An inverse-class-F power amplifier at 2.4GHz using a novel harmonic tuner based on a composite right/left handed (CRLH) transmission line (TL) is proposed and experimentally tested. The structure uses one series CRLH-TL and one open CRLH-TL to suppress 2nd, 3rd harmonics and to match to 50 Omega the fundamental frequency. The interesting properties of the CRLH-TLs allow a size reduction of the harmonic trap as well simplification of the design. The proposed tuner is used to design an inverse-class-F power amplifier with a maximum drain efficiency of 58%