Band-selective interferer rejection for cognitive receiver protection

The concept for a new, frequency-selective limiting filter is presented. This is accomplished by placing a phase change vanadium dioxide (VO₂) film at the proper node of the filter. When the high-powered microwave signal reaches a certain threshold, the VO₂ undergoes a phase transition from the monoclinic “insulator state” to the tetragonal “metallic state”. This crystallographic change is accompanied by a 3 order of magnitude drop in the film´s resistivity, and creates a short circuit at a section of the filter, changing a pole to a zero, and rejecting further undesirable high-powered signals from damaging sensitive receiver components. This paper details the design and simulation of the filter, along with measurement results from VO₂ films and the filter element. This filter element begins rejecting at about 2 W input power, with isolation of over 16 dB to over 23 W input power, and is unaffected by an out-of band interferer of over 25 W. The architecture presented allows for filter banks capable of automatically-rejecting interferers, yet allowing signals of interest to pass.