reader application The final measured and simulated results

show satisfactory performance and good agreement

REFERENCES

1 DH Lee PJ Park JP Kim and JH Choi Aperture coupled UHF

RFID reader antenna for a handheld application Microwave Opt

Technol Lett 50 (2008) 1261ndash1263

2 YF Lin HM Chen SC Pan YC Kao and CY Lin Adjustable

axial ratio of single-layer circularly polarised patch antenna for port-

able RFID reader Electron Lett 45 (2009) 290ndash292

3 HH Li XQ Mou Z Ji H Yu Y Li and L Jiang Miniature

RFID tri-band CPW-fed antenna optimised using ISPO algorithm

Electron Lett 47 (2011) 161ndash162

4 CJ Wang and YC Lin New CPW-fed monopole antennas with

both linear and circular polarisations IET Microwave Antennas

Propag 2 (2008) 466ndash472

5 JW Wu JY Ke CF Jou and CJ Wang Microstrip-fed broad-

band circularly polarized monopole antenna IET Microwave Anten-

nas Propag 4 (2010) 518ndash525

6 A Ghobadi and M Dehmollaian A printed circularly polarized Y-

shaped monopole antenna IEEE Antenna Wireless Propag Lett 11

(2012) 22ndash25

7 JY Jan and LC Tseng Small planar monopole antenna with a

shorted parasitic inverted-L wire for wireless communications in the

24- 52- and 58-GHz bands IEEE Trans Antennas Propag 52

(2004) 1903ndash1905

VC 2014 Wiley Periodicals Inc

RADIATION-REJECTION BANDINSERTED DUAL-BAND ANTENNAUSING A SPLIT RING RESONATORFOR BEYOND 4G APPLICATIONS

In-Yong Park1 Jung-Nam Lee2 Kwang-Chun Lee2

Pyeong-Jung Song2 and Dongho Kim1

1 Department of Electronic Engineering Sejong University 209Neungdong-ro Gwangjin-gu Seoul 143ndash747 Korea Correspondingauthor dongkimsejongackr2 Department of B4G Mobile Communications Research Electronicsand Telecommunications Research Institute 218 Gajeong-roYuseong-gu Daejeon 305-700 Korea

Received 8 August 2013

ABSTRACT We propose a very simple but effective method to switcha single-band antenna into a dual-band antenna by inserting a narrow

radiation-prohibited band in the middle of the single pass band Toinsert the radiation-rejection band we intentionally induce strong reso-nance on a metamaterial-motivated split ring resonator (SRR) by placing

it near a signal feeding transmission line of a proximity-coupled micro-strip patch antenna which blocks out flow of electromagnetic wavesthrough the line To maximize the blockage we cut the SRR into a quad-

rangular loop that is exactly interlocked with the two sides of the right-angled microstrip line Consequently we show that we can split one

pass band into two separated pass bands with an inserted sharp stopband in-between Good agreements between the prediction and the mea-surement prove the validness of our approach VC 2014 Wiley

Periodicals Inc Microwave Opt Technol Lett 56961ndash965 2014 View

this article online at wileyonlinelibrarycom DOI 101002mop28240

Key words radiation-rejection band guard band B4G antenna split

ring resonator

1 INTRODUCTION

Recently mobile communication services have dramatically

evolved to the current fourth generation (4G) system that is rep-

resented by long-term evolution (LTE) or LTE-advanced tech-

nology Currently to support an expected explosive increase of

data transmission speed and cell capacity in future mobile com-

munication environment ongoing study continuously extends its

research areas beyond 4G (B4G) systems [1]

In accordance with evolution of the mobile communication

environment mobile base station antenna (MBSA) technology

has also been developed rapidly As one prominent approach of

useful MBSA techniques inserting a guard band which is a sort

of suppressed radiation frequency band has been reported to

reduce interference between transmitter and receiver systems [2]

With regard to generation of the guard band installing an

artificial magnetic conductor (AMC) or an electromagnetic

(EM) band gap (EBG) material which is incorporated with an

adjacent main radiator is representative conventional approach

[2ndash4] Although the mentioned approaches are fairly effective in

reducing antenna gain in the guard band they generally require

additional layers or spaces to mount AMCs or EBG structures

which increases complexity and fabrication cost of antennas

To overcome the problems we propose a very simple but

valuable method to create a radiation-prohibited guard band

using a split ring resonator (SRR) which is well-known as one

of left-handed metamaterial structures [5 6] As was reported in

[7 8] strong energy coupling between a transmission line and a

nearby scatterer blocks energy transfer through the line The

strength of the energy blockage is proportional to a total number

of scatterers installed near the line which often becomes an

obstructive factor in practical implementation especially under

circumstances of requiring strong blockage with only a limited

small installation space

In spite of the well-known drawbacks in this article we

show that we can introduce a guard band in an existing pass

band by placing only one SRR near a bent microstrip line

which provides relatively high radiation-rejection property For

experimental verification we apply our idea to a dual-band base

station antenna for a B4G mobile communication service which

has a target frequency band covering from 25 to 2695 GHz

(Rx 25ndash252 GHz and Tx 2675ndash2 695 GHz) All simulation

data are obtained using the commercial simulation tool of CST

Microwave Studio [9]

