4522 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 10, OCTOBER 2012

A Simple Dual-Band Electromagnetic Band GapResonator Antenna Based on Inverted Reflection

Phase GradientBasit Ali Zeb, Student Member, IEEE, Yuehe Ge, Member, IEEE, Karu P. Esselle, Senior Member, IEEE,

Zhu Sun, Student Member, IEEE, and Michael E. Tobar, Fellow, IEEE

Abstract—A simple method is presented to obtain a high-gaindual-band electromagnetic band gap (EBG) resonator antenna.The antenna is based on a one-dimensional EBG structure, madeout of two low-cost unprinted dielectric slabs. The EBG struc-ture is implemented as the antenna superstrate, which has beendesigned to provide a locally-inverted, positive reflection phasegradient with high reflectivity, in two pre-determined frequencybands. A composite dual-band antenna has been designed andtested with a stacked patch feed. Experimental results confirm thedual-band performance of the prototype antenna. Measured peakgains of 14.5 dBi and 15.1 dBi, and 3-dB gain bandwidth of 4.5%and 4.6%, are achieved at 10.6 GHz and 13.2 GHz, respectively.Measured 10-dB return-loss bandwidths are 6.4% and 3.9% inlower and upper bands, respectively. Potential enhancements ofantenna radiation characteristics are studied using small 2 2patch array feeds. It was found that such feeds can lead to lowerside lobes, higher peak gains and larger gain bandwidths.

Index Terms—Array, cavity resonator, dual-band, electromag-netic band gap (EBG), Fabry-Perot, high-gain, partially reflectingsurface (PRS), resonant antenna, reflection phase, superstrate.

I. INTRODUCTION

E LECTROMAGNETIC band gap (EBG) structures haveattracted increasing interest from the electromagnetic

community. In particular, their applications in antenna engi-neering have been a prime research focus due to their two distinctproperties: 1) to block the propagation of an electromagneticwave within a frequency bandgap (frequency filtering), and 2) todisplay localized frequency windows within the bandgap whenthe structure periodicity is broken due to the presence of defects.The latter property is exploited in some directive antennaswherethe near-field spreading (and hence far-field focusing) effect of

Manuscript received August 25, 2011; revised April 06, 2012; accepted May04, 2012. Date of publication July 10, 2012; date of current version October 02,2012.B. A. Zeb and Y. Ge are with the Department of Electronic Engineering, Fac-

ulty of Science, Macquarie University, Sydney, NSW 2109, Australia (e-mail:basit.zeb@mq.edu.au).K. P. Esselle was with the University of Western Australia (UWA), Perth

6009, Australia. He is now with the Department of Electronic Engineering, Fac-ulty of Science, Macquarie University, Sydney, NSW 2109, Australia.Z. Sun is with the Department of Electronic Engineering, Faculty of Sci-

ence, Macquarie University, Sydney, NSW 2109, Australia. He is also with theSchool of Communication and Information Engineering, Shanghai University,Shanghai 200435, China.M. E. Tobar is with the Department of Physics, University of Western Aus-

tralia (UWA), Perth 6009, Australia.Color versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TAP.2012.2207331

a partially reflecting surface is utilized. Such directive antennas,known as EBG resonator antennas or Fabry-Perot cavity an-tennas, typically consist of a primary feed antenna located in aresonant cavity that is formed between a perfect reflector [e.g., ametal ground plane or an artificial magnetic conductor (AMC)]and a partially reflective surface, which is usually an EBGstructure. They have the main advantages of design simplicity,better radiation performance and low complexity as comparedto the conventional planar antenna arrays.The basic configuration of the EBG resonator antenna re-

