Electromagnetic scattering from a periodic array of open-ended rectangular waveguide apertures

In this dissertation, the Radar Cross Section (RCS) of a large periodic array of rectangular open-ended waveguide apertures is determined numerically using several methods. The aperture boundaries are presumed to be Perfect Electrical Conductors (PEC). Although the problems of radiation from such a waveguide array and of aperture array scattering have been treated in the literature, the problem of scattering from an array of waveguide apertures does not appear to have been solved before. Considering the case of an array with constituent guides of semi-infinite length, the RCS is computed by several numerical methods based on the Integral Equation (IE) method, a least-squared error minimization technique referred to as Squared Field Error (SFE) method, direct solution of a surface integral equation, the Spectral Domain Method, and by using waveguide modes computed via the Finite Element Method (FEM). The case of finite-length guides is also treated using the IE and SFE methods. The results of these methods are compared with experimental data obtained from an outdoor RCS range. In order to simulate the semi-infinite case, the finite-length waveguides were terminated with radar absorbing foam so that nearly all reflection occurred at the apertures impinged upon by the incident plane wave. For all the methods cited, the infinite array approximation (cell-to-cell field periodicity except for a linear progressive interelement phase shift) is assumed to hold. A derivation of Floquet modes which implement this "phase-periodic" boundary condition is provided in an appendix, where an incidental discussion concerning the scalar and vector Laplacian operators is also furnished. A description of the structure and user interface of the software which has been written to implement the various methods is also given. The purposes of major subroutines and data structures are also delineated and several control-flow diagrams are included. As a foundation to extend the present work to analysis of the electromagnetic fields within an absorber coated PEC waveguide, a brief survey and a discussion of related work is provided.