High-Efficient Inverse Class-F Power Amplifier Utilising Nonuniform Transmission Lines for Wireless Power Transfer

An RF power amplifier (PA) for wireless power transfer (WPT) differs from one used for communication. Particularly, a PA for WPT prioritizes efficiency over linearity. A switching-mode PA (SMPA) is thus ideal for this purpose. In this paper, we present a highly efficient inverse class-F SMPA utilizing nonuniform transmission lines (NUTLs). The load transformation network (LTN) ensures that at the fundamental frequency the optimum impedance and at the harmonics the corresponding impedances are presented to the drain of the transistor for an inverse class-F SMPA operation. A discrete 6W GaN transistor is employed in a prototype, which demonstrates a power-added efficiency of 72.7 % and a gain of 13.4 dB at 2.42 GHz. The measured second and third harmonic suppression are −38.5 dBc and −41 dBc, respectively.