Linearization of efficient harmonically-injected PAs

This paper presents a technique for improving the linearity of a power amplifier using external second harmonic injection at the output. The amplifier is biased in class-A mode with no harmonic terminations in the output network and 50 % drain efficiency at 1 dB compression point. External second harmonic injection at the output is used to shape the drain voltage and current waveforms to minimize the odd order harmonic content produced by the amplifier, simultaneously reducing the total DC power dissipation. Both CW and two-tone measurements with 1 MHz tone spacing are performed on a 2.45 GHz 6-W GaN PA with harmonic injection at one of the two harmonic tones. The lower or upper sidebands for the IMD3 and IMD5 are reduced by > 15 dB and 10 dB respectively along with a 6% increase in the total drain efficiency.