Studies in Tropospheric Propagation Beyond the Horizon

1132 1138 1144 1148 1148 1149 1152 1153 1157 1158 1158 1159 1159 1161 1163 1169 1170 1173 1174 1174 1177 There has been a tremendous increase in interest in tropospheric propagation beyond the horizon since Bullington 1 first suggested its useful properties in 1950. Early studies at Bell Telephone Laboratories and elsewhere2 led to the design and installation of large-scale military and commercial systems. To a great extent, the design of these systems was based on limited data, since time did not permit the implementation of long-term research programs specifically designed to study the mechanism of the propagation. Hand-in-hand with the interest in the systems themselves, several theories were proposed to explain the propagation. These can be classified into three general types: scattering by atmospheric turbulence (Booker-Gordon), 3 mode propagation (Carroll-Iling) 4 and reflection from atmospheric layers (Friis, Crawford and Hogg). 5 This paper describes the results of a series of experiments conducted on a 171-mile overland path between Pharsalia, New York, and Crawford Hill, New Jersey, during the period from May 1955 to September 1958. At the time these experiments were planned, some of the characteristics of beyond-the-horizon propagation were known, but other important properties had not been investigated thoroughly. Some of the aims of our experiment were: to study the effect of antenna size on signal level and fading characteristics; to determine the wavelength dependence of the propagation; to look for seasonal and diurnal effects; to investigate a new form of diversity reception which combines the outputs of twin-feed horns horizontally or vertically disposed at the focal point of a single paraboloid; to study the bandwidth capability of