High-Efficiency Power Amplifier Employing Minimum-Power Harmonic Active Load Modulator

There is an impedance conflict between the fundamental harmonic of f(2) and the second of f(1) if f(2) = 2f(1). In this brief, a methodology employing the harmonic active load modulation (HALM) technique is utilized for solving this problem. A main power amplifier and an active load modulator constitute the overall circuit. This technique transforms the second harmonic load impedance to the optimum by injecting second harmonic power in the lower band. In order to improve the overall efficiency, a method of searching optimal location parameter is proposed to achieve the minimum extra power in harmonic injection. A power amplifier (PA) working at 1.7 and 3.4 GHz is fabricated for validation. At 1.7 GHz, the HALM technique brings an improvement of 14% in overall efficiency and an increase of 0.7 dB in output power. As for 3.4 GHz, the fabricated PA delivers overall efficiency of 78.5% and output power of 41.3 dBm without HALM.