RIS-Based Compact Circularly Polarized Microstrip ... - IEEE Xplore

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 61, NO. 2, FEBRUARY 2013

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RIS-Based Compact Circularly Polarized Microstrip Antennas Kush Agarwal, Student Member, IEEE, Nasimuddin, Senior Member, IEEE, and Arokiaswami Alphones, Senior Member, IEEE

Abstract—Compact, asymmetric\symmetric-slotted\slit-microstrip patch antennas on reactive impedance surface (RIS) are proposed and studied for circularly polarized (CP) radiation. The antennas consist of a slotted-slit-microstrip patch on a RIS substrate. The CP radiation with compact size is achieved by asymmetric\symmetric-slot-slit cut along the orthogonal\diagonal directions of the patch radiator. The asymmetric\symmetric-slotted\slit microstrip patches on the RIS structure are used for further miniaturization of the antenna with improvement in CP radiation. The measured results of the compact asymmetric-cross slotted square patch antenna are 1.6% (2.51–2.55 GHz) for 3-dB axial ratio bandwidth, 5.2% (2.47–2.60 GHz) for 10-dB return loss bandwidth, and 3.41 dBic for gain over 3-dB axial ratio bandwidth. The overall antenna volume is on a low cost FR4 substrate at 2.5 GHz. Index Terms—Circular polarization, microstrip antenna, miniaturization, reactive impedance surface (RIS), slotted\slit patch.

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I. INTRODUCTION

ITH the emerging use of wireless applications, there is always a continuous need for RF community to design low cost, light weight, and miniature antennas which can easily be integrated with small-size communication systems. Depending on the today’s world wireless applications, the circularly polarized microstrip antennas (CPMAs) offer more flexibility for the handheld and portable wireless devices due to their insensitivity towards the device orientation or multipath effects. These antennas are more suitable for wireless communications such as GSM, WLAN, RFID, and biomedical sensing applications. Generally, a single feed patch antenna generates a linearly polarized wave, unless some perturbation is introduced in the radiator structure to excite the two orthogonal modes with 90 phase difference for achieving the CP radiation. This is usually achieved by chamfering the square patch radiator corners [1] or making slots or slits with respect to suitable feeding location [2]–[4]. In the recent years, electromagnetic metamaterials have been intensely studied and used for enhancing the radiation properties of the antennas like frequency bandwidth and direction of antenna radiation for the CPMA designs with size miniaturization. Reactive impedance surfaces (RISs) [5]–[8], comprising of Manuscript received March 29, 2012; revised July 16, 2012; accepted October 11, 2012. Date of publication November 29, 2012; date of current version January 30, 2013. K. Agarwal and A. Alphones are with the Nanyang Technological University, Singapore 639798, Singapore (e-mail: [email protected]). Nasimuddin is with the Institute for Infocomm Research, (A-Star) Singapore (e-mail: [email protected]). 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.2012.2225816

