Miniaturized filtering rat‐race coupler based on hybrid circular substrate integrated waveguide and coplanar waveguide resonators

Abstract

In this paper, an approach to designing filtering rat-race coupler (FRRC) with hybrid circular substrate integrated waveguide (CSIW) and coplanar waveguide (CPW) resonators is proposed. The FRRC is developed in a single CSIW cavity embedded with four CPW resonators and four feeding ports, featuring miniaturized size. The desired 0° and 180° phase characteristics of the RRC are realized by the inherent in-phase and out-of-phase electromagnetic fields of the dual-mode CSIW cavity. By properly arranging the sum, difference and other two output ports, the FRRC is exploited to achieve the desired properties of a RRC with bandpass filtering responses. In addition, transmission zeros are generated in the vicinity of the upper stopband. For validation and demonstration, a miniaturized FRRC utilizing hybrid CSIW and CPW resonators is synthesized, fabricated and experimented in a single-layered process. Comparisons with previously state-of-the-art research, the proposed FRRC prototype indicates the superiorities of miniaturized footprint, high-quality-factor, high-order filtering response and enhanced out-of-band rejection.