ported in [1] consists of an EBG structure made out of appro-priately spaced layers of dielectric rods. The design was laterexplained with the help of defect-mode transmission in the fre-quency domain and its reciprocal space domain [2]. The 1-Dversion of this resonator antenna is essentially an extension ofthe work carried out on gain enhancement methods for printed-circuit antennas using the resonance conditions of a substrate-superstrate assembly [3]. The operation of such antennas canbe explained using the leaky-wave concept [4] and Fabry-Perotcavity model [5], [6] where it is shown in the latter that thepeak gain depends upon the reflection-coefficient magnitudeand phase of the partially reflective surface (PRS). An extensionof this work was carried out using modified analytical expres-sions for enhancing the directivity and beamwidth of an antennaplaced inside a Fabry-Perot cavity [7]. In principle the source di-rectivity could be enhanced, however a high directivity resultsin a small radiation bandwidth. To preserve the required oper-ating bandwidth, one can use fewer elements in a sparse arrayconfiguration [8].Various configurations of EBG resonator antennas have

been developed for single [9], multiple [10]–[17] and widefrequency bands [18]–[20] by employing a variety of EBGstructures. More recently, several dual-band EBG superstratestructures have been designed to enhance the gain of primaryfeed antennas in two frequency bands. These structures include1-D dielectric slabs [10], [11], 2-D dielectric rods [12] and2-D printed frequency selective surfaces (FSS) [13]–[17]. Thedual-band antennas based on fully dielectric 1-D and 2-D EBGstructures use either three dielectric slabs with different per-mittivity and thickness [10], [11] or a row of defect dielectricrods (with different value of dielectric permittivity) in betweentwo identical layers of rods [12] as antenna superstrates. Onthe other hand, the structures based on 2-D FSS/PRS utilize anarray of resonant elements printed on both sides [13]–[15] oron one side [16] of a single dielectric slab or on two separatedielectric layers [17].

0018-926X/$31.00 © 2012 IEEE

ZEB et al.: SIMPLE DUAL-BAND EBG RESONATOR ANTENNA BASED ON INVERTED REFLECTION PHASE GRADIENT 4523

In these EBG resonator antenna designs, irrespective of thetype of EBG structure employed, at least two sets of resonantelements or periodic defects are needed to satisfy the neces-sary conditions of directivity enhancement in two frequencybands. Recently, a new technique has been presented to designa simple 2-D PRS that uses only one set of resonant elementsprinted on a single dielectric slab [21], [22]. By engineering thereflection phase versus frequency curve of this single-resonantPRS, dual-band directivity enhancement was achieved. This de-sign technique was later modified to propose a uniform 1-Ddual-band EBG structure to achieve directivity enhancement intwo frequency bands [23].The primary objective of this paper is to present a detailed

design and implementation of a simple dual-band EBG res-onator antenna. Its EBG superstrate structure is formed usingtwo plain unprinted identical dielectric slabs, i.e., they have thesame thickness and dielectric permittivity. In our method, onlytwo slabs are required to achieve dual-band antenna operationas compared to other methods [11], [12] that require either threeslabs or three layers of dielectric rods (with different permit-tivity and thickness). The paper is organized into the followingsections. In Section II, the working principle of the antenna isexplained using the locally inverted gradient of the reflectionphase curve of the EBG superstrate structure. In Section III,the design of a dual-band EBG resonator antenna is presented.Results of numerical investigations are presented to illustratehow the effective radiating aperture affects the peak directivity.The prototype antenna fabrication and measured results are dis-cussed in Section IV. In Section V, we feed the same cavityusingmore distributed yet small 2 2 patch arrays to studywhatperformance figures could be further improved, as the secondaryobjective of the paper. Finally, Section VI concludes the paperby summarizing the salient antenna features and important mea-surement results.

II. EBG SUPERSTRATE STRUCTURE

A. Principle of Operation

The EBG superstrate structure plays an important role in thedesign of the proposed dual-band antenna shown in Fig. 1(a).This structure, made out of two unprinted and identical dielec-tric slabs, is held above the conducting ground plane and hencetwo resonant cavities are formed: a primary cavity betweenthe ground plane and the superstrate structure, and a secondarycavity between the two slabs of the superstrate structure itself.Following the special application of image theory in previouspublications [2], [11], [16], [21], both the ground plane and thefeed source (patch antenna) are removed and the result is theequivalent model with two additional dielectric slabs, shown inFig. 1(b).The wave reflection coefficient of the two-slab superstrate

structure is denoted by and that of the four-slab model isdenoted by [see Fig. 1(b)]. The reflection coefficientsand were calculated from numerical simulations of the unit-cell model in Fig. 1(b) using the commercial package CST Mi-crowave Studio. Perfect E and perfect H boundary conditionswere applied to lateral side walls, and wave port excitationswere defined on the top and bottom planes.

