4W X-band high efficiency MMIC PA with output harmonic injection

This paper demonstrates a MMIC GaN X-band PA designed to have improved efficiency by second harmonic power injection at the output that helps shape the time-domain waveforms across the drain. The MMIC contains a class-AB PA with a nominal 4-W (36 dBm) output power at 10GHz and a small-signal gain of 14dB. The best results with harmonic injection were measured at 10.6 GHz with 3.5W (35.44 dBm) of output, showing an increase in drain efficiency from 48.5% without injection to 70% when 26.2 dBm was injected at 21.2 GHz. In order to maximize the total efficiency, which includes the efficiency of the injection circuit, a second harmonic efficient amplifier is integrated in the same GaN MMIC. The 20-GHz PA needs to provide a power on the order of P_out - 10dB, and is measured to output 27dBm with 8dB gain and PAE=59%. The relationship between the total efficiency and injector efficiency is derived and shows that the total efficiency is not appreciably affected by the injector efficiency if a second-harmonic amplifier with a gain greater than 6-7dB and with a PAE > 40% is employed.