The Noise Factor for cascaded amplifiers (FN) is given by (F1, F2, F3 .. FN, G1, G2, G3….GN) are the noise factors and the gains of the amplifiers at different stages:
a. FN = F1 + F2/ G1 + F3/ G1G2+ ..+ FN/ G1G2G3GN
b. FN = F1 + (F2 – 1)/ G1 + (F3 – 1)/ (G1+G2)+ ..+(FN – 1)/ (G1+G2+G3+…+GN)
c. FN = F1 + F2/ G1 + F3/ (G1+G2) +…+ FN/ (G1+G2+G3+…+GN)
d. FN = F1 + (F2 – 1)/ G1 + (F3 – 1)/ G1G2+…+(FN – 1)/G1G2G3GN
