2914 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 63, NO. 7, JULY 2015

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1 2914 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 63, NO. 7, JULY 2015 A Switched Beam Antenna With Shaped Radiation Pattern and Interleaving Array Architecture Han Wang, Zhijun Zhang, Fellow, IEEE, Yue Li, Member, IEEE, and Magdy F. Iskander, Fellow, IEEE Abstract A six-beam switched beam antenna (SBA), whose beam patterns are shaped in the azimuth plane, is designed and fabricated. A synthesis method, which is based on a four-elements array and can generate a flat-top beam pattern with 46 flat gain region (gain fluctuation within ±0.5 db), 60 3-dB beam width, and less than 20.1 db side lobe level (SSL), is proposed. By combining six of those beams together, the proposed SBA can provide near consistent gain and good interference rejection in the azimuth plane. Meanwhile, an interleaving array architecture, which minimizes the size of the proposed array, is also implemented. To extend the beam coverage, a series-fed in-phase array with tapered amplitude distribution is introduced in the elevation plane. The peak gain of the beam reaches 16.6 db, and the SLL is controlled under 23.2 db in this plane. Index Terms Antenna array, pattern synthesis, smart antenna, switched beam antenna (SBA). I. INTRODUCTION S MART antenna, as an array technique that can improve the signal to interference/noise level and increase the frequency reuse rate effectively, has been widely deployed in modern wireless communication systems such as 3G and 4G [1]. The form of the implementation comprises two kinds of arrays. One is the adaptive array that can trace the signal with its electrical adjustable beams, and the other is the switched beam antenna (SBA) that can choose the best beam for the user from its preset beams [2]. The former is more powerful with its versatile beam generating ability, whereas the latter has its own advantage in that it can offer attractive performance boost in a simple and cost-effective ways [3]. The SBA is more suitable for small-scale smart antenna applications [4], [5], especially for those who has limit computing power and volume for the antenna system. Manuscript received July 08, 2014; revised January 19, 2015; accepted April 02, Date of publication April 14, 2015; date of current version July 02, This work was supported in part by the National Basic Research Program of China under Contract 2013CB329002, in part by the National High Technology Research and Development Program of China (863 Program) under Contract 2011AA010202, in part by the National Natural Science Foundation of China under Contract , and in part by the National Science and Technology Major Project of the Ministry of Science and Technology of China under Grant 2013ZX H. Wang, Z. Zhang, and Y. Li are with the State Key Laboratory of Microwave and Communications, Tsinghua National Laboratory for Information Science and Technology, Tsinghua University, Beijing , China ( zjzh@tsinghua.edu.cn). M. F. Iskander is with the Hawaii Center for Advanced Communication (HCAC), University of Hawaii at Manoa, Honolulu, HI USA ( iskander@spectra.eng.hawaii.edu). Color versions of one or more of the figures in this paper are available online at Digital Object Identifier /TAP Since the beam pattern of the SBA is fixed, the performance of the SBA is largely determined by these preset beams and the beam forming network (BFN) behind them. In classic designs, such as pencil beam-based SBA [6], [7], the designers may emphasize more on designing high gain and low side lobe level (SLL) beam since it can extend the coverage and lower the interference effectively. However, when combining these beams together to realize a full angular range coverage, the crossover level, defining with the difference between the peak gain and the gain at the intersection of the neighboring beams, is typically high [8]. This causes problem in link budget estimation and may cause communication failure if the users are in these zones. To lower the crossover level, one solution is adding more beams in a given angular range [9]. However, this will increase the complexity of the BFN significantly, which will lose the SBA s advantages in simplicity. Moreover, more beams mean more overlapping area existing between adjacent beams. The performance will deteriorate [10] and the handoff rate will increase, thus stressing the system [11]. If the designers use beam with low gain and slow roll-off characteristics to solve the crossover problem, the advantages of the SBA in interference filtering and range extension will be jeopardized, which is also undesirable in real applications. Ideally, the most suited pattern type for the SBA should be a rectangular-shaped pattern. Its flat top can provide identical gain for all direction, where no crossover problem exists between neighbor beams. Moreover, its instantaneous transition