Quasi-Lumped-Element Filter-Integrated Single-Pole Double-Throw Switch

In this paper, the capacitively coupled LC resonators with loaded p-i-n diodes are used to develop fixed-response filter-integrated single-pole double-throw (SPDT) switch. The filter-integrated on-state channel with reverse-biased p-i-n diodes can be designed and synthesized using the coupled-resonator filter theory, and the off-state channel with forward-biased p-i-n diodes exhibits high suppression. A 1-GHz filter-integrated SPDT switch with ripple bandwidth of 195 MHz is designed to demonstrate the proposed design concept. Measured results show that it has a low on-state insertion loss (IL) of 1.03 dB, a wide passband, high off-state suppression (OSS), high port-to-port isolation, and compact circuit size. Since both the properly misaligned resonant frequencies of LC resonators and weakly coupling between LC resonators also result in high suppression, a frequency-agile filter-integrated switchless SPDT switch without p-i-n diodes can be designed by using the varactor diodes to realize the corresponding capacitors. A frequency-agile filter-integrated switchless SPDT switch with constant 1-dB fractional bandwidth of 19.5% is also designed. Measured results show that its operating frequency can be tuned from 0.612 to 1.088 GHz with corresponding frequency tuning range of 58% and IL varying from 2.8 to 2.3 dB. Good return loss, high OSS, and port-to-port isolation can be also observed.