Foreground terrain effects on overland microwave transmissions

The effect of large scale dominant obstacles such as mountains or ridges on short wave transmissions has been rather extensively investigated. In most cases the diffraction effects of such obstacles have been reasonably well described by use of knife-edge diffraction theory, especially when the diffraction angle is small. When the obstacle is a single mountain or ridge, the geometry of the situation is quite clear-cut. This paper, however, is concerned with the diffraction effects due to small and gently varying irregularities in foreground, terrain near one of the terminals of a microwave link. In this case the diffraction geometry is not so clear cut. Experimental results obtained on two paths indicate, nontheless, that the diffraction geometry is very much like that of knife-edge theory even though the diffracting terrain is very unlike a knife-edge in appearance.