5

0

minus5

minus10

minus15

Theta (degrees)9070503010minus10minus30minus50minus70minus90

Sim

ulat

ed d

irect

ivity

(dBi

)E-plane (array)H-plane (array)H-plane (scan)E-plane (single)H-plane (single)

(a)

25

20

15

10

5

0

minus5

minus10

minus15

minus20

Sim

ulat

ed d

irect

ivity

gai

n (d

Bi)

Theta (degrees) x-zplane cut9075604530150minus15minus30minus45minus60minus75minus90

(b)

0

020

02

TxTy

0

minus20

minus40

minus60

minus02 minus02

Relat

ive p

ower

(dB)

(c)

Contour of sum pattern

0 01 02

0

005

01

015

02

minus02minus02

minus015

minus01

minus005

minus01

Ty -

sin(Th

)lowast

sin(P

hi)

Tx - sin(Th) lowast cos(Phi)

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40minus40

minus40

minus30

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus10

minus10

minus20

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus30minus30

minus30

minus10

minus10

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus20

minus30

minus30

(d)

Figure 3 (a) Comparison of the simulated radiation patterns of a single antenna using HFSS and a 64-element array antenna with elementspacing of 119889119909 = 55mm and 119889119910 = 8mm through (2) in E- andH-planes (119909-119911 and 119910-119911 planes) (b) Comparison of theH-plane radiation patternwith and without the adaptive algorithm demonstrating the nulls on the interference directions (120579∘ and 120601∘) of 13∘ and 0∘ 30∘ and 0∘ and 50∘and 0∘ respectively (c) 3D radiation pattern of the array (d) 2D contour of the radiation patterns

Many feeding design methods can be applied to excitemicrostrip patch antennas but a perpendicular coaxial tran-sition is the most suitable for mmW applications becausethis methodrsquos measurements indicate a return loss betterthan 14 dB and an insertion loss better than 04 dB fromDC to 40GHz [21 22] Therefore we proposed the mmWantenna array comprising 64-element perpendicular coax-fed microstrip patch antennas that resonate at 38GHz(Figure 4) The mmW microstrip patch array is integratedwith eight subarrays each comprising eight microstrippatches printed on the RF substrate with a thickness of 15milThe element spacing of the array is arranged in a triangularlattice (119889119909 = 55mm 119889119910 = 85mm) to obtain a beamscanning azimuth angle of plusmn25∘ whenmaintainingmaximumroom to allocate the modified k-connector

A key parasite of perpendicular transition is the induc-tance triggered by ground currents that must flow aroundthe circumference of the coax outer conductor to reach

the underside of the microstrip section Therefore in eachsubarray substrates with the printed microstrip patches weresoldered on amodified k-connector with four ground pins onthe four corners of the connector base to secure the antenna(Figure 5(a)) After all of the subarrays were integrated ninescrews were used to fix the RF substrate of each subarray ontothe back plane of the array (Figure 5(b)) Subsequently thearray was placed in a tin stove for wave soldering reflow Afterall subarrays were soldered on the back plane of the array allof the screws were removed

3 Numerical and Experimental Study

The design approach of the microstrip patch printed on theLTCC substrate with a dielectric constant of 59 and thicknessof 15mil was verified using HFSS (Figure 6) The transitioneffects of the coaxially fed launcher were considered in thesimulation

6 International Journal of Antennas and Propagation

k-connector

Figure 4 Design concept of the proposed mmWmicrostrip antenna array

1

23

31

21

33

34

(a)

Ground pads

Microstrippatch

(b)

Figure 5 (a) Design of a single microstrip patch (b) Close look of the assembled array

000

minus500

minus1000

minus1500

minus2000

minus2500

minus3000

Freq (GHz)

w = 10mmL = 123mmyo = 025mmdB

(S(11

))

m1

m1 373400

389600

m2

40003900380037003600

Name X Y

m2

minus102285

minus101687

Figure 6 Simulated 11987811 of a single microstrip antenna patch inset shows the simulation layout

The simulation results (Figure 6) showed a return loss ofless than 10 dB at the frequencies of interest ranging from3734 to 3889GHz To experimentally verify this designapproach two identical mmW microstrip patch antennaarrays were built for testing (Figure 7) The measurementsetup was established by connecting one patch with twommW microstrip patch arrays which were placed face-to-face 195 cm apart (Figure 8)

Two-port 119878-parameters were measured using the Rohdeamp Schwarz ZVA40 vector network analyzer (Figure 9) Thesimulated 11987811 (solid line in Figure 9) was computed usinga single microstrip patch to reduce computing time but themeasured 11987811 (the solid line with diamond shapes) and 11987822(the solid line with rectangular shapes) corresponded to thecenter element of two microstrip antenna arrays (Figure 8)Thus the discrepancy between the measured and simulated

International Journal of Antennas and Propagation 7

Figure 7 Photograph of two identical mmWmicrostrip arrays for testing

Figure 8 Measurement setup established by connecting one patch to two arrays placing two arrays face-to-face at a distance of 119877 = 195 cmand testing the 2-port S-parameters using the Rohde amp Schwarz ZVA40 vector network analyzer

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

minus45

S-pa

ram

eter

(dB)

Frequency (GHz)

Simulated_S11Measured_S11

Measured_S22Measured_S21

4039539385383753736536

Figure 9 Measured 119878-parameters of the test setup (Figure 8)

data (Figure 9) can be attributed to the reactive loading effectcaused by the mutual coupling

Next the Friis power transmission formula [23] was usedto calculate the maximum antenna power gain (in the centralforward direction of the antenna)

GrGt = G2 = (PrPt)(4120587R1205820 )

2

= 1003816100381610038161003816S2110038161003816100381610038162 (4120587R1205820 )2

(9)

where Gr and Gt are the power gains of the receiving andtransmitting antennas respectively and Pt and Pr are thetransmitted and received powers respectively Because the

two antennas are identicalGt = Gr = G and the power ratioPrPt is the measured direct transmission coefficient |S21|2which was obtained using the vector network analyzer Bysubstituting the measured |S21| into (9) the measured max-imum antenna power gain was plotted against frequenciesranging from 360 to 40GHz to compare with simulationdata (Figure 10) they indicated an acceptable agreementThemeasured gain of a singlemicrostrip patchwas approximately68 dBi at 38GHz

Finally the radiation pattern at the center element ofthe prototype mmW array (Figure 7) was measured at OIT

8 International Journal of Antennas and Propagation

10

9

8

7

6

5

4

3

2

1

0

Gai

n (d

Bi)

Frequency (GHz)

Measured_GainSimulated_Gain

4039539385383753736536

Figure 10 Comparison of the gain measured by (9) and the gain simulated using HFSS on a single microstrip patch antenna

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Amp45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(a) Amplitude

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Phase45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(b) Phase

