Multipath Propagation at 4, 6, and 11 GHz

Signals at 4, 6, and 11 GHz, transmitted over a 28.5-mile radio relay path in Ohio, were continuously monitored during the late summer of 1966. Previous publications have reported on the observed 4- and 6-GHz multipath fading statistics, and on the improvements available with space or frequency diversity. This paper presents data for the 11-GHz transmission, and, in combination with the earlier results, establishes an empirical frequency dependence for the amplitude statistics. A general treatment of the relationships between the factors underlying multipath propagation is intractable. However, based on the results in this and other papers, a general relationship is given for the probability of deep multipath fading which is linear in frequency, cubic in path length, and varies with meteorological-geographical factors. Temporal aspects of the Ohio data were also investigated at all frequencies, utilizing both a 1-hour and a 1-day clock time interval. It was found that the multipath fade time statistic can be described by a single parameter for either interval. A subset of the multipath fading hours was also analyzed using a 1-minute clock interval, with the result that the difference between the minute median fade and the hourly median fade is frequency independent, and normally distributed with a standard deviation of 5.5 dB.