can provide ideal interference rejection outside the beam, and least number of beams are required for full angular coverage since no overlapping exists between the adjacent beams. In practice, this kind of pattern can be approached with the pattern synthesized method proposed in [12] [14]. It can be viewed as an extension of digital filter design in that the relationship between the synthesis pattern and the excitation of a uniform linear array (ULA) is Fourier transformation, which is similar to the relationship between the frequency response and impulse response of the finite impulse response (FIR) filter. Even though this kind of method is very effective to generate flat-top pattern with low SLL, the space freedom between the array elements are not utilized, which means the number of elements is not optimized. Thus, most of these works request tens or hundreds elements, which is not feasible in small-scale SBA. To improve the performance, Sabharwal et al. [15] proposed a new optimized method targeted to lower the cross-beam interference, which utilizes this space freedom between elements. Nonuniformly spaced array is further introduced, which use X 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. 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2 WANG et al.: SBA WITH SHAPED RADIATION PATTERN AND INTERLEAVING ARRAY ARCHITECTURE 2915 analytical method [16], Bayesian compressive sampling technique [17], and extended matrix pencil method [18], [19] to decrease the number of elements and minimize its effects on array performance. However, these works are still based on large array with around tens or more elements, which is not optimal for small-scale SBA applications. In this paper, a six-beam SBA is designed and fabricated, whose beams are shaped in the azimuth plane. A synthesis method based on a four-element array is proposed, which can generate flat-top pattern with low SLL. In this synthesized pattern, the flat gain region (gain fluctuation within ±0.5 db) reaches 46, and the 3-dB beam width covers 60.Afast roll-off characteristic with less than 20.1 db SLL is also achieved, which can be viewed as a good approximation to the rectangular-shaped pattern. By combining six of these beams together, the proposed SBA can provide near consistent gain in the azimuth plane with least number of beams, and can realize good interference rejection outside the selected beam. To reduce the size of the SBA and improve the aperture efficiency, an interleaving array architecture is proposed, with which one array panel, the physical printed circuit board that supports the arrays, is shared by three adjacent arrays. In the elevation plane, an eight-element series-fed nonuniform amplitude distributed in-phase array is introduced, which extends the beam coverage effectively. The gain of the beam reaches 16.6 db, and the SSL is also controlled under 23.2 db in this plane. The paper is organized as follows. Section II gives the basic idea of the synthesis method and the interleaving array architecture applied in the azimuth plane. The BFN and the doublelayer feeding structure are also introduced, which is designed to satisfy the amplitude/phase requirement of the proposed synthesis method. Section III provides a detailed description of the series-fed nonuniform amplitude distributed in-phase array design in the elevation plane. In Section IV, the built prototype is described, and the measurement results are provided to verify the performance of the proposed array. II. SYNTHESIS METHOD IN THE AZIMUTH PLANE AND THE BFN DESIGN A. Synthesis Method In previous work [20], we proposed a dual-beam SBA with shaped radiation pattern. The synthesis target is to generate two 45 flat-top beams aiming at ±22.5, respectively. Since those two beams share one aperture, a hybrid network is applied in that design. Even though high aperture efficiency is achieved, the SLL of that design is relatively high (around 8 db). In this paper, specifically to lower the SLL and realize a symmetric flat-top pattern, each array in the SBA is designed to support only one beam. The structure of the array is shown in the top right corner of Fig. 1, which is composed of four patch elements. The central two elements are named as the central group and the outer two elements are named as the shaping group. In each group, the elements are fed with the equal amplitude and phase to generate the pattern at broadside direction. Their patterns, namely the original pattern and shaping pattern, respectively, are plotted in Fig. 1. Since the distance Fig. 1. Basic concept of the synthesis method and the structure of the shaped array. between the elements in the shaping group is large, lobes with flipping phase appear in its pattern. By choosing proper phase and amplitude relationship between the central and shaping group, these lobes in the shaping pattern can have different impacts on the original pattern. Thus, the shaping can be performed