Rectangular cavity resonator and microwave filters built from such resonators

Claim 1

A rectangular cavity resonator comprising: a rectangular cavity having its width, length and height freely chosen within limits so that the resonant frequency of said rectangular cavity is above a desired operating frequency; inductive coupling diaphragms disposed in selected walls of said rectangular cavity and having a given configuration to provide a desired coupling factor for coupling energy into and out of said rectangular cavity; a capacitive inner conductor disposed to extend through a first wall of said rectangular cavity into said rectangular cavity toward a second wall thereof opposite said first wall; said inner conductor including a first portion directly connected to said first wall having a first given diameter; a second portion directly connected to the end of said first portion adjacent said second wall having a second given diametEr greater than said first given diameter, and a coaxial bore concentric with the longitudinal axis of said inner conductor having a third given diameter less than said first given diameter; and a cylindrical tuning plunger disposed within said coaxial bore concentric with said longitudinal axis of said inner conductor having fourth given diameter less than said third given diameter; said tuning plunger including being composed of a low-loss insulating material and capable of adjustment relative to said second wall by a screw thread, a given length of said tuning plunger adjacent said second wall being covered with a conductive material to provide a capacitive coupling between said second wall and said second portion; said first, second and third given diameters of said inner conductor, said fourth diameter of said tuning plunger and the length of said tuning plunger extending from said second portion being selected to cooperate in providing said desired operating resonant frequency for said rectangular cavity.