how design microwave power amplifier?

can you be bit specific about the application?

Firstly, you need to choose a device with the power you require over the frequency range (try Toshiba, Fujitsu)

Use the Cripps method to design the output match point (see Cripps book)

In order to achive the bandwidth (2 octaves - quite large) you will need to have a broadband match at the output

use the TWT