The purpose of the invention was to increase the operational power levels of solid-state power amplifiers using state-ofthe- art power amplifier design and combining methodology. Using 1-kW RF modules and proper RF combining techniques, a system was built that generated 16 kW of RF power for use in electric plasma propulsion. The 1-kW units were fault-protected against excessive power, excessive current, and high VSWR, since the RF power devices are extremely sensitive to variations in their operating conditions.

The main components of the architecture are power amplifier modules (power levels can vary widely), 4-port hybrid combiners/splitters, and automatic level control (ALC) control/protection circuitry. The power amplifier modules increase the input power to levels sufficient to satisfy design requirements. Each module is fed a signal that is amplified and then sent to the power combiners where that output is fed to more power combiners to achieve the final 16-kW power level.

The most pronounced unique feature is the ability to generate tens or even hundreds of kilowatts of RF power by combining smaller-stage amplifiers with significant weight reduction when compared to vacuum tube amplifiers. A second unique feature is the graceful degradation of power output. For example, should a stage quit operating the combining techniques as well as the power amplifier stage control circuitry, the overall amplifier will continue to operate, albeit at a reduced power level.

The main advantage of the solid-state multi-amplifier configuration over current large power level amplifiers is the overall savings in weight. Normally, a vacuum tube amplifier weighs approximately 1 to 5 lb (≈0.5 to 2.3 kg) for every 1 W of output power, whereas the solid-state amplifier system generates 1 W for every 0.1 to 1 lb (≈0.05 to 0.5 kg), depending on the power levels involved.

This work was done by William Sims and Greg Chavers of Marshall Space Flight Center, and James Richeson of ICRC. For more information, contact Ronald C. Darty, Licensing Executive in the MSFC Technology Transfer Office, at This email address is being protected from spambots. You need JavaScript enabled to view it.. Refer to MFS-32438-1.

NASA Tech Briefs Magazine

This article first appeared in the November, 2015 issue of NASA Tech Briefs Magazine.

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