The concept of soft and hard surfaces has been introduced in electromagnetic theory as surfaces along which the power density is zero or has a maximum. Two common realizations are the corrugated surface and the strip-loaded grounded dielectric slab. The latter has the advantages of low cost and light weight in comparison with the corrugated surface. Strip-loaded surfaces can be rigorously analyzed by using the periodical property of the structure, thus expanding the field in Floquet modes. This is a complicated procedure in particular if the source is not a plane wave. One simplification of the problem can be made by using the asymptotic strip boundary conditions (ASBC). If the width of the strip is narrow and the periodicity of the strips is small compared to the wavelength (which is common in practice), we can treat the structure in an asymptotic way, as if the width and the periodicity of the strips approach zero. Consequently, there is no need of expanding the field in a series of Floquet modes. We present the use of the ASBC to calculate the Green's functions of a strip-loaded plane surface.
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