Propagation due to tropospheric inhomogeneities

Above about 30 MHz the only tropospheric-propagation mechanism giving a significant field strength far beyond the radio-horizon is the scattering of radiowaves by tropospheric inhomogeneities. This mechanism has been extensively studied and has given rise to discussions between theoreticians, especially during the years 1950 to 1965. From that time, studies have been continued at a lower rate, and this propagation mechanism has been used for the planning of transhorizon radio links. Moreover, troposcatter propagation has to be taken into account for the prediction of long-distance interference. This paper summarises the main characteristics of the propagation by tropospheric inhomogeneities, including long-term and short-term variations of field strength, antenna gain degradation and limitations in bandwidth capabilities.