This article proposes a generalized strongly coupled resonator quartet (GSCRQ) filter along with its synthesis approach. 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.

This paper proposes a design and fine-tuning method for mixed electric and magnetic coupling filters. It derives the quantitative relationship between the coupling coefficients (electric and magnetic coupling, i.e., E_C and M_C) and the linear coefficients of frequency-dependent coupling for the first time. Different from the parameter extraction technique using the bandpass circuit model, the proposed approach explicitly relatesE_C and M_C to the coupling matrix model. This paper provides a general theoretic framework for computer-aided design and tuning of a mixed electric and magnetic coupling filter based on coupling matrices. An example of a 7th-order coaxial combline filter design is given in the paper, verifying the practical value of the approach.