SOLID STATE TECHNOLOGY David G. Weir RCA Laboratories A solid state transmitter could provide the SPS with long life, high reliability, graceful degradation, and low maintenance. These important characteristics are only secondary, however, to the need for high de to rf conversion efficiency. The key question today is, can 80% conversion efficiency be obtained? Analysis of numerous device concepts available for consideration eliminates all but a very few. The gallium-arsenide field effect transistor is today's first choice. Studies of theoretical models and experiments on existing devices seem to indicate that the GaAs FET has the potential for 80% de to rf efficiency. Size and hence power levels must be limited (1 to 10 watt range) for this to be so. NASA has sponsored theoretical device studies through Rockwell International and is now funding an evaluation demonstration program at RCA Laboratories. Samples of the best available devices are being evaluated for maximum performance and then built into demonstration amplifier circuits. A careful study of microwave waveforms is expected to help gain a better understanding of the critical mechanisms affecting efficiency and ultimately to provide parametric information for new device designs. Twenty-five devices of seven types have been tested to date. The best results are 60% efficiency at 5.1 watts and 72% efficiency at 1.2 watts. Two amplifiers were delivered in April, meeting the Task 1 goals of 5 watts, 50% efficiency, and 8 db gain. The waveform analysis has revealed a significant realtionship between efficiency and gate resistance. The results of this program, when completed later this spring, are expected to continue to show that 80% efficiency is achievable and to suggest valid ways in which this goal may be met.
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