Edge diffraction beyond a caustic
Abstract
A uniform formulation for edge diffraction by a curved wedge is obtained for the case where the Fresnelintegral argument becomes negative, as when a caustic of the incident or reflected field occurs in the vicinity of the optical boundary. The physicaloptics approximation to the induced currents on the wedge is used to derive a consistent form of the edgediffracted field for negative values of the Fresnelintegral argument. Diffraction terms of the required form and which are valid on both sides of the caustic are found by evaluating the current integral asymptotically, and the correct geometric diffraction coefficients for the other side of the caustic are inferred by comparing the solution with the known result for positive values of the Fresnelintegral argument. The theory is applied to determine the principal component of the field in the focal region of a paraboloidal reflector fed by an onaxis horizontally polarized plane wave.
 Publication:

Electronics Letters
 Pub Date:
 June 1976
 DOI:
 10.1049/el:19760263
 Bibcode:
 1976ElL....12..344J
 Keywords:

 Electromagnetic Wave Transmission;
 Fresnel Diffraction;
 Ray Tracing;
 Surface Geometry;
 Wave Diffraction;
 Electromagnetic Fields;
 Fresnel Integrals;
 Optical Reflection;
 Parabolic Reflectors;
 Plane Waves;
 Polarization Characteristics;
 Wedges;
 Communications and Radar