Figure 11 Measured (a) amplitude and (b) phase of the aperture field of the mmWmicrostrip antenna array excited at the center element

near- and far-field test ranges The measured amplitude andphase of the aperture field are plotted in Figures 11(a) and11(b) respectively Meanwhile Figures 12(a) and 12(b) displayphotographs of the tested setup and Figure 12(c) illustratesplots of the measured Co-Pol and Cross-Pol for the 2Dradiation pattern cuts in the 119909-119910 and 119909-119911 planes at 3775GHz

4 Conclusion

Our design prototype for an mmW microstrip antennaarray operating at the Ka band frequency range for 5Gcommunication system applications is presented using 64-element microstrip patches printed on an LTCC substratewith a thickness of 15mil and a dielectric constant of 59

Our numerical and experimental study revealed acceptableagreement between themeasured and simulated return lossesand antenna power gain performance This confirms that amicrostrip patch antenna array with a high radiation gainperformance in an mmW range is feasible for future 5Gapplications

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors thank the Chung-Shan Institute of Science andTechnology (Taiwan) for financially supporting this research

International Journal of Antennas and Propagation 9

(a)

y

xz

(b)

0 Co-Pol90 Co-Pol

0 X-Pol90 X-Pol

Max 158

Co-Pol and X-Pol-Amp

Far-field patterns

Scan surface planar rectangularPoints per scan 51Points per scan 51

Frequency 377500

787 cm787 cm

Polarization linear AUT probe separation 394

Freq 37750ndash38250 GHz

Reference power minus4853 dBx-axisy-axis

(c)

Figure 12 (a) Amplitude and (b) phase photographs of the tested setup of the mmWmicrostrip antenna array (c) Measured 2D Co-Pol andCross-Pol radiation patterns

(CSIST-A7I-V1XX) and thank Kevin Peng for assisting in themanufacture and integration of the array

References

[1] J Thompson X Ge H-C Wu et al ldquo5G wireless communica-tion systems prospects and challenges [Guest Editorial]rdquo IEEECommunications Magazine vol 52 no 2 pp 62ndash64 2014

[2] M S Pandey M Kumar A Panwar and I Singh ldquoA surveywireless mobile technology generations with 5Grdquo InternationalJournal of Engineering Research and Technology vol 2 no 42013

[3] Ericsson ldquoMore than 50 billion connected devicesrdquo WhitePaper [Online] httpwwwakos-rssifilesTelekomunikacijeDigitalna agendaInternetni protokol Ipv6More-than-50-bil-lion-connected-devicespdf

[4] CiscoCiscoVisualNetwork Index GlobalMobile Traffic ForecastUpdate 2013

[5] Ericsson ldquoTraffic and market data reportrdquo 2011[6] UMTS Forum Mobile Traffic Forecasts 2010ndash2020 Report

UMTS Forum Zurich Switzerland 2011[7] P E Mogensen K Pajukoski B Raaf et al ldquoB4G local area

high level requirements and systemdesignrdquo inProceedings of the

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

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RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

4 International Journal of Antennas and Propagation

The polarized element pattern function for an individualelement is denoted by 120585(120579 120601) and 119908119894 (119908119894 = 119888119894119890119895120595119894) representsthe complex weighting coefficient with an amplitude of 119888119894and phase of Ψ119894 at the 119894th element of the weight vector Wwhich is generated by the adaptive algorithmThe Hermitiantranspose which combines transposition and conjugationis denoted by H and the radiation pattern of the array isdenoted by 119891(120579 120601) For a given radial vector (defined byangles 120601 and 120579) 119891(120579 120601) yields the magnitude of the arrayresponse in the and directions

The system performance enhancement of the massiveMIMO system was assessed using adaptive algorithms in anoisy environmentThe received signal of a single antenna inan additive white Gaussian noise channel is represented by119909(119905) = 119878(119905) + 119899(119905) where 119878(119905) denotes the received signal inthe direction (1205790 1206010) and 119899(119905) denotes the noiseThe adaptivebeamformerwith the selected algorithm is then derived usingthe conventional phased array approach at radiofrequency(RF) or intermediate frequency (IF) [14 15] The signalscollected from each of the antenna elements are processedand summed in the analog devices and downconverted tothe baseband The weighting process in the RF and IF analogdomains is relatively inflexible and can become complexas the number of space-division multiple-access channelsincreasesThedigital-domain or digital beamforming (DBF)approach has numerous advantages [17 18] but is alsodisadvantaged by its unavailability high cost increased signalbandwidth and the dynamic range of characteristics ofanalog-to-digital and digital-to-analog converters

In this paper themean squared error (MSE) isminimizedby using the LMS algorithm [14 19 20] as an example ofselected adaptive DBF In discrete time at time index 119896 andperiod119879119904 119905 = 119896119879119904 the input signal vector of an equally spaced119872-element array (Figure 1) is

X119896 = [1199091119896 1199092119896 119909119898119896 119909119872119896] (4)

where 119909119898119896 is the transmitted narrowband signal in a complexenvelope and 119898 is the number of antenna elements at 119896MoreoverW119896 is the weight vector at 119896 which can be appliedin the analog portion of the receiver using phase shiftersand attenuators or in the digital domain after digitizing andfiltering the signal For narrowband arrays the output is thelinear combination of the sampled inputs that are multipliedwith complex weights

119910119896 = X119896119867 sdotW119896 (5)

The optimal solution that minimizes MSE leads to theWienerndashHopf solution [14] and is given by

W119896 = R119909119909minus1 sdot r119909119889 (6)

whereR119909119909 denotes the input correlation or covariancematrixand r119909119889 is the cross-correlation vector between the receivedand training (or desired) signals

For stationary input data the process requires only thetime to yield adequate estimates of R119909119909 and r119909119889 R119909119909minus1 isthen computed and the optimal weight vector is determinedHowever because matrix inversion is nontrivial particularlywhen conducted using a digital signal processor iterativetechniques easily yield the optimal solution in a limitedtime The updated equation of these iterative approaches isgenerally expressed by the LMS algorithm [18] given by

Wk+1 =Wk minus Δ (Gk) (7)

where Δ represents the step-size value and is allowed tochange at every iteration and Gk denotes the gradient orderivative of the MSE with respect to the weight vector (W119896)

Gk = minus2rxd + 2RxxWk (8)

Stochastic gradient algorithms attempt to determine theoptimal solution by continually stepping in the negativedirection of the gradient Thus the weight vector is adjustedtoward the minimum optimal MSE surface Therefore theadaptive weighting vector can be computed with the DBFunit (Figure 1) by using (7) the adaptive weighting vector isthen fed into transceivers to adjust the amplitude and phaseof each patch antenna through the automatic gain controllerand phase shifter Consequently the far-field pattern ofthe simultaneously excited adaptive antenna array can beachieved and the SNR can be maximized to optimize thesystem performance under fading environments

