Re: 50 Ohm TO 75 Ohm
Assuming you have a modern RF analysis program to simulate the amplifier on, you do not have to worry, the program will do all that for you.
You transistor is modelled either:
1) as a lumped element model, which does not care what impedance your "system" is in
or
2) Uses an S parameter file (S2P file) where there is a line near the top that reads something like:
# GHZ S MA R 50
The 50 tells your simulation program that these are Sparameters measured in a 50 ohm system, and if you are doing a simulation with another system impedance other than 50 ohms that it will have to numberically convert the sparameters accordingly.
You DO have to change a global variable somewhere in the operating window of your analysis software to tell your software that they system impedance is now 75 ohms!