Reconfigurable bandpass filter based on split ring resonators and vanadium dioxide (VO2) microwave switches

In this paper, we present the design, fabrication and characterization of the first tunable bandpass filter that combines split ring resonators (SRRs) and vanadium dioxide (VO₂)-based microwave switches. The device consists on a pair of coupled SRRs, feed by means of tapped microstrip lines, that can be connected to metallic patches by electronically activating the VO₂-based switches. Through the fast and reversible semiconductor-to-metal transition (SMT) of the VO₂ thin films, the electrical characteristics of the SRRs are modified so that their resonance frequency, and as a result the central frequency of the bandpass filter can be electrically tuned. The fabricated filter, designed to operate in the X-band, exhibits a tuning range of nearly 10% where its electrical characteristics (bandwidth, insertion losses, etc.) are roughly preserved.