. The Bell System technical journal . onsiderations show the reasonableness of regularity ofreflection, they do not enable us to calculate the value of the the over-land tests which we have described, the amplitude of thecoefficient of reflection would have been very near to unity and itsphase angle would have been very near to 180° if the ground had beensmooth. In the absence of data on the reflection from rough surfaces,we have used these same values although it is apparent that thecoefficient will be less than unity due to scattering and increasedpenetration. The fact that a
. The Bell System technical journal . onsiderations show the reasonableness of regularity ofreflection, they do not enable us to calculate the value of the the over-land tests which we have described, the amplitude of thecoefficient of reflection would have been very near to unity and itsphase angle would have been very near to 180° if the ground had beensmooth. In the absence of data on the reflection from rough surfaces,we have used these same values although it is apparent that thecoefficient will be less than unity due to scattering and increasedpenetration. The fact that a fairly good quantitative check has beenobtained experimentally indicates that this assumption is check is somewhat better when the magnitude of the reflectioncoefficient is somewhat reduced (Fig. 16). Diffraction In ultra-short wave propagation, the effect of an obstacle, such as ahill, can be visualized best by considering it from the point of view^ ofthis same principle of Huyghens. Fig. 10-^ represents this. A wave. A Fig. 10 B originates at T and travels unobstructed to R, passing through theplane P. It is, of course, incorrect to say that the eftect travelsexclusively along the line TOR. Consideration must be given toother paths such as TER, and the effect of the latter can be neglectedonly in case the path length TER exceeds TOR by many w^ave-lengths; or more properly, a region about E can be neglected only incase the phases of the components transmitted through the elementswithin it {, along TER) are such as to cause destructive inter-ference among themselves. 138 BELL SYSTEM TECHNICAL JOURNAL When a hill is interposed as shown in Fig. 10-5, elements such as E,below the profile of the hill, are prevented from contributing to thesignal at R, while elements such as E, above the profile, contribute asbefore. This is the simple concept as used in optics and will be usedwithout essential modification in the explanation of non-rectilinearradio transmission.
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