Efficiency and linearity of power amplifiers with external harmonic injection

This paper discusses a method for improving the efficiency of linear power amplifiers by externally injecting power into the output at the second harmonic frequency. An experimental proof-of-concept PA based on class-A/AB mode with a 10-W GaN pHEMT at 2.45GHz is presented, and its efficiency improved from 58% to 75% with −6.5 dBc injected 2
^nd
harmonic power. Two-tone measurements confirm improved linearity with simultaneous increase in efficiency, accompanied by gain compression at higher input power.