High-Selectivity Bandpass Filter-Integrated SPDT Switch Using Switchable Dual-Mode Hybrid Resonators

This article proposes a high-selectivity bandpass filter-integrated single-pole double-throw (SPDT) switch based on switchable dual-mode hybrid resonators. To solve the intrinsic conflict between the high ON-state loss and high OFF-state suppression (OSS), a switchable dual-mode hybrid resonator with two resonant modes constructed by 16-mode SIW, microstrip stub, and PIN diode is proposed. The PIN diode loaded on the open end of the 16-mode SIW is used to switch the resonant state. To enhance the isolation between the ON and OFF channels, a common coupled feed line is used to provide two identical coupling paths, mitigating the impedance impact from the OFF-state channel. In addition, by adjusting the structural parameters of the proposed resonator, the transmission zeros (TZs) of the switch can be controlled independently. For theoretical analysis, the equivalent circuit modeling for the SPDT switch is investigated. Based on the equivalent circuit, the frequencies of TZs are calculated. For experimental verification, the second-order BPF-integrated SPDT switch at center frequency $f₀ =4.9$ GHz with ripple bandwidth 400 MHz is designed, fabricated, and measured. Low insertion loss of only 1.18 dB, high upper stopband suppression, and multiple transmission zeroes are realized.