and the desired pattern can be achieved as shown in Fig. 1. In this figure, the plus sign noted on the lobes of the shaping pattern means that it will have positive effect on the original pattern while the minus sign means the contrary. As a result, ripples can be observed in the main beam of the synthesized pattern, in which the gain in the central region of the original pattern decreases and the falling edge of the main beam is sharpen. This pattern can be viewed as a good approximation to the rectangular-shaped pattern, and can be further optimized with the target shown as P goal1 (ϕ): {max(p (ϕ)) min(p (ϕ))} <1dB 23 <ϕ<23 P goal2 (ϕ): {max(p (ϕ)) min(p (ϕ))} <3 db 30 <ϕ<30 P goal3 (ϕ): SLL < 20dB. (1) In this target, a 46 flat gain region and a 60 3-dB coverage are requested to provide a near consistent gain in its main beam region and 20 db SLL constraint is proposed to realize good interference rejection in its side lobe region. To better describe the optimization process, the synthesis method described above can be expressed numerically as T P e2 (ϕ) Ae jφ j 2π( d2/2λ) sin(ϕ) e P e1 (ϕ) P (ϕ) = P e1 (ϕ) P e2 (ϕ) j 2π( d1/2λ) sin(ϕ) e e j 2π(d1/2λ)sin(ϕ) Ae jφ j 2π(d2/2λ) sin(ϕ) e (2) where P e1 (ϕ) and P e2 (ϕ) are the element patterns of the central and shaping group in angular position ϕ; A and φ represent relative amplitude and phase excitation of the shaping group to the central group; and d 1,d 2 are the elements distance in the central and shaping group, respectively. In the optimization process, the d 1 is tuning first to find proper original pattern profile. After that, the d 2 is adjusted to

3 2916 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 63, NO. 7, JULY 2015 Fig. 2. Beam pattern and structure comparison between the conventional array and the shaped array. align the lobes of the shaping pattern to the desired impact area on the original pattern. Finally, the A and φ are optimized, and the shaping is performed with a proper extend. Fig. 2 shows the optimized synthesized pattern. It can be observed that the ripples on the main beam are minimized, and the 3-dB beam width along with the SLL reach 60 and 27.9 db, respectively, which satisfy all three targets as listed in (1). To demonstrate the effectiveness of the proposed synthesis method, the pattern of a two-element conventional array, whose 3-dB coverage is optimized to 60, is also provided in Fig. 2. It can be observed that the fluctuation of the gain in the main beam region, the falling speed of the main beam outside the 3-dB region, and the SLL have been significantly improved by implementing the proposed synthesis method. However, as indicated by the dimension comparison shown in the bottom of Fig. 2, these advantages are achieved at the expense of a larger array size. If directly arrange the elements of this shaped array on one array panel and combine six of this array panel together to realize 360 azimuth coverage, the diameter of the SBA will be quite large as shown in Fig. 3(a). This is undesirable for small-scale SBA applications. Thus, interleaving array architecture is proposed, which can realize similar performance with a much compact array panel size. Fig. 3. Interleaving array architecture. (a) Size comparison between the array panel and the SBA with/without interleaving architecture. (b) Proposed interleaving array architecture. TABLE I OPTIMIZED ARRAY PARAMETERS OF THE SHAPED ARRAY B. Interleaving Array Architecture By observing the structure of the four elements shaped array shown in Fig. 2, it may be noticed that there is sufficient space to fit another element between the central and the shaping element at both sides of the array panel. Thus, interleaving array architecture is proposed, which utilizes this space to reduce the size of the array panel as shown in Fig. 3(b). In this figure, the elements for specific array, or beam hereafter, are noted with the same color. For any beam in the SBA, its central group elements are fixed at the original position but its shaping group elements are swapped with the one of its neighboring beams. Thus, its largely distanced shaping elements are relocated to its adjacent beams array panels, and the space between its central and shaping elements is now utilized Fig. 4. Pattern and structure comparison between the array with/without interleaving. by the shaping elements of its neighboring beams. As a result, one array panel is now being shared by three beams, and its size is reduced from 3.34λ to 2.36λ as shown in Fig. 3(a). Since the only difference between the shaped array with/without interleaving is the orientation of the shaping elements, the synthesis method proposed above is still applicable. Table I provides the optimized array parameters of these two shaped arrays, and Fig. 4 shows their synthesized patterns. It can be observed that the SLL is increased but its

