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Electric Coupling Structure of Substrate Integrated Waveguide (SIW) for the Application of 140-GHz Bandpass Filter on LTCC Sai Wai Wong, Member, IEEE, Kai Wang, Student Member, IEEE, Zhi-Ning Chen, Fellow, IEEE, and Qing-Xin Chu, Senior Member, IEEE
Abstract— Millimeter-wave (mmW) bandpass filters (BPFs) using substrate integrated waveguide (SIW) are proposed in this paper. The propagation constants of two different types of electromagnetic bandgap (EBG) units are discussed and compared for their passbands and stopbands performance. In among, the slotted-SIW unit shows a very good lower and upper-stopband performance. The mmW BPF with three cascaded uniform slotted-SIW-based EBG units is constructed and designed at 40-GHz. This EBG filter exhibits good out-of-band performance. To further improve the in-band performance, a third-order mmW BPF with nonuniformly cascaded slotted-SIW unit is designed at 140 GHz. The filter is investigated with the theory of electric coupling mechanism. The extracted coupling coefficient (K) and quality factor (Q) are used to determine the filter circuit dimensions. To prove the validity, the two proposed structures are fabricated in a single-circuit layer using low temperature co-fired ceramic technology and measured at 40 and 140 GHz, respectively. The measured results are in good agreement with the simulated results in such high frequency. The measured insertion losses at 40 GHz and 140 GHz are 0.72 and 1.913 dB, respectively. Index Terms— 140 GHz, bandpass filter (BPF), electromagnetic bandgap (EBG), low temperature co-fired ceramic (LTCC), millimeter-wave (mmW), substrate integrated waveguide (SIW).
I. I NTRODUCTION
S
INCE the characteristics of millimeter-wave (mmW) show attractive properties for high data rate wireless transmission, more and more attention has been paid on the mmW circuit design, which led to rapid development of the mmW manufacturing technology. Currently, most of the mmW bandpass filters (BPFs) are mainly fabricated with low temperature co-fired ceramic (LTCC) [1], [2] and complementary metal– oxide–semiconductor technology [3]. On the other hand,
Manuscript received May 12, 2013; revised August 16, 2013; accepted October 7, 2013. Date of publication October 22, 2013; date of current version January 30, 2014. This work was supported in part by the National Natural Science Foundation of China under Grant 61101017 and in part by the State Key Laboratory of Millimeter Waves, Southeast University, under Grant K201327. Recommended for publication by Associate Editor M. S. Tong upon evaluation of reviewers’ comments. S. W. Wong, K. Wang, and Q.-X. Chu are with the School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510641, China (e-mail:
[email protected];
[email protected];
[email protected]). Z.-N. Chen is with the Department of Electrical and Computer Engineering, National University of Singapore, Singapore 119077, and also with the Institute for Infocomm Research, Agency for Science, Technology and Research, Singapore 138632 (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/TCPMT.2013.2285388
the increased attention has been paid to the substrate integrated waveguide (SIW) filters with high performance and compact size for microwave and mmW applications [4]–[6]. Of late, some structures based on SIW technology are proposed in [7]–[10]. A compact SIW BPF with complementary splitring resonators is proposed in [7], by analyzing and studying the couplings, a cross-coupled BPF is formed with wide stopband. The dispersive coupling and frequency-dependent coupling are introduced to obtain a good filter performance in [8] with generalized Chebyshev filter. Transmission zeros are introduced by appropriately using the coupling between the SIW cavities is discussed in [9]; the out-of-band rejection level is quite good compared with traditional microstrip filters [10]. It is interesting to insert a microstrip line between the SIW cavities, which described in [11]; a transmission zero is obtained to improve out-of-band rejection. It is noteworthy that there is a little work about SIW BPF designed at mmW band up to the authors’ knowledge. In [12], a 60-GHz frequency band planar diplexer developed in SIW technology is proposed and presented, the high channel-tochannel isolation is achieved by composing fifth-order SIW bandpass channel filters. An mmW SIW filter buried in LTCC has been analyzed and designed in [13], using the metallic via arrays to control the couplings; a good in-band performance is achieved. In addition to the magnetic coupling, which is controlled by metallic via-holes, a slot etching on the top metal of the SIW cavity to introduce electric coupling as a negative coupling is presented in [14] and [15], a good performance also obtained with low insertion loss and high selectivity. The aforementioned SIW BPFs exhibit a very good filtering performance. However, they are not suitable to design at 140 GHz or higher frequency bands due to the limitation of via-holes’ fabrication. Especially, the magnetic coupling window created by the via-holes is too small to be fabricated at such high frequency. In this paper, only the electric coupling is used in designing mmW BPF at 40 and 140 GHz with a single layer SIW cavity using LTCC technology. The electric coupling is simply controlled by adjusting the height and width of the slot etched on the surface of SIW cavity. Two different types of electromagnetic bandgap (EBG) units are first studied, and the frequency-dependent propagation constants are extracted, respectively, to show the band response of each EBG unit. Using the slotted-SIW EBG unit, an mmW BPF is designed at 40 GHz with three cascaded
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WONG et al.: ELECTRIC COUPLING STRUCTURE OF SIW
Fig. 1.
