UWB Antenna Rạgopal doc

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 5, MAY 2009 1353 Investigations on Ultrawideband Pentagon Shape Microstrip Slot Antenna for Wireless Communications Sunil Kumar Rajgopal and Satish Kumar Sharma, Senior Member, IEEE Abstract—An ultrawideband (UWB) pentagon shape planar microstrip slot antenna is presented that can find applications in wireless communications. Combination of the pentagon shape slot, feed line and pentagon stub are used to obtain 124% (2.65–11.30 GHz) impedance bandwidth which exceeds the UWB requirement of 110% (3.10–10.60 GHz). A ground plane of 50 mm 80 mm size is used which is similar to wireless cards for several portable wireless communication devices. The proposed antenna covers only the top 20 mm or 25% of the ground plane length, which leaves enough space for the RF circuitry. Three variations of the antenna design using the straight and rotated feed lines on two different substrates are considered. Effect of the conducting reflecting sheet on back of the antenna is investigated, which can provide directional radiation patterns but with reduced matching criteria. Finally, experimental verification of the fabricated an- tenna for its impedance bandwidth is carried out, which shows agreement with the simulated data. Index Terms—Directional patterns, finite ground plane, mi- crostrip line feed, microstrip slot antenna, omni-directional patterns, reflecting sheet, ultrawideband (UWB). I. INTRODUCTION T HE federal communications commission (FCC) has allo- cated the frequency spectrum from 3.1 GHz to 10.6 GHz as the ultrawideband (UWB) in the year 2002. Since then the UWB technology has progressed a lot and is still emerging. It has created increased interest in the UWB antennas, as well. The UWB wireless communication antennas are special due to very short and low-power impulse signals, which aretransmitted efficiently with less distortion. Planar forms of the UWB an- tennas can also be integrated between the radio frequency (RF) front end circuitry and the radiating structure. One way of im- plementing planar forms of the antenna is using the microstrip technology, which is widely used in wireless applications. Mi- crostrip antennas are popular because of its low profile, small size, lightweight, low cost, high efficiency and economical fab- rication features [1], [2]. One form of the microstrip antennas is the microstrip slot antenna, which radiates omni-directional ra- diation patterns. Microstrip slot antennas fed by a microstrip line have shown wideband and ultrawideband performances [3], [4]. Manuscript received December 21, 2007; revised August 18, 2008. Current version published May 06, 2009. This work was supported by the University Grant Program (UGP), San Diego State University, CA. The authors are with the Department of Electrical and Computer Engineering, San Diego State University, San Diego, CA 92182-1309 USA (e-mail: sunil.k. rajgopal@gmail.com; ssharma@mail.sdsu.edu). Digital Object Identifier 10.1109/TAP.2009.2016694 A rectangular microstrip slot of the quarter wave length fed by a microstrip line provided wide bandwidths of 60% and 83%, re- spectively [5], [6]. Further, literature search has also shown that among the planar UWB antenna designs, the microstrip slot an- tenna type is one of the most popular candidates for the UWB antennas. In [7], a square slot (arc on one side) with a square shape feed and a triangular slot with a triangular shape feed provided bandwidths of 120% and 110%, respectively. In [8], a U-shaped tuning stub was introduced to enhance coupling be- tween the elliptical/circular slots and feed line so as to broaden operating bandwidth of the antenna. The UWB antennas were achieved in [9] where slot antennas with U-shaped tuning stub and reflector was realized using two different types of the feed mechanisms. In [10], a circular slot fed by a coplanar waveguide (CPW) line through a polygonal patch