Microwave Power Amplifiers - The in-depth study performed by Raytheon in 1975 (ref. 23) on the microwave system focused on investigation of the amplitron (crossed field amplifier) and the klystron (linear beam amplifier). The amplitron was characterized by high efficiency and low gain, while the klystron was characterized by high gain, low noise levels, and moderately high efficiency. Trade-offs were performed on amplitron versus klystron tube parameters, as well as on integration into the microwave system. The study concluded that either 5 KW amplitrons in series, or 50 KW klystrons in parallel could be used. The MSFC study, concluded in November 1976 (ref. 3) selected the amplitron for initial study because of the possible efficiency and lifetime advantage, and so that electrical operation and mechanical integration into the overall system could be analyzed. The JSC studies concluding in August 1976, investigated both the amplitron and the klystron. Traveling wave tubes and solid-state amplifiers were also investigated. It was concluded at that time that both the amplitron and the klystron exhibited the best potential for use on the SPS, with the edge being given to the klystron because of system implementation considerations. The major advantages of the klystron were: (a) much higher power per tube, thus simplifying initial assembly and installation operations, and ameliorating the maintainability requirements-, (b) higher operating voltage, thus reducing power distribution system weights; (c) much lower phase control drive power; and (d) lower RF noise characteristics. The Boeing studies (ref. 5,7,8,9) chose the klystron as the amplifier to investigate further, and performed an in-depth, comprehensive study of klystron configurations, integration into the microwave system, maintenance scenarios, manufacturability, cost, weight, etc. The study demonstrated that a klystron can be integrated into an overall SPS and it does have certain advantages. A comparison of features of the amplitron and klystron designs is shown in Table II.
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