Measurements on Active Cold Loads for radiometer calibration

Two semi-conductor active cold loads (ACLs) to be used as cold references in spaceborne microwave radiometers have been developed. An X-band frequency was chosen, and the target noise temperature value was in the 50 to 100 K range. The ACLs are characterized in the operating temperature range 0-50degC, and long term stability is assessed. To this end a test bed has been developed. This test bed is actually a stable radiometer, and its design is briefly reviewed. The test setup is described, and preliminary test campaign results indicate output temperatures of 77 K and 55 K for the two ACLs. The temperature sensitivity is slightly below 0.4 K/degC for the units, and excellent long term stability prevails.