Analysis of Highly Efficient Self-Synchronous Class-F Microwave Rectifiers Using Waveform Engineering

In this paper, a class-F rectifier based on a $\mathbf{0.25}\ \mu\mathbf{m} \mathbf{6x80}\ \mu\mathbf{m}$ GaN HEMT is investigated using a waveform engineering load-pull/source-pull measurement system to emulate the required harmonic impedance environment. The resulting voltage and current waveforms are de-embedded to the intrinsic current generator plane and then analysed, allowing for the first time a detailed waveform based investigation of this type of high efficiency microwave rectifier. The demonstrated rectifier is shown to have an efficiency of more than 90% over an input power range of 12 dB, reducing to only 80% over an input power range of 25 dB. The gate impedance condition for efficient self-synchronous operation is analysed and verified using measurements. These measurements also demonstrate the effect of an imperfect gate termination. Importantly, these measurements also present new insights into dispersion between measured DC characteristic and the dynamic RF load-line. Despite exhibiting dispersion in the first quadrant, no dispersion is observed in the third quadrant of the IV plane for different DC load impedances and power levels and thus DC voltages.