Fig. 1. (a) Dual-band antenna configuration, (b) Unit-cell model after removingthe ground plane.

Fig. 2. Reflection phase of the EBG superstrate structure and the idealreflection phase required for Fabry-Perot cavity resonance. Material: FR4

mm, mm, mm.

By appropriately selecting the secondary cavity height andthe thicknesses of the dielectric slabs, the phase of can bemade to exhibit a sharp positive (locally-inverted) gradient at adesired frequency, as shown in Fig. 2. The phase of the EBGstructure is defined at the bottom surface of the lowerslab (Fig. 1). Hence is equal to the phase of minustwice the phase delay between the wave port and the bottomsurface of the lower slab. To determine is obtainedfirst from numerical simulations as outlined earlier, and then theabove phase correction is done (using the port de-embeddingfeature within the software).When such a superstrate structure is held above the ground

plane, for each frequency there exists an “ideal” superstrate re-flection phase that makes the primary cavity resonate [7]. Thisideal phase is also shown in Fig. 2. Note that the phase ofis ideal at (10.6 GHz), (11.5 GHz) and (13.2 GHz),which means that the cavity has the potential to resonate at thesefrequencies. However, for cavity resonance, the magnitude ofshould be sufficiently large as well. The magnitudes of

and are shown in Fig. 3. Note that is large enough onlyat 10.6 GHz ( and 13.2 GHz The superstrate structureis nearly transparent at 11.5 GHz because the secondarycavity resonates at . This implies that antenna directivity en-hancement can be expected only at two frequency bands around10.6 GHz and 13.2 GHz. The proposed antenna is thereforedual-band rather than tri-band.The curve in Fig. 3 is helpful in the design process be-

cause it has nulls at as well as at . It therefore givesa useful insight and directly helps the designer to tune the dual-band antenna to specified operating frequencies ( and ).

4524 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 10, OCTOBER 2012

Fig. 3. Reflection magnitudes of the EBG structure with and without image.

Fig. 4. Same can be obtained with different cavity heights and slabthicknesses.

B. Use of Thin or Thick Slabs

The two antenna operating frequencies are determined by theparameters associated with the primary and secondary cavities.Contrary to the typical requirement of maintaining a quarter-wavelength distance between the dielectric slabs [9], can beset to a given frequency by altering the dielectric slab thicknessin combination with the two cavity heights. Fig. 4 shows howthe same and very close antenna operating frequencies,and (having frequency ratio of 1.25), can be reached usingdifferent combinations of and . If 3.2 mm FR4 slabs areused as opposed to 0.8 mm slabs the overall antenna height canbe reduced by 2 mm.

C. Cavity Height and Cavity Resonance Frequencies

It is possible to iteratively design EBG structures suitablefor dual-band antenna operation using the following expression,which gives the cavity height ‘ ’ required to make the cavityresonate at a particular frequency:

(1)

Here, and are the reflection-coefficient phases ofthe EBG structure and the ground plane respectively, “ ” is aninteger and “ ” is the speed of light. Here, is obtained asdescribed earlier. For the same example considered in Fig. 2,

as given in (1) is plotted in Fig. 5. This also indicates threepotential resonance frequencies corresponding to a given cavityheight, when the cavity height is in the range of 10–16 mm.Note that, unlike , the two operating frequencies, and ,depend strongly on the primary cavity height.

Fig. 5. The primary cavity height required for cavity resonance at each fre-quency.

Fig. 6. distribution across the unit-cell model in Fig. 1(b), at and. Dotted line shows the location of the symmetry plane.

