Optimum load impedance estimation for high-efficiency microwave power amplifier based on low-frequency active multi-harmonic load-pull measurement

An accurate design method for high-efficiency microwave power amplifiers based on a low-frequency active multi-harmonic load-pull measurement has been developed to obtain the optimum load impedance. Nonlinear capacitances as parasitic elements in a transistor are taken into account to improve accuracy of the optimum load impedance estimation in comparison with a previous method in which they are approximated with linear capacitances. A GaN HEMT amplifier designed and fabricated by the proposed method achieved a maximum power added efficiency (PAE) of 74% with 30.5 dBm output power at 2.13 GHz. As a comparison, a GaN HEMT amplifier designed and fabricated by the previous method exhibited maximum PAE of 64% with 31.0 dBm output power at 2.14 GHz, which was degraded than that for the proposed method.