Microwave mixer with recovery of the sum frequency

The mixer comprises a microelectronic circuit composed of one or a number of active electronic elements having a nonlinear characteristic and carried on a substrate, the elements being supplied by waveguide lines placed on the substrate. The microelectronic circuit is fixed within a closed casing and connected to terminals placed on the casing in order to mix an incident wave S having a frequency FS applied to a first terminal of the casing with a mixing wave OL having a frequency FL applied to a second terminal of the casing and in order to restitute a mixed wave OR having a frequency FO on a third terminal. The cavity formed by the internal space of the casing is tuned to a "sum" frequency representing the sum of the frequency of the mixing wave FL and of the frequency of the incident wave FS.