Reduction of the radar cross section of arbitrarily shaped cavity structures

The problem of electromagnetic scattering from open-ended cavities is of great importance in both radar cross section (RCS) reduction and electromagnetic pulse (emp) coupling studies. The largest contribution to the RCS of a cavity is that from the interior irradiation. Two methods used in reducing interior irradiation are (1) coating the interior of the cavity with a lossy material and (2) shaping the cavity. This thesis investigates both the issues of coating and shaping in the study of RCS reduction of arbitrary cavity structures.;Second, the problem of calculating the RCS of an arbitrary cavity is addressed. Traditional methods of analysis include such techniques as modal analysis and moment method. These methods have restrictions such as the requirement of idealized geometry models or electrically small cavities which hinder the study of the effects of shaping. A different strategy for analyzing the open cavity problem, based on a modified geometric optics (GO) approach, is presented. This method, entitled "shooting and bouncing rays" (SBR), permits the RCS computation for any arbitrarily shaped cavity.;Third, the effects of shaping on the RCS of cavities are studied. The SBR method is applied to compute the RCS's of uniform and nonuniform cylindrical cavities. The near-axial incidence RCS of cylindrical cavities can be reduced through longitudinal bending.;Finally, the range of validity of the SBR method is investigated. The limitations of SBR are studied by considering the problem of a plane wave impinging on a semi-infinite parallel plate waveguide. A comparison is made of the description of energy flow by the geometric optics ray method versus that for the modal analysis method for the parallel-plate waveguide. It is demonstrated that for a waveguide separation large compared to wavelength, the ray and modal descriptions are in good agreement.;First, the effects of interior coating are studied. With the proper choice of coating material and thickness, a significant RCS reduction can be achieved using only a single coating. However, this reduction is only effective over a narrow frequency band. A generalized method is presented for computing the propagation/attenuation constants for the normal modes of a circular waveguide lined with multiple layers of coating. The method is then applied to multilayered coated structures to show that a greater effectiveness in the attenuation of the normal modes can be achieved over a broader frequency range.