A low-intermodulation, high-efficiency harmonic-controlled amplifier for high-power applications in mobile communications satellites

Recently, research and development of mobile communications satellites has progressed in every country, and the key technologies for improvement have increased the output power and efficiency of solid-state power amplifiers used in high-output transponders for satellite payloads and decreased intermodulation distortion during multicarrier amplification. This paper describes the design method and experimental results for a harmonic-controlled amplifier (HCA) having a theoretical efficiency more than 20 percent higher than existing solid-state power amplifiers (SSPAs) and with nearly the same amount of intermodulation distortion. The HCA is a new type of SSPA which uses the harmonics to produce an amplifier with high efficiency in low-distortion operation. Its operation is analyzed theoretically and experimentally, and new design methods are clarified. The HCA's output power is designed to be below saturation, and the output circuit is designed so that power-added efficiency is maximum in the intermodulation distortion region. Experimental results show that at 69-W output power in the UHF band, power-added efficiency was SI percent. At 110-W output power in the S band, power-added efficiency was 42.5 percent, intermodulation distortion was 20 dBc in the UHF band, and 23 dBc in the S band (output back-off 3-dB point).