Compact Single-Pole-Double-Throw Switchable Bandpass Filter Based on Multicoupled Line

A compact single-pole-double-throw (SPDT) switchable bandpass filter (BPF) composed of capacitively loaded multicoupled line is proposed. By replacing the quarter-wavelength impedance transformer at the common junction in conventional designs with a J-inverter, the circuit size is largely reduced and the design procedure is much simplified. As a demonstration, a proposed SPDT switchable BPF is designed and implemented with a center frequency f(o) 1.0 GHz and a bandwidth of about 10%. Low insertion loss in the on state, good isolation in the off state, and good linearity are obtained. The filter size without bias circuits and input/output traces is only 2.5 cm 2.7 cm, which is about 0.158 lambda(g) X 0.170 lambda(g) at f(o).