How can I calculate power consumption of the amplifier from its datasheet?
This is not an amplifier, it's GaN HEMT where the T stands for Transistor. With such a transistor you can build an amplifier.

You choose a very niche type of transistor, it is designed for high power (more than 100 W) RF applications up to 2.5 GHz. I wonder why you have chosen this type of transistor as it requires a lot of experience to work with them.

By that I mean that this transistor must be used in a certain way, things to consider are:


what is the frequency (band) of interest to you
how much signal gain do you design the amplifier for
what biasing voltages and currents are then needed
what will be the matching components at input and output
signal distortion, a trade-off against efficiency must be made
what cooling solution will you use


To get an indication, from the datasheet, in their 1 GHz measurement / testcase the saturated power is 100 W at an efficiency of 56 %. That means that about 178 Watt is consumed in total. And output is 56% * 178 W = 100 W. So about 78 W is dissipated as heat. That's a lot, good cooling is needed at this power level.

This is just one example case, for your particular case the numbers will be different.