The design and optimisation of a rugged 94 GHz balanced mixer is described. The mixer is of the crossbar type and incorporates novel millimetre wave integrated circuitry. Two monolithic, balanced Schottky diodes are used as the nonlinear elements. The diodes, together with the associated antenna coupling structure, are fabricated using planar processing techniques. Broad band operation is possible, with a double sideband conversion loss of 6.5 dB and a noise temperature of less than 1000 K measured at 90 GHz with a 4 GHz IF at room temperature. The mixer structure is analysed using scale modelling techniques which indicate how this performance can be improved