4 WANG et al.: SBA WITH SHAPED RADIATION PATTERN AND INTERLEAVING ARRAY ARCHITECTURE 2917 Fig. 5. Schematic diagram of the BFN for one beam. Fig. 7. Double-layer feeding structure designed for interleaving array architecture. Fig. 6. Circuit-level implementation of the BFN for one beam. falling edge is shaper with interleaving, and all the targets are achieved as listed in (1). Fig. 8. Structure of the array and its basic element in elevation plane. C. BFN and Feeding Structure Design To implement these optimized phase/amplitude distribution provided in Table I, the BFN is designed and shown in Fig. 5. It is composed of two directional couplers to control the relative amplitude (A) of the shaping group to the central group, and microstrip feeding lines with different electrical lengths to realize the phase difference (φ) between these two groups. Fig. 6 shows its circuit-level implementation, in which a λ/4 impedance transformation line is added to provide 50-Ω interface to the array element. Since interleaving array architecture is applied, a doublelayer feeding structure built with two hexagonal-shaped feeding panels is introduced as shown in Fig. 7. By allocating the BFN of the even number beams on the upper feeding panel and the odd number beams on the lower feeding panel, this doublelayer feeding structure can combine the BFN of six beams together without using crossover. III. PATTERN DESIGN IN THE ELEVATION PLANE In Section II, a flat-top beam pattern is generated with the proposed synthesis method in the azimuth plane. In this section, a high-gain low SLL pattern is achieved in the elevation plane. This pattern is generated by an eight-element series-fed nonuniform amplitude distributed in-phase array [21], and the SLL is controlled by optimizing the amplitude distribution of this in-phase array. Fig. 8 shows the structure of the array, which is also a patch elements-based array. It is fabricated on an 1.5-mmthick Teflon-based substrate (ε r 2.65 and tan δ 0.002),in which the effective wavelength is λ g. An enlarged view of the basic element is shown in the left top of Fig. 8. It is composed of a λ g /2 radiating patch and two λ g /4 microstrip transmission lines. The total equivalent electrical length of this basic element is close to λ g. Thus the in-phase characteristic is guaranteed in this array near the central resonant frequency. While resonating, this array can be equivalent to a series circuit shown in the bottom right of Fig. 8. The amplitude of each basic element is decided by its resonant impedance and can be tuned by changing the width (W f ) of its two λ/4 microstrip transmission lines. By concatenating the basic elements with different W f together, a tapered amplitude distribution can be achieved in the array. Since only the W f is tuned, the dimensions of the radiation patch (L p =16.5 mm and W p =20.0 mm) are identical for all basic elements. Thus, minimized effect is applied on the radiation pattern. Fig. 9 shows the amplitude pattern versus W f at the central resonant frequency (5.22 GHz). It can be observed that the normalized amplitude tuning range is between 0.67 and 1. By optimizing the array s amplitude distribution within this range, 23.2 db SLL is achieved with a peak gain of 16.6 db. The simulated pattern is provided in Section IV, and the optimized amplitude and the W f of these eight basic elements are listed in Table II, in which the order of elements is in accord with the numbers shown in Fig. 8.

5 2918 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 63, NO. 7, JULY 2015 Fig. 9. Relationship between the amplitude pattern and the width of the microstrip transmission line. Fig. 11. Connection between the feeding panel and the array panel. TABLE II OPTIMIZED AMPLITUDE DISTRIBUTION AND THE ARRAY PARAMETERS Fig. 10. Structure and dimensions of the array panel. Fig. 12. Explosive view of the proposed SBA. Because the amplitude distribution in this array is symmetric, the feeding point can also be mirrored to integrate with the double-layer feeding structure as proposed in Section II. Fig. 10 shows the array panel by combining the array designs in the azimuth and the elevation plane together. It can be observed that the feeding points of the central group and shaping group are symmetrically located on the panel. With the array panel and the double-layer feeding structure proposed in Section II, the six beams SBA can now be assembled as shown in Figs. 11 and 12. The array panel and the feeding panel are connected via MMCX connectors, and the double-layer feeding structure provides a good supporting to the arrays via these connectors. IV. ARRAY PROTOTYPE AND THE MEASUREMENT RESULT To verify the performance of the proposed array, a prototype is built and measured in this paper. Fig. 13 shows the photos of the prototype, and its S-parameters, radiation patterns, and gain Fig. 13. Photos of the fabricated prototype. (a) Assembled prototype of the proposed SBA. (b) Array panel. (c) Double layer feeding structure. (d) Feeding panel.

