A Tune-All Wideband Filter Based on Perturbed Ring-Resonators

A dual-mode resonator is presented for tunable wideband filters, which allows tunability in both the centre frequency and bandwidth. It is based on a new perturbation arrangement in a ring-resonator that is electronically tuned with varactor diodes. A filter is designed for a radio astronomy receiver application. It consists of 6 cascaded dual-mode resonators with a 49% bandwidth in the L-band. High selectivity and low insertion losses are achieved. The centre frequency is tunable by 9% and the bandwidth by 25.3%. This design is unique in that it achieves wide bandwidth, is realisable in microstrip and tunable in both the centre frequency and bandwidth.