Diffraction by a circular aperture: a new approach

Abstract

A new approach to the classical problem of diffraction by a circular aperture is given by applying an expansion of the spherical wave into cylindrical waves. The diffracted field appears as a superposition of evanescent and outgoing cylindrical waves in the geometrical shadow zone, whereas in the geometrical illuminated zone what one obtains is the incident field plus a sum of standing and evanescent cylindrical waves. In the limit of great distances from the screen the well-known expression for Fraunhofer diffraction is reobtained.