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  • "Isotropic" coverage on satellites of large diameter as compared with wavelength

    Paper ID



    • N.E. Feldman


    The RAND Corporation






    Although satellite antennas of a few db gain are already in use, and large high gain antennas will become standard as accurate, reliable stabilization techniques are evolved, broad angle coverage antennas will still be advantageous for selected missions. This Memorandum describes techniques for achieving such broad angle coverage. The first method involves extending an antenna on a long mast. A biconical antenna is used which provides omnidirectional coverage (360° in azimuth) above — 1 db relative to isotropic, over 90% or more of the surrounding space. The second method uses two extended balanced logarithmic conical spiral antenna elements, diametrically opposite and circularly polarized in the opposite sense as seen by an observer in the far field to provide “isotropic” (constant power over a sphere although of variable polarization) coverage. An individual element provides circular polarization over a hemisphere. Coverage over 100% of the surrounding space appears achievable with a gain of —3 db relative to isotropic. The third method uses frequency diversity techniques. A number of alternatives are described providing either 100% coverage, or coverage in the direction of the ground receiving terminal by selecting one of two halfwave antennas. Compared on the same basis as the two previous techniques, the resultant gains vary from about —2 db to —6 db depending on the complexity of the satellite and ground terminal equipment and the operating procedure.