Analytic modeling of oblique penetration of early-time high altitude electromagnetic pulse into dispersive underground multilayer structures

In this paper, a formulation for obliquely incident electromagnetic wave has been presented for an analysis of high-power electromagnetic pulse penetration into multilayer dispersive media. Based on generalized models of measured dielectric constants and propagation channels reflecting the Earths general features, the propagation phenomenon of the obliquely incident early-time (E1) high-altitude electromagnetic pulse (HEMP) is analyzed in frequency as well as in time domains. In addition, the polarization and critical angle are also considered. It is found that the total reflection occurs at an incident angle of about 38 at the soil-rock interface, and that the parallel-polarized E1 HEMP penetrates better than the perpendicular-polarized one. The peak level of the penetrating electric field is found to be 5.6 kV/m at normal incidence, regardless of the type of polarization, and 1.1 kV/m for incidence at 30 in perpendicular case.