Design of Wideband Filtering Quadrature Coupler Consisting of Inductor-Loaded Coupled Line With Three-Coupled-Lines
Hongmei Liu, Xiaoting Li, Siran Zhang, Shaojun Fang, Zhongbao Wang
Abstract
In this brief, the design of a wideband filtering quadrature coupler is presented. It is composed of an inductor-loaded coupled line (I-CL), two open-ended stubs, four short-ended stepped impedance resonators, and four three- coupled-lines (TCLs). Wideband operation with three resonant points is generated by using the I-CL with the TCLs. Due to the utilization of short-ended resonators combined with the open stubs, wide stopband is also obtained. Design formulas are derived using the even-odd decomposition technique and optimization process is given for guidance. For demonstration, a 3-dB prototype is designed, fabricated and measured. Measurement results show that a bandpass bandwidth (BPBW) of 43% is realized under the criterions of 15-dB return loss and isolation. While the BPBWs for 0.5-dB amplitude imbalance and 5° phase difference fluctuation are 40.3% and 48%, respectively. Besides, wide stopband extends to 2.64 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f} _{0}$ </tex-math></inline-formula> is realized with more than 10 dB rejection level.