This paper presents a Class-E/F3 switching power amplifier (SPA) with reduced second harmonic leakage using parallel resonant circuit in series for the second harmonics. The proposed Class-E/F3 SPA has a structure utilizing a series resonant circuit in shunt for the third harmonic, designed to function as a shunt capacitor for the fundamental, and an additional parallel resonant circuit for the second harmonic, designed to operate as a series inductor for the fundamental. Using the proposed scheme, a Class-E/F3 SPA was designed and implemented for 6.78 MHz, and was evaluated with various supply voltages. It exhibited output power levels ranging from 10.26 to 59.98 W (40.11 to 47.78 dBm) with supply voltages ranging from 10 to 24 V. The efficiency was maintained at over 89.25%. Additionally, it demonstrated very low second and third harmonic distortion levels, each not exceeding −49.98 dBc, while the total harmonic distortion (THD) ranged from 1.54% to 2.15%.
