Please see the datasheet of MRF171A.
The datesheet shows:
45W, 150MHz, 28V,Efficiency = 50% (typ.)
according to the datesheet, the Idq set to 25mA or 100mA,
MRF171A almost can output 30Watt, but
28v x 0.1A X 50%=1.4(watt)
If you want increase the ID, you must increase the VGS
If the MRF171A output full power, my comprehend as below:
28V X 3.214A X 50%=45(watt)
So I really cannot understand the curve in the datesheet.
Would you please clear up my doubts,
Thank you very much!