On ray and beam expansions for analyzing EM coupling into open-ended waveguide cavities

Summary form only given. The EM coupling into relatively arbitrarily shaped electrically large, open-ended waveguide cavities with slowly varying geometrical properties and with an interior termination, can be analyzed via HF approximations. The fields coupled into the cavity can be expanded in terms of a discrete set of ray tube basis elements launched from the aperture at the open end. It can be shown that the continuation of the source field distribution defined over the subaperture domain can be well approximated in terms of the fields of a dense grid of ray tubes originating from the phase center of each subaperture. Instead of launching ray tubes, it is possible to launch an identical set of spectrally shifted Gaussian beams (GBs) from the phase centers of the subapertures; typically, fewer GBs than ray tubes need to be launched in this phase-space.<>