2 ANTENNA DESIGN

Figure 1 shows the exploded view of the proposed antenna For

polarization diversity of 90 we arrange two signal-feed lines

orthogonally with each other which are shown in Figure 1(a)

Each end of the lines is directly connected to a 50-X coaxial

connector using a direct probe feeding method EM waves flow-

ing along the feed lines couple to the radiating patch shown in

Figure 1(b) which accomplishes proximity coupling from the

lines onto the radiating patch [10 11]

As was aforementioned one of the target applications of our

antenna is a base station antenna required for B4G communica-

tions which usually needs multiple stacks of the proposed

antennas to meet the desired performance of mobile cells under

various operational environments Therefore isolation among

antennas should be secured as highly as possible For that rea-

son we enclosed our antenna with a metallic cavity as shown in

Figure 1(c) which is covered by a top radome As a result

besides high isolation we can also increase both realized gain

and front-to-back ratio (FBR) up to about 7 and 25 dBi (see

Figs 6 and 7) respectively

In Figure 1(a) we can find two SRRs placed near each corner

of the feed lines which are installed to introduce a very narrow

DOI 101002mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol 56 No 4 April 2014 961

stop band into a wide pass band Figure 2(a) tells us how we can

get the very sharp stop band by placing the SRR closed to a nor-

mal microstrip line EM waves propagate into Port 2 along a 50-

X microstrip line etched on the same substrate used in Figure

1(a) When we put the SRR near the line the SRR resonates at a

specific frequency at which the circumferential length of the SRR

becomes about a half of a guided wavelength At the resonant

frequency the SRR strongly resonates as shown in the inset in

Figure 2(a) which conceptually illustrates flowing of induced sur-

face current density The thicker and the longer arrows mean the

stronger current density From Figure 2(b) it is worth noting that

we can change the bandwidth of S11 by increasing or decreasing

the gap distance (g1) between the microstrip line and the SRR

which can be explained by parasitic inductance and capacitance

[12] In other words we can control any radiation-rejection band-

width by changing the distance g1

Figure 1 Geometry of the proposed antenna for (a) signal-feed lines (b) a radiating patch and (c) a side view of a whole structure with wx 5 70 mm

wy 5 70 mm w1 5 63 mm w2 5 1 mm w3 5 80 mm l6 5 37 mm l5 5 19 mm l1 5 37 mm l2 5 29 mm l3 5 973 mm l4 5 902 mm g1 5 3 mm

g2 5 1 mm g3 5 23 mm g4 5 14 mm h1 5 30 mm h2 5 17 mm h3 5 4 mm d1 5 16 mm d2 5 2 mm er1 5 er2 5 43 and er3 5 35

Figure 2 Resonance property of the proposed MTM structure with (a) induced surface current density and (b) S11 for some different gap distances

(g1) Physical dimension of the SRR is exactly the same with that used in Figure 1(a) [Color figure can be viewed in the online issue which is available

at wileyonlinelibrarycom]

962 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol 56 No 4 April 2014 DOI 101002mop

stop band into a wide pass band Figure 2(a) tells us how we can

get the very sharp stop band by placing the SRR closed to a nor-

mal microstrip line EM waves propagate into Port 2 along a 50-

X microstrip line etched on the same substrate used in Figure

1(a) When we put the SRR near the line the SRR resonates at a

specific frequency at which the circumferential length of the SRR

becomes about a half of a guided wavelength At the resonant

frequency the SRR strongly resonates as shown in the inset in

Figure 2(a) which conceptually illustrates flowing of induced sur-

face current density The thicker and the longer arrows mean the

stronger current density From Figure 2(b) it is worth noting that

we can change the bandwidth of S11 by increasing or decreasing

the gap distance (g1) between the microstrip line and the SRR

which can be explained by parasitic inductance and capacitance

[12] In other words we can control any radiation-rejection band-

width by changing the distance g1

Figure 1 Geometry of the proposed antenna for (a) signal-feed lines (b) a radiating patch and (c) a side view of a whole structure with wx 5 70 mm

wy 5 70 mm w1 5 63 mm w2 5 1 mm w3 5 80 mm l6 5 37 mm l5 5 19 mm l1 5 37 mm l2 5 29 mm l3 5 973 mm l4 5 902 mm g1 5 3 mm

g2 5 1 mm g3 5 23 mm g4 5 14 mm h1 5 30 mm h2 5 17 mm h3 5 4 mm d1 5 16 mm d2 5 2 mm er1 5 er2 5 43 and er3 5 35

