of supporting the upper ground plane, extensive investigations onit were abandoned.

In order to achieve a radiation pattern with a good gain andreturn-loss bandwidth, a guide-to-free-space transition with a largeenough Tl, � � 0�, and low dielectric permittivity was decidedupon. Figure 7 shows the relative gain of the radiation patternwhen the ground-plane radius is 100 mm, the transition parametersare Tl � 60 mm and � � 10°, and the platform width is Tpl �3 mm.

In Figure 7(a), the pattern in the azimuth is pointing at theexpected direction and the simulated gain is 3 dB. Both themeasured and simulation results are similar to each other, with themeasured result showing a slightly higher side-lobe level. Theelevation pattern, shown in Figure 7(b), contains both the mea-sured and simulation results. From the simulation, a gain of around8 dB is observed. This gain is slightly lower than that of theantenna array without the upper ground plane, which was 9.5 dBfor the top-hat monopoles in a circular array. As in the azimuthpattern, the measured and simulation results are close to eachother. One discrepancy between the two results is the maximumgain direction of the pattern. The simulation result’s maximumgain is seen when the beam squint off the ground plane is around75°. The measured maximum gain is at 45° beam squint off theground plane.

The return-loss parameters of the array using the above param-eters are shown in Figure 8. The observed 10-dB return-lossbandwidth of this array is 0.65 GHz for the simulation result and0.5 GHz for the measured result. These results compare favorablywith the 0.4-GHz bandwidth obtained for the same array withoutthe upper ground plane.

The discrepancies observed between the simulated and mea-sured results may be due to various reasons, such as manufacturingtolerances. Another source of the observed discrepancies may bedue to the use of coaxial connectors in the experimental part. UsingFEKO, an active monopole was simulated assuming an excitationof a segment adjacent to the ground plane.

5. CONCLUSION

It has been demonstrated that housing a switched-beam circulararray of monopoles in a radial guide with a suitable guide-to-free-space transition offers more degrees of freedom in its design. Byhaving the central element active and the remaining monopolesbeing open or short-circuited, the array is able to steer the beam inthe azimuth. The use of a guide-to-free-space transition provides

means of improving the return-loss bandwidth and shaping thearrays beam in elevation.

ACKNOWLEDGMENT

This work has been financially supported by the Australian Re-search Council under Discovery Research Grant no. DP0450118.

REFERENCES

1. R. Kronberger, H. Lindenmeier, L. Reiter, and J. Hopf, Design methodfor array antennas on cars with electronically short elements underincorporation of the radiation properties of the car body, IEEE AntennasPropagat Symp Dig 1 (1997), 418–421.

2. M. Daginnus, R. Kronberger, and A. Stephan, Ground plane effects onthe performance of SDARS antennas, IEEE Antennas Propagat SympDig 4 (2002), 748–751.

3. K. Yang and T. Ohira, Single-port electronically steerable passive arrayradiator antenna based space-time adaptive filtering, IEEE AntennasPropagat Symp Dig 4 (2001), 14–17.

4. J. Lu et al., Multi-beam switched parasitic antenna embedded in dielec-tric for wireless communications systems, Electron Lett 37 (2001),871–872.

5. N. Scott, M. Leonard-Taylor, and R. Vaughan, Diversity gain from asingle-port adaptive antenna using switched parasitic elements illus-trated with a wire and monopole prototype, IEEE Trans AntennasPropagat 47 (1999), 1066–1070.

6. R. Islam and R. Adve, Beam-forming by mutual coupling effects ofparasitic elements in antenna arrays, IEEE Int Antennas Propagat Di-gest, San Antonio, TX 1 (2002), 126–129.

7. J. Janapsatya and M.E. Bialkowski, Analysis of an array of monopoleswith the use of a radial waveguide approach, Microwave Opt TechnolLett 34 (2002), 235–240.

8. J. Janapsatya and M.E. Bialkowski, Fine beam steering for a monopolesmart antenna system in a circular array configuration, IEEE Int An-tennas Propagat Digest, Columbus, OH 3 (2003), 888–891.

