Compact Switchable Bandpass Filter and Its Application to Switchable Diplexer Design

This later firstly presents a quasi-elliptic bandpass filter (QE-BPF) which consists of a pair of shorted stepped-impedance resonator (SSIR) and a dual-mode resonator (DMR). Then, a 900 MHz switchable bandpass filter (SW-BPF) and a 1250 MHz SW-BPF are designed by loading p-i-n diodes at two open ends of DMR or SSIRs. Finally, a common-T junction constructed by two T-networks is used to combine the above designed 900 and 1250 MHz SW-BPFs to constitute a switchable diplexer. The fabricated QE-BPF, two SW-BPFs and switchable diplexer exhibit wide bandwidth, low insertion loss, sharp passband selectivity, high port isolation and compact size.