Role of spectral purity of down-converting local oscillator in the evaluation of noise figure of microwave amplifiers

The importance of spectral purity of down-converting local oscillator in the accurate measurement of noise figure of microwave DUTs has been discussed. The errors in the noise figure measurements resulting due to spurious frequency components of the down-converting local oscillator have been analyzed. Acceptable spurious levels in the local oscillator spectrum for error-free noise figure measurements has been proposed