Miniaturised dual‐band rat‐race coupler with harmonic suppression using synthetic transmission line
2016; Institution of Engineering and Technology; Volume: 52; Issue: 21 Linguagem: Inglês
10.1049/el.2016.2154
ISSN1350-911X
AutoresChien‐Chia Chen, C. Y. D. Sim, Yunqiu Wu,
Tópico(s)Electromagnetic Compatibility and Noise Suppression
ResumoElectronics LettersVolume 52, Issue 21 p. 1784-1786 Microwave technologyFree Access Miniaturised dual-band rat-race coupler with harmonic suppression using synthetic transmission line C.-C. Chen, Corresponding Author C.-C. Chen cchiang@fcu.edu.tw Department of Electrical Engineering, Feng Chia University, Taichung, TaiwanSearch for more papers by this authorC.Y.D. Sim, C.Y.D. Sim Department of Electrical Engineering, Feng Chia University, Taichung, TaiwanSearch for more papers by this authorY.-J. Wu, Y.-J. Wu Department of Electrical Engineering, Feng Chia University, Taichung, TaiwanSearch for more papers by this author C.-C. Chen, Corresponding Author C.-C. Chen cchiang@fcu.edu.tw Department of Electrical Engineering, Feng Chia University, Taichung, TaiwanSearch for more papers by this authorC.Y.D. Sim, C.Y.D. Sim Department of Electrical Engineering, Feng Chia University, Taichung, TaiwanSearch for more papers by this authorY.-J. Wu, Y.-J. Wu Department of Electrical Engineering, Feng Chia University, Taichung, TaiwanSearch for more papers by this author First published: 01 October 2016 https://doi.org/10.1049/el.2016.2154Citations: 16AboutSectionsPDF 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 dual-band 90° unit module with harmonic suppression (HS) is proposed. This unit module consists of a pair of back-to-back stepped impedance sections and an open stub. The unit module is realised by synthetic transmission lines, and it is successfully implemented into a novel miniature dual-band (2.45/5.8-GHz) rat-race coupler with HS (suppression level ≥16 dB, 6.8–13 GHz). Compared with traditional 1.5λ microstrip ring hybrid, the proposed dual-band rat-race with HS only occupies 13.84% of its area. Introduction The rat-race coupler with splitting/combining function of in-phase and/or out-of-phase signals is one of key circuit modules used in many microwave systems. Recently, additional functions such as harmonic suppression (HS) [1-3] and dual-band [4-7] have been integrated into a miniature rat-race. The relative techniques for achieving miniature rat-race with HS include the use of periodical stepped-impedance resonator [1], T-type open stub (OS) [2], and synthetic transmission line (TL) [3]. From the results reported in [1-3], they have shown excellent HS performance and compact layout, and Lai and Ma [3] have exhibited the smallest relative size of 12.9%. However, the designs in [1-3] are single band type, and they are operating below 2.45 GHz. As for the relative techniques to achieve miniature rat-race designed with dual-band function, they include using two shunt short-stubs [4], OSs to both ends of each stepped impedance section [5], two shunt open-stubs [6], and synthetic TLs [7]. Notably, the authors in [4-7] have shown miniature size and dual-band characteristic with frequency ratios (f2/f1) between 1.60 and 2.42, and their corresponding higher operating bands (f2) are mostly appear in frequencies below 6 GHz. Furthermore, the authors in [3, 7] have demonstrated that the use of synthetic TLs can realise the smallest (most compact size) rat-race with HS/dual-band. Therefore, in this Letter, a novel miniaturised dual-band rat-race coupler with HS based on synthetic TLs technique is proposed. In order to integrate all three characteristics (miniaturisation, dual-band and HS) into a rat-race coupler, a dual-band 90° unit module with HS is initially designed; follow by applying the complementary-conducting-strip (CCS) TLs technique [7] to realise the proposed rat-race coupler. The related equations, synthesis