In ALMA Memo 321, Plambeck points out that saturation (gain compression) is likely to be a significant factor limiting the calibration accuracy of ALMA observations. In this memo, saturation by broadband noise and CW signals is analyzed for representative SIS receivers operating at different frequencies. Many SIS mixers in current use are expected to exhibit a significant degree of gain compression when connected to a room-temperature source. Previous analyses of saturation in SIS mixers have applied only to CW signals. To analyze saturation by noise, the statistics of the output voltage are derived from those of the input signal. A single constant, applicable to all SIS mixers, is determined experimentally by fitting the predicted CW gain compression curve to measured data.
View a pdf version of ALMA Memo 401.
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