The continuing trend toward greater capacity and higher d a ta rates in wireless commu nication systems places increasing dem ands on the radio frequency (RF) power provided by base station transm itters. Conventional R F power amplifiers (PAs) in use today have poor operating efficiencies and require considerable additional power and volume for heat removal. Research on more efficient PA technology is therefore im portant to the growth of the wireless industry. This thesis investigates high-efficiency switched-mode microwave power amplification using a new transistor technology, the Gallium N itride on Silicon High Electron Mobility Transistor (GaN-on-Si HEM T), which promises to deliver high o u tp u t power levels at lower cost th an the alternative GaN-on-SiC technology. The principles of power devices and power amplification modes axe discussed. A new large-signal equivalent model is developed for a 2 mm GaN-on-Si HEM T over the 0 GHz -20 GHz range, based on measured data. The chosen EEsof GaAs nonlinear HEM T model reproduces th e GaN transistor's behavior reasonably well over a large range of bias conditions, signal levels, and frequencies, although several param eter assum ptions are made. Based on this model, the design, optim ization, fabrication and testing of a 3.5 GHz, 1 W, Class E power ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.amplifier proceeds. The PA design is successful, w ith measurements revealing a gain of 10.7 dB, w ith an output power of 942 mW , and a power-added efficiency of 40.4%.This work shows the suitability of lower cost GaN-on-Si transistor technology for switched-mode microwave power amplifiers w ith possible applications in W iMAX base stations. It is recommended th a t further device modeling and other switched-mode am plifier topologies be investigated.iii Reproduced with