Numerical design calculation of a MM-wave mixer with SIS tunnel junction

Conversion efficiency has been calculated as function of local oscillator voltage and signal source conductance for SIS mixer in the 3-port approximation. The corresponding output conductance is determined. The reactance terms due to the nonlinear quantum reactance and the junction's capacitance are considered. Under practical conditions-1/10 tapped waveguide mount, 50 Ω intermediate frequency load-without cancellation of these reactive terms, conversion loss of at least 7 dB is obtained; complete or partly tuning out the reactive terms leads to moderate conversion gain. The calculations have been carried out on the basis of a measured I–V characteristic for local oscillator frequency of 88 GHz in the limit of low intermediate frequency.