Optimum Harmonic Load Prediction for RF Power Amplifier Design Using Polyharmonic Distortion Models

This paper addresses optimal load reflection coefficient prediction in nonlinear radio frequency (RF) power amplifiers (PAs) under large-signal conditions. Traditional measurement-based black box behavioural models are limited to predicting the optimal load at the fundamental frequency. However, as seen in harmonically-tuned amplifiers, the load at the harmonic frequencies can have a significant impact on output power and efficiency. In this work, an harmonic X-parameter model is extracted from a 10 W Cree CGH40010F GaN HEMT device. For the first time, optimum higher-order harmonic load predictions are reported through a constrained optimisation of this multi-harmonic X-parameter model. The results are validated numerically against measured load-pull data at the fundamental and against data simulated directly from a Cree CGH40010F device model for the higher-order harmonic frequencies. The results show that the extracted X-parameter model can predict, very accurately, the optimum loads at both the fundamental and second harmonic frequency.