Direct measurement techniques of transmission line corrections for thermal noise standards

A thermal noise source consists of a matched termination and a transmission line. A method which permits a direct measurement of the correction due to the transmission line effects on the thermal noise source without any measurement of temperature, loss, and reflection distribution in the transmission line is presented. Generalised expressions for the equivalent temperature of the thermal noise source are derived, which are composed of the temperature of the matched termination, the output reflection coefficient, and the transmission corrections. It is shown that the corrections can be determined from reflection coefficients and noise outputs of the source in which the matched termination is replaced by a short. A possibility is suggested, that higher accuracy in the correction will be obtained by the new method than by conventional ones. A 10-GHz noise source is tested by the method.