6 WANG et al.: SBA WITH SHAPED RADIATION PATTERN AND INTERLEAVING ARRAY ARCHITECTURE 2919 Fig. 14. Simulated and measured S-parameters of the proposed SBA. are measured and compared with the simulation results in this section. Consider that the array is rotational symmetric and similar results can be observed for all ports, the results of port one are provided below. A. S-Parameters The central radiation frequency of the fabricated prototype is designed as 5.22 GHz, and the S-parameters are measured with Agilent Vector Network Analyzer E5071B. The measured and simulation return loss and the crossbeam coupling level are provided in Fig. 14. It can be observed that the measured return loss matches the simulation result well, and the mutual coupling level between adjacent beams is low. B. Radiation Pattern The radiation patterns are measured in the ETS anechoic chamber AMS8500. Fig. 15 provides the normalized measured and simulated patterns in both the azimuth plane (H-plane) and the elevation plane (E-plane). It can be observed that the measured patterns fit the simulation results well. In the H-plane, the measured 3-dB beam width is 56, and the stable gain region covers from 20 to 22. A sharp rolloff can be observed at the edge of the main beam, and the SLL reaches 17.8 db. In the E-plane, a pencil beam is achieved as expected, and the measured SLL is 20.8 db. The difference between the simulation and measurement results may due to fabrication and assembly error or inaccurate phase and amplitude generation by the BFN. As for the cross polarization component, the simulated value in E-Plane is not displayed since it is beyond the lower bound, and the difference between the measured and simulated results is due to the dynamic range limitation in the measuring system. Fig. 15. Simulated and measured radiation patterns of the beam in the proposed SBA. (a) Simulated and measured radiation pattern in E-plane. (b) Simulated and measured radiation pattern in H-plane. Fig. 16. Simulated and measured gain of the proposed SBA. C. Gain The gain is also measured in the ETS anechoic chamber. Fig. 16 shows the comparison between the simulation and measured results. It can be observed that the peak gain reaches 16.4 db in the measurement, which matches well with the simulation result near the resonant frequency.

7 2920 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 63, NO. 7, JULY 2015 V. CONCLUSION In this paper, a six-beam SBA is proposed and fabricated, whose beam pattern is shaped that can provide near consistent gain in the azimuth plane. A synthesis method based on a four-element array is described, and a flat-top beam pattern is generated with this method. This flat-top pattern is characterized with 60 3-dB beam width, 46 stable gain region, and fast falling edge with 20.1 db SSL, which can be viewed as a good approximation to the rectangular-shaped pattern. By combining six of these shaped beams together, this proposed SBA not only provides full azimuth coverage with least number of beams, but also achieves good interference rejection out of the selected beam. To minimize the size of the SBA and improve the aperture efficiency, interleaving array architecture is proposed, which shares one array panel with three adjacent beams. As a result, the size of the proposed array panel in the azimuth plane is reduced to 2.36λ, which is comparable to traditional equally spaced four-element array. To extend the beam coverage, a nonuniform amplitude distributed series-fed in-phase array is designed and optimized in the elevation plane. The peak gain reaches 16.6 db, and the SLL is controlled under 23.2 db. [16] B. P. Kumar and G. R. Branner, Design of unequally spaced arrays for performance improvement, IEEE Trans. Antennas Propag., vol. 47, no. 3, pp , Mar [17] G. Oliveri and A. Massa, Bayesian compressive sampling for pattern synthesis with maximally sparse non-uniform linear arrays, IEEE Trans. Antennas Propag., vol. 59, no. 2, pp , Feb [18] S. Yang, Y. Liu, and