Boeing also surveyed current developments in solid-state amplifiers, and concluded they should definitely be considered, but were not emphasized in the studies. Devices surveyed included bipolar silicon, electron beam devices, GaAs IMPATTS, and silicon FET's. In approximately the same time frame, JSC also independently performed a survey of solid-state devices. Although no particular device surfaced as being an outstanding candidate at that time, subsequent research indicated that GaAs FET's showed significant potential. Rockwell studies (ref. 11) investigated amplitrons, klystrons, magnetrons, and solid-state power amplifiers. For purposes of performing trade studies on SPS integration issues, the klystron was also chosen. Similarities were evident between the Boeing study results and the Rockwell study results. Basic requirements for the klystron were similar, with some differences evident in implementation into the transmit antenna. The Boeing study developed a concept for a 70 KW klystron, integrated into a slotted waveguide power module, with 4 to 36 power modules per 10M X 10M subarray. Cooling is accomplished with 300°C body and 500°C collector heat pipes with passive radiators on the backside of each subarray. The Rockwell study developed a concept for a 50 KW klystron, integrated into a resonant cavity radiator with 6 to 50 klystrons per 10M X 10M subarray. Cooling is accomplished with body heat pipes dissipating heat on the front side of each subarray. Blockage of RF radiating slots is estimated to be approximately 3 percent; however, this was required because of the thermal environment on the backside of the transmit antenna. Continuing investigations into solid-state power amplifiers provide an increasingly attractive alternative to the power tube amplifiers, especially in the area of low noise and increased reliability. A concentrated technology advancement program is needed for solid-state, coupled with a comprehensive systems integration study.
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