2008年中国计量科学研究院研制了一台WR28低温标准热噪声源.一个全频带WR28匹配负载浸入液氮中作为该标准的噪声辐射源.为了避免波导内部冷凝结霜在波导壁上设计了氮气导孔和氮气收集筒.详细分析了该标准噪声源输出温度的定标方法和输出噪声温度的不确定度评定.在所有的定标点该标准的输出噪声温度比液氮温度稍高几度,其输出口电压驻波比小于1.04,扩展不确定度小于1.00K(k=2).利用新的标准噪声源校准了商用R347B噪声源,校准结果与被测噪声的标称值一致性很好,测量的相对不确定度小于1.2％.%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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