Design of Balanced Filtering Rat-Race Coupler Based on Quad-Mode Dielectric Resonator

A balanced filtering rat-race coupler is proposed based on a quad-mode dielectric resonator (DR) in this brief. Due to the electromagnetic-field distributions of the DR, the desired balanced performance with high common-mode suppression is realized without additional circuits. Moreover, by setting the feeding probes at the proper locations, the quad-mode DR is also used to obtain the desired coupler topology with filtering responses. Accordingly, a balanced filtering rat-race coupler, integrating three circuit functions of the balanced circuit, rat-race coupler, and bandpass filter, can be designed into a single-cavity configuration, resulting in a very compact size. For verification, the proposed circuit is implemented, which shows good filtering responses, low amplitude imbalance, high common-mode suppression, and excellent phase characteristics.