Q. H. Liu, Combined strategies based on matrix pencil method and tabu search algorithm to minimize elements of nonuniform antenna array, Prog. Electromagn. Res. B, vol. 18, pp , [19] Y. H. Liu, Q. H. Liu, and Z. P. Nie, Reducing the number of elements in multiple-pattern linear arrays by the extended matrix pencil methods, IEEE Trans. Antennas Propag., vol. 62, no. 2, pp , Feb [20] H. Wang, Z. J. Zhang, and Z. H. Feng, A beam-switching antenna array with shaped radiation patterns, IEEE Antennas Wireless Propag. Lett., vol. 11, pp , Jun [21] Z. Chen and S. Otto, A taper optimization for pattern synthesis of microstrip series-fed patch array antennas, in Proc. IEEE Eur. Wireless Technol. Conf. (EuWIT), 2009, pp Han Wang received the B.S. degree in applied physics from Beijing University of Posts and Telecommunications, Beijing, China, in He is currently pursuing the Ph.D. degree in electrical engineering at Tsinghua University, Beijing, China. His research interests include antenna design and theory, particularly in smart antenna, MIMO antenna, and antenna measurement. REFERENCES [1] A. Osseiran and A. Logothetis, Smart antennas in a WCDMA radio network system: Modeling and evaluations, IEEE Trans. Antennas Propag., vol. 54, no. 11, pp , Nov [2] A. El-Zooghby, Smart Antenna Engineering. Norwood, MA, USA: Artech House, 2005, pp [3] S. W. Choi, D. H. Shim, and T. K. Sarkar, A comparison of trackingbeam arrays and switching-beam arrays operating in a CDMA mobile communication channel, IEEE Antennas Propag. Mag., vol. 41, no. 6, pp , Dec [4] M. Maqsood et al., Low-cost dual-band circularly polarized switched-beam array for global navigation satellite system, IEEE Trans. Antennas Propag., vol. 62, no. 4, pp , Apr [5] H. Liu, S. Gao, and T. H. Loh, Small director array for low-profile smart antennas achieving higher gain, IEEE Trans. Antennas Propag., vol. 61, no. 1, pp , Jan [6] J. Butler and R. Lowe, Beam-forming matrix simplifies design of electronically scanned antennas, Electron. Des., vol. 9, pp , [7] J. Shelton and K. S. Kelleher, Multiple beams from linear arrays, IRE Trans. Antennas Propag., vol. 9, no. 2, pp , Mar [8] H. Novak, Switched-beam adaptive antenna system, Ph.D. dissertation, Inst. Telecommunications and High-Frequency Engineering, Vienna Univ. Technology, Vienna, Austria, 1999, pp [9] S. Mosca, F. Bilotti, A. Toscano, and L. Vegni A novel design method for Blass matrix beam-forming networks, IEEE Trans. Antennas Propag., vol. 50, no. 2, pp , Feb [10] M. G. Jansen and R. Prasad, Capacity, throughput, and delay analysis of a cellular DS CDMA system with imperfect power control and imperfect sectorization, IEEE Trans. Veh. Technol., vol. 44, no. 1, pp , Feb [11] J. H. Yea, Smart antennas for multiple sectorization in CDMA cellsites, RF Des. Mag., pp , Apr [12] J. E. Evans, Synthesis of equiripple sector antenna patterns, IEEE Trans. Antennas Propag., vol. 24, no. 3, pp , May [13] A. Ksienski, Maximally flat and quasi-smooth sector beams, IRE Trans. Antennas Propag., vol. 8, no. 5, pp , Sep [14] A. Lopez, Sharp cutoff radiation patterns, IEEE Trans. Antennas Propag., vol. 27, no. 6, pp , Nov [15] A. Sabharwal, D. Avidor, and L. Potter, Sector beam synthesis for cellular systems using phased antenna arrays, IEEE Trans. Veh. Technol., vol. 49, no. 5, pp , Sep Zhijun Zhang (M 00 SM 04 F 15) received the B.S. and M.S. degrees in electronics engineering from the University of Electronic Science and Technology of China, Chengdu, China, in 1992 and 1995, respectively, and the Ph.D. degree in electronics engineering from Tsinghua University, Beijing, China, in In 1999, he was a Postdoctoral Fellow with the Department of Electrical Engineering, University of Utah, Salt Lake City, UT, USA, where he was appointed as Research Assistant Professor in In May 2002, he was an Assistant Researcher with the University of Hawaii at Manoa, Honolulu, HI, USA. In November 2002, he joined Amphenol T&M Antennas, Vernon Hills, IL, USA, as a Senior Staff Antenna Development Engineer and