Bandpass Filter Using Dual Series-Cascaded Ring Resonators with Multiple Transmission Zeros

Abstract

Compact dual series-cascaded ring resonators comprised of three parallel-coupled lines are proposed for design of fifth-order bandpass filter (BPF) with multiple transmission zeros. Two pairs of $\pmb{3\lambda_{\text{g}}/4}$ parallel-coupled lines are cascaded to a pair of $\pmb{\lambda_{\text{g}}/4}$ parallel-coupled lines to construct dual ring resonators, which can achieve a high-performance BPF with five transmission poles and eight transmission zeros. For further demonstration, a filter example centered at 2.08 GHz is designed with source-load cross coupling to obtain nine transmission zeros.