Two ray shooting methods for computing the EM scattering by large open-ended cavities

Abstract

Two ray shooting approaches are presented for analyzing the high frequency external EM scattering by open-ended waveguide cavities of relatively arbitrary shape and with a planar interior termination. The contribution to the external scattering arising from the interior cavity region is found by (i) the shooting and bouncing ray (SBR) method, and (ii) the generalized ray expansion (GRE) method. The basic difference between the two methods is in the way the rays are initially launched into the cavity interior via the open end which is directly illuminated. While the SBR method tracks only the incident geometrical optics field which enters the cavity, the GRE method also intrinsically includes the fields diffracted into the cavity by the edges at the open end. Also, in the SBR method a new set of rays needs to be tracked for each incidence angle, while in the GRE method only one set of rays needs to be tracked independent of the incidence angles, although this is generally a much larger set than that used in SBR for a single incidence angle. Therefore, it is found that the SBR method is preferable for analyzing the scattering from cavities which are very large electrically and for relatively few incidence angles. On the other hand the GRE method is preferable for analyzing not only large but also moderately large cavities and for cases where a large number of incidence angles are needed. Numerical results and comparisons based on these methods are presented.