the square periodic patches on a grounded high dielectric substrate have been used for antenna size miniaturization and performance enhancement. Artificial magnetic conductors (AMC), such as electromagnetic band-gap (EBG) structures [9], [10] have also been used to achieve a zero degree reflection phase for wideband antenna designs and better impedance matching. Conventionally different methods like cutting asymmetric, symmetric slits and slots are used in the single feed patch radiator for generating the CP radiation. The cross slots, asymmetric-circular shaped slots with slits, and asymmetric-slit microstrip patches [2]–[4] have already been used to generate a CP radiation with size miniaturization. Although slits and slots are embedded for the miniaturization of the antenna size with CP radiation, they only achieve good CP radiation with lesser degree of size reduction. Miniaturization of the antenna [11] is achieved using the variable permeability artificial magneto-dielectric material as a substitute for high-permittivity substrates. Overall antenna volume is at 910 MHz with a low gain of 3.75 dBic over the desired frequency band. A compact CP patch antenna loaded with metamaterials was proposed in [12]. The RIS and mushroom-like CRLH structures based metamaterials has been used to miniaturize the CPMA ( at 2.58 GHz). The antenna was designed on a low-loss thick dielectric substrate with a gain of 2.98 dBic. Recently, in [13], miniaturization of CPMA is proposed using RIS with complementary split-ring resonators. And, the antenna gain is 3.7 dBic with overall antenna volume of at 2.8 GHz. The CPMAs were designed over RIS for improving the CP bandwidth [14]–[17]. In this paper, single feed, microstrip antennas on RIS are proposed and studied for CP radiation with compact size. The CP radiation with compact size is achieved by cutting slots or slits in the patch radiator. The RIS is used in the inductive region for further decreasing the resonance frequency and improving the antenna radiation performance. The compact CP patch antennas loaded with RIS are designed, fabricated, and tested. The CST Microwave Studio simulation tool is used to design and optimize proposed antenna structures. II. PROPOSED ANTENNA GEOMETRY AND DESIGNS Fig. 1 shows the cross-sectional view of proposed CPMAs with RIS. The antenna consists of an asymmetric\symmetricslotted\slit-microstrip patch radiator printed on the top of dualand tan ) with thicklayer FR4 substrate ( and , in which ground nesses of plane lies at the bottom of the structure and RIS is printed at the interface between the two dielectric layers. This RIS layer comprises of an array of 5 5 square metallic unit cell patches

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Fig. 1. Cross-sectional view of the proposed antenna.

printed periodically along - and -axis, thus leading to a symmetrical design along the lateral dimensions of the antenna. The feed arrangement is used by a coaxial probe at the location with respect to the patch center. A circular region from the RIS layer is removed to accommodate the coaxial SMA connector, so that the feeding probe does not come in direct contact with the metal RIS units. The CP radiation with antenna miniaturization is achieved by the RIS layer as metasurface and cutting asymmetric\symmetric-slot\slit in the patch radiator. The design of the RIS and the proposed patch radiators for CP radiation are discussed in Sections II-A and II-B, respectively. A. RIS for Proposed CPMAs Top view of the 5 5 metal patch array forming RIS is shown in Fig. 2(a). The RIS for the proposed antennas is composed of the two-dimensional square metal patch structures which are periodically printed on the ground backed substrate in an attempt to miniaturize the antenna size and enhance both bandwidth and the radiation characteristics, inspired by the basic properties of the RIS presented in [5]–[8]. The unit cell of this RIS structure is first designed by exciting a TEM wave to tune it between the perfectly electric and magnetic conductor, i.e., perfectly electric conductor (PEC) and perfectly magnetic conductor (PMC) boundary limits with an aim to achieve the best compromise between optimal bandwidth and miniaturization factor. The simulation model of the unit cell as shown in Fig. 2(b) shows the PEC and PMC boundaries established around the cell structure with the single-mode waveguide port on the top to excite it by a plane wave. The reflection phase response with variation of for a unit RIS cell structure is also shown in Fig. 2(b), while unit cell size of is fixed. As the PEC surface does a reflection phase change of 180 , while PMC of 0 , to the patch’s back radiated waves striking its surface, the actual square metal patch parameter is altered to tune the operating frequency limit in the inductive RIS region, while keeping the overall size of RIS unit cell, as constant. Unlike the frequency selective surfaces (FSS), the periodicity of the RIS patches is kept much smaller as compared to the operating wavelength (Optimized value of in terms of the wavelength is at 2.5 GHz). Miniaturization of patch antenna can also be done using the high permittivity materials where the antenna is printed on a high dielectric substrate with a low loss tangent. But it results in the strong electromagnetic coupling between the patch radiator and the PEC ground plane, thus confining significant amount

Fig. 2. Proposed RIS: (a) top view of the 5 5 metal patch array forming RIS, (b) RIS unit cell enclosed by PEC walls in direction of -field, PMC walls in the direction of -field and illuminated by incident plane wave in negative -direction with the simulated reflection phase of the unit cell with .

