The subarray size selected is 11.64 x 10.2 m. Sets of nine subarrays are then supported by a secondary structure to form a 34.92 x 30.6 m mechanical module. The module is supported by connections to the catenary tapes of the compression-frame/tension-web which forms the primary array structure. The characteristics of the ten mechanical module types is shown in Table R-3. Included are the number of each type required in the baseline antenna array. Power Taper and Density on Antenna - The power level of all power module amplifiers is, by definition, the same. The size of the module radiating surface is varied to vary the power density over the total array area. For instance, with 50 kW klystrons and gaussian distribution, the number of modules per 11.64 x 10.3-m subarray varies from 50 at the array center to 6 at the array edge. The module area thus varies from 2.38 m2 to 19.79 m2 . The power density for the modified gaussian power distribution resulting from the selection of a 10-step approximation is shown in Figure R-18. Rectenna - The ground based element is the rectenna (Rectifying Antenna). The rectenna receives the energy transmitted from geosynchronous altitude at 2.45 GHz, converts the energy to de power and subsequently transforms and routes the energy to a form and level compatible with commercial requirements. Each rectenna is designed to accept power from a single satellite and provide 5 GW of power to the utility interface. As shown in Figure R-19, a typical rectenna site located at 34°N latitude covers an elliptical area 13 km in the north-south direction by 10 km in the east-west direction. This area contains 750 rows of rectenna panels tilted 40 degrees from the horizontal, 2 providing an active intercept area of 78.2 km . The phased array is comprised of stripline patterns of bow-tie dipoles, shown in Figure R-20. This selection was based primarily on the increased efficiency and decreased diode count. A summary of the rectenna characteristics is given in Table R-4. Figure R-21 presents an approximation of the power density at the surface of the rectenna array along the N-S axis. The limits of 23 mW/cm2 at the center,
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