HF outphasing transmitter using class-E power amplifiers

Chireix outphasing systems have been used successfully with power amplifiers operating in class-B and F. However, when class-E PAs are used in these systems, either the efficiency or the dynamic range is poor. The asymmetric combining technique described here uses transmission lines or equivalent networks of different electrical lengths to position the impedance loci to provide good dynamic range while maintaining high efficiency. This in turn allows linear power amplification of amplitude-modulated signals with high average efficiency. The concept is verified by a 28-W PEP transmitter that operates at 1.82 MHz and achieves an efficiency of 85% or better over an amplitude range of 10 dB.