7.2.2 BIT WIGGLE Figure 7-11 demonstrates the bit wiggle approach. The phase shifter in one subarray is phase modulated by switching between at a given rate. The signal received on the ground has a large carrier (all subarrays) and a weak sideband (subarray under test). The sideband is filtered and phase compared with the modulating reference. Providing the same modulating reference at both the transmit array and the ground introduces the reference distribution problem. The modulating reference could be transmitted periodically and a local oscillator could be phase locked to the received signal. Good filtering of the sideband is required so that the carrier does not introduce an error in the measurement. 7.3 CONCLUSIONS AND RECOMMENDATIONS Both adaptive and command approaches will be needed. The adaptive has the accuracy and rapid response potential needed for maximum efficiency the command has the safety and backup features of a ground based monitoring system that is essential to an acceptable control scheme. The command scheme favored is the phase estimation technique which appears less complex and more likely to succeed than the bit wiggle approach. The bit wiggle technique may find a role as a diagnostic tool in assessing the status of individual subarrays on a periodic basis. These may be more briefly stated as follows: a. Adaptive (retrodirective) approach needed for maximum efficiency. b. Command approach needed for safety and back-up. c. Calibrated transmission line and/or subarray-to-subarray transfer of reference phase data for adaptive phase control mechanization. d. Phase estimation for command mechanization. e. Investigate bit wiggle technique as diagnostic tool. f. Detailed investigations should be conducted to minimize phase control electronics costs, weight, and blockage for each subarray.
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