7. 3 MICROWAVE POWER SYSTEM For all SPS concepts under consideration, the microwave system is a common element. Current SPS system concepts require microwave antennas to be capable of transmitting several gigawatts of power at 2. 45 GHz. The microwave system is currently focused on a 5 GW system. 7. 3.1 REQUIREMENTS AND ANALYSIS The microwave power system consists of those elements that are necessary to receive power from some source, transfer it across a rotary gimbal system, convert it to RE, form a nearly coherent beam, and transmit it from synchronous orbit to Earth with high accuracy. The current baseline microwave system consists of two major subdivisions, each contributing to the overall efficiency of the system. The major components are: (1) the 1 km transmit array with its power distribution system, dc-RF conversion devices, phase control subsystems, and radiating waveguide; and (2) the 8. 5 x 11 km rectenna for receiving the RF energy, efficiently converting it to de, and recombining in an appropriate manner for practical power distribution systems. The manner in which the efficiencies of individual devices and systems are weighted in producing an end-to-end dc-to-dc efficiency of 58 percent is indicated in Table 7-15. These efficiencies ultimately determine the performance of the system. TABLE 7-15. MICROWAVE POWER SYSTEM EFFICIENCIES
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