Applicability of GTD in High-Frequency Asymptotic Analysis of Electromagnetic Scattered Field by a Conducting Strip

In this study, we shall examine a high-frequency electromagnetic scattered field by a conducting strip. The high-frequency scattered field by the conducting strip can be represented by applying the UTD (uniform GTD (Geometrical Theory of Diffraction)) solution for a conducting half-plane solved as a canonical problem. Then we shall derive from the UTD the two versions of the Keller’s GTD without applying the “trick" introduced in the paper by Keller: the first version is expressed by using the geometrical optics field, if any, and the edge diffracted rays and the second version is expressed by using only the edge diffracted rays. The first version (the second version) is applicable in the region close to (far away from) the conducting strip. We also derive the novel criterion for applying the GTD. We will show that, as the observation point moves far away from the strip in the illuminated region, the geometrical ray appeared in the UTD will be cancelled by the portions of the edge diffracted rays, thereby validating the second version of Keller’s GTD, which does not include the geometrical ray term. The validity and applicable range of the GTD and the UTD are confirmed by comparing with the reference solution calculated numerically from the method of moments.