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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1.00 K(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%。
In 2008 China Institute of Metrology developed a WR28 low temperature standard thermal noise source. A full-band WR28 matched load is immersed in liquid nitrogen as the standard noise source. In order to avoid condensation and frost inside the waveguide, a nitrogen guide hole and a nitrogen collecting cylinder are designed on the waveguide wall. The calibration method of the standard noise source output temperature and the evaluation of the uncertainty of the output noise temperature are analyzed in detail. At all calibration points the standard output noise temperature is a few degrees farther than the liquid nitrogen temperature, with an output voltage standing wave ratio of less than 1.04 and an extended uncertainty of less than 1.00 K (k = 2). The commercial R347B noise source is calibrated using a new standard noise source. The calibration results are in good agreement with the nominal values of the noise under measurement and the relative uncertainty of the measurement is less than 1.2%.