UHF Class-E Power Amplifier Based Upon Multi-harmonic Approximation

At high frequencies class-E power amplifiers operation is limited by the device drain parasitics so that true transient operation is not possible, hence harmonic approximation is used based upon the second and/or the third harmonic control using either transmission-line or lumped element resonators. The class-E amplifier described in this paper employs a multi-harmonic network to control the device reactances at intrinsic drain up to ten harmonics. Based upon classic design equations, the impedances are close to their optimum values for lower-order harmonics producing 90% efficiency for an ideal device resembling true-transient class-E operation at high frequency. Nevertheless, a working prototype presents an efficiency of 85% with 10-W output power at 400- MHz fundamental-frequency using a GaN FET.