Asymptotic Analyses of Diffracted Field by an Aperture in a Conducting Screen.

In this paper, the integral expressing the field diffracted by an aperture sufficiently larger than the wavelength created in a conducting screen is derived by the aperture field method. By evaluating the integral asymptotically, the extended Fraunhofer approximation and a uniform asymptotic solution for the aperture field methods are derived. By comparison with the reference solution derived by direct numerical integration, the usefulness, applicable range, and physical interpretation of the asymptotic solution are investigated. A new criterion is derived for adopting a nonuniform asymptotic solution applicable outside the transition region and the conventional Fraunhofer approximation from the uniform asymptotic solution. The validity of this technique is demonstrated numerically. The effectiveness of the technique is clarified by comparing a reference solution obtained by the method of moments and uniform asymptotic solutions obtained by the three types of aperture field methods. [ABSTRACT FROM AUTHOR]