Figure 7-4. Phase Front Control Approach Comparison 7.1 ADAPTIVE PHASE FRONT CONTROL The variations in the propagation conditions through the ionosphere and atmosphere have negligible effects on the efficiency of power transmission or location for reception because (1) the path length from the media to earth is short, and (2) the rectenna (described in Section 9) is insensitive to phase variations. However, the media introduces variations of phase across the transmitting antenna that in principle could interfere with an adaptive scheme if the variations were significantly large across the array and occurred in a time interval comparable with the propagation transit time from earth to the satellite in geosynchronous orbit. These effects are estimated, in Section 3, to have correlation lengths long with respect to the transmitting antenna and to have correlation times long with respect to the propagation time, so that the adaptive approach should be feasible for correcting distortions at the transmitter. It potentially is the most accurate of the techniques examined in that it can resolve errors down to a single subarray and has rapid response.
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