Flexible Design of Generalized Strongly Coupled Resonator Triplet Filters by Regulating Redundant Resonant Modes

In this paper, the generalized strongly coupled resonator triplet (GSCRT) block is proposed and studied. The GSCRTs with redundant resonant modes avoid using negative couplings regardless the transmission zero is on lower or upper side of the pass band. The principle of removing negative couplings in GSCRTs is explained from circuit level for the first time. Moreover, the redundant resonances can be regulated to achieve flexible solutions in different scenarios, thus greatly facilitating the design and promoting the application of GSCRT structures. The flexibilities are demonstrated with the simulated 4
^th
-order filters. One fabricated anti-interference C-band eight-pole filter with four TZs verifies the effectivity of the proposed theories even in the design with complex topologies.