Extended resonator electronically tunable band pass filter

Abstract

An electronically tunable narrow band tuned cavity filter includes a housing which bounds a tuned cavity, a plurality of resonator bars secured to the housing, extending across the tuned cavity and having respective extensions that pass through respective openings of the housing to the exterior of the tuned cavity, and a set of tuning capacitor plates for each of the resonator bars. The tuning capacitor plates associated with the respective resonator bar are arranged outside the tuned cavity around the extension in a compartment surrounding the opening, together with respective switching networks driven by an electronic drive and operative for including the capacitor plates in or excluding the same from electric circuit with the respective resonator bar. The capacitor plates may be directly juxtaposed with associated facets of the extension to form respective tuning capacitors therewith. Dielectric spacers may be interposed between the capacitor plates and the associated facets of the extension to determine and maintain the size of the gap therebetween, and to suppress mechanical vibrations of the cantilevered resonator bar. The capacitor plates may be yieldably mounted on the support and urged toward the extension by respective springs. The extension of the resonator bar may be provided with a recess opening onto the respective facet, and an internally threaded bore opening into the recess, and externally threaded trimmer slug may be received in the bore and extend to a greater or lesser degree into the recess to thereby contribute to a greater or lesser degree to the total capacitance of the respective tuning capacitor.