Figure 3(a) indicates that the computed element gain ofa single patch antenna of 686 dBi which is achieved usingHFSS and the theoretical directivity gain improvement fora massive MIMO system with a 64-element array antennaand element spacing of 119889119909 = 55mm and 119889119910 = 85mm is18 dB according to (2) The beamwidth of the array patternis approximately 5∘ and 6∘ on the Az- and El-planes (119909-119911and 119910-119911 planes) respectively and plusmn25∘ beams are capableof electronic steering in the coverage region Furthermorewhen the MSE adaptive algorithms in (5) and (6) are appliedthe massive MIMO can synthesize the radiation pattern withnulls in the interference directions (ie (120579∘ 120601∘) = (13∘ 0∘)(30∘ 0∘) (50∘ 0∘)) to increase the system SNR (Figure 3(b))Figures 3(c) and 3(d) illustrate plots of the 3D and 2D contourradiation patterns of the array respectively

22Microstrip AntennaArrayDesign Considering the draw-backs of working at the Ka band frequencies discussed inSection 1 we employed the microstrip antennas for thisprototype study because the manufacturing process formicrostrip type antenna with the help of modem-printedcircuit technology adapted to testing and constructing pur-poses is simpler less expensive and faster than that of othertypes of antennas Moreover if manufactured carefully theproducts are almost identical implying that verification of thedesign microstrip prototype antenna will also be satisfactoryfor other copies of the antenna However the microstripantennas have notable disadvantages such as low powerhandling and narrow frequency bandwidth

International Journal of Antennas and Propagation 5

25

20

15

10

5

0

minus5

minus10

minus15

Theta (degrees)9070503010minus10minus30minus50minus70minus90

Sim

ulat

ed d

irect

ivity

(dBi

)E-plane (array)H-plane (array)H-plane (scan)E-plane (single)H-plane (single)

(a)

25

20

15

10

5

0

minus5

minus10

minus15

minus20

Sim

ulat

ed d

irect

ivity

gai

n (d

Bi)

Theta (degrees) x-zplane cut9075604530150minus15minus30minus45minus60minus75minus90

(b)

0

020

02

TxTy

0

minus20

minus40

minus60

minus02 minus02

Relat

ive p

ower

(dB)

(c)

Contour of sum pattern

0 01 02

0

005

01

015

02

minus02minus02

minus015

minus01

minus005

minus01

Ty -

sin(Th

)lowast

sin(P

hi)

Tx - sin(Th) lowast cos(Phi)

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40minus40

minus40

minus30

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus10

minus10

minus20

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus30minus30

minus30

minus10

minus10

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus20

minus30

minus30

(d)

Figure 3 (a) Comparison of the simulated radiation patterns of a single antenna using HFSS and a 64-element array antenna with elementspacing of 119889119909 = 55mm and 119889119910 = 8mm through (2) in E- andH-planes (119909-119911 and 119910-119911 planes) (b) Comparison of theH-plane radiation patternwith and without the adaptive algorithm demonstrating the nulls on the interference directions (120579∘ and 120601∘) of 13∘ and 0∘ 30∘ and 0∘ and 50∘and 0∘ respectively (c) 3D radiation pattern of the array (d) 2D contour of the radiation patterns

Many feeding design methods can be applied to excitemicrostrip patch antennas but a perpendicular coaxial tran-sition is the most suitable for mmW applications becausethis methodrsquos measurements indicate a return loss betterthan 14 dB and an insertion loss better than 04 dB fromDC to 40GHz [21 22] Therefore we proposed the mmWantenna array comprising 64-element perpendicular coax-fed microstrip patch antennas that resonate at 38GHz(Figure 4) The mmW microstrip patch array is integratedwith eight subarrays each comprising eight microstrippatches printed on the RF substrate with a thickness of 15milThe element spacing of the array is arranged in a triangularlattice (119889119909 = 55mm 119889119910 = 85mm) to obtain a beamscanning azimuth angle of plusmn25∘ whenmaintainingmaximumroom to allocate the modified k-connector

A key parasite of perpendicular transition is the induc-tance triggered by ground currents that must flow aroundthe circumference of the coax outer conductor to reach

the underside of the microstrip section Therefore in eachsubarray substrates with the printed microstrip patches weresoldered on amodified k-connector with four ground pins onthe four corners of the connector base to secure the antenna(Figure 5(a)) After all of the subarrays were integrated ninescrews were used to fix the RF substrate of each subarray ontothe back plane of the array (Figure 5(b)) Subsequently thearray was placed in a tin stove for wave soldering reflow Afterall subarrays were soldered on the back plane of the array allof the screws were removed

3 Numerical and Experimental Study

The design approach of the microstrip patch printed on theLTCC substrate with a dielectric constant of 59 and thicknessof 15mil was verified using HFSS (Figure 6) The transitioneffects of the coaxially fed launcher were considered in thesimulation

6 International Journal of Antennas and Propagation

k-connector

Figure 4 Design concept of the proposed mmWmicrostrip antenna array

1

23

31

21

33

34

(a)

Ground pads

Microstrippatch

(b)

Figure 5 (a) Design of a single microstrip patch (b) Close look of the assembled array

000

minus500

minus1000

minus1500

minus2000

minus2500

minus3000

Freq (GHz)

w = 10mmL = 123mmyo = 025mmdB

(S(11

))

m1

m1 373400

389600

m2

40003900380037003600

Name X Y

m2

minus102285

minus101687

Figure 6 Simulated 11987811 of a single microstrip antenna patch inset shows the simulation layout

The simulation results (Figure 6) showed a return loss ofless than 10 dB at the frequencies of interest ranging from3734 to 3889GHz To experimentally verify this designapproach two identical mmW microstrip patch antennaarrays were built for testing (Figure 7) The measurementsetup was established by connecting one patch with twommW microstrip patch arrays which were placed face-to-face 195 cm apart (Figure 8)

Two-port 119878-parameters were measured using the Rohdeamp Schwarz ZVA40 vector network analyzer (Figure 9) Thesimulated 11987811 (solid line in Figure 9) was computed usinga single microstrip patch to reduce computing time but themeasured 11987811 (the solid line with diamond shapes) and 11987822(the solid line with rectangular shapes) corresponded to thecenter element of two microstrip antenna arrays (Figure 8)Thus the discrepancy between the measured and simulated

International Journal of Antennas and Propagation 7

Figure 7 Photograph of two identical mmWmicrostrip arrays for testing

Figure 8 Measurement setup established by connecting one patch to two arrays placing two arrays face-to-face at a distance of 119877 = 195 cmand testing the 2-port S-parameters using the Rohde amp Schwarz ZVA40 vector network analyzer

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

minus45

S-pa

ram

eter

(dB)

Frequency (GHz)

Simulated_S11Measured_S11

Measured_S22Measured_S21

4039539385383753736536

Figure 9 Measured 119878-parameters of the test setup (Figure 8)

data (Figure 9) can be attributed to the reactive loading effectcaused by the mutual coupling

Next the Friis power transmission formula [23] was usedto calculate the maximum antenna power gain (in the centralforward direction of the antenna)

