Operating Characteristics: Based on system analysis data, the expected operating characteristics of the rectenna elements have been determined. The systems analysis data on which these calculations are based are as follows: a. A = 12 cm wavelength of transmitted beam. b. a = 10° phase error of transmitted beam. c. Amplitude error = +1 dB. d. Failure rate of Klystrons over 30-year period = 2 percent at any one time. e. 10 dB taper across transmitting antenna. f. Transmit antenna diameter = 1 km. g. Transmit antenna radiated power = 6.5 GW. An overall MW collection efficiency of 87.5 percent can be realized if a rectenna is selected which has a 10 KM diameter on the minor axis. Thus a rectenna located on the equator at the same longitude as the SPS would be 10 KM round. For a rectenna located in New Mexico (latitude = 35°N) the rectenna would be approximately 10 KM on its minor axis and 13.2 KM on its major axis. For a rectenna located near the New York City area (latitude = 42°N) the rectenna would be approximately 10 KM x 15 KM. To determine the power density reaching various points on the rectenna, the above systems analysis data were used. In addition, the reference system efficiencies for atmospheric attenuation were also included. The power densities thus determined for boresight and at the 5 KM radius points are shown in Figure IV-D-1 -5. Taking these figures, it can be determined what the incident microwave power is for each rectenna element. The calculations are based on the center frequency of 2.45 GHz and the corresponding rectenna element cell area of 53 cm2. These results are shown below: The rectenna element efficiency can then be determined by referring to Figure IV-D-1-6. Thus the rectenna element at the center has an RF/DC conversion efficiency of approximately 82 percent. The rectenna element at the outer edge (radius = 5 KM) has an RF/DC conversion efficiency of
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