High-Efficiency Amplifiers with Discretely Variable Output Power

Space-based radar (SBR) requires multiple RF power amplifiers (PAs) to drive phased-arrays antennas. Control of the beam direction requires an amplitude range of 22 dB, and coupling between elements results in load impedances with significant mismatch. Both factors make conventional linear RF PAs very inefficient. The proposed approach employs a high-efficiency RF PA, class-S modulator, and electronically tuned matching network. The class-EF RF PA provides the best combination of efficiency and power output. Wide-bandgap transistors (e.g., SiC or GaN) provide significant output power with reasonable load impedances. The class-S modulator controls signal amplitude, allowing the RF PA to remain saturated for maximum efficiency. A digital signal processor removes amplitude variations due to heating of the transistors. The electronically tuned matching network adapts to impedance changes associated with changes in beam direction. The average efficiency is nearly triple that of a conventional PA. The corresponding reduction in dc-input power in turn produces significant savings in the cost of the satellite power system. The proposed Phase-II program is an experimental evaluation of technologies, culminating in a prototype system.