GrGt = G2 = (PrPt)(4120587R1205820 )

2

= 1003816100381610038161003816S2110038161003816100381610038162 (4120587R1205820 )2

(9)

where Gr and Gt are the power gains of the receiving andtransmitting antennas respectively and Pt and Pr are thetransmitted and received powers respectively Because the

two antennas are identicalGt = Gr = G and the power ratioPrPt is the measured direct transmission coefficient |S21|2which was obtained using the vector network analyzer Bysubstituting the measured |S21| into (9) the measured max-imum antenna power gain was plotted against frequenciesranging from 360 to 40GHz to compare with simulationdata (Figure 10) they indicated an acceptable agreementThemeasured gain of a singlemicrostrip patchwas approximately68 dBi at 38GHz

Finally the radiation pattern at the center element ofthe prototype mmW array (Figure 7) was measured at OIT

8 International Journal of Antennas and Propagation

10

9

8

7

6

5

4

3

2

1

0

Gai

n (d

Bi)

Frequency (GHz)

Measured_GainSimulated_Gain

4039539385383753736536

Figure 10 Comparison of the gain measured by (9) and the gain simulated using HFSS on a single microstrip patch antenna

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Amp45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(a) Amplitude

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Phase45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(b) Phase

Figure 11 Measured (a) amplitude and (b) phase of the aperture field of the mmWmicrostrip antenna array excited at the center element

near- and far-field test ranges The measured amplitude andphase of the aperture field are plotted in Figures 11(a) and11(b) respectively Meanwhile Figures 12(a) and 12(b) displayphotographs of the tested setup and Figure 12(c) illustratesplots of the measured Co-Pol and Cross-Pol for the 2Dradiation pattern cuts in the 119909-119910 and 119909-119911 planes at 3775GHz

4 Conclusion

Our design prototype for an mmW microstrip antennaarray operating at the Ka band frequency range for 5Gcommunication system applications is presented using 64-element microstrip patches printed on an LTCC substratewith a thickness of 15mil and a dielectric constant of 59

Our numerical and experimental study revealed acceptableagreement between themeasured and simulated return lossesand antenna power gain performance This confirms that amicrostrip patch antenna array with a high radiation gainperformance in an mmW range is feasible for future 5Gapplications

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors thank the Chung-Shan Institute of Science andTechnology (Taiwan) for financially supporting this research

International Journal of Antennas and Propagation 9

(a)

y

xz

(b)

0 Co-Pol90 Co-Pol

0 X-Pol90 X-Pol

Max 158

Co-Pol and X-Pol-Amp

Far-field patterns

Scan surface planar rectangularPoints per scan 51Points per scan 51

Frequency 377500

787 cm787 cm

Polarization linear AUT probe separation 394

Freq 37750ndash38250 GHz

Reference power minus4853 dBx-axisy-axis

(c)

Figure 12 (a) Amplitude and (b) phase photographs of the tested setup of the mmWmicrostrip antenna array (c) Measured 2D Co-Pol andCross-Pol radiation patterns

(CSIST-A7I-V1XX) and thank Kevin Peng for assisting in themanufacture and integration of the array

References

[1] J Thompson X Ge H-C Wu et al ldquo5G wireless communica-tion systems prospects and challenges [Guest Editorial]rdquo IEEECommunications Magazine vol 52 no 2 pp 62ndash64 2014

[2] M S Pandey M Kumar A Panwar and I Singh ldquoA surveywireless mobile technology generations with 5Grdquo InternationalJournal of Engineering Research and Technology vol 2 no 42013

[3] Ericsson ldquoMore than 50 billion connected devicesrdquo WhitePaper [Online] httpwwwakos-rssifilesTelekomunikacijeDigitalna agendaInternetni protokol Ipv6More-than-50-bil-lion-connected-devicespdf

[4] CiscoCiscoVisualNetwork Index GlobalMobile Traffic ForecastUpdate 2013

[5] Ericsson ldquoTraffic and market data reportrdquo 2011[6] UMTS Forum Mobile Traffic Forecasts 2010ndash2020 Report

UMTS Forum Zurich Switzerland 2011[7] P E Mogensen K Pajukoski B Raaf et al ldquoB4G local area

high level requirements and systemdesignrdquo inProceedings of the

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of Antennas and Propagation 5

25

20

15

10

5

0

minus5

minus10

minus15

Theta (degrees)9070503010minus10minus30minus50minus70minus90

Sim

ulat

ed d

irect

ivity

(dBi

)E-plane (array)H-plane (array)H-plane (scan)E-plane (single)H-plane (single)

(a)

25

20

15

10

5

0

minus5

minus10

minus15

minus20

Sim

ulat

ed d

irect

ivity

gai

n (d

Bi)

Theta (degrees) x-zplane cut9075604530150minus15minus30minus45minus60minus75minus90

(b)

0

020

02

TxTy

0

minus20

minus40

minus60

minus02 minus02

Relat

ive p

ower

(dB)

(c)

Contour of sum pattern

0 01 02

0

005

01

015

02

minus02minus02

minus015

minus01

minus005

minus01

Ty -

sin(Th

)lowast

sin(P

hi)

Tx - sin(Th) lowast cos(Phi)

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40

minus40minus40

minus40

minus30

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus20

minus10

minus10

minus20

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus30minus30

minus30

minus10

minus10

minus30

minus30

minus30

minus30

minus30

minus30

minus30

minus20

minus30

minus30

(d)

Figure 3 (a) Comparison of the simulated radiation patterns of a single antenna using HFSS and a 64-element array antenna with elementspacing of 119889119909 = 55mm and 119889119910 = 8mm through (2) in E- andH-planes (119909-119911 and 119910-119911 planes) (b) Comparison of theH-plane radiation patternwith and without the adaptive algorithm demonstrating the nulls on the interference directions (120579∘ and 120601∘) of 13∘ and 0∘ 30∘ and 0∘ and 50∘and 0∘ respectively (c) 3D radiation pattern of the array (d) 2D contour of the radiation patterns

Many feeding design methods can be applied to excitemicrostrip patch antennas but a perpendicular coaxial tran-sition is the most suitable for mmW applications becausethis methodrsquos measurements indicate a return loss betterthan 14 dB and an insertion loss better than 04 dB fromDC to 40GHz [21 22] Therefore we proposed the mmWantenna array comprising 64-element perpendicular coax-fed microstrip patch antennas that resonate at 38GHz(Figure 4) The mmW microstrip patch array is integratedwith eight subarrays each comprising eight microstrippatches printed on the RF substrate with a thickness of 15milThe element spacing of the array is arranged in a triangularlattice (119889119909 = 55mm 119889119910 = 85mm) to obtain a beamscanning azimuth angle of plusmn25∘ whenmaintainingmaximumroom to allocate the modified k-connector

