Just use a Wattangel or clamp meter and read the power cord, that's how many watts you are using. You can also use a True RMS meter and a sine wave tone generator to measure the power output, but ...

Linearity Testing RF power amplifier (RFPA) nonlinearities introduce third-order intermodulation distortion (IMD) to the amplifier output signal when driven by a multitone input signal.

Together with the already successfully introduced broadband amplifier series R&S BBA300-CDE for 380 MHz to 6 GHz and R&S ...

UMS’s latest bare-die amplifier covers 27 to 31 GHz and provides 5 W of saturated output, yielding 23% and 24 dB of gain.