to bring the received signal phase into agreement with a reference phase, and then the transmitted signal is passed through the same phase shifter, and phase conjugation results. The heterodyning technique is recommended to be employed in the basis SPS (Solar Power Satellite) phase control system. The conjugation occurs by the process of heterodyning and sideband filtering. Referring to Figure IV-C-4-2, the incoming signal phase is 0R = wt-Br where w, t, b and r are as defined previously. The received signal is mixed (multiplied) by a reference signal of phase <f>Ref = 2 cot + 0R. The signals resulting from the multiplication process include sum and difference terms whose phases are (wt + Br + 0R) and (3 wt - Br + 0R). By frequency selection (filtering), the signal with the desired phase (conjugated) for transmission can be obtained = wt + Br + 0R. This process must be accomplished at each subarray, and the reference phase 0R must be the same at each subarray. To accomplish the subarray phasing, a reference phase distribution system is required. Two approaches have been investigated. Both employ adaptive techniques. The transmission line approach employs a central phase reference/control system and radio frequency transmission line distribution of the phase reference signal to each subarray. This system requires precise control of the phase shifts associated with each transmission line and if each subarray required an independent reference transmission line, cable weight would be extremely large. (A system for 1 km diameter circular transmitting antenna and 10m X 10m subarray has 7854 subarrays.) The subarray-to-subarray approach employs phase conjugating reference receivers at each subarray and distributes the initial reference phase from the first subarray to other subarrays, sequentially, until all subarrays are connected. This approach could result in extremely large phase error build-up at the subarrays furtherest from the initial receiving subarray. As a result of these initial investigations, the proposed SPS phasing system is a combination of the two approaches studied. A central phase reference and distribution system will be employed, and the phase reference signal will be transmitted to groups of subarrays via RF cable. The subarray groups will then employ the subarray-to-subarray reference distribution scheme. This approach will reduce the amount of transmission cable required, and since only 8 or 10 subarrays will be connected in series, the phase error build-up will be insignificant. Figure IV-C-4-3 illustrates the totally sequential distribution system as well as the transmission line/subarray group sequential distribution systems discussed above. Figure IV-C-4-4 shows the overall array approach proposed which utilizes the transmission line and subarray group sequential phase distribution system. The electronics required to accomplish the phase control/conjugating process is shown in the block diagram of Figure IV-C-4-5. The operation of the system is described below. At point 1, the received pilot signal phase ep at the central phase reference receiver is detected, and a locally *R generated reference signal is obtained by phase
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