Improvements in the accuracy of a new coaxial thermal noise standard

A novel approach is presented to an accurate determination of the available noise power of a coaxial thermal noise standard. Taking advantage of special design and construction principles of the primary coaxial thermal noise standard which is in operation at the PTB in the frequency range 0.1-10 GHz, the noise temperature has been calculated very accurately from the measured data of the temperature distribution within the heated RF termination section. By this means the uncertainties of the realization of the unit watt for noise power have been reduced for the PTB coaxial noise standard from 3.6×10^-3 to amounts of between 0.6×10^-3 at 100 MHz and 1.1×10^-3 at 10 GHz