Computer simulations of the performance of quasiparticle heterodyne mixers

Heterodyne mixers for millimeter wavelengths which have conversion gain and noise comparable to the quantum limit can be made using the non-linearity of the quasi-particle I-V curve of SIS or SIN tunnel junctions. When the voltage range of the non-linearity becomes small compared with hω/e, classical device theory breaks down and photon assisted tunneling theory must be used to understand mixer performance. In this paper we describe detailed computer simulations of SIS and SIN quasiparticle mixers. Predictions for conversion efficiency and noise are given for both devices as a function of operating frequency, bias voltage, RF source conductance and local oscillator power. A novel type of SIN harmonic mixer is proposed for which gain is also predicted.