An integrated circuit mixer which is impedance matched to a fundamental waveguide, utilizes a slot coupler and a coplanar transmission line to apply an RF and local oscillator signal to a Schottky-barrier diode. The IF signal which is available at the output of the Schottky-barrier diode is filtered by means of an RF bypass capacitor that is located on the dielectric substrate surface. At 110 GHz, a mixer module when mounted in the end of a waveguide horn, has an uncooled double-sideband (DSB) mixer noise temperature of 339.degree. K. and conversion loss of 3.8 dB.