A cavity filter, including first and second dielectric resonator bodies, each incorporating a piece of dielectric material, each piece of dielectric material shaped to support at least a first resonant mode, at least one excitation device for establishing an electromagnetic field within at least a first dielectric resonator body or extracting energy from an electromagnetic field located within the first dielectric resonator body, a layer of electrically conductive material in contact with and covering a surface of the first and a surface of the second dielectric resonator bodies, an aperture in the layer of electrically conductive material for inputting signals to the second dielectric resonator body and/or outputting signals from the second dielectric resonator body wherein the at least one excitation device is arranged to directly excite the first resonant mode or directly extract energy from the first resonant mode in the second dielectric resonator via the aperture.