Development of load modulated power amplifiers for communications in sub-6 GHz bands

The rapid evolution of wireless communication has led to greater demands on higher data rates and wider spectrum. Being the final stage of the transmitter chain, power amplifiers are driven to adopt signals with high peak-to-average power ratio. Therefore, they play a crucial role and encounter more stringent challenges in terms of achieving wide operational bandwidth and high efficiency at output power back- off. This thesis presents the analysis, design and implementation of an RF-input sequential Load Modulated Balanced Amplifier (LMBA). This architecture is able to modulate the impedance seen by a pair of power amplifiers in a quadrature balanced configuration, by modifying the amplitude and the phase of an external control signal injected into the isolation port of the output coupler. Compared to conventional single-ended or Doherty power amplifiers, LMBAs extend better the high-efficiency power range and are able to achieve high back-off efficiency across a wider bandwidth. A hybrid prototype is designed and simulated, based on commercial 10W GaN packaged transistors, to achieve highly efficient performance in the N77 frequency band (from 3.3GHz to 4GHz) at 9dB output power back-off. The simulation results achieve a wideband performance with 60% drain efficiency and 40% power added efficiency for maximum output power above 44dBm, and 50% efficiency and 40% PAE for 9dB back-off. Future developments of this thesis work would be the measurement and verification of the fabricated circuits.