Figure 2.3-20. Functional Block Diagram of Hytrodyne Phase Control Network fj is the pilot frequency. The frequency and phase of the 25-MHz oscillator is canceled out in the mixing process, so separate incoherent oscillators in each subarray can be used. The retrodirective technique, however, does not correct the phase errors in the 2445-MHz reference frequency or the klystron-to-klystron phase tracking errors. Three methods of transmitting the 2445-MHz reference from a central signal generator to each of the 7854 lO-meter by 10-meter subarrays were identified: 1. Coaxial cable transmission. 2. Fiber optics transmission. 3. Space feed. The coaxial cable technique has been considered in other SPS studies; however, relatively large cable sizes are required for tolerable loss levels. For example, a feed system using 2.2-cm diameter foam dielectric cable would weigh approximately 250,000 kg and the loss in a 500-meter length of such cable is 65 dB. There are other aspects of a coaxial system which should be studied, such as the effects of high input VSWR spikes due to the long cable length, the effect of temperature changes, and the problem of long-term degradation of cable insulation properties due to radiation. A fiber optics transmission system offers potentials on a phase distribution system. Losses and phase errors, however, must be assessed.
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