Abstract: A multi-mode cavity filter, including at least one dielectric resonator body incorporating a piece of dielectric material having a shape to support first resonant mode and a second substantially degenerate resonant mode; excitation device(s) for at least one of: establishing an electromagnetic field external to, but immediately adjacent to, face of the dielectric resonator body or for extracting energy from an electromagnetic field located external to, but immediately adjacent to, a face of the dielectric resonator body, a layer of conductive material in contact with and covering the dielectric resonator body on the face of the dielectric resonator body: at least one aperture in the layer of conductive material for inputting signals to the dielectric resonator body and/or outputting signals from the dielectric resonator body, wherein the excitation device is located, in at least two dimensions, at an electrical centre of the face of the dielectric resonator body.