Design of a switchable selectivity bandpass filter based on diode-loaded resonators

This study utilizes coupled-line feed structure and diode-loaded resonators to realize a switchable selectivity microstrip bandpass filter. The different selectivity in the proposed circuit is controlled by switching between a second-order filter and a fifth-order filter. Because the feed line near input or output port is shared by the two filters designed at the same center frequency, the diode-loaded resonator in each filter is arranged near input or output feed line to avoid loading effect on each operating mode while switching the proposed circuit. An implemented switchable selectivity filter with high isolation to desired blocking circuit is successfully validated in this paper.