provided a large band- width from 2.6–15 GHz. Some other types of the microstrip slot antennas have also been reported in [11]–[17]. In this paper, we investigate a novel planar pentagon shape microstrip slot antenna with the UWB impedance and radia- tion pattern characteristics. Section II presents the proposed an- tenna designs and antenna performance results. Effect of the conducting reflecting sheet on the antenna performance is pre- sented in Section III, where the aim is to get directional radiation patterns. Section IV presents measurement verification of the impedance bandwidth and group delay, in addition to, the UWB antenna characteristics verification using a simulation study. Fi- nally, Section V presents the conclusions. The simulation results were obtained by employing the Ansoft Corporations Designer v3.0 and High Frequency Structure Simulator (HFSS) v10.0 tools, which are method of moments (MOM), and finite element method (FEM) based commercial full wave analysis programs, respectively [18]. II. A NTENNA GEOMETRY AND SIMULATION RESULTS A. Antenna Geometry In this study, three different antenna designs are considered, i.e., Design A: straight feed line on Rogers’s RT/Duroid 5880 substrate ( , ), Design B: tilted feed line on RT/Duroid 5880 substrate ( , ), and Design C: tilted feed line on FR-4 substrate ( , ). The simulation model of the proposed an- tennas and photograph of the fabricated prototype are shown in Fig. 1(a) and (b), respectively, which consists of a pentagon shape microstrip slot, and tilted microstrip transmission feed line with a pentagon stub. Dimension of the pentagon slot are 0018-926X/$25.00 © 2009 IEEE Authorized licensed use limited to: Phan Phuong. Downloaded on October 6, 2009 at 04:47 from IEEE Xplore. Restrictions apply. 1354 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 5, MAY 2009 Fig. 1. The proposed pentagon shape microstrip slot antenna fed in using a 50 microstrip transmission line and a SMA connector (a) simulation model for the antenna Designs A, B & C, and (b) photograph of the fabricated prototype of the antenna Design C on FR-4 substrate. Fig. 2. The reflection coefficient ( , dB) versus frequency (GHz) plot for the antenna Designs A, B, and C generated using the Ansoft Designer. For com- parison, the Ansoft HFSS generated reflection coefficient result of the antenna Design B is also included. shown in Fig. 1(a) which only requires 20 mm or 25% length on the ground plane leaving enough space for the RF circuitry. For all the designs, the pentagon shape slot and stub dimensions are kept invariant, which were selected after parametric study but not shown here for the sake of brevity. The thickness “h” of the substrate material is kept 1.58 mm for all the designs. For the tilted feed line Designs B & C, the feed line is rotated by 15 . The antenna is fed using a 50 coaxial SMA connector connected to 50 microstrip transmission feed line. The ground plane size is 50 mm 80 mm for all the designs which is similar in size to several portable wireless cards. The ground plane size selection is also based on the study presented in [5], [6] on the microstrip slot antennas. B. Impedance and Radiation Characteristics The reflection coefficient results for the three Designs A, B, and C are shown below in Fig. 2 obtained using the Ansoft Designer simulations, which considers infinite substrate mate- rial but a finite ground plane size of 50 mm 80 mm. The tilted feed line Design B was also simulated using the Ansoft HFSS to observe effect on the antenna performance of the fi- nite substrate size, in addition to other finite dimensions of the Fig. 3. Gain radiation patterns of the antenna Design B at frequencies (a) 4 GHz, (b) 7 GHz, and (c) 10 GHz within the UWB range. antenna. It also includes the SMA connector effects on the an- tenna performance which is close to the antenna geometry. The HFSS simulated reflection coefficient result is shown in Fig. 2 along with