Ultra-Short Wave Propagation

W I T H the extension of the radio frequency spectrum to higher and higher frequencies have come new problems, both of experiment and of theory, which require quantitative study for solution. * Presented at New Y o r k M t g . of I. R. E . , N o v . 2, 1932. I. R. E . , M a r c h , 1933. Published in Proc. 125 126 BELL SYSTEM TECHNICAL JOURNAL The fundamental similarity of visual light and radio waves makes it obvious t h a t somewhere between these regions a transition region must occur in which the apparently different phenomena merge into each other. In theoretical studies of this region it is necessary to use concepts borrowed from both the adjacent frequency ranges. A survey of a part of this field has now been in progress for some time and some of the results obtained to date are given in this paper and in a companion paper by Englund, Crawford and M u m f o r d . Since the Kennelly-Heaviside layers do not reflect ultra-short waves sufficiently to be a factor in the ordinary phenomena of this range, our interest is confined to the " g r o u n d " or direct wave. This term refers to any and all signals which arrive at the receiver except those which are affected by the upper atmosphere. It is otherwise noncommittal as to the mechanism of transmission. The physical pictures of this mechanism which have been so useful in the case of long waves are of little help when the length of the wave is of the order of, or smaller than, the dimensions of irregularities of topography which it encounters.