A New Compact Switching Bandpass Filter Using Only a Single Pin Diode

This paper presents an innovative integrated switchable single‐pole double‐throw (SPDT) switch for bandpass filters (BPFs) using a terminal‐loaded coupled line structure. Based on the design principles of terminal‐loaded coupled line structures, the proposed SPDT switch achieves a bandpass on‐state when the p‐i‐n diodes are reverse‐biased, and a high off‐state suppression through detuning when forward‐biased. The on‐state passband selectivity is further enhanced by introducing two pairs of transmission zeros, created by symmetrically loaded series stubs at the coupled line ports. A prototype switch, designed for operation at 1 GHz with a bandwidth of 411 MHz, achieves a low insertion loss of 1.3 dB, a high roll‐off rate, and a strong off‐state rejection of 24 dB.