ten-meter separation between adjacent subarrays is sufficient for accuracies of 0.1 minute of arc (2.45 GHz pilot beam frequency and one degree phase error detection capability). The receivers at C, in adjacent subarrays, are used to resolve phase ambiguities which could be troublesome at the larger separations between receivers A and B. These will be at or near the center of the antenna, so that three receivers, compared in two pairs, suffice. At 2.45 GHz, one wavelength is equivalent to 0.7° pointing error. Since the acquisition mode is expected to be at least this accurate, it should not be necessary to resort to additional frequencies for phase ambiguity resolution. If the pilot beam utilizes a lower frequency, the allowable acquisition error can be even greater. Since existing receivers are used, the only weight associated with the system is the wiring from the receivers, the phase comparators and the computer. For reliability, several receivers and comparators at each location will be used, with their outputs averaged and out-of-tolerance data rejected. Since the cost is minimal, it may be desirable to make the pointing system separate from the retrodirective phase control system.
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