NOISE IN CASCADE SYSTEMS:
Cascade noise figure calculation is carried out by dealing with gain and noise figure as a ratio rather than decibels, and then converting back to decibels at the end. As the following equation shows, cascaded noise figure is affected most profoundly by the noise figure of components closest to the input of the system as long as some positive gain exists in the cascade. If only loss exists in the cascade, then the cascaded noise figure equals the magnitude of the total loss. The following equation is used to calculate cascaded noise figure as a ratio based on ratio values for gain and noise figure (do not use decibel values).