III. DUAL-BAND EBG RESONATOR ANTENNA

A. Conception of the Dual-Band Antenna

To realize efficient dual-band antenna operation, three condi-tions must be satisfied in each frequency band: 1) the phase ofmust be close to the ideal value, 2) the magnitude of must

be sufficiently large (typically dB), and 3) in the modelshown in Fig. 1(b), the tangential component of the electric fieldmust vanish at the symmetry plane.The proposed simple EBG structure satisfies the first two con-

ditions. To check for the third condition, let us consider thedistribution inside the unit-cell model with image, shown

in Fig. 6. It can be seen that the third condition is also satis-fied at frequencies and but not at . Hence a conductingground plane can be placed at the symmetry plane to realize adual-band EBG resonator antenna operating around and .

B. Computed Results

A dual-band EBG resonator antenna was designed using thecommercially available HFSS software. Due to its low cost, FR4

was considered for the slabs with the cavity heightand area set to 12.1 mm and 110 110 mm respectively. Asingle horizontal Hertzian electric dipole (HED) was initiallyused to excite the antenna, instead of a real feed antenna, forquick validation of the proposed design technique. HED is aninfinitely thin broadband theoretical radiation source that is veryuseful to excite the antenna in HFSS simulations. Subsequently,a probe-fed dual-band stacked microstrip patch was used to feedthe cavity simultaneously at 10.6 GHz and 13.2 GHz. The di-rectivities obtained by HED excitation are slightly higher thanthose by the patch feed, since the HED illuminates the cavitymore uniformly.

ZEB et al.: SIMPLE DUAL-BAND EBG RESONATOR ANTENNA BASED ON INVERTED REFLECTION PHASE GRADIENT 4525

Fig. 7. Comparison of the computed peak directivity with and without the dual-band EBG superstrate structure.

Fig. 8. Electric field distribution on the second dielectric slab above the groundplane with stacked patch excitation: (a) at 10.6 GHz (b) at 13.2 GHz. Horizontaland vertical scales are in millimeters.

The computed peak directivities, shown in Fig. 7, indicatethat directivity enhancement is possible in two frequency bands.A maximum directivity of 16.0 dBi and 15.95 dBi is predictedat 10.6 GHz and 13.2 GHz, respectively. To illustrate the im-provement in the overall antenna performance with the EBGslab structure, the directivity of the feed antenna (stacked patch)is compared in Fig. 7 with and without the superstrate structure.When the two-slab structure is introduced to the patch feed, thepeak directivities increase by about 8 dB and 6 dB in lower andhigher bands, respectively.

C. Effective Radiating Aperture

The dependency of the peak achievable directivity on theaperture field distribution is crucial to optimize the overall an-tenna performance. Fig. 8 shows the lateral electric field dis-tributions, as created by the patch antenna feed, on the secondslab above the ground plane. Fig. 8 shows that the physical aper-ture is not fully utilized in both bands. Most of the energy isconcentrated in the centre, forming an effective circular radi-ating aperture, while its relatively non-uniform distribution re-sults in lower peak directivity. Increasing the slab area does notincrease the antenna directivity unless either the feed arrange-ment is changed to illuminate the cavity more uniformly or theEBG structure is modified to increase the quality factor of theresonant cavity.To increase the effective radiating aperture, we considered

two different solutions. First, the EBG structure can be excitedby an array feed [18] to get more uniform aperture illuminationwithout making changes to the EBG structure. By using sparse

Fig. 9. Computed peak directivity of the dual-band EBG resonator antenna fortwo different dielectric slabs. HED excitation is used.

arrays, thinning of the array elements will result in a simplerfeed structure while still avoiding grating lobes [8]. By doingso, higher directivity levels, an enhanced radiation bandwidthand good sidelobe levels can also be achieved. Secondly, wecan modify the EBG structure itself, either by increasing its lat-eral dimensions or by improving the quality factor of the pri-mary resonant cavity underneath it. For the former case, simula-tions show that increasing the slab area beyond 110 110 mmdoes not significantly increase the peak directivity. However,the quality factor can be increased by constructing the EBGstructure from higher-permittivity materials, thus increasing thereflection-coefficient magnitude and peak directivity.An example EBG structure, made from TMM10

material, was considered. It was excited by the HED feed andthe computed peak antenna directivity is shown in Fig. 9. Toget the same operating frequency bands, the thickness of theTMM10 slabs are adjusted to 1.4 mm. Due to the increased re-flection-coefficient magnitude and quality factor of the primaryresonant cavity, the peak directivity is increased by 2.2 dB at10.6 GHz and 3 dB at 13.2 GHz, compared to the case of theEBG structure made from 3.2 mm-thick FR4.