Figure 2 Resonance property of the proposed MTM structure with (a) induced surface current density and (b) S11 for some different gap distances

(g1) Physical dimension of the SRR is exactly the same with that used in Figure 1(a) [Color figure can be viewed in the online issue which is available

at wileyonlinelibrarycom]

962 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol 56 No 4 April 2014 DOI 101002mop

The resonance can be explained by strong energy coupling

from the line to the SRR which blocks transfer of almost all

energy through the line Thus we can introduce a very narrow

stop band into a single wide pass band Consequently from the

remarkably reduced signal transmittance we can naturally

expect that much less power will be radiated through the

antenna shown in Figure 1

There are two important features that should be pointed out

one is that we can place a sharp stop band in an existing pass

band with almost no change in overall antenna performance

such as impedance matching bandwidth and antenna gain and

so forth In other words we can make the antenna operate as a

single-band antenna just by eliminating the SRRs without any

change in antenna geometry and properties The other is sim-

plicity in implementation To maximize energy blockage we

intentionally bend the feed lines at a right angle which is help-

ful to increase interlocked lengths between the SRR and the

line Consequently only one small SRR is sufficient to effec-

tively block waves Hence additional layers are totally

unnecessary which are often unavoidable when we use con-

ventional AMC or EBG structures for a similar band separation

approach

Figure 3 Photograph of the proposed antenna (a) the signal-feed lines (b) the radiating patch and (c) the whole structure assembled in a metallic

cavity [Color figure can be viewed in the online issue which is available at wileyonlinelibrarycom]

Figure 4 Comparison of input reflection coefficients with (a) the SRR (dual-band) and without (b) the SRR (single-band) [Color figure can be viewed

in the online issue which is available at wileyonlinelibrarycom]

DOI 101002mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol 56 No 4 April 2014 963

3 FABRICATION AND EXPERIMENTS

The fabricated components of the proposed antenna are given

in Figure 3 Even though the figure is only about the dual-

band antenna every elements of the single-band antenna are

exactly the same as those shown in Figure 3 except for the

SRRs

Figure 5 Comparison of realized gain with (a) the SRR (dual-band) and without (b) the SRR (single-band) Ports 1 and 2 are used for V- and H-

polarization respectively [Color figure can be viewed in the online issue which is available at wileyonlinelibrarycom]

Figure 6 Comparison of radiation patterns measured at 254 GHz (in the lower pass band) (a) E-plane and (b) H-plane [Color figure can be viewed

in the online issue which is available at wileyonlinelibrarycom]

Figure 7 Comparison of radiation patterns measured at 27 GHz (simulation) and 276 GHz (experiment in the higher pass band) (a) E-plane and (b)

H-plane [Color figure can be viewed in the online issue which is available at wileyonlinelibrarycom]

964 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol 56 No 4 April 2014 DOI 101002mop

The measured input reflection coefficients (S11) are com-

pared with prediction data obtained by computer simulations

which are given in Figure 4 In Figure 4(a) there is a narrow

stop band around 26 GHz which is introduced by resonance of

the SRR It is worth noting that the resonant frequency shown

in Figure 2(b) is very close to the frequency at the peak of the

stop band which proves the validity of our idea to divide one

pass band into two ones

Regarding the dual-band data the peak value of S11 in the

inserted stop band is not large enough This is mainly because

of high material loss of the substrate used for feed lines In fab-

rication we have used a commercial FR-4 substrate which has

large loss tangent of about 013 However it can be clearly

shown that our approach of introducing a sharp stop band is so

effective which explains that we can make the dual-band

antenna have good impedance matching and high antenna gain

properties in a wide single band as a single-band antenna by

only detaching the SRRs [see Fig 4(b)]

The impedance matching bandwidths (S11 5 210 dB) of the

single-band antenna is about 315 MHz (from 2460 to 2775

MHz) which is about 12 of a fractional bandwidth (FB)

And those of the dual-band antenna are 130 MHz (from 2590 to

2460 MHz) and 170 MHz (from 2620 to 2790 MHz) which are

49 and 63 of FBs respectively The frequency separation

ratio (FR) is determined by [2]

