Diffraction of Ultra-Short Radio Waves

Abstract

WE have pointed out1 that ultra-short radio waves polarized with the electric vector vertical are propagated into the shadow of hills more readily than horizontally polarized waves. We have since observed the opposite effect for receiver positions beyond hills but just outside their shadow. Fig. 1 represents roughly the terrain over which these results, shown in the table, were obtained. The transmitter T was near the top of one ridge and the field strength investigated over the region ABCD ; horizontally and vertically polarized radiation was emitted in turn from the transmitter on a wave-length of 3 metres, and the aerial at the receiver oriented to correspond for each measurement with the appropriate transmitter polarization. Over the region ABC within the geometrical shadow of the ridge having a crest at A, the vertical electric field, in agreement with our earlier note, was greater than the horizontal field, the ratio of these two fields, as will be seen from the table, being unity near the edge of the shadow at A and C and a maximum near the bottom of the valley at B. Just outside, however, the horizontal field was greater than the vertical, the ratio showing a flat maximum.