Comments on "Class-E, Class-C, and Class-F Power Amplifier Based Upon a Finite Number of Harmonics"

In this comment, we would like to call attention to a qualitative fact that the maximum attainable efficiencies of finite harmonic class C, contrary to the claim suggested in the above paper, differ from maximum attainable efficiencies of finite harmonic class-F power amplifiers (PAs). The difference is not significant and could be easily overlooked in numerical treatment of the problem. This probably explains how the claim came into being. The best way to prove that difference between efficiencies of finite harmonic class-C and class-F exists is to solve the problem in closed analytical form. In this comment, we provide closed form for maximum attainable efficiency of finite harmonic class-C using a famous Fejer's result which goes back to 1915.