9. FEKO: Comprehensive EM solutions, http://www.feko.co.za.

© 2004 Wiley Periodicals, Inc.

A COMPACT VERY-HIGH-PERMITTIVITYDIELECTRIC-EYE RESONATORANTENNA FOR MULTIBAND WIRELESSAPPLICATIONS

Binu Paul,1 S. Mridula,1 P. Mohanan,1 P. V. Bijumon,2 andM. T. Sebastian2

1 Centre for Research in Electromagnetics and Antennas (CREMA)Department of ElectronicsCochin University of Science and TechnologyKochi 682 022, Kerala, India2 Ceramics Technology DivisionRegional Research LaboratoryThiruvananthapuram 695 019, Kerala, India

Received 31 March 2004

ABSTRACT: A very-high-permittivity (�r � 100) multiband dielectric-eye resonator antenna is presented. The compact antenna, excited by amicrostrip line, resonates at two frequencies centered around the 1.9-GHz and 2.4-GHz bands with identical polarization. The behavior of theantenna at different positions along the feed line is studied and opti-mized. Multiple resonances with the same polarization and broad radia-tion patterns suggest the suitability of the antenna for multiband wire-less applications. © 2004 Wiley Periodicals, Inc. Microwave OptTechnol Lett 43: 118–121, 2004; Published online in Wiley InterScience(www.interscience.wiley.com). DOI 10.1002/mop.20394

Figure 8 S11 parameters of the radial guide with dielectric taper

118 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 43, No. 2, October 20 2004

Key words: dielectric resonator antenna; multiband wireless applica-tions

1. INTRODUCTION

The development of numerous mobile-communication systemshas led to increased demand for compact, efficient antennas.Small integrated antennas play a significant role in the progressof the rapidly expanding military and commercial communica-tions applications. Recently, with the booming wireless mobile-communications market, the urgency to design compact multi-band antennas is even more pronounced [1–3]. Dielectricresonator antennas (DRAs) are attractive to antenna designersdue to their excellent radiation characteristics. In addition, thisclass of antennas exhibits all the desirable characteristics of amicrostrip antenna. Since its inception in the early 1980s, therehas been a steady progress of research in this area over the years[4 – 6]. S. Mridula et al. [7] studied the reflection and radiationcharacteristics of a microstrip-line-excited rectangular DRA. Inthis paper, we propose an eye-shaped DRA suitable for wirelessapplications.

2. ANTENNA GEOMETRY

The antenna is comprised of an eye-shaped dielectric resonator(DR), excited directly by a 50� microstrip line of width 3 mmand fabricated on a substrate of dielectric constant �r � 4.28 andthickness 1.6 mm. The DR is made of very high permittivity(�r � 100) ceramic material TiO2 doped with 1 mole % Fe2O3

prepared using conventional solid-state ceramics. The eyeshape is defined by the intersection of two identical circles ofradius 31.5 mm with their centers displaced by 7.5 mm, asshown in Figure 1. A broadband dual-frequency oval-shapedmicrostrip antenna was proposed by M. Deepukumar et al. [8].This novel geometry provides two independent ports with or-thogonal polarization and excellent isolation between the twoports. However, in this paper dual-band operation is obtained byexciting the various resonant modes of the eye-shaped DRA byusing a single feed. The DR can be placed in two orthogonalorientations upon the feed line. Figure 2 illustrates the twoconfigurations of the antenna. To the best knowledge of theauthors, a DRA with this novel geometry has not been reporteduntil now.

3. EXPERIMENTAL RESULTS

The DR is excited directly by a microstrip line of length 35 mm.It is moved symmetrically along the feed line and the variation inreturn loss as a function of frequency is studied for variouspositions. The measurements are repeated for the orthogonal ori-entation of the DR upon the feed line. Numerous resonant modesof the DRA are observed, with the most prominent being the bandscentered around �1.9 and �2.4 GHz. The position of the DRalong the feed line is experimentally optimized for minimumreturn loss. The return loss at the optimum position of the DR isplotted in Figure 3 for configuration 1. The antenna exhibits 2.4%and 0.97% 2:1 VSWR bandwidth at these two frequencies, respec-tively.

