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Progress In Electromagnetics Research Symposium Proceedings, Taipei, March 25–28, 2013 905

Efficient Characterization of Fabry-Perot Resonator Antennas

Yuehe Ge1, 2 and Wang Can1

1College of Information Science and Engineering, Huaqiao UniversityXiamen, Fujian 361021, China

2

State Key Laboratory of Millimeter Waves, Nanjing 210096, China

Abstract— In this paper, an extended transmission line method is applied to characterizehigh-performance Fabry-Perot resonator antennas, showing its effectiveness and efficiency. Inthis method, ABCD network is used to represent electromagnetic band-gap (EBG) structures orpartially reflective surfaces (PRSs) and reciprocity is used together with the extended model tocharacterize the radiation properties of Fabry-Perot resonator antennas. An 1D wideband dielec-tric Fabry-Perot resonator antenna, an 1D dual-band dielectric Fabry-Perot resonator antennaand a 2D wideband Fabry-Perot resonator antenna, which have clear wideband or dual-banddesign principles. were successfully analyzed using the extended method.

1. INTRODUCTION

Dielectric leaky-wave antennas (DLWAs) have been studied in the past decades [1], as a means toenhance the directivity of small antennas. In recent ten years, electromagnetic band-gap (EBG)materials and other partially reflective surfaces (PRSs) based on frequency selective surfaces (FSS)have been developed and applied to leaky-wave antennas [2–5] for the same purpose.

The transmission line method was successfully applied to the analysis of DLWAs [1], where thesize of the dielectric superstrate is considered infinite. In [6], antenna superstrate is equivalent toa shunt admittance in the transmission line model, making it possible the analysis of 2D and 3DFabry-Perot resonator antennas using the transmission line method. However, the method is notreliable when the superstrate of Fabry-Perot resonator antennas is thick and radiation propertiesconcerned is far from the broadside of the antenna. An extended Transmission line method [7, 8],where ABCD network is applied to represent the EBG superstrate, was developed to accuratelycharacterize Fabry-Perot resonator antennas. In this paper, the extended method is applied tocharacterize 1D and 2D Fabry-Perot resonator antennas to demonstrate its advantages includingsimplicity, versatility, efficiency and occupying less computer resource.

2. THE EXENDED TRANSMISSION LINE METHOD

As demonstrated in [1], the analysis of dielectric Fabry-Perot resonator antennas can be performedwith the aid of the transmission line method, by reciprocity. To extend the method to accuratelycharacterize 2D or 3D Fabry-Perot resonator antennas, the ABCD network can be applied to char-acterize the performance of the EBG superstrate forming the Fabry-Perot cavity. Other dielectriclayers and the PEC ground are still modeled by transmission line model. The details of the methodand the related calculation of the radiation field are given in [7, 8], and not provided in this paper.According to the method, as well as the ABCD network parameters of the EBG/PRS periodicsuperstrate are obtained, other radiation properties, such as directivity, beamwidth, etc., can becalculated correspondingly.

3. WIDEBAND DIELECTRIC FABRY-PEROT RESONATOR ANTENNAS

A wideband Fabry-Perot resonator antenna, presented in [9], has a configuration shown in Fig. 1.Based on the design principle in [10], the antenna has two resonant cavities, which resonate attwo close frequencies, resulting in a wider transmission bandwidth. Here this antenna is takenadvantage of to demonstrate the effectiveness of the design principle in [9, 10] using the extendedtransmission line method. It can be seen from Fig. 1 that the antenna is composed of three dielectricslabs N 1, N 3, N 5 and a PEC ground. A horizontal electric dipole (HED) is considered to excite theantenna. The magnitude and phase of the reflection from the bottom surface of slab N 5, obtainedfrom the commercial software CST Microwave Studio, are plotted in Fig. 2(a). As can be seen,the reflection phase from the three-layer-slab superstrate increases with frequency from 11.5 GHzto 12.3 GHz but decreases at other frequencies. Based on the antenna design principle in [10], awideband Fabry-Perot resonator antenna is expected.

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906 PIERS Proceedings, Taipei, March 25–28, 2013

Figure 1: A wideband 1D Fabry-Perot resonator antenna.

(a) (b)

Figure 2: (a) Magnitude and phase of reflection coefficients; (b) Computed and measured directivity andgain.

Applying the antennas parameters to the extended transmission line method, S  parameters of the three dielectric-layer superstrate can be analytically obtained. These S parameters can be easilyconverted to ABCD network parameters. Then the performance of the antenna can be estimated

using the extended transmission line method [7, 8].The directivity of the antenna was calculated and is plotted in Fig. 2(b). For comparison,

the same antenna was also analyzed using the transmission line method presented in [6] and thedirectivity result is also plotted in Fig. 2(b). It can be seen that the extended method gives twopeak gains, perfectly verifying the wide-band design principle for wide-band Fabry-Perot resonatorantennas presented in [10]. This antenna has been fabricated and measured. As can be seen fromFig. 2(b), a good agreement between the computed and measured results is obtained.

4. DUAL-BAND DIELECTRIC FABRY-PEROT RESONATOR ANTENNAS

The design principle of dual-band Fabry-Perot resonator antennas have been introduced in [11] anddemonstrated using an 2-D EBG/PRS superstrates with strong resonant inclusion. Dual-band 1Ddielectric Fabry-Perot resonator antennas can also be designed using this method [12].

