Kenneth A. Norton, George A. Hufford, Harold T. Dougherty, and Robert E. Wilkerson

Abstract:

The various causes of fading and the various kinds of diversity are described. Detailed design procedures are given for the two most popular diversity systems, a redundant technique in which two channels at different frequencies are used and a non-redundant technique in which two vertically spaced receiving antennas are used. A description is given of the distribution of the vertical gradient of refractive index near the surface and its importance to optimum diversity design is described. Many examples are given to illustrate the proposed diversity design procedures and it is shown that a properly designed space diversity system should provide substantially better protection against phase interference fading than a frequency diversity system with optimum frequency spacing. Methods are given for calculating the percent time that the transmission loss is expected to exceed various levels with and without the use of diversity. Although the paper is concerned primarily with within-the-horizon microwave radio relay systems, it is pointed out that the fading on an obstacle gain beyond-the-horizon path is similar to that on within-the-horizon paths and that it should, in principle, be possible to use the diversity design methods described in the paper in this case as well.

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