In this article, 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 described and analyzed. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1157–1160, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25923