antenna would be substantially less than the continuous microwave exposure standard presently accepted in the United States (i.e., 10mW/cm2). Within several kilometers beyond the receiving antenna, the microwave density levels drop to less than 1 pW/cm2(23). (See Figure 5.) The data in Figure 5 are for a total power of 1.17 x 107 kW for a single SSPS whereas the SSPS baseline design is for about half that value. The curves, however, indicate the significant decay rate with increased radius. FIGURE 5. - HYPOTHETICAL DISTRIBUTIONS OF MICROWAVE POWER DENSITY FROM THE BEAM CENTER (Ideal Gaussian) To achieve the desired high efficiency for microwave transmission, the phased-array antenna will be pointed by electronic phase shifters (24). Proper phase setting for each subarray must be established to form and maintain the desired phase front. Deviations can be detected and appropriate phase shifts made to minimize microwave beam scattering. A master phase control in the antenna will have to be developed if the microwaves are to be transmitted efficiently and the microwave beam always directed toward the receiving antenna (25). The master phase front control system can be designed to compensate for the tolerance and position differences between the subarrays by sensing the phase of a pilot signal beamed from the center of the area occupied by the receiving antenna to control the phase of the microwaves transmitted by each subarray. The pilot signal will be of a substantially different frequency than that of the microwave power beam, so wave filters could be used to separate them.
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