A generalized ray expansion method for analyzing the EM scattering by open-ended waveguide cavities

The high-frequency scattering from the interior of a relatively arbitrarily shaped open-ended waveguide cavity in free space is analyzed by a generalized ray expansion (GRE) method, when the cavity is terminated within by a planar boundary and illuminated by an external EM plane wave. In the GRE method, the aperture at the open end of the cavity is first divided into subapertures, and a cone of rays (or a fan of rays in the 2-D case) is shot within the cavity from each subaperture. The initial amplitudes of these rays can be found from the radiated far-field patterns of each of the subapertures in the absence of the slowly varying cavity walls. These rays, based on the GRE, implicitly contain the effects of the waves diffracted into the cavity via the edges at the open end without having to explicitly track the more cumbersome edge diffracted rays into the interior cavity region. The difference between the manner in which the GRE and the conventional geometrical optics methods launch rays within the cavity is illustrated.<>