A cryogenic microwave measuring system for satellite receiver testing

A cryogenic microwave test system for the 70 GHz Planck satellite receiver has been built. It consists of 4 K and 20 K active helium coolers mounted in large 2/spl times/ 10/sup -7/ mbar vacuum chamber. Special RF-components have been designed for the test, e.g. a 4 K load for the continuous comparator reference temperature stimulus. External electronics has been constructed to measure the two orthogonal polarizations from two parallel receiver units. The noise temperature measurement uncertainty is better than 4 K and the test system's post-detection noise characteristics with a matched load is better than 1.6/spl middot/10/sup -6/ V//spl radic/Hz from 15 mHz, when the integration time constant is 0.5 s.