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Half‐mode substrate integrated waveguide bandpass filter loaded with horizontal–asymmetrical stepped‐impedance complementary split‐ring resonators

2016; Institution of Engineering and Technology; Volume: 52; Issue: 12 Linguagem: Inglês

10.1049/el.2016.0372

1350-911X

Yong Mao Huang, Zhenhai Shao, Wei Jiang, Tao Huang, Guoan Wang,

Microwave and Dielectric Measurement Techniques

Electronics LettersVolume 52, Issue 12 p. 1034-1036 Microwave technologyFree Access Half-mode substrate integrated waveguide bandpass filter loaded with horizontal–asymmetrical stepped-impedance complementary split-ring resonators Yong Mao Huang, Yong Mao Huang School of Communication and Information Engineering, University of Electronic Science and Technology of China, Chengdu, 611731 People's Republic of China Yong Mao Huang: Also with Department of Electrical Engineering, University of South Carolina, Columbia, SC 29208, USASearch for more papers by this authorZhenhai Shao, Corresponding Author Zhenhai Shao shao_zh@uestc.edu.cn School of Communication and Information Engineering, University of Electronic Science and Technology of China, Chengdu, 611731 People's Republic of ChinaSearch for more papers by this authorWei Jiang, Wei Jiang Department of Electrical Engineering, University of South Carolina, Columbia, SC, 29208 USASearch for more papers by this authorTao Huang, Tao Huang School of Communication and Information Engineering, University of Electronic Science and Technology of China, Chengdu, 611731 People's Republic of ChinaSearch for more papers by this authorGuoan Wang, Guoan Wang Department of Electrical Engineering, University of South Carolina, Columbia, SC, 29208 USASearch for more papers by this author Yong Mao Huang, Yong Mao Huang School of Communication and Information Engineering, University of Electronic Science and Technology of China, Chengdu, 611731 People's Republic of China Yong Mao Huang: Also with Department of Electrical Engineering, University of South Carolina, Columbia, SC 29208, USASearch for more papers by this authorZhenhai Shao, Corresponding Author Zhenhai Shao shao_zh@uestc.edu.cn School of Communication and Information Engineering, University of Electronic Science and Technology of China, Chengdu, 611731 People's Republic of ChinaSearch for more papers by this authorWei Jiang, Wei Jiang Department of Electrical Engineering, University of South Carolina, Columbia, SC, 29208 USASearch for more papers by this authorTao Huang, Tao Huang School of Communication and Information Engineering, University of Electronic Science and Technology of China, Chengdu, 611731 People's Republic of ChinaSearch for more papers by this authorGuoan Wang, Guoan Wang Department of Electrical Engineering, University of South Carolina, Columbia, SC, 29208 USASearch for more papers by this author First published: 01 June 2016 https://doi.org/10.1049/el.2016.0372Citations: 15 AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract A half-mode substrate integrated waveguide (HMSIW) bandpass filter loaded with modified complementary split-ring resonators (CSRRs) is presented. The modified CSRR, realised by utilising horizontal–asymmetrical stepped-impedance (SI) structure in the conventional CSRR, can enhance the equivalent capacitance and inductance of the CSRR and consequently shift the resonant frequency downwards. Therefore, for the same operation frequency, the SICSRR can occupy smaller size than the conventional CSRR, which provides a promising method to achieve size-reduction in microwave circuits. To verify the effectiveness of miniaturisation introduced from the proposed HMSIW-SICSRR resonator, a two-pole bandpass filter is implemented. Moreover, the measured results are in good agreement with the simulated ones. Introduction Early arising around 2000, the substrate integrated waveguide (SIW) has been regarded as a potential alternative for system integration in wireless communication, radar and sensing applications [1]. Subsequently, the half-mode and quarter-mode SIW (HMSIW, QMSIW), with only half or quarter size of their corresponding SIW counterparts while maintaining similar performance, were developed [2-4]. Compared with other concepts of size-reduction such as integrating dual functions into one single device [5], method of utilising HMSIW and QMSIW is more straightforward and easier to realise. As a metamaterial structure, the complementary split-ring resonator (CSRR) has been loaded into SIW and HMSIW to support backward or forward propagation below the characteristic cut-off frequency of conventional SIW and HMSIW, which provides an effective method to realise miniaturised components [6-8]. Furthermore, by employing the stepped-impedance resonator (SIR) in double split-ring resonator (DSR or SRR), the SIR-DSR metamaterial unit cell was developed to achieve a miniaturisation factor about 0.75, i.e. achieving a size-reduction about 25% compared with its corresponding DSR counterparts [9]. Whereas CSRR was derived from SRR based on the reciprocity theorem [10], the SIR can also be employed into CSRR to form the SICSRR. However, till now, neither seldom job is reported on the SICSRR, nor its utilisation in SIW, HMSIW or QMSIW. In this Letter, the horizontal–asymmetrical SICSRR is developed and loaded into HMSIW to constitute a resonant unit cell, can operate at a lower frequency than that of the conventional HMSIW-CSRR resonator as they occupy the same physical circuitry size. Secondly, transmission property of the proposed resonator is discussed briefly. Afterwards, a bandpass filter is realised to show the size-reduction capability contributed from the proposed SICSRR, followed by a conclusion at last. HMSIW-SICSRR resonator Fig. 1 shows brief derivation progresses from the conventional