Iterative Synthesis of Equi-Ripple Dual-band Filtering Functions With One Additional Transmission Zero

This paper presents and discusses an iterative approach to generating a class of equi-ripple dual-band filtering functions. The proposed technique can ensure the same return loss level for the two passbands of a filter by introducing an additional transmission zero (TZ). The position of the additional TZ is automatically determined by the iterative filtering function synthesis procedure. The proposed approach can be used to synthesize symmetric or asymmetric dual-band filter responses where the additional TZ is realized together with prescribed TZs. A dual-passband waveguide filter is synthesized, designed and measured to demonstrate the effectiveness of the proposed method.