A Multiple Unit Steerable Antenna for Short-Wave Reception

A MULTIPLE UNIT STEERABLE A NT EN NA 339 If, however, the directivity can be varied or "steered" to meet the various conditions imposed by nature, a new field is opened in which a new order of antenna sharpness and gain is possible. In addition to the gain in signal-to-noise ratio afforded by directivity, a reduction in selective fading is possible if the sharpness is increased to the point where a separation of differently delayed waves is achieved. As early as 1927, Edmond Bruce 2 - 3 found remarkable reductions in shortwave fading by using a receiving antenna having an extremely sharp directional pattern. The successful employment of sharp directivity is, of course, predicated upon considerable stability of wave directions. The experiments reported by R. K. Potter 4 in 1930 suggested that short waves are propagated in a more or less orderly manner and that stable wave directions might exist. Later experiments,6 made in cooperation with the British Post Office, using pulse transmission to resolve angles in time, gave confirming data and demonstrated clearly the physical facts upon which is based the system to be described in the present paper. These fundamental facts, outlined in the paper describing the experiments just mentioned, are recapitulated here because a clear understanding of their nature and significance is an essential introduction to the subject in hand. In the pulse tests it was found that: "1. To the extent that we have been able to resolve the propagation into separate (vertical) angles, the separate angles are found not to be erratic; they vary slowly.