CLASS-F POWER-AMPLIFIERS WITH MAXIMALLY FLAT WAVE-FORMS

Class-F power amplifiers (PA's) employ harmonic-frequency resonators t o shape their drain or collector waveforms to improve efficiency, Gene rally, the output network must present the drain with either an open o r short circuit at the harmonic frequencies, At VHF and higher frequen cies, the drain capacitance, lead inductance, lead length, and dispers ion make implementation of reasonably ideal tuned circuits difficult. However, it is possible to control the impedances at a finite number o f harmonies, This note first derives the basic relationships among the Fourier coefficients of the waveforms and the performance of the ampl ifier, Fourier coefficients for maximally hat waveforms are then deriv ed for inclusion of up to the fifth harmonic, Amplifier performance is then tabulated as a function of which harmonics are included in the v oltage and current waveforms, Efficiency increases from 50% of class A toward 100% as harmonics are added, Power-output capability increases by up to 27%.