Filtering Rat-Race Couplers with Impedance Transforming Characteristics Based on Terminated Coupled Line Structures

In this study, a series of rat-race couplers with bandpass filtering responses and impedance transforming characteristics are presented based on novel coupled-line structures. Firstly, a novel filtering rat-race coupler core circuit is proposed by introducing coupled-line structures into conventional rat-race coupler. Then, a series of rat-race couplers with enhanced filtering responses and stopba...