Tuneable dielectric resonator

A method of tuning a dielectric resonator which resonator comprises a cavity within which is mounted a dielectric which method comprises changing the frequency of the resonator by a frequency changing means which is operated using a ferroelectric element in which a DC bias is applied across the ferroelectric element to decrease the relative permittivity of the ferroelectric element which affects the dielectric resonator electric field and changes the resonance frequency of the resonator, in which the ferroelectric element is a ferroelectric film, in which the ferroelectric film is mounted on a conductive base on which is positioned a spacer and the dielectric is mounted on the spacer, in which the conductive base, on which is formed the ferroelectric element, is supported on a floor of the resonator, the dielectric element and spacer are ring shaped, the spacer is positioned on the ferroelectric element and the dielectric element is placed on the spacer, and in which there is a wire electrode which passes through the spacer and the dielectric element and is connected to the ferroelectric element, there being a means to apply a DC bias to the ferroelectric element through the conductive base and the wire.