A Critical Study of the Characteristics of Broadcast Antennas as Affected by Antenna Current Distribution

Abstract

The action of broadcast antennas with various current distributions is examined in an endeavor to determine the combinations which are most likely to be useful. In each case, the vertical radiation characteristics, the radiation resistance, and the electric field intensity at the surface of the earth one mile from the antenna are determined. The relative merits with respect to fading suppression are also considered. Of the several arrangements examined, some have been very disappointing. In no case where the total antenna height is at all reasonable for broadcast use does the field strength at one mile go to exceptionally high values. For heights of the order of a half wavelength, it is hard to find anything better than a straight vertical wire. Some of the arrangements save a small amount in height, but in no other respect do they improve on the straight wire. The analysis of the antenna with decreased velocity and antennas spread in the horizontal plane shows that both are definitely ruled out of the picture. The results show that the Franklin antenna would be very useful if it were not for the great heights required.