Advanced tuning algorithms for high-frequency SIS mixers

Three tuning parameters are key to SIS performance: SIS bias voltage, LO pumping level and Josephson current suppression. The former two are relatively easy to perform automatically, although there are a couple of pitfalls. The suppression of the Josephson current, however, is much more complicated, especially in the high-current-density AlN-barrier junctions used in ALMA Band 9. The tuning parameter sets that were supplied with the receivers were always biased towards safer and more repeatable regimes for operational reasons. Here we present results of the ALMA Band 9 Advanced Tuning Study commissioned by ESO. The objective of this study is to investigate more "intelligent" tuning algorithms which should enable the receivers to operate in more critical regimes that were previously avoided, but with possibly a considerable increase in performance.