Couplings of microstrip square open-loop resonators for cross-coupled planar microwave filters

TLDR

The authors propose a new cross‑coupled planar microwave filter based on coupled microstrip square open‑loop resonators and develop a rigorous method for calculating coupling coefficients of its three basic coupling structures. Empirical models for the coupling coefficients are derived, experimentally verified, and used to design and fabricate a four‑pole elliptic function filter of this type. Theoretical predictions and experimental measurements demonstrate the filter’s performance.

Abstract

A new type of cross-coupled planar microwave filter using coupled microstrip square open-loop resonators is proposed. A method for the rigorous calculation of the coupling coefficients of three basic coupling structures encountered in this type of filter is developed. Simple empirical models are derived for estimation of the coupling coefficients. Experiments are performed to verify the theory. A four-pole elliptic function filter of this type is designed and fabricated. Both the theoretical and experimental performance is presented.