A WR28 cryogenic thermal noise standard was constructed at NIM in Dec 2008. A full band WR28 matched load immersed in the liquid nitrogen is served as the noise radiation source of the standard. To avoid condensation and freeze in the waveguide the nitrogen-gas guide holes and the collection tank are designed. The evaluation of the output noise temperature and the uncertainty assessment are discussed in detail. The output noise temperature of this standard is a few degrees above the temperature of the liquid nitrogen, the VSWR of the noise standard is below 1.04 and the extension uncertainty is within 1.00 K (k = 2) for all the frequency points that had been evaluated. A calibration example using the new standard noise source is shown at the end. The results are very consistent with the nominal values of the DUT and the relative measurement uncertainty is within 1.2%
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梁伟军. WR28低温标准噪声源[J]. 科学技术与工程, 2011, (31): . Liang Weijun. A WR28 Cryogenic Standard Noise Source[J]. Science Technology and Engineering,2011,(31).