Methods for direct-reading noise measurements of low-gain two-ports

This paper describes direct-reading measurement methods of noise figure F_m displayed by an automatic noise figure indicator. The F_m readings should be equal to F_x, which are the true noise figure values of the two-port under test, regardless of its available power gain G_Ax, and the noise figure of the measurement receiver F_t. Technical problems of these F_x direct readings are shown. They particularly occur while using the conventional measurement methods. Methods that allow elimination of the influence of the F_r value on F_m readings as well as the influence of both F_r and G_ax on F_m are discussed. An important advantage of using the method with elimination of the F_r value is presented. Formulas are given which allow the estimation of the technical requirements for additional blocks of measurement systems or to count measurement error components, specific for the chosen measurement method