IV. MEASUREMENTS AND RESULTS

In order to validate the predicted results, a prototype ofthe dual-band EBG resonator antenna has been built. TheEBG structure, made form two 150 150 mm slabs of 3.2mm-thick FR4, is held by nylon spacers above an aluminumground plane. These slab parameters are chosen to use in-stockmaterial and so to expedite the fabrication process. A dual-bandsquare microstrip stacked patch, shown in Fig. 10(a), hasbeen employed as the feed antenna to cover both frequencybands. The lower patch, connected to the probe input via amicrostrip section, has the dimensions of 8 8 mm whilethe upper patch, held 1.2 mm above the lower patch usingnylon spacers, have the dimensions of 8.5 8.5 mm . The twocopper patches are etched on 0.787 mm-thick RT/Duroid5880substrates .The return loss was measured using a HP8720D vector

network analyzer, while the radiation patterns and gains in eachfrequency band were measured using an NSI-700S-50 sphericalnear-field antenna measurement system. The measured inputreflection coefficients of the composite antenna, shown inFig. 11, present very good impedance matching in both bands.The 10 dB return-loss bandwidths extend from 10.35 GHz to

4526 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 10, OCTOBER 2012

Fig. 10. Parts of the prototypes (a) the stacked microstrip patch feed and theEBG structure, lifted from a side to show the feed (b) 2 2 patch array feeds.

Fig. 11. Input reflection coefficients of the EBG resonator antenna with astacked patch feed designed to cover both bands.

11.05 GHz (6.4%) and 12.85 GHz to 13.35 GHz (3.85%) in thelower and higher frequency bands, respectively. The measuredreflection coefficients of the composite antenna agree well withthe values predicted from HFSS simulations.The measured radiation patterns of the prototype dual-band

EBG resonator antenna, fed using the stacked patch, are shownin Figs. 12 and 13. In the lower band at 10.6 GHz, the measuredsidelobes are below dB in the -plane and below dBin the -plane. In the upper band at 13.2 GHz, the sidelobesremain below dB in the -plane; however the sidelobeswere between 5–8 dB down in the -plane. The measured 3-dBbeamwidths in the -plane are 26 and 22 at 10.6 GHz and13.2 GHz, respectively. Overall, the measured radiation patternsagree reasonably well with the predicted patterns.The realized gain of the prototype antenna was found by the

gain comparison method, using a standard gain horn antenna(with known gain), and the results are shown in Fig. 14. Themeasured directivity peaked at 10.55 and 13.15 GHz andreached values of 15.85 dBi and 16.1 dBi, respectively. Thegain of the antenna peaked at 10.6 GHz and 13.2 GHz andreached values of 14.5 dBi and 15.1 dBi, respectively. The3-dB gain bandwidths of the antenna are from 10.325 GHz to10.8 GHz, or 4.5%, in the lower band and from 12.775 GHz to13.375 GHz, or 4.6%, in the higher band. The measured antennaradiation efficiency is 74% and 81% at 10.6 GHz and 13.2GHz, respectively. The antenna efficiency can be increased byreducing the substrate dielectric loss, using low-loss materialinstead of low-cost FR4 , e.g., Rogers TMM4( ).

Fig. 12. Radiation patterns at 10.6 GHz: (a) -plane (b) -plane.

Fig. 13. Radiation patterns at 13.2 GHz: (a) -plane and (b) -plane.

