Microwave noise standards

Attention is given to precise measurement techniques for microwave noise in terms of establishing national standards in Japan. Thermal noise sources are considered primary standards, and a general expression is derived for estimating the equivalent temperature of thermal noise sources. It is composed of termination temperature, output reflection coefficient, and corrections for transmission line characteristics. A short circuit method is used to evaluate these corrections. On the 10 GHz band, two types of precision noise sources are identified: a hot noise source in which the freezing temperature of gold is the reference temperature, and a cold noise source cooled with liquid nitrogen. Using the short circuit method, equivalent temperatures of these sources are found with 0.3% and 0.25% accuracies, respectively. Two precise noise power measuring techniques have been developed. The first is a noise injection method applicable to low noise measurement; the second is a reflection compensation method.