A key parasite of perpendicular transition is the induc-tance triggered by ground currents that must flow aroundthe circumference of the coax outer conductor to reach

the underside of the microstrip section Therefore in eachsubarray substrates with the printed microstrip patches weresoldered on amodified k-connector with four ground pins onthe four corners of the connector base to secure the antenna(Figure 5(a)) After all of the subarrays were integrated ninescrews were used to fix the RF substrate of each subarray ontothe back plane of the array (Figure 5(b)) Subsequently thearray was placed in a tin stove for wave soldering reflow Afterall subarrays were soldered on the back plane of the array allof the screws were removed

3 Numerical and Experimental Study

The design approach of the microstrip patch printed on theLTCC substrate with a dielectric constant of 59 and thicknessof 15mil was verified using HFSS (Figure 6) The transitioneffects of the coaxially fed launcher were considered in thesimulation

6 International Journal of Antennas and Propagation

k-connector

Figure 4 Design concept of the proposed mmWmicrostrip antenna array

1

23

31

21

33

34

(a)

Ground pads

Microstrippatch

(b)

Figure 5 (a) Design of a single microstrip patch (b) Close look of the assembled array

000

minus500

minus1000

minus1500

minus2000

minus2500

minus3000

Freq (GHz)

w = 10mmL = 123mmyo = 025mmdB

(S(11

))

m1

m1 373400

389600

m2

40003900380037003600

Name X Y

m2

minus102285

minus101687

Figure 6 Simulated 11987811 of a single microstrip antenna patch inset shows the simulation layout

The simulation results (Figure 6) showed a return loss ofless than 10 dB at the frequencies of interest ranging from3734 to 3889GHz To experimentally verify this designapproach two identical mmW microstrip patch antennaarrays were built for testing (Figure 7) The measurementsetup was established by connecting one patch with twommW microstrip patch arrays which were placed face-to-face 195 cm apart (Figure 8)

Two-port 119878-parameters were measured using the Rohdeamp Schwarz ZVA40 vector network analyzer (Figure 9) Thesimulated 11987811 (solid line in Figure 9) was computed usinga single microstrip patch to reduce computing time but themeasured 11987811 (the solid line with diamond shapes) and 11987822(the solid line with rectangular shapes) corresponded to thecenter element of two microstrip antenna arrays (Figure 8)Thus the discrepancy between the measured and simulated

International Journal of Antennas and Propagation 7

Figure 7 Photograph of two identical mmWmicrostrip arrays for testing

Figure 8 Measurement setup established by connecting one patch to two arrays placing two arrays face-to-face at a distance of 119877 = 195 cmand testing the 2-port S-parameters using the Rohde amp Schwarz ZVA40 vector network analyzer

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

minus45

S-pa

ram

eter

(dB)

Frequency (GHz)

Simulated_S11Measured_S11

Measured_S22Measured_S21

4039539385383753736536

Figure 9 Measured 119878-parameters of the test setup (Figure 8)

data (Figure 9) can be attributed to the reactive loading effectcaused by the mutual coupling

Next the Friis power transmission formula [23] was usedto calculate the maximum antenna power gain (in the centralforward direction of the antenna)

GrGt = G2 = (PrPt)(4120587R1205820 )

2

= 1003816100381610038161003816S2110038161003816100381610038162 (4120587R1205820 )2

(9)

where Gr and Gt are the power gains of the receiving andtransmitting antennas respectively and Pt and Pr are thetransmitted and received powers respectively Because the

two antennas are identicalGt = Gr = G and the power ratioPrPt is the measured direct transmission coefficient |S21|2which was obtained using the vector network analyzer Bysubstituting the measured |S21| into (9) the measured max-imum antenna power gain was plotted against frequenciesranging from 360 to 40GHz to compare with simulationdata (Figure 10) they indicated an acceptable agreementThemeasured gain of a singlemicrostrip patchwas approximately68 dBi at 38GHz

Finally the radiation pattern at the center element ofthe prototype mmW array (Figure 7) was measured at OIT

8 International Journal of Antennas and Propagation

10

9

8

7

6

5

4

3

2

1

0

Gai

n (d

Bi)

Frequency (GHz)

Measured_GainSimulated_Gain

4039539385383753736536

Figure 10 Comparison of the gain measured by (9) and the gain simulated using HFSS on a single microstrip patch antenna

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Amp45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(a) Amplitude

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Phase45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(b) Phase

Figure 11 Measured (a) amplitude and (b) phase of the aperture field of the mmWmicrostrip antenna array excited at the center element

near- and far-field test ranges The measured amplitude andphase of the aperture field are plotted in Figures 11(a) and11(b) respectively Meanwhile Figures 12(a) and 12(b) displayphotographs of the tested setup and Figure 12(c) illustratesplots of the measured Co-Pol and Cross-Pol for the 2Dradiation pattern cuts in the 119909-119910 and 119909-119911 planes at 3775GHz

4 Conclusion

Our design prototype for an mmW microstrip antennaarray operating at the Ka band frequency range for 5Gcommunication system applications is presented using 64-element microstrip patches printed on an LTCC substratewith a thickness of 15mil and a dielectric constant of 59

Our numerical and experimental study revealed acceptableagreement between themeasured and simulated return lossesand antenna power gain performance This confirms that amicrostrip patch antenna array with a high radiation gainperformance in an mmW range is feasible for future 5Gapplications

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors thank the Chung-Shan Institute of Science andTechnology (Taiwan) for financially supporting this research

International Journal of Antennas and Propagation 9

(a)

y

xz

(b)

0 Co-Pol90 Co-Pol

0 X-Pol90 X-Pol

Max 158

Co-Pol and X-Pol-Amp

Far-field patterns

Scan surface planar rectangularPoints per scan 51Points per scan 51

Frequency 377500

787 cm787 cm

Polarization linear AUT probe separation 394

Freq 37750ndash38250 GHz

Reference power minus4853 dBx-axisy-axis

(c)

Figure 12 (a) Amplitude and (b) phase photographs of the tested setup of the mmWmicrostrip antenna array (c) Measured 2D Co-Pol andCross-Pol radiation patterns

(CSIST-A7I-V1XX) and thank Kevin Peng for assisting in themanufacture and integration of the array

References

[1] J Thompson X Ge H-C Wu et al ldquo5G wireless communica-tion systems prospects and challenges [Guest Editorial]rdquo IEEECommunications Magazine vol 52 no 2 pp 62ndash64 2014

[2] M S Pandey M Kumar A Panwar and I Singh ldquoA surveywireless mobile technology generations with 5Grdquo InternationalJournal of Engineering Research and Technology vol 2 no 42013

[3] Ericsson ldquoMore than 50 billion connected devicesrdquo WhitePaper [Online] httpwwwakos-rssifilesTelekomunikacijeDigitalna agendaInternetni protokol Ipv6More-than-50-bil-lion-connected-devicespdf

