On the Daylight Transmission Characteristics of Horizontally and Vertically Polarized Waves from Airplanes

The investigation described below was carried out for the purpose of comparing the transmission characteristics from an airplane of horizontally and vertically polarized waves in daytime. A frequency of about 6 megacycles was arbitrarily chosen. In view of the fact that modern practice is tending towards the elimination of the trailing wire antenna, an antenna producing vertically polarized waves must of necessity be of small dimensions. The transmissions were therefore compared using a doublet antenna, each arm of which stretched from wing tip to tail for the horizontally polarized wave, and a rigid antenna six feet high for the vertically polarized wave. It was found that the sky ray began to be appreciable with the horizontally polarized wave at a distance of 20 miles, while on the vertically polarized wave it became important at a distance of 50 miles. The signal from the sky ray for distances of the order of 150 miles was always stronger with horizontal polarization than with vertical. The result with the direct ray was different. The signal from the vertically polarized wave was stronger than that from the horizontally polarized wave over highly conducting ground, while the reverse was the case over badly conducting ground. For this reason, the signal from the vertically polarized wave sometimes became very weak at a distance of 40 to 50 miles, before the sky ray was able to arrive with sufficient strength. This occurred particularly on badly conducting ground and when the airplane was flying low.