A technique for the maintenance of FET power amplifier efficiency under backoff

An operational technique for FET power amplifiers which allows the maintenance of high efficiency as the amplifier is backed off from its rated output power level is described. Using this technique, an experimental single-state 1-W C-band amplifier, capable of 65% power-added efficiency at its rated output power, maintains a minimum efficiency of 55% for a 10-dB output backoff range. Comparable amplifiers operating under conventional Class B or Class A demonstrate efficiencies of about 18% and 4%, respectively. An analytic basis for the technique is given. Experimental results are also presented for a three-stage, 2-W C-band amplifier.<>