of EM energy inside the substrate, i.e., the near-field region. As a result, the overall reduction in the antenna size will be achieved on the cost of common desirable features such as low antenna efficiency, lesser bandwidth (due to increase of Q of antenna), and poor impedance matching of the antenna due to low characteristic impedance. In the last few years, use of PEC (zero impedance plane) and PMC (infinite impedance surface) ground planes was attempted for enhancing the desirable antenna characteristics. While the fields of image current from the PEC surface that is in close proximity and opposite to the antenna current cancel out the radiated fields from the antenna patch, thus making it difficult to match the input impedance and also narrowing the bandwidth; PMC surfaces are quite lossy and lower the overall antenna efficiency [8]. So it is observed that the image cancellation problem in PEC and the dissipative loss problem in PMC make both of these surfaces inappropriate to be used as the antenna ground plane for low-profile planar antennas. An RIS with a purely reactive impedance of as demonstrated in [5] reduces the mutual coupling between the patch radiator and the ground plane. As a result, shows much better per-

AGARWAL et al.: RIS BASED COMPACT CIRCULARLY POLARIZED MICROSTRIP ANTENNAS

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Fig. 3. Top view of proposed patch radiators over RIS: (a) ACSSP, (b) SCSNSP, (c) ASNSP, (d) ASSNSP, (e) TCSP, and (f) NSP.

formance than PEC and PMC surfaces when used as the antenna ground plane with an objective of achieving the optimal bandwidth, miniaturization factor, and reduced antenna back radiations at the same time. As a result, the RIS improves three main backdrops of conventionally used ground planes: (a) reduces the

mutual coupling between the patch radiator and ground plane, thus showing better impedance matching over a wider bandwidth, (b) combines inductive (capacitive) behavior of RIS with capacitive (inductive) behavior of the patch radiator at relatively lower frequency than resonant frequency, thus showing

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antenna size miniaturization, and (c) improving front to back ratio. An inductive RIS (below the PMC resonance freq.) made up of square patches printed on PEC backed dielectric substrate is capable of storing the magnetic energy, thus increasing the total inductance of the patch and compensating for the electric energy stored in the near field of the antennas resulting in the antenna miniaturization. The PEC plane exhibits an inductive behavior after the thickness of the substrate, which is in parallel with the existent capacitance between the patches. Thus the composite periodic structure behaves equivalent to a parallel LC circuit providing the desired impedance characteristics [6] and giving the expected results. Also, the bandwidth of the same sized patch and substrate antenna over RIS is much higher as compared to the conventional planar antennas, thus making it more suitable for the wideband antenna applications. B. Proposed Patch Radiators on RIS for CP Radiation The asymmetric-cross slotted square patch (ACSSP), symmetric-cross slotted nearly square patch (SCSNSP), asymmetric-slit nearly square patch (ASNSP), asymmetric-slit-slotted nearly square patch (ASSNSP), truncated corners square patch (TCSP), and nearly square patch (NSP) are proposed and designed on RIS for CP radiation and compact antenna size. All proposed square and nearly square patch radiators are shown in Fig. 3(a)–(f), respectively. The lateral dimensions of the proposed antennas are fixed as ground plane size for all patch radiator configurations. For good impedance matching of the CPMAs, the optimized feed-locations (in mm) w.r.t. the patch centers are given in the proposed patch radiator sketches. The total antenna thicknesses for all antennas are fixed as . Fig. 3(a) shows the ACSSP for CP radiation and compact antenna size. An asymmetric-cross slot of optimized unequal arm lengths [ and ] is etched at centre of the square patch with side length, for good CP performance. The SCSNSP [see Fig. 3(b)] achieves a good CP radiation for optimized width, and arm length, . The ASNSP [see Fig. 3(c)] is designed for CP radiation based on asymmetric-slits and patch width with optimized dimensions being: , , , and . The ASSNSP method is used to achieve CP radiation for antenna over RIS [see Fig. 3(d)]. Again, asymmetric-circular slots [ , , , and ] and asymmetric-slits [ and ] are optimized for good CP radiation for patch width, . Fig. 3(e) shows CP TCSP with the optimized truncated length, . The NSP radiator can also be used for good CP radiation [see Fig. 3(f)] for width . C. Comparison of Simulated Results for Proposed RIS based CPMAs In this section, the simulated return loss, axial-ratio (AR) at the boresight, and gain at the boresight of the proposed CPMAs over the RIS are discussed and compared. All proposed CPMAs over RIS are designed with good impedance matching and CP radiation . Simulated return loss of the CPMAs