the Designer simulated reflection coefficient data. The impedance bandwidth is generally defined for range of the frequencies which satisfy the VSWR 2:1 or the reflection coef- ficient, criteria. It is observed that, for the an- tenna Design A, bandwidth is 106% (2.6–8.4 GHz with respect to the (w.r.t.) center frequency). For the antenna Design B, band- width is 124% covering a frequency range from 2.65–11.3 GHz. The antenna Design C showed a bandwidth from 2.4–9 GHz, Authorized licensed use limited to: Phan Phuong. Downloaded on October 6, 2009 at 04:47 from IEEE Xplore. Restrictions apply. RAJGOPAL AND SHARMA: INVESTIGATIONS ON UWB PENTAGON SHAPE MICROSTRIP SLOT ANTENNA 1355 Fig. 4. The antenna Design B results for the (a) gain (dBi) versus frequency (GHz) at the broadside angle , and (b) Peak gain (dBi) versus fre- quency (GHz). which is 116%. Similarly, the Design B, also simulated using the HFSS, showed a bandwidth of 127% (2.8–12.6 GHz). There are visible multiple resonances within the bandwidth, which when joins provide impedance bandwidth exceeding the UWB requirement of 110% (3.1–10.6 GHz). It can be observed that, the Designs B & C with rotated feed lines exhibit enhanced bandwidth than Design A which uses straight feed line. It is also evident that, the antenna Design B provides the maximum band- width among all. Further, the antenna Design B, which was sim- ulated using both the Designer and HFSS programs, predicted almost similar bandwidths of 124% and 127%, respectively, and thus they agree well. Fig. 3(a)–(c) shows the radiation patterns of the antenna De- sign B within the UWB range obtained using the HFSS sim- ulations. The co-polarization ( at plane and at plane) and cross-polarization ( at plane and at plane) components gain patterns are plotted at frequencies 4 GHz [Fig. 3(a)], 7 GHz [Fig. 3(b)], and 10 GHz [Fig. 3(c)]. It is evident that, near omni-directional radiation pat- terns can be obtained, which deteriorate towards the higher fre- quency end. The radiation patterns variation within the band- width is attributed to the irregular pentagon shapes of both the slot and the stub, and its effective electrical dimension varia- tion with the frequency. This can generate undesired current distributions at higher frequencies, which is responsible for the pattern deterioration at higher frequency end. It can also be ob- served that, the cross-polarization components increase with the Fig. 5. (a) Geometry of the antenna Design B backed by a reflecting sheet at a spacing of d from the antenna, and its effect on the (b) reflection coefficient ( , dB). increase in frequency, which is attributed to the pentagon shape stub and tilt of the feed line. The co- and cross-polarization components gain values at the broadside angle for both the and 90 cut planes, and the peak gain values with the frequency variation are also shown plotted in Fig. 4(a) and (b), respectively. An ex- amination of Fig. 4(a) reveals that, the co-polarization gain com- ponents vary from 5.80 dBi at 2.80 GHz (start of the bandwidth) to almost 0 dBi as frequency exceeds 8 GHz, and then it become 4.10 dBi at 12.60 GHz (end of the bandwidth). Similarly, Fig. 4(b) shows that the peak gain varies between 3.00–6.25 dBi from around 3.50–13.0 GHz. Therefore, the peak gain variation is around 3.25 dBi for most of the frequencies falling within the UWB range, though at 3.10 GHz the peak gain increases to 7.50 dBi. Thus the antenna radiates well throughout the range. III. E FFECT OF REFLECTING SHEET ON ANTENNA PERFORMANCE The effect of a conducting reflecting sheet on back of the an- tenna Design B on the impedance matching and radiation pat- tern performance was also studied to see, if the reflecting sheet can be used to provide unidirectional radiation patterns such as in the case of a microstrip patch antenna [1], [2]. A square re- flecting sheet of dimension 50 mm 50 mm is placed at spacing “d” from the antenna, as shown in Fig. 5(a). The spacing “d” was Authorized licensed use limited to: Phan Phuong. Downloaded on October 6, 2009 at 04:47 from IEEE Xplore. Restrictions apply. 