Chebyshev-Response Branch-Line Couplers with Enhanced Bandwidth and Arbitrary Coupling Level

Abstract

A new approach to the synthesis of broadband branch-line couplers with arbitrary coupling level was investigated in this paper. It was shown that the operational bandwidth of a classic branch-line coupler can be increased by utilizing N-section impedance transformers added to each of the coupler’s ports. Furthermore, the obtained response can be approximated by the Chebyshev polynomial. Moreover, it was proven that for such couplers a range of coupling coefficient values can be obtained by the modification of classic branch-line topology. The analysis of the electrical parameters of the proposed branch-line couplers was comprehensively investigated. To verify the correctness of the proposed design procedures, 3-dB, and 6-dB broadband branch-line couplers operating at the center frequency of 2 GHz having return losses greater than 20 dB were designed, fabricated, and measured.

A Comprehensive Review on Microstrip Couplers

“…For designing most of BLCs mathematical theory, methods have been presented. Design methods sometimes include calculating the transfer matrix and extracting the necessary information from it (Salehi and Noori, 2014;Rezaei, Noori and Hosseini, 2018;Abouelnaga and Mohra, 2017;Nie, et al, 2019;Khan, Mehdi and Zhao, 2019;Kim and Kong, 2010;Smolarz, Wincza and Gruszczynski, 2020(. In some cases, the LC equivalent circuit of a small part of the couplers is presented and analyzed (Chi, et al, 2012;Rezaei, Noori and Hosseini, 2018;Sun, et al, 2005;Lai and Ma, 2013;Lalbakhsh, et al, 2021;Noori and Rezaei, 2018;Roshani, et al, 2022;Abdulbari, et al, 2021;Chiu, et al, 2014;Liou, et al, 2009).…”

“…Having very good isolation and return loss is two advantages of this work. Two 3-dB and 6-dB broadband BLCs working at 2 GHz with chebyshev frequency responses have been designed in (Smolarz, Wincza and Gruszczynski, 2020). Another 90º microstrip hybrid coupler with a wide fractional bandwidth (FBW) of 84.3% is presented in (Sun, et al, 2019) which has no isolation port.…”

A Flexible Miniaturized Wideband Branch-Line Coupler Using Shunt Open-Stubs and Meandering Technique

“…Many different approaches are presented in the literature to obtain compact size and wideband BLC (WBBLC) circuits [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. In [12], a compact WBBLC is realized using an open complementary split-ring resonator and open stubs.…”

“…A series transmission line loaded with unequal length open stubs is reported in [19], and it is utilized in realizing a compact and harmonic suppressed three-section BLC. In [20], additional N-section impedance transformers with Chebychev polynomial response are connected to the coupler's ports and results in enhancing the coupler bandwidth and the coupling level. The implementation of gap waveguide technology such as substrate integrated gap waveguide (SIGW) and printed ridge gap waveguide (PRGW) are proposed to develop branch-line couplers, which result in better impedance matching within high-frequency range and therefore obtaining high wideband response [21,22].…”