Fig. 4. Simulated results of the antennas: (a) return loss, (b) axial ratio at the boresight, and (c) gain at the boresight for proposed patch radiators over RIS.

over RIS is compared in Fig. 4(a). The center frequency of TCSP antenna is highest amongst all the proposed antennas with NSP antenna’s centre frequency being almost the same as that of TCSP antenna. Consequently, the truncated corners method and nearly square patches are not useful for size reduction of CPMAs. The centre frequency of TCSP antenna is even higher than conventional square patch antenna with same side length. The lowest centre frequency is achieved for ACSSP. Fig. 4(b) shows the AR of the CPMAs at the boresight with respect to the frequency. The 3-dB AR bandwidths for all patch radiator based CPMAs [see Fig. 3(a)–(f)] are listed in Table I. All antennas are optimized


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TABLE I COMPARISON OF SIMULATED PERFORMANCES OF THE ANTENNAS

Fig. 5. Simulated return loss graphs for proposed ACSSP over RIS, square patch over RIS, ACSSP without RIS, and square patch without RIS.

for best CP radiation . The minimum AR operating frequency is lowest for ACSSP antenna and thus it has the smallest electrical antenna size amongst all the proposed antennas. Simulated gain at the boresight of the CPMAs is compared in Fig. 4(c). Simulated gain is more than 4.0 dBic for the TCSP and NSP antennas over the 3-dB AR bandwidth. Gains of the asymmetric/symmetric-slit-slotted square/nearly square patch antennas are low owing to these antennas being electrically smaller. As the gain and bandwidth of the antenna are functions of the overall antenna size, electrically small antennas exhibit poor gain and narrow bandwidth. Gain variation over the 3-dB AR bandwidth is less than 0.2 dB for all CPMAs. For CPMAs, the 3-dB AR bandwidth should be within 10-dB impedance bandwidth for proper operation of the CPMA. The global bandwidths (common 10-dB impedance bandwidth and 3-dB AR bandwidth) of the antennas are also tabulated in the Table I. To have a better understanding about the frequency reduction (or size miniaturization) caused by RIS and slotted-slit patch CPMAs, the proposed ACSSP over RIS, same size square patch over RIS, ACSSP without RIS, and square patch without RIS are compared and studied. Fig. 5 shows the return loss plot for all four different antenna designs. It is seen that just by introducing RIS layer under the square patch (keeping the patch to ground plane spacing constant), the resonance frequency is shifted down from 3.035 to 2.6 GHz (i.e., 435 MHz) due to the equivalent inductive reactance of the RIS. The ACSSP without RIS reduces the resonance frequency to 2.725 GHz (i.e., 310 MHz), demonstrating that the resonance frequency reduces with increase in lengths of cross-slot arms. The proposed ACSSP over RIS has resonance frequency at 2.474 GHz, thus showing an overall resonance frequency reduction of 561 MHz. III. EXPERIMENTAL RESULTS The six proposed CP asymmetric\symmetric-slotted\slittruncated corner-nearly square microstrip patch radiators over

Fig. 6. Photograph of the proposed compact CP ACSSP antenna over RIS.

