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.