Figure 1 Two identical circles of radius r and center-to-center spacingd, intersecting to form the eye geometry (r � 31.5 mm, d � 7.5 mm, a �30.5 mm, b � 23.5 mm)

Figure 2 Geometry and configuration of the DRA: (a) geometry of theproposed eye DRA (h � 1.6 mm, t � 7.5 mm); (b) top view ofconfiguration 1 (a � 30.5 mm, b � 23.5 mm, lf � 35 mm, df � 12.5mm); (c) top view of configuration 2 (a � 30.5 mm, b � 23.5 mm, lf �35 mm, df � 6 mm, s � 7.5 mm)

Figure 3 Return loss at the optimum symmetrical position of the DRplaced in configuration 1: F1 � 1.93 GHz (1.907–1.958 GHz) at 2.4%bandwidth; F2 � 2.353 GHz (2.343–2.365 GHz) at 0.97% bandwidth

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 43, No. 2, October 20 2004 119

The 2:1 VSWR bandwidth exhibits considerable increase forthe asymmetrical positions of the DR upon the feed line. Figure 4illustrates the reflection characteristics of the DR placed asym-metrically upon the feed line for configuration 2. Here, the band-width of operation is �5% and 1% at 1.99 and 2.23 GHz, respec-tively.

The radiation pattern of the DRA is measured using an HP8510C Network Analyser. Figure 5 shows the measured radia-tion patterns of the DRA. The patterns are reasonably broad inboth E- and H-planes, thus indicating the usefulness of theproposed antenna configuration for wireless applications. The

Figure 4 Return loss at the asymmetrical position of the DR placed inconfiguration 2: F1 � 1.99 GHz (1.917–2.02 GHz) at 5.17% bandwidth;F2 � 2.23 GHz (2.215–2.245 GHz) at 1.1% bandwidth

Figure 5 Radiation patterns of the DRA placed in different configurations: (a) configuration 1 in the first band centered at f � 1.93 GHz; (b) configuration1 in the second band centered at f � 2.353 GHz; (c) configuration 2 in the band centered at f � 1.99 GHz

TABLE 1 3-dB Beamwidth of the Proposed Antenna inDifferent Configurations

Configuration 1

Configuration 2Band 1 Band 2

E-plane 98° 122° 84°H-plane 94° 102° 86°

120 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 43, No. 2, October 20 2004

3-dB beamwidths obtained are given in Table 1. The gain of theproposed antenna configuration is also compared to that of astandard circular microstrip patch antenna. Figure 6 illustratesthe gain of the antenna in various configurations. The measuredgain of the antenna is �2-dB greater than that of a standardcircular microstrip patch antenna resonating in the same band inall the configurations, except for the higher-order mode at 2.353GHz.

The antenna is compact in geometry, with considerable reduc-tion in area as compared to rectangular and circular patch antennas.Table 2 compares the dimensions of the proposed DRA with thatof other microstrip patches resonating at the same frequency. Sincethe proposed antenna exhibits similar polarization for both 1.9-GHz and 2.4-GHz bands, it is highly suitable for mobile commu-nications and Bluetooth applications.

4. CONCLUSION

A very-high-permittivity dielectric-eye resonator antenna (�r �100) has been excited by a 50� microstrip line. Numerous reso-nant modes have been excited at different positions of the DRalong the feed line. Dual-band operation was observed centeredaround 1.9 and 2.4 GHz. Broad radiation patterns were obtained,suggesting the relevance of the proposed antenna configuration forwireless applications.

ACKNOWLEDGMENTS

S. Mridula acknowledges SERC, Department of Science and Tech-nology, Govt. of India, for financial assistance under the FastTrack Scheme and P. Mohanan acknowledges UGC for financialsupport.