1356 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 5, MAY 2009 Fig. 6. Gain radiation patterns of the antenna backed by a reflecting sheet at or 10 mm within the UWB range frequencies (a) 4 GHz, (b) 5 GHz, (c) 6 GHz, (d) 7 GHz, (e) 9 GHz, and (f) 10 GHz. varied from 5–25 mm at a step of 5 mm for the parametric study. All the design parameters of the antenna were kept the same including thickness of the substrate material. Fig. 5(b) shows the reflection coefficient variation versus frequency with the re- flecting sheet spacing variation from to 25 mm. From Fig. 5(b) it can be observed that, between to 15 mm, the antenna shows matching level starting from about 5dBto better. However, for and , the antenna is matched better than 10 dB level from almost 2.50–11.50 GHz. For case, the impedance bandwidth is about 129% (2.5–11.5 GHz). For obtaining directional radiation patterns within the UWB range, a combined spacing between and 10 mm can be used. Fig. 6(a)–(f) show the gain radiation patterns with or 10 mm spacing for frequencies in the UWB range, i.e., 4, 5, 6, 7, 9, and 10 GHz, respectively generated using the HFSS simulations. For the lower (3–7 GHz) and upper (8–11 GHz) halves of the frequencies and spac- ings are found suitable, respectively. An evaluation of the ra- diation patterns from Fig. 6(a)–(f) reveals that, the patterns are fairly directional at the broadside angle (gain variation between 3–8 dBi) with front-to-back (F/B) ratios between 7–15 dB. The patterns also show asymmetry and scan for some of the frequen- cies providing beam peak gain values between 4–8 dBi at angles other than the broadside angle . Not presented here, but a single spacing can also be used to achieve directional patterns but with slightly reduced direction- ality. This antenna can be further improved to achieve better antenna performance characteristics by implementing a recon- figurable spacing “d”. Thus, a directive antenna within the UWB range can be obtained using the proposed slot antenna and a re- flective conducting sheet, which is also planar and compact in size. It can be used for some wireless communication applica- tions if matching criteria of is acceptable. Further, this can also be used to reduce the back lobe radiation in hand- held devices. Authorized licensed use limited to: Phan Phuong. Downloaded on October 6, 2009 at 04:47 from IEEE Xplore. Restrictions apply. RAJGOPAL AND SHARMA: INVESTIGATIONS ON UWB PENTAGON SHAPE MICROSTRIP SLOT ANTENNA 1357 Fig. 7. (a) S-parameters (dB) versus frequency (GHz), and (b) phase (de- grees) versus frequency (GHz) plots for the transmit-receive antenna system. IV. VERIFICATION OF THE ANTENNA The antenna was verified using the HFSS simulation for the UWB communications using the technique outlined in [19], [20], where a transmit/receive antenna combination was considered. Both transmit and receive antennas were similar (Design B) and placed 100 mm apart facing each other as suggested in [19]. This transmit-receive antenna combination can also be considered as a two-port network. The S-param- eters and phase versus frequency variations are shown in Fig. 7(a) and (b). The reflection coefficient results show similar impedance matching behavior for most of the frequencies, except that at the start and end of the bandwidth they do not overlap. The parameters provide all the important system parameters in terms of the gain, impedance matching, polarization matching, path loss and phase delay. Therefore, these parameters can be used to predict performance of the UWB antenna system which is frequency dependent [19]. From Fig. 7(a) it can be observed that, the transmission coefficients of the antenna system cover the UWB frequency range within near to the 10 dB variation. Further as expected, the phase is nonlinear within