interference levels at large distances from any given rectenna because of frequency allocation problems. The SRS downlink power beam lies in the 2400-2500 MHz frequency band which has been reserved for Government and non-Government industrial, medical, and scientific (IMS) usage. By definition, anyone operating in an IMS band must accept interference from any other user within this band. However, this 100 MHz band is not recognized by some of the eastern European countries which reserve 2375 MHz + 50 MHz for the IMS band. The far sidelobe levels as shown in figure 19 indicate the peak levels for one 5 gigawatt SPS system are three to four orders of magnitude below 0.01 mW/cm . For simultaneous operation of 200, 5 gigawatt SPS systems, the average peak level is still one to two orders of magnitude lower than 0.01 mW/cm2. Grating lobes, which occur at 440 km intervals from the rectenna, are functions of subarray size and mechanical misalinement of the subarrays within the 1 km phase array. The grating lobes occur at spatial distances corresponding to angular directions off axis of the antenna array where the signals from each of the subarrays add in-phase. When the boresights of the subarrays are not alined with the uplink pilot beam transmitter at the rectenna, the unwanted contributions of the array factor of the antenna do not lie in the null-points of the subarray pattern as shown in figure 20. Even though the phase control system will still point the composite beam at the rectenna, some energy will be transformed from the main beam into the grating lobes. The amount of energy in the grating lobes depends upon the misalinement (or how far the array factor is displaced from the null points of the subarray pattern). These grating lobes are somewhat unique in that they do not spatially move with misalinement changes, rather they are stationary with an amplitude dependence upon the mechanical misaline- ments. This behavior is due to the operating characteristics of the retro- directive phasing system. Based on environmental considerations, the grating o lobes are constrained to be less than 0.01 mW/cm . The total mechanical aline- ment requirements for both the subarrays and the total array can be determined from this constraint. The 10.4 meter X 10.4 meter subarray which is considered
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