Al-Tarifi, MonjedMonjedAl-Tarifi2025-12-052025-12-052023 the A2023http://hdl.handle.net/10197/30809This thesis proposes two high efficiency power amplifier designs for the Fifth Generation (5G) communication system applications using Gallium Nitride (GaN) High Electron Mobility Transistors (HEMT). The first design focuses on the direct integration between the power amplifier (PA) and the antenna at the radio frequency (RF) transmitter. A high efficiency amplifier is achieved by manipulating the antenna to the optimum load of the transistor instead of matching the PA and the antenna to the standard 50 Ohm. A slot antenna is modified to match its fundamental impedance to the optimum load at the packaged transistor's drain, and to terminate the second harmonic to achieve a continuous inverse class-F mode. The simulation results show an over 68% power added efficiency (PAE) over 3.5-4 GHz band. In the second work, a dual-band sequential load modulated balanced amplifier (DB-SLMBA) design is proposed by designing a dual-band branch-line quadrature coupler in the LMBA architecture. The design is based on recent developments of the load modulated balanced amplifier (LMBA) to achieve high efficiency at deep output back-off (OBO) power. The design can afford dual-band operation with wide bandwidth at each band; 2.4-2.75 GHz at the first band and 3.35-3.6 GHz at the second. The simulation results shows a drain efficiency of 53.5%-78.1% at saturation and 44.3%-53% at 12 dB OBO power.enPower amplifierAntennaIntegrationLoad modulated balanced amplifierDual bandMaster Thesishttps://creativecommons.org/licenses/by-nc-nd/3.0/ie/