the UWB range [shown in Fig. 7(b)]. The phase centers vary with frequency because the Fig. 8. (a) Comparison of the simulated and measured reflection coefficient ( , dB) results for the fabricated prototype antenna shown in Fig. 1(b), and (b). Measured group delay for the transmit-receive combination of the antennas when facing each other. antenna radiation behavior is dependent upon the effective antenna dimension, which changes with frequency for a given physical antenna dimension. Two prototypes of the proposed antenna Design C were fab- ricated. The photograph of one of them is already shown in Fig. 1(b). Since the previously considered FR-4 substrate thick- ness of was not readily available in the Antenna and Microwave Laboratory (AML), being developed at the San Diego State University, therefore, the substrate thickness used for the fabrication was . The antenna was again simulated using the HFSS for this substrate thickness, so that it can be compared with the measured data. The antenna re- flection coefficient was measured using a HP8510C Vector Net- work Analyzer. The measured reflection coefficient along with the simulated data is shown plotted in Fig. 8(a). The measured impedance bandwidth w.r.t. is 117% which covers a frequency range from 2.6–10 GHz. In comparison to this, the simulated bandwidth is 115% (2.5–9.3 GHz). Both sim- ulated and measured results show multiple resonances which are responsible for such a wide bandwidth performance. The slight variation in frequency range can be attributed the fabrication er- rors. Thus, it can be observed that, the simulated and measured Authorized licensed use limited to: Phan Phuong. Downloaded on October 6, 2009 at 04:47 from IEEE Xplore. Restrictions apply. 1358 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 5, MAY 2009 results are in good agreement. The antenna was also experimen- tally verified for the group delay using the two antenna arrange- ment [20], where the transmit and receive antennas are facing each other while connected to the two ports of the Network An- alyzer. The 100 mm spacing between the antennas is equivalent to (free space wavelength) at the 3 GHz and at 10 GHz. The group delay result is shown in Fig. 8(b). The ripples may be attributed to the scattering effect from the network cables. It can be observed that, the group delay between the antennas is around 0.7 ns and varies by 0.125 ns within the bandwidth. Thus the antenna shows fairly constant group delay. V. C ONCLUSION In this paper, a planar ultrawideband (UWB) pentagon shape microstrip slot antenna is investigated for the impedance matching and radiation pattern characteristics. This antenna occupies only 25% space on the 50 mm 80 mm size ground plane along the length. The antenna can find applications in portable wireless communication devices. Both straight feed line and tilted feed line designs were investigated with two different substrate materials of the same thickness. It was observed that, for the tilted feed line Design B an impedance bandwidth of 124% (2.65–11.3 GHz) can be obtained, which exceeds the required UWB range of 110% (3.1–10.6 GHz). However, all three antenna Designs A, B, and C almost met the UWB frequency range requirements, and provided nearly omni-directional radiation patterns. Further, by employing a conducting reflecting sheet on the back of the antenna, di- rectional radiation patterns can be obtained within the UWB range but with the reduced matching criteria. It can be used not only to get directive antenna within the UWB range but also to reduce the back lobe radiation. The measured impedance bandwidth of the fabricated antenna showed good agreement with the simulated data. The transmit/receive combination of the proposed antenna showed acceptable UWB communication performance in terms of the S-parameters and group delay. A CKNOWLEDGMENT Authors would also like to thank C. Meagher for helping in the measurements, and the anonymous