distance from the microwave transmitter array. (The klystrons emit significant levels of x-rays since electrons of up to 45 keV are constantly bombarding the metal collector plates.) Access to all parts of the power satellite would probably have to be provided by electric crawlers running along the support structures. The crawlers could carry enough shielding to shelter the crews from solar flares. 2.5 Rectenna The receiving antenna array (rectenna) on the ground converts the microwave beam into DC electrical power. The Reference Design system assumes that the DC power will be converted to high voltage alternating current for distribution via existing transmission systems in industrialized countries, including the United States. Power collection antennas. At the surface of the Earth the circular crosssection of the microwave power beam contains 88% of the total power within a 5 km radius of the centerline. At a latitude of 34°, the '’footprint" of the beam is an ellipse 10 km wide (east-west) and 13 km long (north-south) . The microwave power is collected by half-wave dipoles feeding Schottky barrier diodes (a kind of solidstate rectifier). Dipole panels arranged in east-west rows covering the 10 km by 13 km footprint of the power beam provide a total active area of 78.5 km^2 . A total of nearly 11 billion dipoles is required for each 5 GW rectenna site. Power conversion and conditioning. Power from a few dozen dipoles is gathered together and fed to the Schottky barrier diodes through two-stage low-pass filters to suppress reradiation of harmonics by the dipoles. Support structures. The dipoles and diodes are mounted on panels of steel mesh and lightweight steel framing. Panels are mounted, inclined, in rows aligned east- to-west, supported by steel posts implanted in concrete footings in the ground. For ease of access, the panels should be as low as possible; for alternate land use beneath the rectenna, it would be advantageous to elevate the panels several meters above the ground.
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