Automatic null radiometer for the 3-4 mm wavelength region

The paper describes a frequency-tunable automatic null interferometer for the 3-4 mm wavelength region that is sensitive enough to measure fluctuations in the brightness temperature of the atmosphere on cloudless days. The radiometer is based on the superheterodyne design, and the high frequency circuit is built up from waveguides of 23 x 10 mm cross section. Null reception is achieved by means of a comparator and a Faraday-effect ferrite-gate control element. The accuracy of the recording of relative atmospheric brightness temperature fluctuations is about 0.1%.