Efficiency and Linearity Enhancement of a Broadband Continuous Class-F PA Using Harmonic Injection

A broadband continuous class-F power amplifier (PA) is presented with active second-harmonic injection to enhance drain efficiency and linearity. Based on waveform analysis, the higher efficiency of the class-F power amplifier is achieved through injection of the second harmonic into the drain node of the transistor. The required power and the load impedance of the fundamental and the second harmonic input signal are calculated to guide the design using an expression for the waveform. The drain efficiency of a measured prototype is larger than 69% within 1.0 GHz-1.6 GHz, which is about 5% higher than the class-F PA without harmonic injection. The measurement results show that the third-order intermodulation (IMD3) is also improved at saturation power levels with appropriate second harmonic injection.