A four slot cylindrical antenna for VOR service

This antenna was originally developed for the Air Navigation Development Board under a U. S. Navy contract. Four equally spaced longitudinal slots in the wall of a cylindrical cavity constitute the radiating elements. The four slots are energized by three independent feeders in such a way that one circular radiation pattern and two figure of eight patterns are obtained. When the antenna is used in conjunction with a goniometer, a rotating limacon pattern results. Intercoupling among the feeders is very low. The antenna is 7 feet high, 15 inches in diameter and weighs 110 pounds. The antenna may be readily tuned with the aid of a calibration chart to any frequenay between 108 mc. and 118 mc. Experience with a number of installations shows that the overall course errors are around ∠ 1.5° although the antenna error itself can be kept down to about one half of this value. The design of the antenna, flight tests and the several sources of course errors are discussed in detail.