[4] CiscoCiscoVisualNetwork Index GlobalMobile Traffic ForecastUpdate 2013

[5] Ericsson ldquoTraffic and market data reportrdquo 2011[6] UMTS Forum Mobile Traffic Forecasts 2010ndash2020 Report

UMTS Forum Zurich Switzerland 2011[7] P E Mogensen K Pajukoski B Raaf et al ldquoB4G local area

high level requirements and systemdesignrdquo inProceedings of the

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

6 International Journal of Antennas and Propagation

k-connector

Figure 4 Design concept of the proposed mmWmicrostrip antenna array

1

23

31

21

33

34

(a)

Ground pads

Microstrippatch

(b)

Figure 5 (a) Design of a single microstrip patch (b) Close look of the assembled array

000

minus500

minus1000

minus1500

minus2000

minus2500

minus3000

Freq (GHz)

w = 10mmL = 123mmyo = 025mmdB

(S(11

))

m1

m1 373400

389600

m2

40003900380037003600

Name X Y

m2

minus102285

minus101687

Figure 6 Simulated 11987811 of a single microstrip antenna patch inset shows the simulation layout

The simulation results (Figure 6) showed a return loss ofless than 10 dB at the frequencies of interest ranging from3734 to 3889GHz To experimentally verify this designapproach two identical mmW microstrip patch antennaarrays were built for testing (Figure 7) The measurementsetup was established by connecting one patch with twommW microstrip patch arrays which were placed face-to-face 195 cm apart (Figure 8)

Two-port 119878-parameters were measured using the Rohdeamp Schwarz ZVA40 vector network analyzer (Figure 9) Thesimulated 11987811 (solid line in Figure 9) was computed usinga single microstrip patch to reduce computing time but themeasured 11987811 (the solid line with diamond shapes) and 11987822(the solid line with rectangular shapes) corresponded to thecenter element of two microstrip antenna arrays (Figure 8)Thus the discrepancy between the measured and simulated

International Journal of Antennas and Propagation 7

Figure 7 Photograph of two identical mmWmicrostrip arrays for testing

Figure 8 Measurement setup established by connecting one patch to two arrays placing two arrays face-to-face at a distance of 119877 = 195 cmand testing the 2-port S-parameters using the Rohde amp Schwarz ZVA40 vector network analyzer

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

minus45

S-pa

ram

eter

(dB)

Frequency (GHz)

Simulated_S11Measured_S11

Measured_S22Measured_S21

4039539385383753736536

Figure 9 Measured 119878-parameters of the test setup (Figure 8)

data (Figure 9) can be attributed to the reactive loading effectcaused by the mutual coupling

Next the Friis power transmission formula [23] was usedto calculate the maximum antenna power gain (in the centralforward direction of the antenna)

GrGt = G2 = (PrPt)(4120587R1205820 )

2

= 1003816100381610038161003816S2110038161003816100381610038162 (4120587R1205820 )2

(9)

where Gr and Gt are the power gains of the receiving andtransmitting antennas respectively and Pt and Pr are thetransmitted and received powers respectively Because the

two antennas are identicalGt = Gr = G and the power ratioPrPt is the measured direct transmission coefficient |S21|2which was obtained using the vector network analyzer Bysubstituting the measured |S21| into (9) the measured max-imum antenna power gain was plotted against frequenciesranging from 360 to 40GHz to compare with simulationdata (Figure 10) they indicated an acceptable agreementThemeasured gain of a singlemicrostrip patchwas approximately68 dBi at 38GHz

Finally the radiation pattern at the center element ofthe prototype mmW array (Figure 7) was measured at OIT

8 International Journal of Antennas and Propagation

10

9

8

7

6

5

4

3

2

1

0

Gai

n (d

Bi)

Frequency (GHz)

Measured_GainSimulated_Gain

4039539385383753736536

Figure 10 Comparison of the gain measured by (9) and the gain simulated using HFSS on a single microstrip patch antenna

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Amp45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(a) Amplitude

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Phase45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(b) Phase

Figure 11 Measured (a) amplitude and (b) phase of the aperture field of the mmWmicrostrip antenna array excited at the center element

near- and far-field test ranges The measured amplitude andphase of the aperture field are plotted in Figures 11(a) and11(b) respectively Meanwhile Figures 12(a) and 12(b) displayphotographs of the tested setup and Figure 12(c) illustratesplots of the measured Co-Pol and Cross-Pol for the 2Dradiation pattern cuts in the 119909-119910 and 119909-119911 planes at 3775GHz

4 Conclusion

Our design prototype for an mmW microstrip antennaarray operating at the Ka band frequency range for 5Gcommunication system applications is presented using 64-element microstrip patches printed on an LTCC substratewith a thickness of 15mil and a dielectric constant of 59

Our numerical and experimental study revealed acceptableagreement between themeasured and simulated return lossesand antenna power gain performance This confirms that amicrostrip patch antenna array with a high radiation gainperformance in an mmW range is feasible for future 5Gapplications

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors thank the Chung-Shan Institute of Science andTechnology (Taiwan) for financially supporting this research

International Journal of Antennas and Propagation 9

(a)

y

xz

(b)

0 Co-Pol90 Co-Pol

0 X-Pol90 X-Pol

Max 158

Co-Pol and X-Pol-Amp

Far-field patterns

Scan surface planar rectangularPoints per scan 51Points per scan 51

Frequency 377500

787 cm787 cm

Polarization linear AUT probe separation 394

Freq 37750ndash38250 GHz

Reference power minus4853 dBx-axisy-axis

(c)

Figure 12 (a) Amplitude and (b) phase photographs of the tested setup of the mmWmicrostrip antenna array (c) Measured 2D Co-Pol andCross-Pol radiation patterns

(CSIST-A7I-V1XX) and thank Kevin Peng for assisting in themanufacture and integration of the array

References

[1] J Thompson X Ge H-C Wu et al ldquo5G wireless communica-tion systems prospects and challenges [Guest Editorial]rdquo IEEECommunications Magazine vol 52 no 2 pp 62ndash64 2014

[2] M S Pandey M Kumar A Panwar and I Singh ldquoA surveywireless mobile technology generations with 5Grdquo InternationalJournal of Engineering Research and Technology vol 2 no 42013

[3] Ericsson ldquoMore than 50 billion connected devicesrdquo WhitePaper [Online] httpwwwakos-rssifilesTelekomunikacijeDigitalna agendaInternetni protokol Ipv6More-than-50-bil-lion-connected-devicespdf

[4] CiscoCiscoVisualNetwork Index GlobalMobile Traffic ForecastUpdate 2013

[5] Ericsson ldquoTraffic and market data reportrdquo 2011[6] UMTS Forum Mobile Traffic Forecasts 2010ndash2020 Report

UMTS Forum Zurich Switzerland 2011[7] P E Mogensen K Pajukoski B Raaf et al ldquoB4G local area

high level requirements and systemdesignrdquo inProceedings of the

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of Antennas and Propagation 7

