Proceedings of Asia-Pacific Microwave Conference 2007

Silicon Supported Microwave Zeroth-order ResonanceAntenna on Metamaterial Approach

George Sajin, Stefan Simion, Florea CraciunoiuNational Research Institute for Microtechnologies, IMT

Bucharest, Romania.

in. stefa.sim Xo(aaoo.rfloreac,a.Jlmt.ro

Abstract This paper presents the results in modeling,technological realization and measurements of a zeroth-order resonating antenna based on CRLH (CompositeRight/Left-Handed) transmission lines. The CRLHconsists of series connected CPW interdigital capacitorsand parallel connected CPW transmission lines. Thestudied devices were fabricated on silicon substrate for asubsequent integration in a more complex circuit. A verygood agreement between the simulation data and theexperimental results has been found out in the 10- 14 GHzfrequency domain.

Keywords-CRLH transmission lines, coplanar waveguides,antenna

I. INTRODUCTION

Due to their unusual but interesting characteristics whichare not encountered in nature, the microwave circuits based onmetamaterial (MTM) properties became a very interestingtopic in the actual research field [1], [2]. One possibility toobtain transmission media having these characteristics is todevelop circuits which under certain conditions may model thehomogeneous MTMs.

For microwave applications, a very promising possibilityto implement artificial metamaterials is to use the artificial LH(Left-Handed) transmission lines consisting of series andparallel connected capacitors and inductors, respectively. LHtransmission lines based circuits such as branch coupler [3]and ring coupler [4] have been reported, the main advantage ofthese type of circuits comparing to the classical ones being thedual frequency response to any frequency ratio.

For higher frequencies, it is more convenient to use seriesconnected interdigital capacitors and parallel connected short-ended microstrip lines inductors, obtaining CRLH (CompositeRight/Left-Handed) artificial transmission lines [5]. TheCRLH cells were the key concept for a new class of devicesand applications such as backward-wave directional couplers[6], leaky-wave (LW) tunable radiation angle antennas [7] andzeroth-order resonating antennas [8]. More recently, high gainactive CRLH based leaky-wave antenna was also reported [9].

Up to now, all devices reported in this domain wererealized using microstrip lines and hybrid technology. In the

Romolo Marcelli(l)'CNR- Institute for Microelectronics and Microsystems,Microwave Microsystems Group, 00133Rome, Italy

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next future, these types of devices are expected to bemonolithically integrated in more complex circuits using CPW(CoPlanar Waveguide) transmission lines.

In this paper, the design, fabrication process andmeasurements performed on a silicon supported zeroth-orderresonating antenna are presented.

All computer modeling results were obtained using thefull-wave analysis capabilities of IE3D - Zeland software[10].

II. CRLH ARTIFICIAL LINES ZEROTH-ORDER ANTENNA

A) Antenna design and layout

The antenna presented in this paper consists of an open-ended array of CRLH cells, each one having a T - circuittopology. The elementary cell consists oftwo series connectedCPW interdigital capacitor and two parallel connected short-ended CPW transmission lines. The equivalent circuit of theCRLH cell is presented in Fig. 1, where 2CL and LR12 arethe equivalent inductance and the equivalent capacitance ofthe series capacitor, while CR and LL are the equivalent parallelcapacitance and respectively the equivalent parallel inductanceof the two CPW transmission lines.

2CL LR 2C1 LR 2

uT-ICR

I LLFig. 1. Equivalent circuit of the CRLH cell used for the antenna design

The parallel capacitance CR includes the equivalentcapacitance of the short-ended CPWs and the equivalentparallel capacitance of the interdigital capacitors. It isimportant to point out that LR12 and CR are strongly relatedto 2CL and LL values.

Using CPW transmission lines, the circuit area could bemuch smaller compared to equivalent circuit made withmicrostrip lines because no large patch area is needed in order

1-4244-0749-4/07/$20.00 @2007 IEEE.

to obtain a virtual-ground capacitance by connecting theinductance LL to the ground.

For an open-ended CRLH antenna, the zeroth-orderresonance occurs at the frequency:

1Ph = LLCR

which is the parallel resonance due to the two CPW short-ended transmission lines.

Also, there are resonance frequencies corresponding to theright-hand (RH) and the left-hand (LH) CRLH behavior [5].For the operating frequency of the zeroth-order antenna, fh ,

D = 0 where D is the equivalent phase constant of the CRLHcell, this frequency being the highest one for the LH frequencyrange.

