On the use of homogeneous models for the calculation of the near field excited by 2-D sources in 1-D periodic structures

Recently, there has been significant research activity related to the development of periodic structures such as EBG structures and artificial materials (including metamaterials). The goal of the present paper is the study of the near field of onedimensional (1-D) periodic structures excited by a two-dimensional (2-D) source (e.g., an electric line source). In particular, the possible use of homogeneous models is investigated through a comparison with a reliable full-wave analysis. In the past it has been shown that, for periods much smaller than the operating wavelength, these homogeneous models can effectively be used to obtain accurate results for far-field quantities and modal properties of the periodic structures. However, in problems involving the presence of near-field sources or for observation points close to the periodic structure, the use of standard homogeneous models (mainly derived assuming a plane-wave excitation) is likely to fail. In fact, near-field sources contain in their spectrum contributions with arbitrary small effective wavelengths (and therefore also significantly smaller than the spatial period of the periodic structure); in addition, for observation points close to the structure, the effect of higher-order Floquet harmonics could not be simply lumped into a shunt susceptance or taken into account by effective parameters. For this reason, the accuracy of classical homogeneous models for the Metal Strip Grating (MSG) and the Wire Medium (WM) are here investigated in critical situations, i.e., for points very close to the source and to the structure and for spatial periods not very small with respect to the operating wavelength.