Multi-pole microstrip directional filters for multiplexing applications

Abstract

Theory and experiment of multi-pole microstrip directional filters for multiplexing networks are presented in this paper. Conventional microstrip directional filters present only a single-pole filter response. By applying stopband filter theory, two Butterworth microstrip directional filters are designed and tested. The desired multi-pole filter response is achieved by cascading two or more similar single stages connected by immitance inverters. These types of directional filters are ideal candidates for multiplexing applications since they present the characteristics of easy implementation and the capacity of a modular concept. Moreover, a flat response is obtained along the passband due to the multi-pole filter behavior.