FR5fchigh

fclow

(1)

where fc high and fc low are higher and lower resonant frequencies

respectively From Figure 4(a) fc high 5 271 GHz and fc low 5 253

GHz FR is about 107 which is very difficult to obtain using ordi-

nary dual-band techniques

Realized gain properties are compared in Figure 5 As we can

see in the figure there is a radiation-rejection band around 26

GHz [see Fig 5(a)] On the maximum gain basis the simulation

and the experiment show gain rejection of more than 8 and 3 dBi

in the stop band respectively Here the relatively low gain rejec-

tion in the experiment is also due to high material loss in the sub-

strate The measured peak values of realized gain are about 66

and 69 dBi for dual- and single-band antennas respectively It is

also important that we obtain very similar characteristics in the

realized gain both for vertical and horizontal polarization which

is desirable for commercial base station antennas Although there

is a little frequency shift in measured and predicted data overall

tendency in the S11 and realized gain shows good agreement

Radiation behavior of the dual-band antenna is also given in

Figures 6 and 7 which are measured at frequencies of peak

radiation that is 254 and 276 GHz for the lower and the

higher bands respectively For more reasonable comparison

simulated patterns are picked up at the maximum gain frequen-

cies of 254 and 27 GHz respectively

The half power beam widths in an E-plane and an H-plane are 80

and 79 in the lower band and 75 and 74 in the higher band

respectively The measured FBR is greater than 25 dBi Though radi-

ation characteristics of the single-band antenna is not shown here it is

very similar to those in Figures 6 and 7 apart from the frequencies of

a radiation gap shown in Figure 5(a) Experimental patterns show rel-

atively good agreement with the predicted ones

4 CONCLUSION

We have proposed a dual-band antenna for B4G applications

Instead of applying a conventional complicated multiple reso-

nance scheme we have used coupled resonance of the SRR

which provides a very high-quality factor Consequently we can

successfully split a single pass band into two individual pass

bands that locates very close from each other

In terms of spectrum management and quality enhancement

of communication services a narrow stop band inserted between

Rx and Tx bands plays a fairly important role of providing a

guard band which potentially relieves burdens of band stop fil-

ter circuits used for the blocking of noise signals

Although additional fine tuning to mitigate unwanted fre-

quency shift is required our approach has great importance in

that it can be directly applicable to commercial base station

antennas

REFERENCES

1 B Raaf W Zirwas K-J Friederichs E Tiirola M Laitila P

Marsch and R Wichman Vision for beyond 4G broadband radio

systems In Proceedings of IEEE PIMRCrsquo11 Toronto Canada Sept

2011 pp 2369ndash2373

2 D Kim Novel dual-band Fabry-Perot cavity antenna with low frequency

separation ratio Microwave Opt Tech Lett 51 (2009) 1869ndash1872

3 A Pirhadi M Hakkak F Keshmiri and RK Baee Design of com-

pact dual band high directive electromagnetic bandgap (EBG) reso-

nator antenna using artificial magnetic conductor IEEE Trans

Antennas Propag 55 (2007) 1682ndash1690

4 F Yang and Y Rahmat-Samii Electromagnetic band-gap structures

in antenna engineering Cambridge University Press Cambridge

2008

5 JB Pendry AJ Holden DJ Robbins and WJ Stewart Magne-

tism from conductors and enhanced nonlinear phenomena IEEE

Trans Microwave Theory Tech 47 (1999) 2075ndash2084

6 D Jeon and B Lee Simplified modeling of ring resonators and split

ring resonators using magnetization J Electromagn Eng Sci 13

(2013) 134ndash136

7 Y Zhang W Hong C Yu Z Kuai Y Dong and J Zhou Planar

ultra wideband antennas with multiple notched bands based on

etched slots on the patch andor split ring resonators on the feed

Line IEEE Trans Antennas Propag 56 (2008) 3063ndash3068

8 F Falcone T Lopetegi JD Baena R Marques F Martin and M

Sorolla Effective negative-epsilon stopband microstrip lines based

on complementary split ring resonators IEEE Microwave Wireless

Compon Lett 14 (2004) 280ndash282

9 CST Microwave Studio Workflow amp solver overview CST Studio

Suite 2012 CST-GmbH Wellesley Hills MA 2012

10 V Crnojevic-Bengin V Radonic and B Jokanovic Left-handed

microstrip lines with multiple complementary split-ring and spiral

resonators Microwave Opt Technol Lett 49 (2007) 1391ndash1395

11 R Garg P Bhartia I Bahl and A Ittipiboon Microstrip antenna

design handbook Artech House Norwood MA 2001

12 D Kim and J Yeo Dual-band long range passive RFID tag antenna

using an AMC ground plane IEEE Trans Antennas Propag 60

(2012) 2620ndash2626

VC 2014 Wiley Periodicals Inc

DESIGN OF A MIMO ANTENNA WITHLOW ECC FOR A 4G MOBILE TERMINAL

Xing Zhao and Jaehoon ChoiDepartment of Electronics and Communications EngineeringHanyang University Seoul 133ndash791 Korea Corresponding authorchoijhhanyangackr

Received 8 August 2013

ABSTRACT A MIMO antenna with low ECC is proposed for a 4G

mobile terminal Apart from the resonant mode induced by the ordinary

DOI 101002mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol 56 No 4 April 2014 965