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Two different types of EBG units with same L p = 700 μm.
slotted-SIW units. To further improve the in-band performance and verify the advantage of electric coupling controllability, a 140-GHz third-order mmW SIW Chebyshev BPF is proposed. The three resonators are formed by etching four rectangular slots on the top metal plane of a SIW transmission line and the filter is investigated with the theory of coupled resonator circuits. The design curves of coupling coefficient K and quality factor Q are extracted subjected to the slot height and width [16]. II. S TUDY OF T WO D IFFERENT T YPES OF EBG C ELLS There are technical researches for more than 10 years in the area of using planar EBG structures for noise isolation [17]–[19]. Recently, planar EBG structures, which consist of periodic etched power plane and solid ground plane, have been proposed to efficiently suppress the propagation of the power/ground resonance mode at gigahertz range [20]–[23]. In this paper, two different types of EBG units are proposed and shown in Fig. 1; their passband and stopband are studied at 40-GHz band. The unit cell of the EBG-I structure is formed by etching a rectangular slot with the length λg /2 (where λg is the wavelength at the frequency f1 ) on the transmission line, and the unit cell of the EBG-II structure is constituted with SIW transmission line with the length λg /2 (where λg is the wavelength at the frequency f 2 ) and a slot on the top metal layer. The f 1 and f2 are pointed out in Fig. 2(a), which implies the stopband limiting frequencies. The two EBG cells have the same size of the cavity, and their dimensions are: W = 2000 μm, S = 100 μm, V = 380 μm, T = 330 μm, and R = 50 μm. To further investigate the transmission behaviors of these three EBG cells, the guided-wave propagation constants (γ = α+jβ) are numerically extracted from the EM simulator (CST) [24]. The propagation constant is generally expressed in terms of two ABCD-matrix elements, A p and D p [25] A P + DP (1) 2 where L P is the length of each EBG cell. The term α represents the attenuation constant, a nonzero value of α implies a stopband. The extracted normalized attenuation constant (α/κ0 ) and phase constant (β/κ0 ) of each EBG cell are shown in Fig. 2 by virtue of the EM simulation [23]. The κ0 is the phase constant in free space. Fig. 2(a) and (b) shows the frequency responses of the attenuation constant α/κ0 and the phase constant β/κ0 of two different types of EBG cells. The α/κ0 of EBG-I structure is close cosh(γ L P ) =
Fig. 2. Extracted frequency-dependent propagation constant of three different types of EBG units. (a) Normalized attenuation constant. (b) Normalized phase constant.
