A Simple Stepped-Impedance Transmission-Line Load Network for Inverse Class F Power Amplifiers

In this letter, a novel simple load network with harmonic tuning which is based on a stepped-impedance transmission line is presented. Based on effect of a spectrum narrowing when poles of the reactance function are approaching adjacent zeros with higher transmission-line impedance ratio, an open circuit at the second harmonic and a short circuit at the third harmonic are achieved, thus satisfying inverse Class F conditions. Design example of the load network with second- and third-harmonic tuning and effect of the device output shunt capacitance Cout and series inductance Lout with design equations are also described and analyzed. Key words: RF power amplifier, load network, harmonic tuning, Class F, inverse Class F, stepped-impedance transmission line. 1. INTRODUCTION