For 18-26 GHz A-Class amplifier, you can not work with ordinary semiconductor companies such as NXP, Freescale..
If you have never designed an amplifier, to be honest forget this project.Eventough you designed some try-outs to learn something, it's really really hard for you and it needs so high experiences on amplifier design and layout.Because there is neither discrete bipolar nor discrete fet transistor working in this band with these output level and linearity (maybe few with lower specs.) .You have to work with some specialized foundries like Triquint,M/A-COM or Hittite etc. but there are many technological restrictions for some countries.
However good luck..