Fig. 3. Layout of proposed mmW bandpass filter using three cascaded EBG-II structures.
to zero at the frequency ranged from 0 to 43 GHz and then increases to a nonzero value in the frequency range from 43 to 70 GHz. Thus, EBG-I is known as a low-pass filter. For the EBG-II, the α/κ0 is a nonzero value ranged from 0 to 31 GHz, then it stays nearly zero from 31 to 44 GHz and quickly increases to nonzero value at the frequency ranged from 44 to 70 GHz. The properties show that EBG-II is a BPF. The lower stopband is obtained due to the zero value of β/κ0 as shown in the red solid line of Fig. 2(b), which implies that the electromagnetic (EM) wave is not propagating at the frequency ranged from 0 to 31 GHz. The passband of EBG-II is achieved due to the attenuation is zero, as shown in the shade region of Fig. 2(a). The 44–70 GHz is the upper-stopband of the EBG-II. This stopband is caused by the bandgap behavior of the EBG unit. According to the previous analysis of three different types of EBG cells, the EBG-II shows an attractive bandpass response. To make use of this property, an mmW BPF is designed with three cascaded EBG-II units, the layout is shown in Fig. 3. The estimated circuit dimensions from previous discussion are used to design the mmW BPF in CST [24]. The finetuned circuit dimensions are W0 = 2200 μm, W1 = 285 μm,
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Fig. 5. Top-view and cross-sectional view of field distribution (a) magnetic and (b) electric couplings.
Fig. 6.
Fig. 4. Predicted and measured frequency responses of the proposed mmW bandpass filter. (a) Top-view photograph of the fabricated mmW bandpass filter. (b) |S21 | and |S11 |.
W2 = 2000 μm, W3 = 1340 μm, S0 = 2100 μm, S1 = 350 μm, S2 = 550 μm, S3 = 100 μm, V = 380 μm, T = 330 μm, and R = 50 μm. To prove the validity, the proposed structure is fabricated in a single-circuit layer using LTCC technology. The photograph shows in Fig. 4(a) with the compact size of 2.1 mm × 2.2 mm. The LTCC substrate used herein has a dielectric constant of 5.9, a substrate thickness of 0.193 mm, and a loss tangent of 0.002. The comparison between the simulated and measured results is shown in Fig. 4(b). The simulation results in Fig. 4(b) show a bandpass response at the center frequency of 40 GHz, and this verified our previous work on the EBG structure. The measured 3-dB passband ranges from 32.75 to 49.3 GHz, or a bandwidth of 40.3% and the measured insertion loss at 40 is 0.72 dB including the ground-signal-ground transitions, the return loss is better than 9 dB within the passband. A good agreement is shown between the simulation and measured results in Fig. 4(b). On the other hand, the shortcoming of this mmW BPF is also obvious, that is the in-band performance; the return loss at a higher frequency of the passband is a fatal drawback of the proposed structure. This is due to simply cascading three EBG-II cells without optimizing the coupling between these EBG cells. Obviously, if the pitch number of this SIW periodic structure goes higher, the bandpass response can also achieve but accompanied with poorer in-band performance. This is due to the resonance frequencies within the passband
Layout of proposed 140-GHz mmW bandpass filter.
is not systematically implemented. This would be solved by implementing the Chebyshev filter synthesize method in the next section. In the following section, we are going to use the coupled resonator theory [16] to apply in designing a 140-GHz mmW BPF, and the shining point of this structure is the electric coupling. The electric coupling is controlled by simply adjusting the height and width of the slots, which are etched on the top metal layer of the single SIW cavity. III. 140-GH Z MM W BPF BASED O N C OUPLED R ESONATOR T HEORY Traditionally, the SIW filter uses mainly magnetic coupling by via-hole coupling window. The coupling coefficient is controlled by the width of the window, as shown in Fig. 5(a). In 140 GHz; the via-hole diameter is relatively large when compared with the free space wavelength of 2 mm at 140 GHz. Thus, the physical dimension adjustability of the coupling window is limited and the desired values of the coupling coefficient cannot be physically implemented. To solve this problem, the rectangular slot is proposed to provide the electric coupling instead of via-hole magnetic coupling window, as shown in Fig. 5(b). The coupling coefficient is controlled by the width and length of the slot. Thus, one more degree of freedom is provided when compared with traditional magnetic coupling window as shown in Fig. 5(a). Moreover, the physical dimension adjustability of the slot is much easier than the viahole coupling window. In Section II, a BPF constituted with three cascaded EBG-II cells is proposed by studying the characteristics of the EBG-II cell-like attenuation constant (α) and phase constant (β). The response of the 40 GHz case is not good, which is shown in Fig. 4(b), so we applied the design method of the
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Fig. 7.
