An experimental investigation of the diffraction of electromagnetic waves by a dominating ridge

The diffraction of electromagnetic waves by a dominating tree-covered ridge north of Ottawa has been the subject of an experimental investigation. The measurements were made at 173, 493, and 1785 mc using both horizontally and vertically polarized radiation. The measurement period extended from late in the winter until early in the summer of 1955. The bulk of the experimental data consists of the results of height-gain and azimuth-gain measurements. Estimates of diffraction loss have been deduced from these results for the component of the radiation which was not reflected by the terrain between the ridge and the terminals of the experimental circuits. These deduced experimental diffraction losses exceed the predictions of Fresnel-Kirchhoff knife-edge diffraction theory, the discrepancies increasing with increasing frequency. There was no evidence of either a pronounced polarization dependence or a pronounced seasonal dependence.