V. INVESTIGATION OF ARRAY-FEED EXCITATION

The radiation patterns in Section IV confirmed the dual-bandgain enhancement of the prototype antenna and the proposeddesign methodology. In an effort to study potential improve-ments of antenna radiation performance, we then investigatedone of the directivity-enhancement techniques mentioned inSection III—the use of sparse arrays to feed the dual-bandcavity. In contrast to previous experiments, two separate 2 2

ZEB et al.: SIMPLE DUAL-BAND EBG RESONATOR ANTENNA BASED ON INVERTED REFLECTION PHASE GRADIENT 4527

Fig. 14. Gain and directivity of the dual-band EBG resonator antenna, mea-sured in each band using the stacked patch feed.

Fig. 15. Radiation patterns with 2 2 array feeds: (a) 10.6 GHz -plane (left)and -plane (right), (b) 13.2 GHz -plane (left) and -plane (right).

patch array feeds were designed, one for each band, and weresimultaneously integrated to the structure for the measure-ments. The aim was to increase the effective radiating apertureby illuminating the cavity more uniformly and hence to achievebetter radiation patterns with enhanced gain and radiationbandwidth in each frequency band.Two 50 SMA input connectors, one for each band, are

used to feed the patch arrays [shown in Fig. 10(b)] behind thealuminum ground plane. The arrays are fabricated on 0.787mm-thick Rogers RT/Duroid 5880 substrate and theinter-element spacing is one guided wavelength. Each patchelement, which is fed by a microstrip corporate feed network,has dimensions of 8 13.5 mm and 6.8 11 mm in the lowerand higher bands, respectively. The dimensions of the individualpatch elements were fine tuned to get best impedance matchingin each band, when placed inside the primary resonant cavity.The radiation patterns, measured with the 2 2 array feeds,

are shown inFig. 15. In the lower band at 10.6GHz, themeasuredsidelobes are below dB in the -plane and below dBin the -plane. This gives an improvement in sidelobes levelof 10 dB in the -plane and 4 dB in -plane, as compared tothe case with a single patch feed. Similarly, in the upper band at13.2 GHz, the sidelobes remain below dB in the -plane

Fig. 16. Peak gain and directivity with 2 2 patch array feeds.

TABLE IMEASURED PERFORMANCE FEATURES

(an improvement of 6 dB) and below dB in the -plane (animprovement of 10 dB). The measured 3-dB beamwidths in the-plane are 20 and22 at 10.6GHz and13.2GHz, respectively,

which indicate an increase in peak directivities. A slight shift inthemainbeamat 10.6GHz is observed.This is because the centreof the low-band array feed has been shifted from the centre ofthe resonant cavity by 20 mm. The center of the high-band arrayfeed has also been shifted from the center of the resonant cavity,by 5 mm. Thus when the cavity is fed by small 2 2 patch arrayfeeds, overall improvement in the radiation patterns and sidelobelevels are noted in each frequency band.The peak measured gain and directivity, shown in Fig. 16,

also increased as expected. The gain of the antenna peaked at10.5 GHz and 13.2 GHz and reached values of 17.15 dBi and17.44dBi, respectively.The3-dBgainbandwidthsof the antennaare from 10.15 GHz to 10.9 GHz, or 7.13%, in the lower bandand from 12.775 GHz to 13.8 GHz, or 7.7%, in the higher band.Table I compares the performance figures measured with

single patch and patch array feeds. It is clear that, when theEBG structure is excited by a simple 2 2 array feed, theeffective radiating aperture increases. The array feed improvesthe sidelobe levels, the gain and the 3-dB gain bandwidths.

VI. CONCLUSION

The computed and measured results for a simple dual-bandEBG resonator antenna were presented. The antenna consists ofanEBGstructuremade from twounprinted slabsof low-costFR4material. Using only one additional resonant element, which isthe secondary cavity formed between the two dielectric slabs, thegradient of the reflection phase versus frequency curve is engi-neered to satisfy all the necessary conditions of directivity en-hancement in two frequency bands. The experimental results ofa prototype antenna have validated the design methodology andindicate that dual-band gain enhancement can be achieved usingonly two unprinted slabs. The prototype antenna givesmeasured