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Coupling mechanism of the proposed structure.
capacitive gap coupling structure to optimize the SIW periodic structure. Moreover, we want to demonstrate the slot coupling can be applied in higher frequency, therefore a third-order SIW BPF at 140 GHz based on EBG concepts and applied theory of coupled resonator circuit is proposed. The proposed filter with marked dimensions is shown in Fig. 6. The filter consists of two microstrip feed lines and one SIW cavity. There are four etching slots on the top metal layer of the SIW cavity to divide the SIW cavity into three resonators, namely R1 , R2 , and R3 (the dotted line region as marked in Fig. 6). The resonators are excited by the electric coupling of the slots, as shown in Fig. 5(b). The coupling mechanism among the resonators of proposed filter is shown in Fig. 7. S and L stand for the source and load excitation. The Q E represents the external quality factor and K ij stands for the coupling coefficient between the i th and j th resonators (i, j = 1, 2, 3, and i = j ). The adjacent coupling coefficient K 12 and K 23 are strong coupling, and K 13 is coupling between the two nonadjacent resonators negligibly weak in this case, as shown in Fig. 7. Moreover, the K 12 = K 23 causes the resonator R1 to have the same size and same coupling slot dimensions with resonator R3 . As the coupling between the resonators has been introduced, the passband performance is mainly determined by Q E , K 12 , and K 23 . According to the coupled resonator theory, the external quality factor can be obtained by the following [16]: QE =
f0 f ±90◦
(2)
where f 0 is the resonance frequency of the excitation port of the first resonator, and the value of f ±90o is determined from the frequency at which the phase shifts ±90° with respect to the absolute phase at f0 . With (2) and the simulated results of the structure shown at top-left corner of Fig. 8, the Q E versus the physical dimensions are extracted and shown in Fig. 8. Q E is a function of the variable W2 , as shown in Fig. 8. Three curves are plotted at various S2 values. Obviously, the Q E increases slowly as the slot height (W2 ) increases, and the Q E gradually increases as the slot width (S2 ) increases. On the other hand, the coupling coefficient can be extracted from EM simulation results of the coupled resonators using the following [16]: f R1 f R2 + K 12 = K 23 = ± f f R1 R2 2 2 2 2 2 2 f p2 − f p1 f R2 − f R1 − (3) 2 + f2 2 + f2 f p2 f R2 p1 R1
Fig. 8. Extracted quality factor Q E versus the slot width and the slot height.
Fig. 9. Extracted coupling coefficient K 12 versus the slot width and the slot height.
where f Ri (i = 1, 2) represents the self-resonator frequency of each resonator and f pi (i =1, 2) denote the two split resonator frequencies when two resonators coupled to each other. In our proposed structure, f R1 is unequal to f R2 , but they are not too far away from each other to guarantee that the coupling coefficient is a real number. With (3) and the simulated results of the structure shown at the bottom-left corner of Fig. 9, the K 12 versus the slot width (S3 ) and slot height (W3 ) is extracted and shown in Fig. 9. The coupling coefficient K 12 depends on two parameters, they are the slot width (S3 ) and the slot height (W3 ). The extracted values of K 12 are shown in Fig. 9. From the curves, the coupling coefficient K 12 increases when the slot width and the slot height are decreasing. The extracted quality factor and coupling coefficient are used to determine the physical circuit dimensions. In this case, the Chebyshev low-pass prototype with third order and the passband ripple of 0.5 dB are selected. The prototype element values are looked up in [16]. Then, we designed an mmW BPF at center frequency of 140 GHz and with 10% fractional bandwidth (FBW). The calculated external quality factor and coupling coefficients are obtained as follows [16]: g0 g1 FBW FBW = √ . g1 g2
QE =
(4a)
K 12
(4b)
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high frequency. Notice that the measurement system has some calibration errors in the frequency range 164 GHz, which is slightly >0 dB. In addition, an unexpected transmission zero appears in this frequency. Except this frequency range, the simulation and measured results are in reasonable agreement. The discrepancy is mainly due to the fabrication errors as the circuit dimensions are very small in the range of micrometer. IV. C ONCLUSION
Fig. 10. Predicted and measured frequency responses of the proposed mmW BPF. (a) Top-view photograph of the fabricated mmW BPF. (b) |S21 | and |S11 |.