RIS were fabricated and measured. To validate the proposed technique, the measured results of the electrically smallest ACSSP over RIS are compared with the simulations. The photograph of the fabricated ACSSP antenna prototype is shown in Fig. 6. Simulated and measured results of the CP ACSSP antenna are plotted in Fig. 7(a) and (b), respectively, for return loss and AR at the boresight with frequency. A slight shift in measured operating frequency is observed as compared to the simulation due to small air gap introduced in the multilayered microstrip antenna prototypes prepared in our fabrication lab. The frequency shift will not be observed if the antennas will be fabricated using the standard professional multilayered PCB fabrication process. Consequently, the measured operating frequency is slightly higher as compared to that predicted by the simulation. To confirm the effect of air gap between the upper and lower substrate layers, the antenna performance was studied with variation of small air gap. The simulated results with air gap of 0.04 mm are in good agreement with the measured results of the antenna. The measured 10-dB return loss bandwidth is 5.2% (2.47–2.60 GHz). The CP radiation is measured using the rotating linearly polarized transmitting horn antenna. The measured 3-dB AR bandwidth is around 1.6% (2.51–2.55 GHz) in the boresight direction. The measured gain of 3.41 dBic is achieved over the 3-dB AR bandwidth with a maximum gain variation of 0.2 dB. The measured and simulated normalized radiation patterns with both the principal planes ( and ) are plotted in Fig. 8 for 2.515 and 2.530 GHz, respectively. The proposed antenna is right-handed CP (RHCP), so the RHCP is the copolarization and left-handed CP (LHCP) is the cross-polarization

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Fig. 7. Measured and simulated results of the proposed ACSSP over RIS antenna: (a) return loss and (b) axial ratio at the boresight.

of the antenna. The simulated LHCP is also plotted in the figures. The 3-dB AR beamwidth is more than 90 for 3-dB AR bandwidth frequency range. The cross-polarization level [RHCP—LHCP] over the 3-dB AR bandwidth is better than 28 dB at the boresight. IV. COMPARISON OF MEASURED RESULTS FOR CPMAS The measured results of the six proposed compact CP antennas over RIS and other published compact CPMAs over RIS [12], [13] are compared in this section. Table II shows the comparison of the proposed antennas and previously published antennas over RIS. The proposed antennas are designed on low cost FR4 substrate but gain of the proposed antennas is better than the antennas on low loss substrate [12]. Also, overall volume of the proposed ACSSP over RIS antenna is smallest with slightly larger 3-dB AR bandwidth as compared to the published antenna in [12]. The miniaturization as reported in [12] and [13] is achieved by using the CRLH mushroom-like structure and CSRR with RIS on a high cost substrate “MEGTRON 6” which has a dielectric constant of 4.02 and loss tangent of 0.009. Usually the usage of mushroom based structures makes the antenna quite lossy and the fabrication more complex and costly, thus making it inappropriate for industrial usage when

Fig. 8. Measured and simulated normalized radiation patterns of the ACSSP and ): (a) 2.515 GHz over RIS antenna for both the principal planes ( and (b) 2.530 GHz.

compared to conventional miniaturization techniques like slits and slots. The antenna presented in [13] has the largest overall


TABLE II COMPARISON OF MEASURED PERFORMANCES OF THE CPMAS

antenna volume with almost same antenna performances when compared with the proposed compact antennas. Also, the proposed CP, NSP, and TCSP antennas have much better performances than almost same sized CP antenna as in [13]. V. CONCLUSION The different types of asymmetric\symmetric-slotted\slit microstrip patch radiators have been studied for CP radiation with compact antenna size over the RIS. The nearly square and truncated corners square patch radiators have also been studied on RIS for CP radiation for comparison purpose. The proposed antennas were studied on a low cost FR4 substrate. The asymmetric\symmetric-slotted-slit patches are used to generate the CP radiation with compact size. The further antenna size reduction has been achieved from RIS. The asymmetric-cross slotted square patch over RIS has the largest miniaturization factor with good CP radiation. The proposed combined technique (slotted\slit and RIS) is useful for compact CP microstrip antenna design. REFERENCES [1] P. C. Sharma and K. C. Gupta, “Analysis and optimized design of single feed circularly polarized microstrip antennas,” IEEE Trans. Antennas Propag., vol. 31, no. 6, pp. 949–955, Nov. 1983.

