Novel Synthesis for Generalized Strongly Coupled Resonator Triplet Filters with Self-Suppressed Spikes

This paper proposes a novel and general circuit synthesis approach for generalized strongly coupled resonator triplet (GSCRT) filters. Regardless of the positions where GSCRTs are extracted in the prototype, flexible circuit solutions with only positive couplings can be always achieved with controllable node self-coupling (diagonal entries in coupling matrix). Moreover, the spikes rendered by redundant resonances in the final synthesized circuit are “self-suppressed” even without additional band-stop sections. This significantly expands the application scope of GSCRT filters. One compact anti-interference nine-pole filter with five transmission zeros are fabricated, which has strongly validated the effectiveness of the proposed theories. Specially, this filter exhibits exceptional abilities to reject C-band terrestrial signals from 5G applications.