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Auxiliary-Transmission-Line Method for Calibrating Noise Temperature of a Microwave Thermal Noise Source

We have proposed and discussed a method to calibrate the effective noise temperature (ENT) of a noise source by using an auxiliary transmission line (ATL). A cryogenic 7-mm coaxial noise source was developed for verifying the ATL method. The ENT is determined from the parameters evaluated by a radiometer and the available power ratio of the transmission line measured by a vector network analyzer. The calibrated ENT by this method was 139.8 K-143.6 K with an expanded uncertainty of 4.0 K-4.6 K (k = 2) in the frequency range of 8-12 GHz. We also performed a comparison of the ENT using two different methods: an ordinary radiometer measurement using two reference noise sources and a theoretical calculation method analyzing temperature and loss distribution along the transmission line. The experimental results show the validity of the ATL method for determining the ENT.