Noise Temperature and Uncertainty Evaluation of a Cryogenic Noise Source by a Sliding Short Method

A cryogenic noise source (CNS) that was cooled by liquid nitrogen was constructed and evaluated in the 8-12 GHz frequency range (the WR-90 waveguide band). A noise temperature of the CNS requires a correction with respect to the boiling point of liquid nitrogen, depending on loss and temperature distributions of a transmission line. We have investigated the transmission line correction factor (TLCF) of the CNS with a sliding short method using a total-power radiometer that is suitable for broadband measurements. The equivalent noise temperature was 79.56-82.90 K, with an uncertainty of 3.89-6.13 K (k = 2). A comparison of the noise temperature that is obtained by the radiometer with two calibrated noise sources proved the validity of the TLCF.