where FBW is the fractional bandwidth. The g0 , g1 , and g2 are the third-order element values of the low-pass prototype. For demonstrating a third-order filter, the calculated value of Q E is 15.96 and K 12 is 0.071 with FBW of 10%. Look up at Figs. 8 and 9 for Q E =15.96 and K 12 = 0.071. The corresponding values of physical dimensions of the slots are about: S2 = 60 μm, S3 = 160 μm, W2 = 400 μm, and W3 = 420 μm. The estimated circuit dimensions are used in full-wave EM simulator for further optimization. The fine-tuned circuit dimensions by an EM simulator CST are W0 = 790 μm, W1 = 590 μm, W2 = 400 μm, W3 = 420 μm, W4 = 90 μm, S0 = 1200 μm, S1 = 150 μm, S2 = 60 μm, S3 = 160 μm, S4 = 175 μm, S5 = 110 μm, T1 = 95 μm, T2 = 85 μm, V = 200 μm, and R = 50 μm. To prove the validity, the proposed filter is fabricated and shown in Fig. 10(a) with a size of 1.2 mm × 0.79 mm. The comparison between the simulated and measured results is shown in Fig. 10(b). The simulation results show a good performance of the proposed structure; the insertion loss is 1.46 dB of the center frequency of the passband, i.e., 140 GHz, and three modes are allocated in the passband clearly. Moreover, the return loss is better than 15 dB. By comparing with the in-band performance of the 40 GHz case, which is shown in Fig. 4(b), we concluded that the advantage of the SIW periodic structure is quite simple only by cascading several EBG cells, but the shortcoming is the poor in-band performance. However, a good performance can be achieved when applying the design method of capacitive gap coupling on the periodic structure. The measured 3-dB passband ranges from 131.3 to 149.6 GHz with a bandwidth of 13.03%. The return loss is better than 11 dB within the passband and the measured inband insertion loss is 1.913 dB at 140 GHz, which is very good in such
Two electric coupling mmW BPFs using SIW are proposed in this paper. One is constructed by three cascaded uniform slotted-SIWbased EBG units operating at 40 GHz. This EBG filter exhibits good out-of-band performance. To further improve the in-band performance, another third-order mmW BPF with nonuniformly cascaded slotted-SIW units is designed at 140 GHz. The filter is investigated with the theory of coupled resonator circuits. The filter circuit dimensions are determined by the extracted coupling coefficient (K ) and quality factor (Q); the design procedures and curves are given in this paper. The two proposed filters are fabricated and measured at 40 and 140 GHz; the measured results are in good agreement with the simulated results in such high frequency. The measured insertion losses at 40 and 140 GHz are 0.72 and 1.913 dB, respectively. ACKNOWLEDGMENT The authors would like to thank Y. S. Bee for her help in circuit measurements. R EFERENCES [1] J.-H. Lee, S. Pinel, J. Papapolymerou, J. Laskar, M. M. Tentzeris, H.