Planar filter and filter system using a magnetic tuning member to provide permittivity adjustment

Abstract

There is disclosed a planar filter which can variably control a pass frequency band with a high precision and which is superior in skirt property and little in ripple. A planar filter member and tuning member are disposed opposite to each other via a predetermined gap. The filter member is structured in such a manner that an input/output portion formed of a superconductor and a plurality of resonance elements are formed on a substrate. The tuning member is structured in such a manner that on the surface of a magnetic plate with a permeability changing by an applied magnetic field, a plurality of dielectric thin films, and a plurality of electrodes for applying electric fields to the dielectric thin films are arranged. Each of the dielectric thin films is disposed in a position opposite to a gap between the resonance elements of the filter member, or a gap between the filter member and the input/output portion. By applying a voltage between the electrodes, an effective permittivity ∈ of the gap between the resonance elements, or the gap between the resonance element and the input/output portion is variably controlled, and the skirt property and ripple are adjusted. Moreover, a resonance frequency of the resonance elements, a coupling between the resonance elements, and a coupling between the resonance element and the input/output portion may be individually and independently controlled.