Noise in SIS microwave mixers

It is proposed that the noise in an SIS (superconductor-insulator-superconductor) microwave mixer is shot noise, and that it can be treated in a similar manner to the noise in Schottky barrier diodes. A noise temperature is defined, and how it can be optimized is indicated. An extension of the noise temperature concept of the source is used that makes noise temperatures additive at all frequencies.