Spurious coupling compensation through iris structure in coax cavity filters

This paper presents a novel spurious coupling compensation technique for coax cavity resonator based filters. It has been found that cross coupled coax cavity filter suffers from the problem of spurious coupling between non-adjacent resonators which leads to asymmetric transmission response and group delay characteristics, which, in turn leads to deterioration in the RF performance. An exhaustive study has been performed for identification of this spurious coupling and coupling structure has been suitably modified in such a way that the spurious couplings get cancelled within the filter and eventually results in symmetric transmission and group delay response. The simulation results have been validated through the measurements.