Planar GaAs Mott Low Noise mm-Wave (35 and 85 GHz) Mixer Diodes

Conversion losses of 5.0 dB have been achieved at 35 GHz, with SSB noise figures of 6 dB (including 1 dB IF) using coplanar Mott diodes in finline balanced mixers. [l] The variation of noise figure with local oscillator power is significantly less than for conventional Schottky diodes, and results from the voltage independence of the capacitance of Mott diodes [2]. The series resistance of these diodes is about 4Ω, with a total capacitance of .05 pF. Smaller diodes, with capacitances of .03 pF, have been evaluated in 85 GHz balanced mixers. Conversion losses as low as 6.5 dB have been observed at 85 GHz, with improved operation over a wide range of local oscillator power, and further improvements are expected as devices and circuits are optimised at this frequency. In addition to achieving high performance the coplanar Mott diodes are made by low cost planar processing and are rugged.