CIRCUIT-BASED ANALYSIS OF TAPPED-IN COUPLING BETWEEN COMBLINE RESONATORS APPLICABLE IN WIDEBAND FILTER DESIGNS

We showed that creating coupling between resonators through transverse electromagnetic transmission line directly tapped into both resonators provides a viable solution for the design of wideband microwave components where strong coupling values are required. However, more analysis is needed to explain the coupling mechanism and its limitation. In this work, we present the developed equivalent circuit model which is comprised only of lumped elements for comprehensive analysis of the tapped-in coupling between planar or cavity combline resonators. The efiects of lumped elements which are in correspondence to physical parameters on coupling value and resonant center frequency are derived. The circuit model predicts that this coupling mechanism by adjusting the design parameters of coupling section simply realizes any required strength of coupling between resonators, i.e., from weak values close to zero up to strong values close to unity. Therefore, wideband fllters are easily designed and their bandwidth can be controlled based on inter-resonator tapped- in coupling. This fact is validated through measurements for two- coupled resonators with unloaded resonant frequency of 1.45GHz. The bandwidth is extended to 90% via tapped-in method. The total dimensions of structure are ‚=4 £ ‚=18 £ ‚=72.