S11 , S21 and Gain relationship ?

Hi guys,

Can we write this for a certain block like LNA ?

S21 = (1+S11) vout /Vin

IF yes, where is it coming from ?

Yes, there is a relationship between Gain and the Scattering Parameters of an amplifier.

Where is what coming from? There are derivations in Pozar's Microwave Engineering, Chapter 11 (3rd Ed.).

Ok tnx man I will check the book :)

It can easily derived from ADS functions