-M. Lee, et al., “Low-loss LTCC cavity filters using system-onpackage technology at 60 GHz,” IEEE Trans. Microw. Theory Tech., vol. 53, no. 12, pp. 3817–3824, Dec. 2005. [2] R. E. Amaya, A. Momciu, and I. Haroun, “High-performance, compact quasi-elliptic band pass filters for V-band high data rate radios,” IEEE Trans. Compon. Packag. Manuf. Technol., vol. 3, no. 3, pp. 411–416, Mar. 2013. [3] M. Miao and C. Nguyen, “A novel multilayer aperture-coupled cavity resonator for millimeter-wave CMOS RFICs,” IEEE Trans. Microw. Theory Tech., vol. 55, no. 4, pp. 783–787, Apr. 2007. [4] F. Xu and K. Wu, “Guided-wave and leakage characteristics of substrate integrated waveguide,” IEEE Trans. Microw. Theory Tech., vol. 53, no. 1, pp. 66–73, Jan. 2005. [5] X.-P. Chen, K. Wu, and Z.-L. Li, “Dual-band and triple-band substrate integrated waveguide filters with Chebyshev and quasi-elliptic responses,” IEEE Trans. Microw. Theory Tech., vol. 55, no. 12, pp. 2569–2578, Dec. 2007. [6] D. Deslandes and K. Wu, “Single-substrate integration technique of planar circuits and waveguide filters,” IEEE Trans. Microw. Theory Tech., vol. 51, no. 2, pp. 593–596, Feb. 2003. [7] Q.-L. Zhang, W.-Y. Yin, S. He, and L.-S. Wu, “Compact substrate integrated waveguide (SIW) bandpass filter with complementary split-ring resonators (CSRRs),” IEEE Microw. Wireless Compon. Lett., vol. 20, no. 8, pp. 426–428, Aug. 2010. [8] L. Szydlowski, N. Leszczynska, A. Lamecki, and M. Mrozowski, “A substrate integrated waveguide (SIW) bandpass filter in a box configuration with frequency-dependent coupling,” IEEE Trans. Microw. Theory Tech., vol. 22, no. 11, pp. 556–558, Nov. 2012. [9] X. P. Chen and K. Wu, “Self-packaged millimeter-wave substrate integrated waveguide filter with asymmetric frequency response,” IEEE Trans. Compon. Packag. Manuf. Technol, vol. 2, no. 5, pp. 775–782, May 2012. [10] A. Genc, R. Baktur, and R. J. Jost, “Dual-bandpass filters with individually controllable passbands,” IEEE Trans. Compon. Packag. Manuf. Technol, vol. 3, no. 1, pp. 105–112, Jan. 2013.
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[11] W. Shen, W.-Y. Yin, X.-W. Sun, and L.-S. Wu, “Substrate-integrated waveguide bandpass filters with planar resonators for system-onpackage,” IEEE Trans. Compon. Packag. Manuf. Technol, vol. 3, no. 2, pp. 253–261, Jan. 2013. [12] N. Athanasopoulos, D. Makris, and K. Voudouris, “Development of a 60 GHz substrate integrated waveguide planar diplexer,” in Proc. Microw. Workshop Ser. Millim. Wave Integr., Sep. 2011, pp. 128–131. [13] P. J. Qiu, Y. Zhang, and B. Yan, “A novel millimeter-wave substrate integrated waveguide (SIW) filter buried in LTCC,” in Proc. Asia-Pacific Microw. Conf., Dec. 2008, pp. 1–4. [14] G.-H. Lee, C.-S. Yoo, J.-G. Yook, and J.-C. Kim, “SIW (substrate integrated waveguide) quasi-elliptic filter based on LTCC for 60-GHz application,” in Proc. 4th Eur. Microw. Integr. Circuits Conf., Sep. 2009, pp. 204–207. [15] C. J. You, Z.-N. Chen, X. W. Zhu, and K. Gong, “Single-layered SIW post-loaded electric coupling-enhanced structure and its filter applications,” IEEE Trans. Microw. Theory Tech., vol. 61, no. 1, pp. 125–130, Jan. 2013. [16] J.-S. Hong and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications. New York, NY, USA: Wiley, 2001. [17] T. K. Wang, C. Y. Hsieh, H. H. Chuang, and T. L. Wu, “Design and modeling of a stopband-enhanced EBG structure using ground surface perturbation lattice for power/ground noise suppression,” IEEE Trans. Microw. Theory Tech. , vol. 57, no. 8, pp. 2047–2054, Aug. 2009. [18] R. Abhari and G. V. Eleftheriades, “Suppression of the parallel-plate noise in high-speed circuits using a metallic electromagnetic band-gap structure,” in IEEE MTT-S Int. Microw. Symp. Dig., vol. 1. Jun. 2002, pp. 493–496. [19] T.