4528 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 10, OCTOBER 2012

peak gains of 14.5 dBi and 15.1 dBi and efficiencies of 74% and81%, at 10.6 GHz and 13.2 GHz, respectively, when excited bya single stacked patch. Also, 3-dB gain bandwidths of 4.5% and4.6% are achieved in the lower and upper frequency bands.The antenna efficiency can be increased by employing low-

loss dielectric slabs. The radiation performance can be furtherenhanced by using sparse array feeds. When the cavity is fedby small 2 2 patch arrays, a 2.5 dB increase in peak gains and2.5%–3% increase in 3-dB gain bandwidths were noted experi-mentally. The use of higher-permittivity material may also pro-vide similar performance gains, even without array feeds. Dueto the simple configuration, the antenna offers a promising solu-tion for many point-to-point communication links at microwaveand millimeter-wave frequencies.

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Basit A. Zeb (S’11) received the B.S. degree withfirst class honors in electrical engineering fromUniversity of Engineering and Technology, Lahore,Pakistan, and the M.S. degree in telecommunica-tions from the Technical University of Denmark,Lyngby, Denmark, in 2001 and 2005, respectively.He is currently working towards the Ph.D. degreein electronic engineering at Macquarie University,Sydney, Australia.From 2005 to 2008, he was a Research and Devel-

opment Engineer in Pakistan, and contributed in thedesign, integration, and testing of antennas and microwave sub-systems. From2008 to 2010, he was a Senior Lecturer in the Electrical Engineering Depart-ment, Air University, Islamabad, Pakistan. His current research interests are inthe areas of photonic bandgap structures for microwave and millimeter-waveantenna applications including Fabry-Perot resonator antennas and frequencyselective surfaces.

Yuehe Ge (S’99–M’03) received the Ph.D. degreein electronic engineering fromMacquarie University,Sydney, Australia, 2003.Currently he is a Professor with the College of

Information Science and Engineering, HuaqiaoUniversity, China. Previously, he was a ResearchFellow in the Department of Electronic Engineering,Macquarie University. Before joining to MacquarieUniversity, he was an Antenna Engineer at NanjingMarine Radar Institute, China. His research interestsare in the areas of antenna theory and designs for

radar and communication applications, computational electromagnetics and op-timization methods, metamaterials and their applications. He has authored andcoauthored over 90 journal and conference publications and 2 book chapters.Dr. Ge received several prestigious prizes from China State Shipbuilding

Corporation and China Ship Research & Development Academy, due to hiscontributions to China State research projects. He received 2000 IEEE MTT-SGraduate Fellowship Awards and 2002 Max Symons Memorial Prize of IEEENSW Section, Australia, for the best student paper. He is the co-winner of 2004Macquarie University Innovation Awards-Invention Disclosure Award. He hasserved as a technical reviewer for over 10 international journals and confer-ences.

ZEB et al.: SIMPLE DUAL-BAND EBG RESONATOR ANTENNA BASED ON INVERTED REFLECTION PHASE GRADIENT 4529

Karu P. Esselle (M’92–SM’96) received theB.Sc. degree in electronic and telecommunicationengineering (with First Class Honors) from theUniversity of Moratuwa, Sri Lanka, and the M.A.Sc.and Ph.D. degrees in electrical engineering from theUniversity of Ottawa, Ottawa, ON, Canada, with anearly perfect GPA.He is a Professor of engineering at Macquarie Uni-

versity, Sydney, and the Immediate Past AssociateDean—Higher Degree Research of the Division ofInformation and Communication Sciences. He has

