S21 is less than zero when designing a AsGa PA,is all right?

Hi:


I am designing a 2.4GHz PA using AsGa, but the S21 is less than zero.

I want to know whether it is normal?

thanks very much!

When S21 (dB) is below 0 you have an Attenuator not an Amplifier.
But your design has no sort of matching input or out put, so you are
basically seeing the S-Parameters.

Plot S11 & S22 on a Smith chart and find their values at 2.4GHz.
Then put the Conjugate of those Impedance as matching networks
and you should get a lot more gain. But if this is a PA you will need
to match the Output for Max Power and not Gain (typically a lower impedance).

Cheers