-K. Wang, C.-Y. Hsieh, H.-H. Chuang, and T.-L. Wu, “Design and modeling of stopband-enhanced EBG structure using ground surface perturbation lattice for power/ground noise suppression,” IEEE Trans. Microw. Theory Tech. , vol. 57, no. 8, pp. 2048–2054, Aug. 2009. [20] C.-H. Huang and T.-L. Wu, “Analytical design of via lattice for ground planes noise suppression and application on embedded planar EBG structures,” IEEE Trans. Compon. Packag. Manuf. Technol, vol. 3, no. 1, pp. 21–30, Jan. 2013. [21] Y. Shi, W. Tang, S. Liu, X. Rao, and Y. L. Chow, “Ultra-wideband suppression of power/ground noise in high-speed circuits using a novel electromagnetic bandgap power plane,” IEEE Trans. Compon. Packag. Manuf. Technol, vol. 3, no. 4, pp. 653–660, Apr. 2013. [22] B. Gao and M. M. F. Yuen, “Passive UHF RFID packaging with electromagnetic band gap (EBG) material for metallic objects tracking,” IEEE Trans. Compon. Packag. Manuf. Technol, vol. 1, no. 8, pp. 1140–1146, Aug. 2011. [23] S. W. Wong and L. Zhu, “Ultra-wideband bandpass filters with improved out-of-band behavior via embedded electromagnetic-bandgap multimode resonators,” IET Microw., Antennas Propag., vol. 2, no. 8, pp. 854–862, Dec. 2008. [24] [Online]. Available: http://www.cst.com/ [25] L. Zhu, “Guided-wave characteristics of periodic coplanar waveguides with inductive loading-unit-length transmission parameters,” IEEE Trans. Microw. Theory Tech., vol. 51, no. 10, pp. 2133–2138, Oct. 2003.
Sai Wai Wong (S’06–M’09) received the B.S. degree in electronic engineering from the Hong Kong University of Science and Technology, Hong Kong, and the M.Sc. and Ph.D. degrees from Nanyang Technological University, Singapore, in 2003, 2006, and 2009, respectively, both in communication engineering. He has been an Associate Professor with the School of Electronic and Information Engineering, South China University of Technology, Guangzhou, China, since 2010. From July 2003 to July 2005, he was with the Electronic Engineering Department in manufacturing companies, Hong Kong. From May 2009 to October 2010, he was a Research Fellow with the Institute for Infocomm Research, Singapore. His current research interests include microwave passive components and wideband antenna design. Prof. Wong received the New Century Excellent Talents in University in 2013. He is currently serving as a Reviewer of the IEEE Microwave and Wireless Components Letters and the IEEE T RANSACTIONS ON M ICROWAVE T HEORY AND T ECHNIQUES .
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Kai Wang (S’13) was born in Luan, China, in 1990. He received the B.S. degree from the School of Electronic Information Engineering, Anhui University, Hefei, China. He is currently pursuing the M.S. degree with the School of Electronic and Information Engineering, South China University of Technology, Guangzhou, China. His current research interests include planar microwave filter and antenna design.
