AbstractIn 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 capacitanceCoutand series inductanceLoutwith 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