Values of these parameters (except B and t)b) are displayed graphically as functions of h in (8). The case h = 0 corresponds to uniform illumination with its -17.6 dB first sidelobe, while larger values of h lead progressively to lower sidelobes. CHARACTERISTICS OF THE MAGENTRON-POWERED SPS In this system, waste heat from the magnetron tubes, each generating 3.5 kW of RF power, is dissipated by means of pyrolytic graphite discs attached to the tubes. Calculations show that a maximum of 28 kW of RF power can be generated for each square meter of spacetenna surface while maintaining a satisfactory operating temperature. Thus, ST = 28,000 W/m2. The allowable power density in the ionosphere is not yet known with certainty; a conservative estimate, used also in the klystron system, puts at 23 mW/cm2 (230 W/m2). For the baseline or reference system a modestly tapered illumination was chosen that results in an environmentally safe power density level at the peak of the first sidelobe. The taper level, -9.54 dB or 1/9, corresponds to h = 2.378 and results in a sidelobe level of -23.2 dB. The associated power density is slightly above 0.1 mW/cm2. The parameterss K and £ have the values 0.436 and 0.914, respectively. The reference system design further calls for the rectenna to intercept the spacetenna beam at the 1 mW/cm2 density contour level, i.e., 13.6 dB below the beam peak. This fixes the beam efficiency and beamwidth constants, = 0.937 and B = 2.20 rad. It is proposed that a safety fence be located at the 0.1 mW/cm2 contour, where BF = 2.60 rad. Finally, the two catch-all efficiency factors rf and rj" have been estimated to be 0.7476 and 0.8172, respectively, while r)H = 0.99. When these numbers are used in Eqs. 5 through 9, assuming a rectenna located at 40° latitude (R - 37,500 km), the system characteristics are uniquely determined and are shown in Table 1.
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