The aim of this chapter is to provide to the reader insights into field plate operation and itsgeometrical optimization. After giving some basic definitions concerning the operation of anRF-power device, which will be used in order to quantify the performance of the devicesstudied, the optimization of a gate-connected single field-plate GaAs-based pHEMT will bepresented. Field plate geometrical parameters will be varied in order to show how they canaffect device properties such as breakdown voltage, maximum output power and smallsignal performances. It will be thus possible to quantify the maximum improvement thatcan be achieved by using a gate connected single field plate. Finally, some advanced fieldplate structure will be discussed and compared in order to point out their advantages withrespect to the gate connected single field plate structure
