lock techniques. This reference signal will then have a phase of wRt - <|>R and occurs at point 2 on the diagram. In order to provide the necessary signals for phase conjugation and phase shift control of the transmission lines, the reference signal is coherently synthesized into several different frequencies, point 3 on the diagram. These signals are then transmitted via the distribution system to each subarray group, point 4. When the reference signals are received at the control subarray, the transmission phase control signals are recovered and transmitted back to the central phase control system for automatic adjustment of the transmission line time delay to maintain a constant phase shift at each subarray group. The phase control signals are formed by multiplying two of the phase reference terms and filtering the upper sideband signal. The control signal thus has a phase 487 () as seen at point 5 on the diagram. Figure IV-C-4-6 showsK the frequency spectrum of the phase reference distribution signals, the received pilot signal, , transmitted power signal u^, and the phase control feedback signal cd^. The two reference signals used in the conjugating process are 242 wR and 247 . These are filtered and used as reference signals for the two mixers (multipliers) shown at points 6 and 7, on Figure IV-C-4-5 respectively. At point 6, the 247 phase reference signal is mixed with the pilot signal received at the particular subarray pilot receiver. This occurs at one of the subarrays in each subarray group, and the conjugation process is referenced to that pilot phase for all subarrays in that group. The lower sideband of the multiplication process is selected by filtering and the signal is locked to by a phase lock receiver. It should be noted here that the pilot signal is assumed to be modulated or coded to insure that other SPS systems will not interfere with the phase control process. This coding must be removed coherently and a clean unmodulated signal delivered to the power tubes. The cleaned-up signal is then mixed at point 7 with the 242 (wRt - <j>R) phase reference signal and the upper sideband of the multiplication terms is filtered. This signal is then the phase conjugated transmit signal desired with phase . The signal is then amplified by the PA driver amp., (point 8) and transferred to the subarray transmitter via precisely controlled waveguide lengths. The properly phased "exciting power" must be distributed from the "electronics" on each subarray to the microwave generators. The path length between each tube and the electronics must be maintained constant and represent an integral number of wave lengths. Thinwalled aluminum waveguide is proposed for this function. The guide must be securely fixed to the subarray support structure and distortion of the guide should be minimized. Waveguide is selected over coax cable because of low RF losses. A typical subarray layout is shown in Figure IV-C-4-7 for the center of the antenna. The total run of waveguide is 45m for a subarray weight of 18 kg.
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