Zhi-Ning Chen (M’99–SM’05–F’08) received the B.Eng., M.Eng., and Ph.D. degrees in electrical engineering from the Institute of Communications Engineering (ICE), China, and the Ph.D. degree from the University of Tsukuba, Ibaraki, Japan. He was at ICE, as a Lecturer, from 1988 to 1995, and later an Associate Professor, as well as with Southeast University, Nanjing, China, as a PostDoctoral Fellow and then as an Associate Professor. From 1995 to 1997, he was with the City University of Hong Kong, Hong Kong, as a Research Assistant and then as a Research Fellow. In 2001 and 2004, he was with the University of Tsukuba, under a JSPS Fellowship Program. In 2004, he was with the IBM T. J. Watson Research Center, Yorktown Heights, NY, USA, as an Academic Visitor. From 1999 to 2012, he was with the Institute for Infocomm Research (I2R), as a Member of Technical Staff (MTS), Senior MTS, Principal MTS, Senior Scientist, Lead Scientist, and Principal Scientist, as well as the Head of the RF and Optical Department. Since 2012, he has been with the Department of Electrical and Computer Engineering, National University of Singapore, Singapore, as a Full Professor. He concurrently holds a joint appointment as Advisor with I2R, as well as being a Visiting/Adjunct/Guest Professor with Southeast University, Nanjing University, Nanjing, China, Shanghai Jiaotong University, Shanghai, China, Tsinghua University, Beijing, China, Tongji University, Shanghai, University of Science and Technology, Seoul, Korea, Dalian Maritime University, Dalian, China, Chiba University, Chiba, China, National Taiwan University of Science and Technology, Taipei, Taiwan, and the City University of Hong Kong, Hong Kong. He has authored or coauthored over 400 technical papers. He has authored or edited Broadband Planar Antennas, UWB Wireless Communication, Antennas for Portable Devices, and Antennas for Base Stations in Wireless Communications. He contributed chapters to UWB Antennas and Propagation for Communications, Radar, and Imaging, Antenna Engineering Handbook, and Microstrip and Printed Antennas. He holds 27 granted and filed patents with 31 licensed deals with industry. His current research interests include electromagnetic engineering, antennas for communication, radar, and imaging and sensing systems. Dr. Chen serves an Associate Editor for the IEEE T RANSACTIONS ON A NTENNAS AND P ROPAGATION. He served as a Distinguished Lecturer for the IEEE A NTENNAS AND P ROPAGATION S OCIETY from 2009 to 2011. He was the Founding General Chair of the International Workshop on Antenna Technology (iWAT), the International Symposium on InfoComm and Media Technology in Bio-Medical and Healthcare Applications (IS 3T-in-3A), the International Microwave Forum, and the Asia–Pacific Conference on Antennas and Propagation. He was a recipient of the International Symposium on Antennas and Propagation Best Paper Award in 2010, the CST University Publication Award in 2008, the IEEE AP-S Honorable Mention Student Paper Contest in 2008, the IES Prestigious Engineering Achievement Award in 2006, the I2R Quarterly Best Paper Award in 2004, and the IEEE iWAT 2005 Best Poster Award.
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Qing-Xin Chu (M’99–SM’11) received the B.S., M.E., and Ph.D. degrees in electronic engineering from Xi’dian University, Xi’an, China, in 1982, 1987, and 1994, respectively. He is currently a Full Professor with the School of Electronic and Information Engineering, South China University of Technology, Guangzhou, China. He is the Director of the Research Institute of Antennas and RF Techniques, South China University of Technology. From January 1982 to January 2004, he was with the School of Electronic Engineering, Xi’dian University. From 1997 to 2004, he was a Professor and later the Vice-Dean with the School of Electronic Engineering, Xi’dian University. From July 1995 to September 1998 and from July to October 2002, he was a Research Associate and Visiting Professor with the Department of Electronic Engineering, Chinese University of Hong Kong, Hong Kong. From February
to May 2001 and from December 2002 to March 2003, he was a Research Fellow and Visiting Professor with the Department of Electronic Engineering, City University of Hong Kong. From July to October 2004, he was with the School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore. From January to March 2005, he was with the Department of Electrical and Electronic Engineering, Okayama University, Okayama, Japan. From June to July 2008, he was a Visiting Professor with Ecole Polytechnique de I’Universite de Nantes, Nantes, France. He has authored or co-authored over 300 papers in journals and conferences. His current research interests include antennas in mobile communication, microwave filters, spatial power-combining array, and numerical techniques in electromagnetics. Prof. Chu is a Senior Member of the China Electronic Institute. He was a recipient of the Tan Chin Tuan Exchange Fellowship Award, the Japan Society for Promotion of Science Fellowship, the 2002 and 2008 Top-Class Science Award of the Education Ministry of China, and the 2003 First-Class Educational Award of Shaanxi Province.
