distances of 400 miles or more, consideration should be given to high-voltage DC (HVDC) since it can be used to improve the stability of the AC system to which it is connected. One important area of concern from the EMI point of view is harmonic reradiation and scattering from the rectenna. There are enough scattering mechanisms for harmonics from the diode rectifier and associated noise to warrant the question of meeting current requirements. In the baseline design, two low pass filter sections which attenuate the second and higher order harmonics by over 25 dB are used. More filter sections add approximately 17 dB more suppression, each at a cost of approximately 1% efficiency loss. Other alternatives, also with an efficiency penalty, are to use stub line filters or full wave rectification. All of these approaches have mechanical configuration problems that, while solvable, will increase rectenna diode array assembly costs. These will be subjects of further SPS investigation. Scattering losses due to Fresnel edge diffraction are estimated at between 1 to n. Optimization of a rectenna system design to minimize costs is carried out at several levels. The rectenna size is determined by the point where the incremental rate of return from sales of the intercepted power are marginal. Much of the cost of the rectenna is in the structural support material required to support it against wind drag and snow loads. The present rectenna panel support structure evolved from stiff edge-supported panels to a hierarchial more centrally supported frame which uses much less material. Construction of the rectenna is, by necessity, highly automated. Starting with prefabricated dipole assembly components, a dipole machine manufactures complete dipole/diode assemblies at a high rate. These are then combined with other prefabricated parts to manufacture receiving element sticks. The sticks, metal frame and ground plane are then tack-welded together to form panels. The completed panels are then taken to the rectenna site where specialized equipment prepared the site through the emplacement of panel support arches. The panels are then lowered on the support arches, fastened and connected electrically. The rectenna cost breakdown is indicated below for a 5 GW installation:
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