uniform-impedance resonator (UIR) to SIR, SRR, CSRR, SIR-SRR (with single split-ring, just distinguishing from the DSR SIR-DSR) and the proposed SICSRR. As described in Fig. 1, the proposed SICSRR can be derived from two aspects: the first aspect is employing horizontal–asymmetrical stepped impedance (SI) structure into CSRR, and the other one is developing from the reported SIR-SRR based on the reciprocity theorem. Whichever resonant structure is, its equivalent-circuit model can be simplified as a parallel inductor and capacitor (LC) circuit, as shown at the end of Fig. 1. Therefore, for the conventional CSRR and the proposed SICSRR, their resonant frequencies fc and fSI can be given as [11] (1) (2)where L0, C0, LSI and CSI represent the equivalent inductance and capacitance of CSRR and SICSRR, respectively. Obviously, LSI and CSI are with higher flexibility than L0, C0 due to the influence introduced from the horizontal–asymmetrical SI structure. By choosing the impedance ratio ZH/ZL and phase ratio 2θH/θL properly, LSI and CSI can be smaller or larger than or even equal to L0 and C0. Fig 1Open in figure viewerPowerPoint Derivation progresses from conventional UIR to SIR, SRR, CSRR, SIR-SRR and proposed SICSRR, with their equivalent-circuit models By loading the proposed SICSRR into an HMSIW section, the HMSIW-CSRR resonant unit cell is developed, as shown in Fig. 2b, with the conventional HMSIW-CSRR unit cell in Fig. 2a as comparison. To illustrate the transmission property of the proposed unit cell more clearly, several 3D full-wave analyses are carried out with a commercial finite element method simulator, on a substrate with a thickness of 0.508 mm, a permittivity of 2.2 and a loss tangent of 0.001. Moreover, some fixed geometrical parameters are: w = 3, b = 2.7 and t = 0.2 [unit:millimetres (mm)]. The comparison between conventional HMSIW-CSRR and the proposed HMSIW-SICSRR resonators is given in Fig. 3, with other geometrical parameters c = 0.2, a = 0.4, a1 = 0.2, b1 = b2 = 0.6 and a2 = 1 (unit:mm). It can be obtained from Fig. 3a that the proposed unit cell operates at a lower frequency (8.5 GHz) than that of the conventional one (10.8 GHz) as they occupy the same physical circuit size which is determined by w and b. That is to say, compared with the HMSIW-CSRR unit cell, the proposed unit cell is with larger electrical size, which allows it operating at the same frequency with smaller physical size. Meanwhile, the proposed unit cell is with sharper selectivity since its transmission zero occurs closer than that of the HMSIW-CSRR. Fig 2Open in figure viewerPowerPoint Configurations of conventional HMSIW-CSRR and proposed HMSIW-SICSRR resonant unit cells a HMSIW-CSRR unit cell b HMSIW-SICSRR unit cell Fig 3Open in figure viewerPowerPoint Simulated results comparison between conventional HMSIW-CSRR and proposed HMSIW-SICSRR unit cells Two-pole filter To verify the miniaturisation capability of the proposed HMSIW-SICSRR unit cell, a two-pole bandpass filter is implemented. The filter is designed with a central frequency fc of 8.6 GHz, a fractional bandwidth (FBW) of 10% and passband ripple of 0.1 dB. Its inter-coupling coefficient between two resonators can be calculated as , which is mainly determined by the inductive coupling window [9]. For the external quality factor Qe, it is mainly influenced by the transition between 50 Ω microstrip line and the HMSIW-SICSRR resonator. Here, in consideration both circuits size and insertion loss performance, the direct transition is chosen. With a standard PCB process, the filter is fabricated on a Rogers/Duroid 5880 substrate with a thickness of 0.508 mm, a permittivity of 2.2 and loss tangent of 0.001. The fabricated filter, with photograph shown in Fig. 4, is measured with a Keysight Vector Network Analyser. As shown in Fig. 5, the fabricated filter is with a central frequency around 8.4 GHz, an FBW about 7.9% and an insertion loss about 1.53 dB. Owing to the fabrication inaccuracy and permittivity deviation, FBW is compressed about 0.2 GHz, consequently with central frequency shifts lower. Furthermore, the filter is with a wide stopband with rejection over 20 dB up to 24 GHz. Fig 4Open in figure viewerPowerPoint Photograph of fabricated filter Fig 5Open in figure viewerPowerPoint Simulated and measured results of fabricated filter Table 1 summarises some comparison between several related works and the proposed HMSIW-SICSRR filter. In the size calculations, feeding line lengths are exclusive, only function parts considered. It can be obtained that the proposed filter is more compact, with a size of (λg represents the guided wavelength at central frequency). Typically, compared with the HMSIW-CSRR filter in [8], the proposed HMSIW-SICSRR filter achieves a size-reduction about 33%. Table 1. Comparison between related works and proposed HMSIW-SICSRR filter Refs. Poles Unit cell fc/FBW (GHz, %) Size () [4] – Type III 2 SIW-broadside coupled-CSRR 5.15/16.5 0.129 [6] – Type I 2 SIW-CSRR 5.05/6.6 0.109 [8] – Type I 2 HMSIW-CSRR 5.25/5.0 0.063 Proposed 2 HMSIW-SICSRR 8.40/7.9 0.042 Conclusion In this Letter, a two-pole HMSIW bandpass filter loaded with the proposed SICSRR is designed, fabricated and measured. The size-reduction capability introduced from the proposed SICSRR is discussed. Compared with some reported related jobs, the proposed filter is with more compact size, as well as good insertion loss and stopband performance. Acknowledgment This work was supported by the Excellent Ph.D. Candidate Academic Foundation of University of Electronic Science and Technology of China (UESTC) (grant YBXSZC20131054). References 1Deslandes, D., Wu, K.: 'Single-substrate integration technique of planar circuits and waveguide filters', IEEE Trans. Microw. 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