approach and experimental results are carefully introduced and discussed. To the best of authors' knowledge, this proposed rat-race coupler using synthetic TLs to realise miniaturisation, dual-band, and HS characteristics has never been reported in the open-literature or anywhere else. Synthesised TL The two-port network diagram of the dual-band 90° unit module with HS is presented in Fig. 1a, and its corresponding back-to-back stepped impedance section with OS in the middle is shown in Fig. 1b [1, 5]. To further comprehend the operational principle of the unit module, Fig. 1c shows the equivalent lumped model of Fig. 1b, in which the low and high impedance sections, (Z1, θ1) and (Z2, θ2), respectively, are equivalent to the shunt capacitor (C1) and serial inductor (L2). Here, the shunt OS is equivalent to the shunt element with serial inductor (L3) and capacitor (C3). Fig 1Open in figure viewerPowerPoint Dual-band 90° unit module a Two-port network diagram of dual-band (f1, f2) 90° unit module with HS b One of unit cells of periodic stepped-impedance rat race coupler with OS line c Equivalent lumped model By equating the ABCD matrix of the lumped model to that of a uniform TL with (Zc, θ), the equivalent characteristic impedance (Zc) and phase delay (θ) of the lumped model can be expressed as (1) and (2). The serial L3C3 resonator can provide a finite-frequency transmission zero, which is located at ftz, as denoted in (3). Notably, (1)–(3) are the key equations for the synthesised TL. (1) (2) (3)The design parameters of Fig. 1 are summarised in Table 1, which are extracted from the scattering parameter of Figs. 1b and c using commercial microwave circuit simulator (Agilent ADSTM). Table 1. Design parameters of the dual-band 90° unit module with HS f1/f2, GHz Zc, Ω θ, Deg ftz, GHz C1, pF C3, pF L2, nH L3, nH 2.45/5.8 70 ±90 3f1 0.635 0.271 2.90 1.703 Z1, Ω Z2, Ω Z3, Ω θ1, Deg θ2, Deg θ3, Deg 42 143 108 21 15 29 By referring to the schematic diagram of Fig. 1b and its design parameters (Z1, θ1; Z2, θ2; Z3, θ3), as shown in Table 1, different Zc and electrical length's CCS synthetic TLs will be adopted, and in order to implement a dual-band (2.45/5.8-GHz) 90° unit module with HS, 0.0508 mm thick RO4003C substrate with relative dielectric constant (εr) of 3.38 is used. The signal and grounding layers (CCS layout) of the dual-band 70-Ω 90° synthetic line are shown in Figs. 2a and b, respectively. To achieve compact layout design and lower Zc TL (Z1 = 42 Ω), a pair of two-dimensional (2D) meandering CCS dual-transmission-lines (DTLs) are applied. Compared with 2D meandering CCS DTL, the conventional lower Zc microstrip (MS) TL has wider line-width and is difficult to realise compact circuit design. The 2D meandering CCS OS used to control a finite-frequency transmission zero. In Fig. 2, the dimensions (in mm) are l1 = 3.5, l2 = 1.7, l3 = l5 = 0.275, l4 = 0.35, l6 = 1.8, l7 = 0.25, l8 = 5.6, l9 = 3.35, w1 = 0.35, w2 = 0.1, w3 = 0.2, w4 = 0.15, g1 = 0.1, g2 = 0.175, g3 = 0.3, h1 = 0.2, h2 = 0.35, h3 = 0.3, s1 = 0.25, s2 = 0.175, s3 = 0.1 and s4 = 0.125. Fig 2Open in figure viewerPowerPoint CCS layout of dual-band 70-Ω 90° synthetic line a Signal layer b Grounding layer Dual-band rat-race coupler with HS The above proposed CCS dual-band 90° unit module with HS has been applied to design a novel miniaturised dual-band rat-race coupler with HS. In this case, the six 70-Ω 90° MS TLs of a conventional 1.5λg (at f1) MS ring coupler are directly replaced by six proposed CCS dual-band (f1/f2) 70-Ω 90° synthetic lines in cascade. To reduce the size of the occupied area, the six synthetic lines can be arranged in two rows (three synthetic lines in each row). The final layout of proposed CCS (inside pattern) is shown in Fig. 3, and the conventional MS ring coupler (outside pattern) is also included for comparison purposes. Here, the dimensions (in mm) are lc = 18.35, wc = 