In order to design the CRLH cell, the following formulasmust be also used:

I IfL= 1 ;fR1R

1 ; LLf2- LRCL VC

(1)

For this layout the elements of the CRLH equivalentcircuit have been computed, obtaining (see Fig. 1):LL =0.55 nH, CL= 0.18 pF, LR =0.3 nH and CR= 0.23 pF,corresponding to fL= 8 GHz, fh = 14 GHz, fi, = 22 GHz andfR= 38 GHz.

The dispersion characteristic of the CRLH cell is presentedin [11].

The zeroth-order resonating antenna is made of threeidentical CRLH cells (see Fig. 2), each one having thegeometrical dimensions previously given. A CPW line of4.5 mm length was used to connect the device to themeasurement system.

(2) - (3)

(4) - (5)

where fL and fR are the cutoff frequencies for the LH and RHmodes respectively, fie is the series resonance of theinterdigital capacitor and Zc is the LH characteristicimpedance. The frequency range for the LH mode extendsfrom fL to fh , while the frequency range for RH modeextends from fe to fR. The condition to be fulfilled by thesefrequencies iSfR >fe >fh >fL-

The starting point in designing the capacitor is to considerthe 10 ptm width of a metallic line due to technologicallimitations, the length ofthe capacitor fingers to 0.5 mm (mustbe much smaller comparing to the operating wavelengths) andthe resonance frequency fh = 14 GHz. The preliminary valuesfor the elements of the CRLH equivalent circuit (see Fig. 1)have been computed using (1) - (5), for Zc =50 Q and theCPW characteristic impedance equals to 60 Q (to minimizethe losses). After that, the layout of an elementary CRLH cellhas been designed and optimized using IE3D - Zelandsoftware. Finally, for the layout of a CRLH cell, the followingresults were obtained: CPWs length- 1.5 mm; CPWs centralconductor width - 100 ptm; width of the CPWs slot- 100 ptm;length of the interdigital capacitor at the end of antenna- 1 mm; length of the internal interdigital capacitor- 0.5 mm;width of the metallic finger of the interdigital capacitor- 10 ptm; space between two fingers of the interdigitalcapacitor- 10 ptm; space between the interdigital capacitorand the ground planes of the CPW structure - 100 pm and thenumber of the metallic fingers of the interdigital capacitor -

10.

liplut

(a) (b)

Fig. 2. The whole antenna layout (a) and detail ofthis layout for the areaaround the junction between the CPW interdigital capacitors and the two

CPW stubs (b)

B) Antenna technological realization, simulated andexperimental results

The technological process for antenna fabrication was astandard one mask positive photolithography. A 500 ptmthickness high resistivity (5000 Qcm) silicon wafer(r,si = 11,9) was used as substrate in order to a subsequentdevice integration in a more complex circuit. The wafer wasthermally covered by 1 ptm thickness SiO2 (6r-Si02 = 4.7) andon the entire surface of this substrate, 500A Cr adherencelayer followed by 0.6 ptm Au conduction layer has beenevaporated. After that, the metallization pattern has beendefined by wet etching. The microscope photo of the obtaineddevice are shown in Fig. 3.

The area occupied by the antenna is 3.9x3.4 mm2, showinga size reduction of approx. 300o, comparing to a )/2 patchantenna.

The complete electromagnetic analysis of the wholeantenna layout was obtained by use of IE3D - Zelandprogram.

The simulated return-loss is shown in Fig. 4 (a). It may beseen that the return-loss is close to 20 dB, at14.34 GHz, which is the zeroth-order resonance frequency.

The measurements of antenna return losses wereperformed using a network analyzer (UP 8510C) and an on-wafer probe heads station (Karl Suiss PM5), the results being

presented in Fig. 4 (b). It is to see that the resonance frequency

and the return-loss at this frequency are quite the same as they

were predicted by simulation. The errors are less than 0.200 for

the resonance frequency and around 2 dB for the return-loss.

0

-25

Fig. 3. Microscope photo for the fabricated antenna

In order to measure the antenna gain and pattern of the

radiating beam, a mechanical system involving two antennas

was prepared. Each antenna was mounted on a SMlAconnector test fixture, as it is shown in Fig. 5. For the gain

measurement, the two antenna method and the Friis formula,

cf. [12], were used. The distance between the two antennas

was 6x2k and the magnitude of S21 at the resonance frequencywas measured for this antenna system. Following this

procedure, the measured value for the antenna gain was

6.4 dBi, meaning 1IdB difference from the simulated value.

