## Electrical Engineering and Computer Science - Dissertations

12-2012

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Electrical Engineering and Computer Science

Arvas Ercument

#### Keywords

Apertures, Coupling, Method of Moments, Scattering, Thick ground plane, Transmission

#### Subject Categories

Electrical and Computer Engineering

#### Abstract

The problem of electromagnetic scattering from and transmission through an arbitrarily shaped aperture is considered. The aperture is in a thick infinite perfectly conducting ground plane. The conducting walls of the cavity inside the ground plane are of arbitrary shape. The apertures at both ends of the cavity are also of arbitrary shape. The structure is illuminated by an incident plane electromagnetic wave. The Green's function for this complicated problem is almost impossible to determine. Therefore the surface equivalence principle is used to reduce this complex problem into three simpler ones. Each such problem consists of equivalent surface currents radiating in unbounded media. Therefore the free space Green's function is used for each problem. An equivalent surface magnetic current placed on the top aperture produces the scattered field in the region where the impressed sources are. The total field inside the cavity is produced by two surface equivalent magnetic currents on the apertures and an equivalent surface electric current residing on the walls of the cavity as well as on both apertures. The transmitted field on the opposite side of the impressed sources is computed by an equivalent surface magnetic current residing on the bottom aperture. Enforcing the boundary conditions on the tangential components of electric and magnetic fields on both apertures and on the tangential components of electric field on the cavity walls results in a set of three coupled integral equations for the equivalent surface currents. Whenever possible, image theory is used to simplify the equations. These equations are numerically solved using the method of moments. The surfaces are approximated by planar triangular patches. RWG functions are used for expansion functions. An approximate Galerkin method is used for testing. The method is applicable for the general case where all three regions have different material parameters. Results are computed for the case where all these parameters are the same. The method is applicable for arbitrary sized apertures and cavities. However due to limited computing resources, only problems in the resonance region, where dimensions are comparable to wavelength, are considered here.

Computed results are given for the case of two square apertures connected by a square prism, two cross apertures connected by a square prism cavity, two circular apertures connected by a cylindrical cavity, and finally two circular apertures connected by a conical cavity. Our computed results are compared with results in the literature obtained by using other methods. Very good agreement is observed.

Open Access

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