Casing contained filter

Abstract

A filter is provided which maintains a low insertion loss characteristic of a filter contained in a casing with a very simple construction that the internal wall of the casing is formed by a superconductor. A coplanar waveguide filtercomprises a dielectric substrate, a plurality of resonatorsandand input/output terminal sectionsand, each of which is formed by a center conductorand ground conductorsand, both formed on the same surface of the dielectric substrate, with the ground conductorstobeing formed on the opposite sides of and in parallel relationship with the center conductor. The filteris contained within a casinghaving an internal wall, the surface of which is formed with a layer of superconductor. By way of example, a high temperature superconductor such as lanthanum-, yttrium-, bismuth- or thallium-superconductor is deposited as a film on a substrate of a metal oxide material such as MgO, SrTiO, LaGaO, LaAlOto provide a superconductor filmed substrate, which is applied to the internal surface of the casing. Electromagnetic power which is irradiated from the filterdoes not produce a power loss when it impinges on the layer of superconductorin its superconducting state, but is reflected therefrom to be absorbed by the filter, thus reducing the filter insertion loss.