Figure 7 Photograph of two identical mmWmicrostrip arrays for testing

Figure 8 Measurement setup established by connecting one patch to two arrays placing two arrays face-to-face at a distance of 119877 = 195 cmand testing the 2-port S-parameters using the Rohde amp Schwarz ZVA40 vector network analyzer

0

minus5

minus10

minus15

minus20

minus25

minus30

minus35

minus40

minus45

S-pa

ram

eter

(dB)

Frequency (GHz)

Simulated_S11Measured_S11

Measured_S22Measured_S21

4039539385383753736536

Figure 9 Measured 119878-parameters of the test setup (Figure 8)

data (Figure 9) can be attributed to the reactive loading effectcaused by the mutual coupling

Next the Friis power transmission formula [23] was usedto calculate the maximum antenna power gain (in the centralforward direction of the antenna)

GrGt = G2 = (PrPt)(4120587R1205820 )

2

= 1003816100381610038161003816S2110038161003816100381610038162 (4120587R1205820 )2

(9)

where Gr and Gt are the power gains of the receiving andtransmitting antennas respectively and Pt and Pr are thetransmitted and received powers respectively Because the

two antennas are identicalGt = Gr = G and the power ratioPrPt is the measured direct transmission coefficient |S21|2which was obtained using the vector network analyzer Bysubstituting the measured |S21| into (9) the measured max-imum antenna power gain was plotted against frequenciesranging from 360 to 40GHz to compare with simulationdata (Figure 10) they indicated an acceptable agreementThemeasured gain of a singlemicrostrip patchwas approximately68 dBi at 38GHz

Finally the radiation pattern at the center element ofthe prototype mmW array (Figure 7) was measured at OIT

8 International Journal of Antennas and Propagation

10

9

8

7

6

5

4

3

2

1

0

Gai

n (d

Bi)

Frequency (GHz)

Measured_GainSimulated_Gain

4039539385383753736536

Figure 10 Comparison of the gain measured by (9) and the gain simulated using HFSS on a single microstrip patch antenna

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Amp45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(a) Amplitude

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Phase45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(b) Phase

Figure 11 Measured (a) amplitude and (b) phase of the aperture field of the mmWmicrostrip antenna array excited at the center element

near- and far-field test ranges The measured amplitude andphase of the aperture field are plotted in Figures 11(a) and11(b) respectively Meanwhile Figures 12(a) and 12(b) displayphotographs of the tested setup and Figure 12(c) illustratesplots of the measured Co-Pol and Cross-Pol for the 2Dradiation pattern cuts in the 119909-119910 and 119909-119911 planes at 3775GHz

4 Conclusion

Our design prototype for an mmW microstrip antennaarray operating at the Ka band frequency range for 5Gcommunication system applications is presented using 64-element microstrip patches printed on an LTCC substratewith a thickness of 15mil and a dielectric constant of 59

Our numerical and experimental study revealed acceptableagreement between themeasured and simulated return lossesand antenna power gain performance This confirms that amicrostrip patch antenna array with a high radiation gainperformance in an mmW range is feasible for future 5Gapplications

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors thank the Chung-Shan Institute of Science andTechnology (Taiwan) for financially supporting this research

International Journal of Antennas and Propagation 9

(a)

y

xz

(b)

0 Co-Pol90 Co-Pol

0 X-Pol90 X-Pol

Max 158

Co-Pol and X-Pol-Amp

Far-field patterns

Scan surface planar rectangularPoints per scan 51Points per scan 51

Frequency 377500

787 cm787 cm

Polarization linear AUT probe separation 394

Freq 37750ndash38250 GHz

Reference power minus4853 dBx-axisy-axis

(c)

Figure 12 (a) Amplitude and (b) phase photographs of the tested setup of the mmWmicrostrip antenna array (c) Measured 2D Co-Pol andCross-Pol radiation patterns

(CSIST-A7I-V1XX) and thank Kevin Peng for assisting in themanufacture and integration of the array

References

[1] J Thompson X Ge H-C Wu et al ldquo5G wireless communica-tion systems prospects and challenges [Guest Editorial]rdquo IEEECommunications Magazine vol 52 no 2 pp 62ndash64 2014

[2] M S Pandey M Kumar A Panwar and I Singh ldquoA surveywireless mobile technology generations with 5Grdquo InternationalJournal of Engineering Research and Technology vol 2 no 42013

[3] Ericsson ldquoMore than 50 billion connected devicesrdquo WhitePaper [Online] httpwwwakos-rssifilesTelekomunikacijeDigitalna agendaInternetni protokol Ipv6More-than-50-bil-lion-connected-devicespdf

[4] CiscoCiscoVisualNetwork Index GlobalMobile Traffic ForecastUpdate 2013

[5] Ericsson ldquoTraffic and market data reportrdquo 2011[6] UMTS Forum Mobile Traffic Forecasts 2010ndash2020 Report

UMTS Forum Zurich Switzerland 2011[7] P E Mogensen K Pajukoski B Raaf et al ldquoB4G local area

high level requirements and systemdesignrdquo inProceedings of the

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

8 International Journal of Antennas and Propagation

10

9

8

7

6

5

4

3

2

1

0

Gai

n (d

Bi)

Frequency (GHz)

Measured_GainSimulated_Gain

4039539385383753736536

Figure 10 Comparison of the gain measured by (9) and the gain simulated using HFSS on a single microstrip patch antenna

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Amp45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(a) Amplitude

Thet

aY(d

eg)

Theta X (deg)

Co-Pol-Phase45

45

30

30

15

15

0

0

minus15

minus15

minus30

minus30minus45

minus45

(b) Phase

Figure 11 Measured (a) amplitude and (b) phase of the aperture field of the mmWmicrostrip antenna array excited at the center element

near- and far-field test ranges The measured amplitude andphase of the aperture field are plotted in Figures 11(a) and11(b) respectively Meanwhile Figures 12(a) and 12(b) displayphotographs of the tested setup and Figure 12(c) illustratesplots of the measured Co-Pol and Cross-Pol for the 2Dradiation pattern cuts in the 119909-119910 and 119909-119911 planes at 3775GHz

4 Conclusion

Our design prototype for an mmW microstrip antennaarray operating at the Ka band frequency range for 5Gcommunication system applications is presented using 64-element microstrip patches printed on an LTCC substratewith a thickness of 15mil and a dielectric constant of 59

Our numerical and experimental study revealed acceptableagreement between themeasured and simulated return lossesand antenna power gain performance This confirms that amicrostrip patch antenna array with a high radiation gainperformance in an mmW range is feasible for future 5Gapplications

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors thank the Chung-Shan Institute of Science andTechnology (Taiwan) for financially supporting this research

International Journal of Antennas and Propagation 9

(a)

y

xz

(b)