The configuration of the 1D dielectric Fabry-Perot resonator antenna is shown in Fig. 3. TwoFR4 dielectric slabs and a PEC ground form the antenna that is excited by a HED. The reflectionmagnitude and phase from the bottom surface of the lower slab, obtained from CST MicrowaveStudio, are plotted in Fig. 4(a). The reflection phase, which is required to maintain the cavityresonance condition at the entire concerned frequency band, is also plotted in Fig. 4(a). It canbe seen that there are three cross points between the PRS reflection phase and the ideal phase,however, as detailed in [11] the antenna can only operate at two cross points, around 10.7 GHz and13.2GHz.

Using the extended transmission line method, the directivity of the antenna is calculated andplotted in Fig. 4(b). It can be seen that two peak directivities, 16 dBi and 14.3 dBi, appear atabout 10.5 GHz and 13.2 GHz, respectively. This antenna has also been fabricated and tested. Themeasured gain is also plotted in Fig. 4(b), for comparison. It can be seen that a good agreementbetween the theoretical and measured results is obtained.

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Progress In Electromagnetics Research Symposium Proceedings, Taipei, March 25–28, 2013 907

Figure 3: A 1D dual-band Fabry-Perot resonator antenna.

(a) (b)

Figure 4: (a) Computed reflection magnitude and phase and the expected phase of the superstrate; (b) Com-puted directivity and measured gain.

(a) (b)

Figure 5: (a) Configuration of the concerned wideband 2D Fabry-Perot resonator antenna; (b) Characteri-zation model of the PRS for the calculation of ABCD parameters.

5. WIDEBAND 2D FABRY-PEROT RESONATOR ANTENNAS

The configuration of the wideband 2D Fabry-Perot resonator antenna concerned here is shown inFig. 5(a). It is composed of a feed antenna, a single-layer PRS and a PEC ground plane. The PRS

is made out of Rogers RT/Duriod 5880 material, which has a thickness of 1.5 mm and a dielectricconstant of 2.2, with two dipole arrays printed on its two surfaces. The details of the PRS can befound in [10]. This periodic PRS can be characterized using a single unit cell, as shown in Fig. 5(b),with the aid of the periodic boundary condition [11]. The reflection from the surfaces of the PRS,obtained from commercial software CST Microwave Studio, are plotted in Fig. 6(a). It can beseen that the reflection phase from the top surface (port 1) of the PRS decreases with frequency,while that from the bottom surface (port 2) increases with frequency within the frequency band of 12.1 Hz–13.15 GHz. As described in [10], the increasing reflection phase is helpful to maintain theresonance condition within the Fabry-Parot cavity over a wide operating frequency band, resultingin a wideband Fabry-Perot resonator antenna.

In this work, CST Microwave Studio is applied to obtain the S  parameters of the 2D PRS.ABCD network parameters are then evaluated. Applying the obtained ABCD network parametersand the extended transmission line method [7, 8], the wideband 2D Fabry-Perot resonator antenna

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908 PIERS Proceedings, Taipei, March 25–28, 2013

(a) (b)

Figure 6: (a) Reflection magnitude and phase from the top and bottom surface of the PRS; (b) Calculateddirectivities and the measured gain.

can be characterized. Fig. 6(b) shows the calculated directivity. The 3-dB directivity bandwidth is11.3 GHz–13.2 GHz, up to 15.5%. The prototype of the antenna was also fabricated and measured.The measured gain is also plotted in Fig. 6(b). One can see that a wide bandwidth, up to 13.2%, is

obtained, and a good agreement with the theoretical result is achieved. For comparison, the sameantenna was also analyzed using the TEN method [6] and the result is also plotted in Fig. 6(b). Itcan be seen that the wide bandwidth that should be achieved by the antenna is not obtained usingthe TEN method [6].

6. CONCLUSIONS

It is demonstrated that the extended transmission line method, based on the reciprocity and themodeling of EBG/PRS structures using ABCD network, can be used to efficiently determine theradiation properties of Fabry-Perot resonator antennas. For 1D dielectric Fabry-Perot resonatorantennas, the ABCD parameters of the superstrate and the radiation properties of the antenna canbe determined analytically. For 2D and 3D Fabry-Perot resonator antennas, full-wave numericalmethods have to be used to determine ABCD network parameters of the EBG/PRS structures,

and then radiation properties of these antennas can be calculated analytically.The method has been successfully applied to the characterization of wideband and dual-band1D dielectric Fabry-Perot resonator antennas and a 2D wideband Fabry-Perot resonator antenna.The wideband [10] and dual-band design principles [11, 12], used to design these antennas, havebeen confirmed. This in turn verifies the effectiveness of the method. Compared to other full-wavenumerical methods, this method has the advantages of versatility, simplicity and efficiency.

ACKNOWLEDGMENT

This research was supported by the start-up grant (11BS301) of Huaqiao University, Xiamen 361021,China, and Open Research Program (K201212) from State Key Laboratory of Millimeter Waves,Nanjing 210096, China.

REFERENCES

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2. Thevenot, M., C. Cheype, A.Reineix, and B. Jecko, “Directive photonic-bandgap antennas,”IEEE Trans. Microw. Theory Tech., Vol. 47, No. 11, 2115–2122, Nov. 1999.

3. Pirhadi, A., F. Keshmiri, M. Hakkak, and M. Tayarani, “Analysis and design of dual bandhigh directive EBG resonator antenna using square loop FSS as superstrate layer,” Progress In Electromagnetics Research , Vol. 70, 1–20, 2007.

4. Boutayeb, H., T. A. Denidni, and M. Nedil, “Bandwidth widening techniques for directiveantennas based on partially reflecting surfaces,” Progress In Electromagnetics Research , Vol. 74,407–419, 2007.

5. Ge, Y., K. P. Esselle, and Y. Hao, “Design of low-profile high-gain EBG resonator antennasusing a genetic algorithm,” IEEE Antennas Wireless Propag. Lett., No. 6, 480–483, 2007.

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