Design of BPF-Integrated SPDT Switch Based on Slotline Resonators Loaded With Diodes

Slotline Stepped-impedance resonators (SIR) loaded with p-i-n diodes are used to develop bandpass filter (BPF) integrated switches in this brief. The loaded diodes are used to switch the resonant conditions of the short-ended slotline resonators. The equations for their resonant conditions under different loads at different locations are derived and discussed. With these derived equations, the switchable filters are designed and synthesized using the classical coupled-resonator filter theory. The design concept is demonstrated by a Cascaded Quadruplet (CQ) BPF-integrated single-pole single-throw (SPST) switch at center frequency $f_{0}\,\,=$ 1 GHz with 47.7 dB OFF-state suppression (OSS). Finally, two compact BPF-integrated single-pole double-throw (SPDT) switches are designed and fabricated. One of them combines source-load (S-L) coupling and introduces two additional zeros outside the desired passband to improve the frequency selectivity. The other on fractal common feeding line is developed to reduce the impact of accumulated residual admittances from OFF-state channels, which shows high roll-off rate of sidebands as well as high port-to-port isolation of 53.1 dB, and its overall circuit size is only $0.051 \lambda \text{g} ^{\mathrm{ 2}}$ .

I. Introduction

Microwave switch [1] and bandpass filter [2] are two essential components in the modern radio-frequency (RF) systems. In recent years, more and more attention has been paid to the research of filter-integrated switches, which provide switching and band selection functions. Several filter-integrated switches using various design methods have been proposed and explored so far.