In this paper, remodeling of Lee's piecewise knife diffraction loss model is presented. The original Lee's piecewise knife diffraction loss model is expressed as a function of Fresnel-Kirchoff diffraction parameter. The computation of the Fresnel-Kirchoff diffraction parameter requires detailed terrain and link parameters. However, for quick link planning the Fresnel-Kirchoff diffraction parameter can be computed from the knowledge of the line of site percentage clearance alone. Moreover, in line of site link design, the required or acceptable obstruction clearance is specified in terms of line of site percentage clearance. Consequently, in this paper, the Lee's model is remodeled into new piecewise functions that are entirely functions of line of site percentage clearance. The new version of Lee's model is validated with the results of knife edge diffraction loss obtained from the original Lee's piecewise knife diffraction loss model. With the new model it is easier to determine the diffraction loss that will be caused by any obstruction at a given line of site percentage clearance.

Abstract:In this paper, the effect of the radius of curvature on the diffraction loss of rounded edge obstruction is presented.The study is conducted for C-band microwave link with a plateau in its path. The plateau has flat to that spans about 1922 m. Two different approaches are used to determine the radius of curvature of the rounded edged fitted to the plateau top. Among the two methods employed, the ITU-R 526-13 method overestimated the radius (about 12,374,693.37 m) as against 59,031.42 m estimated by the second method at the same C-band frequency of 4 GHz. Also, high radius of curvature by the ITU-R 526-13 method gave very high diffraction loss value for the plateau. Furthermore, with the ITU-R 526-13 method, the radius of curvature does increase with increase in frequency. In all, the results indicate that the ITU-R 526-13 method is not particularly suitable for estimating the radius of curvature for the rounded edge when applied to a plateau. In addition, a more accurate method is required to estimate the radius of curvature for computing rounded edge diffraction loss.