reviewer’s comments that helped in improving the presentation of this paper. R EFERENCES [1] R. Garg, P. Bhartia, I. Bahl, and A. Ittipiboon, Microstrip Antenna De- sign Handbook. Norwood, MA: Artech House, 2001. [2] J. L. Volakis, Antenna Engineering Handbook, 4th ed. New York: McGraw Hill, 2007. [3] A. A. Eldek, A. Z. Elsherbeni, and C. E. Smith, “Microstrip-fed printed lotus antenna for wideband wireless communication system,” IEEE An- tennas Propag. Mag., vol. 46, no. 6, pp. 164–173, Dec. 2004. [4] A. M. Abbosh, M. E. Bialkowski, J. Maziersha, and M. V. Jacob, “A planar UWB antenna with signal rejection capability in the 4–6 GHz band,” IEEE Microw. Wireless Compon. Lett., vol. 16, no. 5, pp. 278–280, May 2006. [5] S. K. Sharma, L. Shafai, and N. Jacob, “Investigation of wide-band microstrip slot antenna,” IEEE Trans. Antennas Propag., vol. 52, no. 3, pp. 865–872, Mar. 2004. [6] S. I. Latif, L. Shafai, and S. K. Sharma, “Bandwidth enhancement and size reduction of microstrip slot antennas,” IEEE Trans. Antennas Propag., vol. 53, no. 3, pp. 994–1003, Mar. 2005. [7] Y. F. Liu, K. L. Lau, Q. Xue, and C. H. Chan, “Experimental studies of printed wide-slot antenna for wide-band applications,” IEEE Antennas Wireless Propag. Lett., vol. 3, pp. 273–275, 2004. [8] P. Li, J. Liang, and X. Chen, “Study of printed elliptical/circular slot an- tennas for ultrawideband applications,” IEEE Trans. Antennas Propag., vol. 54, no. 6, pp. 1670–1675, June 2006. [9] R. Chair, A. A. Kishk, K. F. Lee, C. E. Smith, and D. Kajfez, “Mi- crostrip line and CPW fed ultrawideband slot antennas with u-shaped tuning stub and reflector,” Progr. Electromagn. Res., PIER, vol. 56, pp. 163–182, 2006. [10] S Y. Lin, H R. Huang, C W. Guan, and S A. Yeh, “A novel com- pact slot antenna for ultra-wideband communication,” in Proc. IEEE Antennas Propag. Society Int. Symp., HI, 2007, pp. 5123–5126. [11] I T. Tang, D B. Lin, G H. Liou, J H. Horng, and C M. Li, “A compact slot UWB antenna with CPW-fed,” in Proc. IEEE Antennas Propag. Society Int. Symp., HI, 2007, pp. 5143–5146. [12] J Y. Jan and C Y. Hsiang, “Microstrip-line fed printed slot antenna for ultra-wideband operation,” in Proc. IEEE Antennas Propag. Society Int. Symp., HI, 2007, pp. 5139–5142. [13] S. H. Choi, J. K. Park, S. K. Kim, and J. Y. Park, “A new ultra-wideband antenna for UWB applications,” Microw. Opt. Technol. Lett., vol. 40, no. 5, pp. 399–401, Mar. 5, 2004. [14] A. Vasylchenko, W. D. Raedt, and G. A. E. Vandenbosch, “Electric and magnetic type compact UWB antenna using u-shaped slot with band-rejection characteristic,” in Proc. IEEE Antennas Propag. Society Int. Symp., HI, 2007, pp. 4617–4620. [15] J M. Ju, G T. Jeong, J H. Yoon, C S. Kim, H S. Kim, and K S. Kwak, “Design of multiple u-shaped slot microstrip patch antenna in 5 GHz band WLAN,” IEICE Trans. Commun., vol. E88-B, no. 2, pp. 821–825, Feb. 2005. [16] T. Dissanayke and K. P. Esselle, “UWB performance of compact l-shaped wide slot antennas,” IEEE Trans. Antennas Propag., vol. 56, no. 4, pp. 1183–1187, Apr. 2008. [17] A. M. Abbosh and M. E. Bialkowski, “Design of planar ultrawideband planar monopole slot antennas of circular and elliptical shapes,” IEEE Trans. Antennas Propag., vol. 56, no. 1, pp. 17–23, Jan. 2008. [18] Ansoft Corporations, Designer and High Frequency Structure Simu- lator (HFSS) [Online]. Available: www.ansoft.com [19] Z. N. Chen and T. S. P. See, “Antennas for UWB applications,” in Antennas for Portable Devices, Z. N. Chen, Ed. Hoboken, NJ: Wiley, 2007. [20] Z. N. Chen, X. H. Wu, H. F. Li, N. Yang, and M. Y. W. Chia, “Consid- erations for source pulses and antennas in UWB radio systems,” IEEE Trans. Antennas Propag., vol. 52, no. 7, pp. 1739–1748, Jul. 2004. Sunil Kumar Rajgopal was born in Tuticorin, Tamil Nadu, India, in 1985. He received the B.Eng. degree in electronics and telecommunication from Thakur College of Engineering and Technology, Mumbai, India, in 2006, and the M.Sc. degree in