Satellite communications become more interesting because of an increasing number of satellite launches for especially Ku-band very small aperture terminals (VSAT). Recently, the systems push the frequency specifications towards millimeter-wave such as Ka-band. Also, the fifth generation mobile communications (5G) are expected to accommodate the forthcoming huge traffic demands with using millimeter-wave as well as sub-6GHz. Here, PAs have been always the working horse for RF frontend in any radio transmitters. In particular, advanced GaN PAs occupy the attentions with evolving to deal with ever-increasing system level requirements. This paper presents the prototyped results of state-of -the art GaN PAs for millimeter-wave applications and novel modelling techniques for their designs.