Beugung elektromagnetischer Wellen in Braunbekscher Näherung. I.

An approximation method proposed by Braunbek for the diffraction of scalar waves by plane obstacles, or apertures in a plane screen, is extended to the diffraction of electromagnetic waves. As an example, the diffraction of a linearly polarized plane electromagnetic wave normally incident on a circular aperture in a perfectly conducting plane screen and on a perfectly conducting plane circular disk is considered in detail. The results are compared with those obtained from the exact solution of Meixner and Andrejewski and with the results of Kirchhoff's approximations. It is shown that, in contrast to the Kirchhoff approximations, Braunbek's method leads in all cases to the correct 'optical' limits and represents a good approximation even for wavelengths comparable with the size of the obstacle. After a general formulation of Braunbek's method in the electromagnetic diffraction problem, we calculate in the present paper the far field of the circular aperture and the transmission coefficient by means of the cross section theorem. The near field of the circular aperture and the circular disk will be considered in a subsequent paper. [ABSTRACT FROM AUTHOR]