Conversion loss limitations on Schottky-barrier mixers

A set of criteria involving diode area, material parameters, and temperature is introduced for the Schottky-barrier mixer diode. The effect that a reduction in diode area can have on the intrinsic conversion loss of the diode resulting from its nonlinear resistance is analyzed, focusing on the competing requirements of impedance-matching the diode to its imbedding circuit and the finite dynamic range of the nonlinear resistance. As a result, intrinsic conversion loss can increase rapidly as the area is reduced. Results are expressed in terms of dimensionless parameters, and some representative examples are investigated in detail. The following conclusions are drawn: a large Richardson constant extends the usefulness of the diode to smaller diameters, and hence, shorter wavelengths; cooling a thermionic emitting diode can have a very detrimental effect on intrinsic conversion loss; impedance mismatching is found, in general, to be a necessity for minimum conversion loss; and large barrier heights are desirable for efficient tunnel emitter converters.