Efficiency enhancement of Doherty amplifier with combination of class-F and inverse class-F schemes for S-band base station application

A new efficiency enhancement technique for the Doherty amplifier for use in S-band base stations is presented. The proposed technique includes a scheme in which the carrier amplifier operates under the class-F condition, while the peak amplifier operates under the inverse class-F condition. In a conventional Doherty scheme, however, both the carrier and the peak amplifiers operate at the same operational class. Theoretical analysis projects that the back-off power level from the power saturation to obtain the peak efficiency is improved from 6 dB for the conventional scheme to 8.2 dB for the proposed design. The saturation output power is also projected to be improved by 1 dB. The fabricated amplifier being verified exhibits a 45% efficiency at 10 dB back-off. This paper describes the advantages of the proposed design scheme by showing theoretical analyses and a circuit design followed by experimental verification at 2.1 GHz.