Noise figure sensitivity to gain uncertainty

Measured noise figure displayed by an automatic noise figure indicator should be equal to the true noise figure value of the two-port under test (TUT), regardless of its available power gain and noise figure of the receiver used in the measurement system. Technical problems of direct-reading noise figure measurements of the low-gain TUT are briefly presented in the paper. The known methods for true value of the TUT noise figure measurement are compared using the mathematical expressions which describe noise figure sensitivities to TUT gain uncertainty.