0191-9067/81/010151-04$02.00/0 Copyright ® 1981 SUNSAT Energy Council SOME ASPECTS OF ANTENNA TECHNOLOGY FOR EUROPEAN SPS R. V. GELSTHORPE, B. CLAYDON, and A. W. RUDGE RF Technology Centre ERA Technology LTD. Leatherhead, Surrey, UK INTRODUCTION A geostationary orbiting solar power satellite system has been proposed by NASA. It consists of a 50 km2 array of photovoltaic cells which utilizes solar energy to generate electrical energy for transmission to earth. The NASA reference system design employs a 1 km diameter phased array antenna powered by over 100,000 klystrons to transmit this energy to earth in the form of a highly collimated beam of microwave energy at a frequency of 2.45 GHz. This energy is intercepted by means of a ground receiving/rectifying antenna (rectenna) which consists of a large number of individual dipoles (~ 1010). Associated with each dipole, there are a number of filters and a Schottky diode rectifier which converts the incoming microwave energy into direct current. The receiving elements are mounted in rows of reflecting panels which are inclined such that the incoming energy from the satellite is at normal incidence. At latitude 52°, the rectenna site would occupy an ellipse having a N-S axis of length 16 km and an E-W axis of length 10 km. Due to the fact that the transmitting antenna is illuminated with a truncated Gaussian power distribution, there is a power density variation across the rectenna from 23 mW/cm2 at its centre to 1 mW/cm2 at the edge. The upper limit of 23 mW/cm2 is established as the maximum power density which may be transmitted through the ionosphere before the onset of nonlinear heating effects. INCREASE OF SYSTEM EFFICIENCY FOR EUROPEAN APPLICATION In an area such as Western Europe, the implementation of such a system could pose significant problems since large populations might have to be displaced in order to create the vast areas required for rectenna sites. Even in areas of the world having sparsely populated terrain suitable for this purpose, it may be necessary to locate the rectennas more closely to centres of high population since this leads to minimum transmission line losses. Due to the large land area requirement there may be a considerable shortfall in land-based sites and a probable alternative is the use of sea-based sites.
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