Helical resonator having variable capacitor which includes windings of reduced diameter as one plate thereof

Claim 1

A helical resonator for passing radiofreqnency signals within a predetermined frequency range, such helical resonator including in combination: a helical coil comprised of conductive windings, said windings having a first cross-sectional diameter along a first portion of said coil and a second cross-sectional diameter which is less than said first cross-sectional diameter along a second portion of said coil including an endmost windings; a conductive member forming a cavity enclosing said coil to form a resonant structure; a coupling surface forming part of said conductive member which is positioned in a plane that is essentially parallel to said endmost winding, said surface thereby forming a first plate and said endmost winding forming a second plate of an equivalent capacitor with the distance between said coupling surface and said endmost winding being the thickness of the dielectric of said capacitor; movable conductive means having a portion extending through said coupling surface toward said endmost winding of the coil, said means being adjustable to vary said portion thus changing The effective surface area of said first plate and the thickness of said dielectric to change the capacitance of said equivalent capacitor thereby adjusting the resonant frequency of the helical resonator.