electrical engineering from San Diego State University, San Diego, California, in 2008. His main research interests are in small, planar and broadband antennas including ultrawideband antennas for handheld wireless applications. Authorized licensed use limited to: Phan Phuong. Downloaded on October 6, 2009 at 04:47 from IEEE Xplore. Restrictions apply. RAJGOPAL AND SHARMA: INVESTIGATIONS ON UWB PENTAGON SHAPE MICROSTRIP SLOT ANTENNA 1359 Satish Kumar Sharma (M’00–SM’04) was born in Sultanpur, Uttar Pradesh, India, in 1970. He received the B.Tech. degree from Kamla Nehru Institute of Technology, Sultanpur, India and the Ph.D. degree from the Institute of Technology, Banaras Hindu Uni- versity, Varanasi, India, in 1991 and 1997, respec- tively, both in electronics engineering. From February 1992 to December 1993, first he was a Lecturer and then Project Officer at Kamla Nehru Institute of Technology, Sultanpur and the Institute of Engineering and Rural Technology, Allahabad, respectively. From December 1993 to February 1999, he was a Research Scholar, and then Junior/Senior Research Fellow of the Council of Scientific and Industrial Research (CSIR) in Department of Electronics Engi- neering, Institute of Technology, Banaras Hindu University. From March 1999 to April 2001, he was a Postdoctoral Fellow in the Department of Electrical and Computer Engineering, University of Manitoba, Manitoba, Canada. He was a Senior Antenna Engineer with InfoMagnetics Technologies Corporation in Winnipeg, Manitoba, Canada, from May 2001 to August 2006. Simultaneously, he was also a Research Associate at University of Manitoba from June 2001 to August 2006. In August 2006, he joined San Diego State University (SDSU), San Diego, CA, as an Assistant Professor in the Department of Electrical and Computer Engineering. Here, he has developed an Antenna Laboratory, teaches courses in applied electromagnetics, and advises several graduate students. He is author/coauthor of approximately 75 research papers published in the refereed international journals and conferences, in addition to several academic and industrial technical reports. He also holds one U.S. and one Canadian patent. His main research interests are in microstrip antennas, ultrawide bandwidth antennas, reconfigurable antennas, feeds for reflector antennas, waveguide horns and polarizers, phased array antennas, wire antennas, and RF MEMS microwave passive components. Dr. Sharma is also a registered Professional Engineer (P. Eng.) in the Province of Manitoba, Canada. He received the Young Scientist Award from the URSI Commission B, Field and Waves, during the URSI Triennial In- ternational Symposium on Electromagnetic Theory, Pisa, Italy, in 2004. He is a reviewer of research papers for the IEEE T RANSACTIONS ON ANTENNAS AND PROPAGATION, IEEE TRANSACTIONS ON MICROW AVE THEORY AND TECHNIQUES, IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, and IET’s Microwave and Antennas Propagation journals. He has served on the Technical Program Committee and Steering Committee of the IEEE Antennas and Propagation Symposia. He was Chair of the Student Paper Contest of the IEEE Antennas and Propagation Society International Symposium 2008 held in San Diego. Authorized licensed use limited to: Phan Phuong. Downloaded on October 6, 2009 at 04:47 from IEEE Xplore. Restrictions apply. . interests are in microstrip antennas, ultrawide bandwidth antennas, reconfigurable antennas, feeds for reflector antennas, waveguide horns and polarizers, phased array antennas, wire antennas, and RF MEMS. ultrawideband (UWB) in the year 2002. Since then the UWB technology has progressed a lot and is still emerging. It has created increased interest in the UWB antennas, as well. The UWB wireless. elliptical/circular slots and feed line so as to broaden operating bandwidth of the antenna. The UWB antennas were achieved in [9] where slot antennas with U-shaped tuning stub and reflector was realized using