Variable-temperature microwave cryogenic noise source

A compact variable-temperature microwave cryogenic noise source was designed and tested. It works at (26, 5...40) GHz and (75...110) GHz frequency range (two outputs) with VSWR as low as 1, 1. Output temperature may be set at (100...300) K range with 1 K error. The noise source may work during 5 hours without refilling liquid nitrogen. A metal Dewar of the source has 3-liter capacity. A high performance of the noise source is due to oversized circular waveguides used between cooled absorbers and output waveguides.