was then promoted as Antenna Engineer Manager. In 2004, he joined Nokia Inc., San Diego, CA, USA, as a Senior Antenna Design Engineer. In 2006, he joined Apple Inc., Cupertino, CA, USA, as a Senior Antenna Design Engineer and was then promoted as Principal Antenna Engineer. Since August 2007, he has been a Professor with the Department of Electronic Engineering, Tsinghua University. He is the author of Antenna Design for Mobile Devices (Wiley, 2011). Dr. Zhang is serving as an Associate Editor of the IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION and the IEEE Antennas and Wireless Propagation Letters. Yue Li (S 11 M 12) received the B.S. degree in communication engineering from Zhejiang University, Zhejiang, China, in 2007, and the Ph.D. degree in electronic science and technology from Tsinghua University, Beijing, China, in In 2012, he was a Postdoctoral Fellow with the Department of Electronic Engineering, Tsinghua University. Since January 2014, he has been a Postdoctoral Fellow with the Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, PA, USA. He was also a Visiting Scholar at the Institute for Infocomm Research (I 2 R), A*STAR, Singapore, and Hawaii Center of Advanced Communication (HCAC), University of Hawaii, Hilo, HI, USA. He has authored and coauthored over 50 journal papers, and holds over 10 granted and filed Chinese patents. His research interests include metamaterials, electromagnetics, and antennas. Dr. Li is serving as a Reviewer of the IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION and the IEEE Antennas and Wireless Propagation Letters.

8 WANG et al.: SBA WITH SHAPED RADIATION PATTERN AND INTERLEAVING ARRAY ARCHITECTURE 2921 Magdy F. Iskander (F 93 LF 12) is a Professor of electrical engineering and the Director of the Hawaii Center for Advanced Communications (HCAC), College of Engineering, University of Hawaii at Manoa, Honolulu, HI, USA. He is Co-Director of the NSF Industry/University Cooperative Research Center with four other universities. He joined the University of Hawaii in 2002 and prior to that he was a Professor of electrical and computer engineering and the Engineering Clinic Endowed Chair Professor at the University of Utah. He has authored over 250 papers in technical journals, holds nine patents, and has made numerous presentations at national/international conferences. He authored/edited several books including the textbook Electromagnetic Fields and Waves (Prentice Hall, 1992, and Waveland Press, 2001; second edition 2012), and four books published by the Materials Research Society (MRS) on Microwave Processing of Materials. He is the Founding Editor of the Computer Applications in Engineering Education (CAE) journal (Wiley, 1992 present). His research in computational and biomedical electromagnetics and wireless communications is funded by the National Science Foundation, National Institute of Health, Army Research Office, U.S. Army CERDEC, Office of Naval Research, and several corporate sponsors. Dr. Iskander was the 2002 President of the IEEE Antennas and Propagation Society, Distinguished Lecturer, and a Program Director in the Electrical, Communications, and Cyber Systems Division at the National Science Foundation. He was the recipient of many awards for excellence in research and teaching including the University of Hawaii Board of Regents Medal for Excellence in Research (2013), the Board of Regents Medal for Teaching Excellence (2010), and the Hi Chang Chai Outstanding Teaching Award (2011, 2014) which is based on votes by graduating seniors. He was also the recipient of the IEEE MTT-S Distinguished Educator Award (2013), IEEE AP-S Chen- To Tai Distinguished Educator Award (2012), and Richard R. Stoddard Award from the IEEE EMC Society in He received the Northrop Grumman Excellence in Teaching Award in 2010, the American Society for Engineering Education (ASEE) Curtis W. McGraw National Research Award in 1985, and in 1991 the ASEE George Westinghouse National Award for Excellence in Education.