IV. CONCLUSION In our last section we illustrated how simple designs can be used to eliminate the 7T-ambiguity and reduce the ionospheric biases and biases from dispersive transmission lines. We also note that none of these designs require extra components in the receiving circuitry. All one is required to do is to obtain <£, which can be achieved rather easily, and simply conjugate it and use it as the phase of the downlink signal leaving the space antenna. These designs of pilot beam can be implemented easily in any large retrodirective arrays. Their advantages are as follows: (i) avoiding use of a phase-locked receiver, (ii) free from phase ambiguity, (iii) greatly reducing biases due to dispersion of the transmission line and medium, (iv) very simple to be constructed. It will be extremely interesting to have such a system built and tested in the very near future. Acknowledgement — The author would like to thank W. Finnell III, R. H. Durrett, and R. A. Inman of MSFC for their many enlightening discussions. REFERENCES 1. R. C. Chernoff, Large Active Retrodirective Array for Space Application, IEEE Trans. Antennas Propag. 27. 489-496, 1979. 2. M. I. Skolnik and D. D. King, Self-Phasing Array Antennas, IEEE Trans. Antennas Propag. 12, 142-149, 1964. 3. B. A. Sichelstiel, W. M. Waters, and T. A. Wild, Self-focusing Array Research Model, IEEE Trans. Antennas Propag. 12, 150-154, 1964. 4. P. E. Glaser, Power From the Sun: Its Future, Science 162, 857-861, 1968. 5. Raytheon Report No. ER79-4032, Solar Power Satellite (SPS) Pilot Beam and Communication Link Sybsystem Investigation Study - Phase 1, Contract No. NAS8-33157, 1979. 6. Boeing Report No. DI80-24635-1, Microwave Power Transmission System, 1978. 7. A. K. Nandi and C. Y. Tomita, Ionospheric Effects in Active Retrodirective Array and Mitigating System Design, NASA, Solar Power Satellite. Workshop on Microwave Power Transmission and Reception, Jan. 15-18, 1980.
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