. The Bell System technical journal . tions, therefore, the signal would varyinversely as the square of the distance, D, directly as the square ofelevation, H, and inversely as the wave-length. Qualitatively, atleast, all of these tendencies have been observed experimentally. UL TRA-SHOR T \VA\ E PROP A GA TION 147 Even with vertical polarization, the reflection coefficient is alsoapproximately — 1 for transmission over smooth land with near-grazing incidence. The same inverse square tendency is therefore tobe expected with vertical polarization under these conditions. Non-Optical Paths We sha
. The Bell System technical journal . tions, therefore, the signal would varyinversely as the square of the distance, D, directly as the square ofelevation, H, and inversely as the wave-length. Qualitatively, atleast, all of these tendencies have been observed experimentally. UL TRA-SHOR T \VA\ E PROP A GA TION 147 Even with vertical polarization, the reflection coefficient is alsoapproximately — 1 for transmission over smooth land with near-grazing incidence. The same inverse square tendency is therefore tobe expected with vertical polarization under these conditions. Non-Optical Paths We shall now discuss one type of non-optical path which is of interestboth because it occurs frequently and because on the basis of theassumptions made it is amenable to approximate calculation. It isrepresented in simplified form in Fig. 15. T and R are located on opposite sides of a hill, M, and the distancesTM and TR are great compared with the altitudes involved. Thelow land on both sides of the hill is comparatively flat, though not. Fig. 15 necessarily coplanar. As previously discussed, the magnitude of the coefficient of reflection to be expected will be close to unity ^^ for many conditions likely to be met and the phase change will be not much different from 180°. In other words, the wave reflected from the ground between T and M will appear to have come from a negative virtual image, T. The disturbance above the mountain, M, will be made up of two components corresponding to the antenna and its negative image. In passing from the region above M to the receiver, R, each of these components is broken down into two new components due to reflection between M and R. One of these proceeds directly to the receiving antenna. The other proceeds indirectly, being reflected by the intervening ground; it may be thought of as traveling - An exception of this occurs in the case of vertical polarization over surfaceshaving appreciable conductivity, such as sea-water. Recent experimenta
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