The simulated and measured radiation pattern of the

antenna is presented in Fig.6.

CONCLUSIONS

A zeroth-order resonating antenna made by CPW CRLH

artificial transmission lines on silicon substrate has been

proposed. The silicon substrate, the CPW interdigital capacitor

short ended CPW stubs and transmission lines were chosen for

the future device integration in a more complex monolithically

integrated circuit. Both antenna and coupler were designed

and numerically analyzed using a full-wave electromagnetic

analysis software (IE3D -Zeland).

The antenna was fabricated and on-wafer measured for the

return-loss. The experimental results for the return-loss show a

good agreement comparing to the simulation results (errors

less than 0.20o for the resonance frequency and around 2 dB

for the return-loss on the resonance frequency). Also, the

experimental results for the gain and for the the radiation

pattern show a good agreement comparing to the simulation

results (for the gain, the error is around dB).

REFERENCES

[1] V. G. Veselago, "The electrodynamics of substances with

simultaneously negative values of r- and jt", Soy. Physics.

-Usp., vol.47, pp.509-5 14, January-February 1968.

9 1 0 1 1 1 2 1 3 1 4 1 5 1 6

Fieqtieiic~y (GHz)

0

1 0

-25

Experihertal data

5 7 8 9 1i 12 13 14 15 10 17 18 19 20

Frequency [GHZ]

(a)

(b)

Fig. 4. Simulated (a) and measured (b) return-loss ofthe CPW CRLH

resonating antenna

Fig. 5. The SMA test fixture used for the antenna gain and the radiation

pattern measurements

2

-10

-14

~~~-IE3D Simulation

*1 - Experiment-20

-90-T5S-60 -45 -30-1E 153Z) 45 60 75SO

Elevation angle [deg]

Fig. 6. Simulated and measured E- plane radiation pattern for the CPW

CRLH resonance antenna

SI 1 [dB] ]E3D Siiiutlatioli

-1 0

[2] N. Engheta, R. W. Ziolkowski, "A positive future fordouble-negative metamaterials", IEEE Trans. onMicrowave Theory and Techniques, vol.53, no.4,pp.1535-1556, April 2005.

[3] I.-H. Lin, C. Caloz, T. Itoh, "A branch-line coupler withtwo arbitrary operating frequencies using left-handedtransmission lines", in IEEE MTT-S Digest, pp.325-328,2003.

[4] H. Okabe, C. Caloz, T. Itoh, "A compact enhanced-bandwidth hybrid ring using an artificial lumped-elementleft-handed transmission-line section", in IEEE Trans. onMicrowave Theory and Techniques, vol.52, no.3, pp.798-804, March 2004.

[5] C. Caloz, T. Itoh, "Electromagnetic metamaterials:transmission line theory and microwave applications",John Wiley & Sons, Inc., 2006.

[6] C. Caloz, A. Sanada, T. Itoh, "A novel composite right-/left-handed coupled-line directional coupler witharbitrary coupling level and broad bandwidth", in IEEETrans. on Microwave Theory and Techniques, vol.52,no.3, pp.980-992, March 2004.

[7] S. Lim, C. Caloz, T. Itoh, "Metamaterial-basedelectronically controlled transmission-line structure as anovel leaky-wave antenna with tunable radiation anglebeamwidth", in IEEE Trans. on Microwave Theory andTechniques, vol. 52, no. 12, December 2004, pp.2678-2690.

[8] A. Sanada, M. Kimura, I. Awai, S. Caloz, T. Itoh, "Aplanar zerothorder resonator antenna using a left-handedtransmission line", in Proc. of the 34th EuropeanMicrowave Conference, Amsterdam, 2004, pp. 1341-1344.

[9] F. P. C.- Miranda, C. C.- Penalosa, C. Caloz, "High-gainactive composite right/left-handed leaky-wave antenna",in IEEE Trans. on Antennas and Propagation, vol. 54,no.8, August 2006, pp. 2292-2300.

[10] IE3D, Zeland Software Inc., Fremont, CA, U.S.A.[11] S. Simion, G. Sajin, R. Marcelli, F. Craciunoiu, "Silicon

resonating antenna based on CPW composite right/left-handed transmission line", accepted paper to EuropeanMicrowave Conference, EuMC 2007, Munich, Germany.

[12] C. A. Balanis, "Antenna theory - Analysis and design",John Wiley & Sons Inc., 1997.