The ratio (in dB) between the signal-to-noise ratio applied to the
input of a microwave component and the signal-to-noise ratio
measured at its output. NF is an indication of the amount of noise
added to a signal by the component during normal operation.
Lower noise figures mean less degradation and better
The noise figure is a measure of the degradation of the
signal-to-noise ratio (SNR) between the input and output ports of a
device. As a standard reference the source temperature is
assumed to be 290K.
The noise figure is most often expressed in decibels:
NF (dB) = 10 logl0 FC (cascaded noise figure)
Throughout this note, noise figures are in decibels unless stated
Noise figure may also be expressed as an Effective Noise
Temperature in Kelvin:
Te = 290 [log-1 (NF dB/10) -1]