Abstract: An electronic device comprises a waveguide block defining a cavity therein. The device has a monolithic microwave or millimetre-wave integrated circuit device positioned at least partially in the cavity. The integrated circuit device comprises a dielectric substrate and a metal foil layer that extends outwards from an external edge of the dielectric substrate. The metal foil layer and the dielectric substrate define a through hole, wherein a first edge of the through hole is an edge of the metal foil layer and defines an end of the elongate waveguide channel, and wherein the metal foil layer at least partly determines both a length and a width of an elongate waveguide channel within the cavity.