History of Class-F and Inverse Class-F Techniques: Developments in High-Efficiency Power Amplification from the 1910s to the 1980s

Today, class-F amplification is a well-established technique for increasing the efficiency of RF power amplifiers (PAs). The increase in efficiency afforded by class F reduces power consumption and increases talk time, both of which are driving forces in the design of RF PAs. The operational efficiency of radio transmitters was of great interest right at the dawn of the development of high-power radiotransmission systems. Many if not most readers will be surprised to learn that the basic concepts of class-F amplification were discovered at the end of the 1910s, just a few years after the first vacuum tube transmitters were developed.