Systematic Design of a Compact Lumped-Element Outphasing Class-E Power Amplifier for HF Band

This paper presents a novel design methodology for an outphasing Class-E power amplifier operating at 27.12 MHz, specifically addressing limitations inherent to traditional outphasing combiners that utilize distributed microstrip transmission lines for harmonic termination. At MHz frequencies, conventional microstrip techniques become impractical due to excessively large physical dimensions. To overcome this, the proposed design employs an entirely lumped-element combiner network, eliminating the need for distributed microstrip harmonic terminations. A rigorous analytical framework is derived using two-port impedance matrices, ensuring simultaneous impedance matching at both peak and back-off power conditions. Parametric studies optimize component values, resulting in enhanced efficiency and stable output power across a broad range of outphasing angles. A prototype employing GaN-based transistors demonstrates high efficiency of 73.2% at peak output power and maintains above 50% efficiency at 6 dB output back-off, validating the effectiveness and practicality of the proposed lumped-element approach. This compact and efficient configuration offers significant advantages for MHz-band RF transmitters and wireless power transfer systems.