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[2] Nasimuddin, X. Qing, and Z. N. Chen, “A compact circularly polarized cross-shaped slotted microstrip antenna,” IEEE Trans. Antennas Propag., vol. 60, no. 3, pp. 1584–1588, Mar. 2012. [3] Nasimuddin, X. Qing, and Z. N. Chen, “Asymmetric-circular shaped slotted microstrip antennas for circular polarization and RFID applications,” IEEE Trans. Antennas Propag., vol. 58, no. 12, pp. 3821–3828, Dec. 2010. [4] Nasimuddin, X. Qing, and Z. N. Chen, “Compact asymmetric-slit microstrip antennas for circular polarization,” IEEE Trans. Antennas Propag., vol. 59, no. 1, pp. 285–288, Jan. 2011. [5] H. Mosallaei and K. Sarabandi, “A novel artificial reactive impedance surface for miniaturized wideband planar antenna design: Concept and characterization,” in Proc. IEEE Antennas Propag. Soc. Int. Symp., 2003, pp. 403–406. [6] K. Buell, D. Cruickshank, H. Mosallaei, and K. Sarabandi, “Patch antenna over RIS substrate: A novel miniaturized wideband planar antenna design,” in Proc. IEEE Antennas Propag. Soc. Int. Symp., 2003, pp. 269–272. [7] H. Mosallaei and K. Sarabandi, “Embedded-circuit and RIS meta-substrates for novel antenna designs,” in Proc. IEEE Antennas Propag. Soc. Int. Symp., 2004, pp. 301–304. [8] H. Mosallaei and K. Sarabandi, “Antenna miniaturization and bandwidth enhancement using a reactive impedance substrate,” IEEE Trans. Antennas Propag., vol. 52, no. 9, pp. 2403–2414, Sep. 2004. [9] D. Sievenpiper, L. Zhang, R. F. J. Broas, N. G. Alexopolous, and E. Yablonovitch, “High impedance electromagnetic surfaces with a forbidden frequency band,” IEEE Trans. Microw. Theory Tech., vol. 47, no. 11, pp. 2059–2074, 1999. [10] D. Sievenpiper, “High Impedance Electromagnetic Surfaces,” Ph.D. dissertation, University of California, Los Angeles, CA, 1999. [11] H. Chung, Y. Lee, and J. Choi, “Miniaturization of an UHF RFID reader antenna using an artificial magneto-dielectric,” Microw. Opt. Technol. Letters, vol. 52, no. 9, pp. 1926–1930, Sep. 2010. [12] Y. Dong, H. Toyao, and T. Itoh, “Compact circularly-polarized patch antenna loaded with metamaterials,” IEEE Trans. Antennas Propag., vol. 59, no. 11, pp. 4329–4333, Nov. 2011. [13] Y. Dong, H. Toyao, and T. Itoh, “Design and characterization of miniaturized patch antennas loaded with complementary split-ring resonators,” IEEE Trans. Antennas Propag., vol. 60, no. 2, pp. 772–785, Feb. 2012. [14] L. Bernard, G. Chertier, and R. Sauleau, “Wideband circularly polarized patch antennas on reactive impedance substrates,” IEEE Antennas Wireless Propag. Lett., vol. 10, pp. 1015–1018, 2011. [15] C. Ren, L. Bernard, and R. Sauleau, “Investigations and design of small-size printed antennas on a reactive impedance substrate,” presented at the Eur. Conf. Antennas Propag, Barcelona, Spain, Apr. 2010. [16] G. Chertier, L. Bernard, and R. Sauleau, “Design of a circularly polarized patch antenna over a reactive impedance substrate,” in Proc. 5th Eur. Conf. Antennas Propag., Rome, Italy, April 2011, pp. 1056–1060. [17] L. Bernard, G. Chertier, and R. Sauleau, “Design of printed antennas on reactive impedance substrates for circular polarization operation in s-band,” in Proc. 6th Eur. Conf. Antennas Propag., Prague, Czech Republic, Mar. 2012, pp. 2339–2342.

