FDTD scattering analysis of cavities with dielectric protrusions

Dielectric protrusions over cavities are difficult to analyze due to modeling complexities. The FDTD method is employed for an efficient scattering analysis of loaded cavities with dielectric protrusions. For this application, the cavity is recessed in a ground plane and it is assumed that a dielectric protrusion of arbitrary shape may exist above the aperture of the cavity. Because of the protrusion, previously presented analyses based on the impedance approximation or on the finite element-boundary integral method are not applicable. Basically, the protrusion requires that the computational domain of the finite element method (FEM) or FDTD method be extended above the cavity and to truncate the mesh using an approximate boundary condition or an artificial absorber. The introduction of Berenger's (see J. Comput. Phys., vol.114, p.185-200, 1994) PML for FDTD mesh truncation provides us with a very accurate technique for mesh truncation and makes the FDTD method quite appropriate for the characterization of the dielectric protrusions. We first describe the application of the FDTD method for the configuration shown. An accuracy study of the analysis is then presented to determine the proper enforcement of the PML and obtain scattering patterns of acceptable accuracy. Subsequently, the scattering by a number of cavities loaded with isotropic and uniaxial layered dielectrics are considered, and the effect of different shape protrusions on the overall scattering is examined.