Synthesis and Design of Generalized Strongly Coupled Resonator Quartet Combline Filters With Redundant Resonance

Abstract: This article proposes a generalized strongly coupled resonator quartet (GSCRQ) filter and the synthesis approach for this type of filter. By introducing out-of-band reflection zeros (RZs), the proposed GSCRQ can generate a transmission zero on each side of the passband without negative couplings. The coupling coefficients in this coupling structure change with the positions of the out-of-band RZs. Thus, the GSCRQ configuration admits flexible design solutions. For GSCRQ coaxial combline filters, all couplings can be implemented as inductive couplings, simplifying the design and manufacturing process. In this article, a 6-2 filter in the GSCRQ configuration is synthesized and designed. The simulated results of the designed filter agree very well with the theoretical characteristics.

Keywords: filter synthesis; generalized strongly coupled resonator quartets (GSCRQ); out-of-band reflection zero; transmission zero