The Use of a Ring Array as a Skip Range Antenna

The problem involved here is the development of a shore antenna for shore-to-ship communications at distances from 40 to 500 miles. The difficulty at these distances is due to interference between ground-wave and sky-wave modes of propagation. The propagation factors involved are considered and it is shown that (1) A frequency less than 3.3 mc should be used, (2) The ground wave should be used during the day and (3), The sky wave should be used at night. An azimuthally omnidirectional antenna is described which consists of vertical monopoles equally spaced around the circumference of a circle. The antenna can be excited in either of two ways, one of which concentrates the radiated energy along the ground for use with the ground wave, and the other of which gives maximum radiation at a polar angle of 30 degrees and a null in the ground plane for use with the skywave. The results of model tests at 30 mc and at 1,200 mc are given. Results of calculations showing the expected coverage for noon and midnight are included.