A Compact Wideband SPDT Switch Using Compensating Inductors and Highpass Matching Network

This paper presents a compact PIN-diode-based single-pole double-throw (SPDT) switch for wideband RF systems. The series-shunt topology is adopted for the proposed switch. Compensating inductors are introduced to parallelly resonate with the off-capacitance of series diodes, creating an isolation peak. A two-pole highpass matching network is realized by introducing an additional inductor and reusing existing DC components, which ensures compact size and wideband capability. Moreover, the matching network enables independent control of ON-state operating band over the OFF-state, allowing optimized insertion loss and isolation at the desired center frequency. To assist analytical design, closed-form equations of the highpass matching network are derived through equivalent circuit analysis. For demonstration, one SPDT switch utilizing commercial PIN diodes and lumped RLC components is designed, fabricated, and measured. The measured results exhibit superior return loss of better than 20dB across 1.02-3.36 GHz attributed to the two-pole response. The insertion loss remains below 0.81 dB, reaching 0.457 dB at 2.6 GHz, while isolation is better than 27 dB, with a maximum of 71.8 dB at 2.25 GHz. Importantly, the proposed design can be scaled to mm-wave bands with better performances than their widely developed lowpass counterpart.