Investigations of Angular Scattering and Multipath Properties of Tropospheric Propagation of Short Radio Waves beyond the Horizon

Abstract

Experiments designed to investigate the potential communications capacity of uhf and shf tropospheric propagation beyond the radio horizon were conducted by the MIT Lincoln Laboratory on circuits of from 161 to 188 miles in length along the coastal regions of the northeastern United States. Some of these tests were made in cooperation with the Bell Telephone Laboratories and the late Major E. H. Armstrong. A study of the following aspects of tropospheric propagation was considered necessary in order to gain a better understanding of the factors involved in design of communications systems: 1. The extent of useful communication bandwidths. 2. Variation of uhf and shf median signal levels over a full seasonal cycle. 3. The range and rates of fading. 4. The effective gain of highly directional antenna systems. 5. The effect of multipath propagation on modulated signals. 6. The polarization properties of scattered fields. 7. The angular dependence of scattered fields. Such experiments made from 1953 to 1955 have confirmed the utility of tropospheric circuits for wide-band communication systems and have provided information useful in the evaluation of tropospheric propagation mechanisms.