Fully-Reconfigurable Bandpass/Bandstop Filters and Their Coupling-Matrix Representation

A new type of a tunable microwave filtering device with reconfigurable bandpass-filter (BPF) and bandstop-filter (BSF) operational modes is reported. It consists of series-cascaded BPF/BSF stages which are formed by two resonating nodes, one non-resonating node (NRN), and two impedance inverters. Each BPF/BSF stage results in two transmission zeros (TZs) that are generated at the natural frequencies of the constituent resonators, whose spectral locations can be reconfigured by tuning the resonating elements. Thus, multi-TZ BPF/BSF responses can be synthesized in the overall circuit which features fully-controllable performances by means of TZ reallocation. The coupling-matrix representation of the proposed frequency-agile BPF/BSF scheme is demonstrated. Moreover, an S-band two-stage prototype based on frequency-reconfigurable evanescent-mode cavity resonators is fabricated to experimentally validate the predicted behavior.