Efficiency Optimization of Class-F Power Amplifier at Different Power Levels for Microwave Power Transmission

Power amplifier (PA) plays a key role in improving the overall efficiency of microwave power transmission (MPT) system. The efficiency deterioration of PA operating at lower output power is a challenge that restricts the application of MPT. To obtain the optimal efficiency of PA at different power levels, a power pulse width modulation (PPWM) method is proposed. According to the loss analysis and efficiency characteristics of class-F PA, it can be found that the drain efficiency (DE) of PA in pulse mode is higher than that in continuous mode. Furthermore, the optimal efficiency can be achieved by selecting a proper duty cycle at different power levels. A 5.8-GHz/20-W class-F PA is fabricated and tested to verify the proposed PPWM method and mathematical analysis.