problem with input power in ADS

i have a problem with input power in ads,harmonic balance.
in harmonic balance simulation i put 3 element:

1-v1_tone(sin wave AC signal) in input
2-a s2p file block for a broadband internally matched transistor(FET)
3-a 50 ohm term(port) in output

i want to have a constant average power in input in all of my bandwidth.because of internally matched fet(constant resistant) and constant voltage we must have constant average power. {Paverage=(Vpeak^2)/(2*R)}
but when i change the frequency,for a fixed average power in that freq i have to change input peak voltage.
please guide me.

Internally matched FET has been matched to 50 Ohm and you use ideal voltage source consequently there is a mismatch and a mismatch loss.
In additional to this, even tough this FET is internally matched, input resistance can not be purely resistive because of FETs nature.
Use 50 Ohm Power Source and try once again.In this case available power will be constant and delivered power will variable due to mismatch.

thank you but i want to use this for a power amplifier, i want to know my source in reality equalls to which source and i must use which in ADS?(i want to use computer power source for biasing the transistors, and assume to use this amp for radar applications)

in addition to this when i used a 50 Ohm power source, my input power still changed with frequency chqnge but less than previous time.

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