REFERENCES

1. N. Chiba, T. Amano, and H. Iwasaki, Dual-frequency planar antenna forhandsets, Electron Lett 34 (1998), 2362–2363.

2. Y.-X. Guo, M.Y.W. Chia, and Z.N. Chen, Miniature built-in quad-bandantennas for mobile handsets, IEEE Antennas Wireless Propagat Lett 2(2003), 30–32.

3. D.S. Yim, J. Kim, and S.O. Park, Novel wideband internal chip antennafor PCS/IMT-2000 dual-band applications, Microwave Opt TechnolLett 40 (2004), 324–326.

4. A. Petosa, A. Ittipiboon, Y.M.M. Antar, D. Roscoe, and M. Cuhaci,Recent advances in dielectric resonator antenna technology, IEEE An-tennas Propagat Mag 40 (1998), 35–48.

5. J.-I. Moon and S.-O. Park, Dielectric resonator antenna for dual-bandPCS/IMT-2000, Electron Lett 36 (2000), 1002–1003.

6. D. Cormos, A. Laisne, R. Gillard, F. Le Bolzer, and C. Nicolas,Compact dielectric resonator antenna for WLAN applications, ElectronLett 39 (2003), 588–590.

7. S. Mridula, S.K. Menon, P. Mohanan, P.V. Bijumon, and M.T. Sebas-tian, Characteristics of a microstrip-excited high-permittivity rectangu-lar dielectric resonators antenna, Microwave Opt Technol Lett 40(2004), 316–318.

8. M. Deepukumar, J. George, C.K. Aanandan, P. Mohanan, and K.G.Nair, Broadband dual-frequency microstrip antenna, Electron Lett 32(1996), 1531–1532.

© 2004 Wiley Periodicals, Inc.

A BROADBAND SLOPE-STRIP-FEDMICROSTRIP PATCH ANTENNA

Wei Wang,1 Sheng-Bing Chen,2 and Shun-Shi Zhong1

1 School of Communication and Information EngineeringShanghai UniversityShanghai 200072, P.R. China2 Institute of Antennas and EM ScatteringXidian UniversityXi’an 710071, P.R. China

Received 27 March 2004

ABSTRACT: A novel slope-strip feeding technique for a microstripantenna is presented in order to achieve a broad bandwidth. The experi-mental results show that the optimal bandwidth attained is 53.4% forless than �10-dB return loss. © 2004 Wiley Periodicals, Inc.Microwave Opt Technol Lett 43: 121–123, 2004; Published online inWiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20395

Key words: microstrip antenna; antenna feed; broadband antenna

1. INTRODUCTION

In recent years, microstrip patch antennas have been popular withantenna engineers due to their well-known characteristics of lowcost, light weight, and high conformability. But the inherentlynarrow bandwidth, of which only a few percent can be attained, isthe major weakness of a microstrip patch antenna. Some efforts toachieve bandwidth enhancements been made presented in theliterature, including the use of thick substrate [1] and variousfeeding methods [2]. With the employment of the aperture-cou-pling technique introduced by Pozar in 1985 [3], the typicalbandwidth attained was about 22% for the single-layer case and37% for the stacked dual-patch antenna. Another feeding methodwith a U-shaped slot for a probe-fed patch [4] has typicallyachieved 30% bandwidth. Recently, a proximity feeding techniquewith an L-strip [5] was applied to a microstrip antenna, resulting in

Figure 6 Gain of the proposed antenna placed in different configurations

TABLE 2 Comparison of the Dimensions of the ProposedAntenna with Patch Antennas Operating in the Same Band

ResonantFrequency

Dimensions in mm

Eye DRA Rectangular MPA Circular MPA

1.9 GHz a�30.5,b�23.5,t�7.5

L � 37.8,W � 48.6

r � 22.35

2.4 GHz L � 29.8,W � 38.5

r � 17.7

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 43, No. 2, October 20 2004 121