Earth’s surface as a function of the distance to the beam center. Comparing the U.S. and the USSR microwave exposure limits, one can find a difference of three orders of magnitude, from 2 2 10 mW/cm to 0.01 mW/cm . Since there is relatively little known about the effects of microwave radiation on biological life, we think that the public should not live in an area, where the 2 power density is higher than 0.01 mW/cm until total safety is guaranteed for higher levels. The power level remains beneath this limit beyond the second sidelobe at a radius of 15 km from the beam center. Within this radius no habitation should be allowed, but exposure to people for some hours in an area between 15 km and 10 km radius might 2 be accepted, because the power density does not exeed 0.02 mW/cm . This area is furtheron called safety zone 2. The area between 10 km and 5 km radius (rectenna edge) has power densities up to 2 1 mW/cm and will be called furtheron safety zone 1. Only short time exposure should be allowed here or longer time exposure with special shielding suits or vehicles. It should be noticed, that this definition of safety zones is only for the purpose of calculations within the scope of this study! II.1.4 Calculation of Rectenna and Safety Zone Sizes as a Function of Latitude and Longitude Offset Some limiting conditions result from the geometry of the microwave beam. The special literature reports the size of the elliptical rectenna near 40° latitudes as 10 km for the short axis and around 14.5 km for the long axis (South-North-axis for rectennas without longitude offset). The following calculation presents the sizes of the ellipse axis and the areas for the rectenna and the safety zones in a latitude range from 36° to 72° with longitudinal offsets up to 35°. For reasons of simplicity the rectenna sites have been considered as tangential planes to an ideal spherical Earth-geometry. The short axis varies in a very small range due to the expansion of the microwave beam. This range is from 9.92 km for 36° latitude to 10.44 km for 60° latitude for the rectenna. Since the variations of the long axes are much greater, the short axes are not drawn in fig. 1.3. This figure shows the variations
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