Analysis and experimental waveform study on inverse class class-F mode of microwave power FETs

The new inverse class F operation mode for high-efficiency power amplifiers is analyzed. Unlike regular class F, it requires an open circuit termination at the second harmonic and a small impedance termination at the third harmonic. The inverse class F features higher PAE than class F but requires transistors with higher breakdown voltages. A study performed using the waveform measurement technique in conjunction with the active/passive load-pull system showed PAE=83% for the inverse class F compared to PAE=64% for the class F. The measured results are in good agreement with the analytical prediction.