Overwater propagation of millimeter waves

A field test program conducted to determine the short-and long-term fading characteristics and atmospheric absorption effects on an overwater millimeter-wave transmission path is described. A 6.1-nautical-mile overwater link was established using a 53-GHz transmitting frequency. Low grazing angles were used with antenna heights of 15 to 30 feet above sea level. The results of the program indicate 1) that short-term fading is Rayleigh distributed in the severest cases and is caused by surface reflections, and 2) that long-term fading variations occur more frequently and with greater intensity during warm weather periods.