Figure IV-C-4-8 illustrates an optical distribution technique under investigation. The system incorporates fiber optics transmission lines rather than RF cables for distribution of the phase reference RF signals. The techniques proposed have been determined to be feasible; however, space qualifiable fiber optic transmission lines are not presently available and a great deal of development will be required in this area. Because of the potential weight savings aspect of the fiber optics transmission lines, further investigation is recommended. Additional recommendations include the investigation of the optimum phase distribution of the RF cables with respect to the reference phase. The subarray group size should be studied to reduce the number of RF transmission links and still limit the accumulated phase errors so that phase control is effective. The RF frequency spectrum should be investigated to establish a pilot reference signal. The goal would be to reduce transmitter interference problems, reduce the complexity of the phase electronics and reduce the weight of the electronics circuits. Possibilities of major concern involve potential requirements of phase control for each klystron or each amplitron. The phase stability of the system components outside of the phase control system loop should be analyzed and tested. Electromagnetic and radio frequency interferences by the microwave power generators and the antenna array transmissions on the phase reference system need to be investigated. The cost/weight estimates for the baselined phasing system is shown in Table IV-C-4-1. Losses due to beam pointing error caused by designed frequency offset between the received pilot signal 244 and the transmitted signal 245 ujp produces a pointing error in the transmitted beam. A received signal at a subarray at a distance L from the antenna reference receiver has a phase offset with respect to the reference signal of
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