also served as a member of the Division Executive from 2003 to 2008 and as theHead of the Department several times including six months in 2011–2112. Hehas authored over 320 research publications. Since 2002, his research team hasbeen involved with research grants, contracts and Ph.D. scholarships worth overnine million dollars. His research interests include periodic and electromagneticband gap (EBG) structures including frequency selective surfaces and EBG res-onator antennas, metamaterials, dielectric-resonator antennas, ultra-wideband(UWB) antennas and systems, broadband and multi-band antennas, biomedicaldevices, on-body and through-body wireless communication, millimetre-waveand MMIC devices, antenna and EBG applications in mobile and wirelesscommunication systems, theoretical methods, and lens and focal-plane-arrayantennas for radio astronomy. His research activities are posted in the webat http://www.engineering.mq.edu.au/research/groups/celane/. He served inall Macquarie University HDR-related committees at the highest level. Heis the Director of the Centre for Electromagnetic and Antenna Engineering(CELANE) and the Deputy Director of the Research Centre for Microwaveand Wireless Applications, which are parts of the Concentration of ResearchExcellence in Wireless Communications. He has been invited to serve asan international expert/research grant assessor by several nationwide re-search funding bodies overseas including the Netherlands, Canada, Finland,Hong-Kong, and Chile. He has been invited by Vice-Chancellors of otheruniversities to assess applications for promotion to full professor level. He hasalso been invited to assess grant applications submitted to Australia’s mostprestigious schemes such as Australian Federation Fellowships and AustralianLaureate Fellowships. His industry experience includes full-time employmentas Design Expert by the Hewlett Packard Laboratory, USA, and several consul-tancies for local and international companies, including Cisco Systems (USA),Cochlear, Optus Networks, Locata (USA)/QX Corporation, ResMed, FundEdand Katherine-Werke (Germany) through Peter-Maxwell Solicitors. He wasan Assistant Lecturer at the University of Moratuwa, a Canadian Governmentlaboratory Visiting Postdoctoral Fellow at Health Canada, a Visiting Professorof the University of Victoria, Visiting Research Fellow of the University ofWestern Australia and a Visiting Scientist of the CSIRO ICT Centre. He is anEditor of the International Journal of Antennas and Propagation.Prof. Esselle’s recent awards include the 2011 Outstanding Branch Coun-

sellor Award from IEEE headquarters (USA), 2009Vice Chancellor’s Award forExcellence in Higher Degree Research Supervision and 2004 Inaugural Inno-vation Award for best invention disclose. The CELANE, which he founded, hasprovided a stimulating research environment for a strong team of researchers

including many fellows. His mentees have been awarded six extremely com-petitive postdoctoral fellowships and many awards and prizes for their researchachievements. Ten international experts who examined the theses of his recentPh.D. graduates ranked them in the top 5% or 10%. He has served in technicalprogram committees or international committees for many international confer-ences. He was a Technical Program Committee Chair of APMC 2011 and thePublicity Chair of APMC 2000. He is the Chair of the IEEE New South Wales(NSW) MTT/AP Joint Chapter, Counsellor of IEEE Student Branch at Mac-quarie University, Foundation Editor-in-Chief of MQEC, the past Chair of theEducational Committee of the IEEE NSW, and a member of the IEEE NSWCommittee.

Zhu Sun (S’11) was born in Shanghai, China. Hereceived the B.S. and M.S. degrees in electronicengineering from Shanghai University, Shanghai, in2004 and 2009, respectively. He is currently a jointPh.D. degree student of Shanghai University andMacquarie University, Sydney, Australia.His main research interests are in phased arrays

and wideband arrays.

Michael E. Tobar (S’87–M’88–SM’01–F’07)received the Ph.D. degree in physics from the Uni-versity of Western Australia, Perth, W.A., Australia,in 1993.He is currently an ARC Laureate Fellow with the

School of Physics, University of Western Australia.His research interests encompass the broad disciplineof frequency metrology, precision measurements,and precision tests of the fundamental of physics.He is also the focal point of Australian participationin space experiments involving precision clocks and

oscillators.Prof. Tobar was the recipient of the 2009 Barry Inglis medal presented by

the National Measurement Institute for precision measurement, the 2006 Boasmedal presented by the Australian Institute of Physics, 1999 Best Paper Awardpresented by the Institute of Physics Measurement Science and Technology, the1999 European Frequency and Time Forum Young Scientist Award, the 1997Australian Telecommunications and Electronics Research Board (ATERB)Medal, the 1996 Union of Radio Science International URSI) Young ScientistAward, and the 1994 Japan Microwave Prize. During 2007 he was elevated toFellow of the IEEE, during 2008 the Australian Academy of TechnologicalSciences and Engineering and during 2012 the Australian Academy of Science.