Results of Horizontal Microwave Angle-of-Arrival Measurements by the Phase-Difference Method

This paper gives the results of horizontal microwave angle-of-arrival measurements made at a location on the King Ranch, a few miles south of the Naval Air Station at Corpus Christi, Texas. Small deviations of the angle of arrival in a landward direction from the geometric path were noticed at nearly all times. Sixty per cent of the measurements showed angular deviations less than 0.015°, and 90 per cent showed deviation less than 0.03°. The angular deviation is directly proportional to path length if constant gradient persists over the path. Under this condition, deviations greater than 0.10° will be expected, 10 per cent of the time, on a path 23 miles long. The measured angular deviations show a general correlation with the measured horizontal gradient of index of refraction. Meteorological soundings showed overwater ducts present nearly all of the time, with a maximum difference of approximately 50 M units between the surface of the water and the 38-foot level.