Kush Agarwal (S’12) received the B.Tech. degree from the College of Engineering Roorkee (COER), Roorkee, India, in 2010, and the M.Sc. degree from Nanyang Technological University (NTU), Singapore, in 2012. During his M.Sc., he was engaged in research on metamaterial based circularly polarized compact/low profile antennas at Department of RF, Antenna, and Optical, Institute for Infocomm Research (I2R), A*Star, Singapore. He is currently working as a Research Engineer at National University of Singapore (NUS) Microwave and RF Lab under the supervision of Prof. Yong Xin Guo in the Electrical and Computer Engineering Department where his research focuses primarily on improving the performance of wearable antennas and sensors and reducing their body absorbed radiations using metamaterials. His research interests include the characterization and development of RF and microwave components, circuits, miniaturized antenna and electromagnetic band gap structures, metamaterial applications, flexible antenna for wearable applications, and bio-implanted wireless communications. Mr. Agarwal is the recipient of URSI Young Scientist Award and EuMA Student Grant during his M.Sc. studies.

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Nasimuddin (M’05–SM’09) was born in Bulandshahar, Uttar-Pradesh, India. He received the B.Sc. degree from Jamia Millia Islamia, New Delhi, India, in 1994, and the M.Tech. degree in microwave electronics from the University of Delhi, New Delhi, India, in 1998, and the Ph.D. degree from University of Delhi, New Delhi, India, in 2004, for theoretical work in the field of multilayered slow-wave microstrip structures and microstrip patch antennas. From 2004 to 2006, he was an Australian Postdoctoral Fellow with the Macquarie University, Sydney, Australia. Currently, he is working as a Scientist at the Department of RF, Antenna, and Optical, Institute for Infocomm Research, Singapore. He has published 101 technical journal and conference papers in the area of microstripbased microwave components. His research interest includes include multilayered microstrip based structures, millimeter-wave antennas, RFID reader antennas, UWB antennas; meta-materials based microstrip antennas, circularly polarized microstrip antennas, and small antennas for TV White Space Communications. Dr. Nasimuddin is a Senior Member of the IEEE Antennas and Propagation Society. He was awarded the prestigious Senior Research Fellowship from CSIR, Government of India in Engineering Science (2001–2003). He was also awarded a Discovery Projects Fellowship from the Australian Research Council (2004–2006) and was the recipient of the Young Scientist Award from International Union of Radio Science (URSI), in 2005.

Arokiaswami Alphones (M’92–SM’98) received the B.Tech. degree from Madras Institute of Technology, Madras, India, in 1982, the M.Tech. degree from Indian Institute of Technology (IIT), Kharagpur, India, in 1984, and Ph.D. degree in optically controlled millimeter wave circuits from the Kyoto Institute of Technology Kyoto, Japan, in 1992. He was a JSPS Visiting Fellow from 1996–1997 at Japan. From 1997 to 2001, he was with Centre for Wireless Communications, National University of Singapore as Senior Member of Technical Staff, involved in the research on optically controlled passive/active devices. Currently he is Professor at the School of Electrical and Electronic Engineering, Nanyang Technological University (NTU), Singapore. He is also Program Director of OPTIMUS (Photonics Centre for Excellence) and Program Director of M.Sc. Communications Engineering. He has 28 years of research experience. He has published and presented over 200 technical papers in International Journals/Conferences. His current research interests are electromagnetic analysis on planar RF circuits and integrated optics, microwave photonics, and metamaterial based leaky wave antennas. He was involved in many IEEE conferences held in Singapore and was General Chair of APMC 2009, and MWP 2011.