0 Co-Pol90 Co-Pol

0 X-Pol90 X-Pol

Max 158

Co-Pol and X-Pol-Amp

Far-field patterns

Scan surface planar rectangularPoints per scan 51Points per scan 51

Frequency 377500

787 cm787 cm

Polarization linear AUT probe separation 394

Freq 37750ndash38250 GHz

Reference power minus4853 dBx-axisy-axis

(c)

Figure 12 (a) Amplitude and (b) phase photographs of the tested setup of the mmWmicrostrip antenna array (c) Measured 2D Co-Pol andCross-Pol radiation patterns

(CSIST-A7I-V1XX) and thank Kevin Peng for assisting in themanufacture and integration of the array

References

[1] J Thompson X Ge H-C Wu et al ldquo5G wireless communica-tion systems prospects and challenges [Guest Editorial]rdquo IEEECommunications Magazine vol 52 no 2 pp 62ndash64 2014

[2] M S Pandey M Kumar A Panwar and I Singh ldquoA surveywireless mobile technology generations with 5Grdquo InternationalJournal of Engineering Research and Technology vol 2 no 42013

[3] Ericsson ldquoMore than 50 billion connected devicesrdquo WhitePaper [Online] httpwwwakos-rssifilesTelekomunikacijeDigitalna agendaInternetni protokol Ipv6More-than-50-bil-lion-connected-devicespdf

[4] CiscoCiscoVisualNetwork Index GlobalMobile Traffic ForecastUpdate 2013

[5] Ericsson ldquoTraffic and market data reportrdquo 2011[6] UMTS Forum Mobile Traffic Forecasts 2010ndash2020 Report

UMTS Forum Zurich Switzerland 2011[7] P E Mogensen K Pajukoski B Raaf et al ldquoB4G local area

high level requirements and systemdesignrdquo inProceedings of the

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of Antennas and Propagation 9

(a)

y

xz

(b)

0 Co-Pol90 Co-Pol

0 X-Pol90 X-Pol

Max 158

Co-Pol and X-Pol-Amp

Far-field patterns

Scan surface planar rectangularPoints per scan 51Points per scan 51

Frequency 377500

787 cm787 cm

Polarization linear AUT probe separation 394

Freq 37750ndash38250 GHz

Reference power minus4853 dBx-axisy-axis

(c)

Figure 12 (a) Amplitude and (b) phase photographs of the tested setup of the mmWmicrostrip antenna array (c) Measured 2D Co-Pol andCross-Pol radiation patterns

(CSIST-A7I-V1XX) and thank Kevin Peng for assisting in themanufacture and integration of the array

References

[1] J Thompson X Ge H-C Wu et al ldquo5G wireless communica-tion systems prospects and challenges [Guest Editorial]rdquo IEEECommunications Magazine vol 52 no 2 pp 62ndash64 2014

[2] M S Pandey M Kumar A Panwar and I Singh ldquoA surveywireless mobile technology generations with 5Grdquo InternationalJournal of Engineering Research and Technology vol 2 no 42013

[3] Ericsson ldquoMore than 50 billion connected devicesrdquo WhitePaper [Online] httpwwwakos-rssifilesTelekomunikacijeDigitalna agendaInternetni protokol Ipv6More-than-50-bil-lion-connected-devicespdf

[4] CiscoCiscoVisualNetwork Index GlobalMobile Traffic ForecastUpdate 2013

[5] Ericsson ldquoTraffic and market data reportrdquo 2011[6] UMTS Forum Mobile Traffic Forecasts 2010ndash2020 Report

UMTS Forum Zurich Switzerland 2011[7] P E Mogensen K Pajukoski B Raaf et al ldquoB4G local area

high level requirements and systemdesignrdquo inProceedings of the

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

10 International Journal of Antennas and Propagation

IEEE Globecom Workshops (GC Wkshps rsquo12) pp 613ndash617 IEEEAnaheim Calif USA December 2012

[8] T S Rappaport J N Murdock and F Gutierrez ldquoState ofthe art in 60-GHz integrated circuits and systems for wirelesscommunicationsrdquo Proceedings of the IEEE vol 99 no 8 pp1390ndash1436 2011

[9] F Khan and Z Pi ldquoMillimeter wave mobile broadband (MMB)unleashing the 3ndash300GHz spectrumrdquo in Proceedings of the 34thIEEE Sarnoff Symposium March 2011

[10] Z Pi and F Khan ldquoAn introduction to millimeter-wave mobilebroadband systemsrdquo IEEE Communications Magazine vol 49no 6 pp 101ndash107 2011

[11] P Pietraski D Britz A Roy R Pragada and G CharltonldquoMillimeter wave and terahertz communications feasibility andchallengesrdquo ZTE Communications vol 10 no 4 pp 3ndash12 2012

[12] Y P Zhang and D Liu ldquoAntenna-on-chip and antenna-in-package solutions to highly integrated millimeter-wave devicesfor wireless communicationsrdquo IEEE Transactions on Antennasand Propagation vol 57 no 10 pp 2830ndash2841 2009

[13] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cel-lular wireless networks potentials and challengesrdquo Proceedingsof the IEEE vol 102 no 3 pp 366ndash385 2014

[14] B Widrow L J Griffiths P E Mantey and B B GoodeldquoAdaptive antenna systemsrdquo Proceedings of the IEEE vol 55 no12 pp 2143ndash2159 1967

[15] W F Gabriel ldquoAdaptive arraymdashan introductionrdquo Proceeding ofIEEE vol 55 no 12 pp 2144ndash2159 1967

[16] C-N Hu ldquoA novel method for calibrating deployed activeantenna arraysrdquo IEEE Transactions on Antennas and Propaga-tion vol 63 no 4 pp 1650ndash1657 2015

[17] J E Hudson Adaptive Array Principles (IEEE ElectromagneticWaves Series) Institution of Engineering and TechnologyStevenage UK 1981

[18] J G ProakisDigital Communications McGraw-Hill NewYorkNY USA 4th edition 2001

[19] MWennstromOnMIMO systems and adaptive arrays for wire-less communication [PhD thesis] Uppsala University UppsalaSweden 2002

[20] G Tsoulos M Beach and J McGeehan ldquoSpace divisionmultiple access (SDMA) field trials Part 2 calibration andlinearity issuesrdquo IEE Proceedings-Radar Sonar and Navigationvol 145 no 1 pp 79ndash84 1998

[21] M Morgan and S Weinreb ldquoA millimeter-wave perpendicularcoax-to-microstrip transitionrdquo in Proceedings of the IEEE MSS-S International Microwave Symposium Digest pp 817ndash820 June2002

[22] J Chenkin ldquoDC to 40GHz coaxial-to-microstrip transitionfor 100- m-thick GaAs substratesrdquo IEEE Transactions onMicrowave Theory and Techniques vol 37 pp 1147ndash1150 1989

[23] D K Misra and K M Devendra Radio-Frequency andMicrowave Communications Circuits-Analysis and Design Ch24 Antenna Systems John Wiley amp Son Inc Hoboken NJUSA 2nd edition 2004

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of