Channel Switchable Filter Design Based on PIN Diode Reconfigurable Microstrip Resonators

A multi-pole reconfigurable bandpass filter with a digital switchable passband employed four identical tunable microstrip resonators is described in this paper. Each tunable resonator mainly consists of a stepped impedance resonator (SIR) and two loaded PIN diodes. The PIN diodes are placed at both ends of the half-wavelength SIR. By controlling the PIN diodes in an on/off state, the dominant resonant frequency can be easily switched and four distinct passband frequency responses can be obtained. The even- and odd-mode method is employed to analyze the presented resonator. To validate the proposed tunable filter circuits, the switchable bandpass filter is designed, fabricated, and measured. It is demonstrated that the center frequency of the fabricated tunable filter is tuned from 1.28 to 1.71 GHz with the broad stopband. The electromagnetic simulated results show good agreements with the measurements.