High-efficiency linear amplification by dynamic load modulation

Load modulation is a new technique in which amplitude-modulated signals are produced with high efficiency by dynamic variation of the load impedance of the power amplifier. The prototype MOSFET PA operates in class E and produces a peak output of 19 W at 30 MHz with an efficiency of 66 percent. Load modulation is accomplished by a T network with a pair of high-voltage MOSFETs that act as a voltage-variable capacitor. The envelopes of a variety of different signals are successfully generated. For a Rayleigh (multi-carrier) envelope with a 10-dB peak-to-average ratio, the average efficiency is twice that achieved in linear operation of the same PA.