7.55, r = 16.9, and wt = 0.95. The occupied area of proposed CCS design (feeding network not included) is 18.35 × 7.55 mm2, which cover merely 13.84% of the MS design (with an area of π × (17.85 mm)2, at 2.45-GHz). Fig 3Open in figure viewerPowerPoint Layout comparison of CCS and conventional MS rat-race The scattering parameter frequency responses, including return loss (|S11|), insertion loss (|S21|&|S31|), isolation (|S41|), and phase difference (|∠S21 − ∠S31|) of proposed CCS dual-band rat-race with HS were successfully simulated by using three-dimensional electromagnetic full-wave simulator (Ansoft HFSSTM). The simulated results as shown in Fig. 4 are then used to compare with conventional MS ring coupler at 2.45-GHz. Here, the conventional MS ring coupler has displayed single operating band with odd harmonic frequency responses at 3f1 and 5f1. On the other hand, the proposed CCS rat-race has shown dual operating band (2.45/5.8-GHz) with HS function. The prototype of proposed CCS dual-band rat-race with HS was fabricated, and its performances were measured by using vector network analyser (Agilent N5227A). Fig. 5 shows the measured and simulated results of proposed CCS rat-race. The measured and simulated results are in fairly good agreement with each other. Besides showing good harmonic suppression of approximately 50 dB at 3f1, suppression levels of at least 16 dB were also measured between 3f1 and 5f1 (6.8–13 GHz). Fig 4Open in figure viewerPowerPoint Simulated S-parameters of conventional MS design and proposed CCS rat-race design Fig 5Open in figure viewerPowerPoint Measured and simulated S-parameters of proposed CCS rat-race coupler Table 2 summarises the performances of various rat-race couplers [1-7] and this proposed work. In comparison, the proposed design has shown small relative size of 13.84%. Even though the relative size of [3] is smaller (12.9%) than the proposed one, it is a single band type operating at 2.4-GHz. Thus, besides achieving compact size, this proposed work also includes dual operating band (2.45/5.8-GHz) and remarkable harmonic suppression, which is not shown anywhere else in the open-literature. Table 2. Performance summary of various rat-race couplers Refs. fo, GHz aFBW, % bRelative size, % 10 dB-BW, % cHS Remarks Return Loss Isolation [1] 2.45 54.2 21.5 75.5 69.4 up to 6f0 (10 dB) HS [2] 0.5 63.5 18.4 68.3 68.45 2f0-10f0(15 dB)2f0-7f0(20 dB) HS [3] 2.4 44.9 12.9 44.9 55.1 2f0,3f0(21 dB) HS [4] 0.882 32.9911.09 NA 32.9916.33 60.7627.34 None dual-band [5] 2.455.2 35.9213.2 21 36.0113.2 42.217.25 None dual-band [6] 0.91.9 23.611.98 42.94 66.131.3 4422.32 None dual-band [7] 1024 NA NA 41.314.4 NA None dual-band/CMOS This Letter 2.455.8 42.04.27 13.84 42.05.28 60.39.72 3f1-5f1(16 dB) dual-band/HS aFBW: return loss and isolation >10 dB. bRelative size: compared with a conventional design. cHS: harmonic suppression. NA: not available. Conclusion A miniaturised dual-band rat-race coupler with harmonic suppression capability has been successfully designed and implemented by using the CCS synthetic TLs. The proposed coupler has demonstrated compact size (13.84%), dual operating band (2.45/5.8-GHz), and approximately 50 dB suppression at 3f1 and at least 16-dB suppressions level from 3f1 to 5f1 (6.8–13 GHz). Acknowledgments This work was supported by the Ministry of Science and Technology (formerly known as National Science Council) and Feng Chia University of Taiwan, R.O.C., under Grants NSC 101-2221-E-035-051- and 15I42157, respectively. References 1Kuo, J.-T., Wu, J.-S., Chiou, Y.-C.: 'Miniaturized rat race coupler with suppression of spurious passband', IEEE Microw. Wirel. Compon. Lett., 2007, 17, (1), pp. 46– 48 (https://doi/org/10.1109/LMWC.2006.887254) 2Velidi, V.K., Mandal, M.K., Bhattacharya, A.: 'Uniplanar harmonic suppressed compact rat-race couplers', Microw Opt. Tech. 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