Miniaturized filtering trans‐directional coupler with enhanced input‐reflectionless feature using two types of coupled multi‐line sections

Abstract

This paper presents a miniaturized filtering trans-directional (TRD) coupler with enhanced input-reflectionless feature. Coupled two-line and three-line sections are loaded at through and coupled ports of a basic TRD coupler to realize the filtering performance. The basic TRD coupler based on a periodically loaded coupled-line (CL) can be independently designed to realize tight coupling degree and wideband bandwidth. Coupled three-line structure has been applied to obtain a higher coupling factor and wider bandwidth in various components. Since the coupled multi-line sections exhibit open-circuit at f 0 , by selecting the appropriate coupling coefficient and type of coupled multiline sections, the filtering bandwidth and transmission zeros (TZs) can be independently controlled. Moreover, the input-reflectionless feature can be realized by the signal-interference of the reflected stop-band signals of two output ports. Explicit equations and limitations of implementations are derived and discussed. Two 3-dB prototypes are designed and built to verify the design theory.