Design of a mounting plate for a low reflection level over a wide range of incidence angles from a profiled lossy dielectric plate

This paper presents the design of a mounting plate with such a complex permittivity profile as to minimize the reflection off the mounting plate over a broad range of incidence angles white also providing the mechanical rigidity necessary for mounting a styrofoam jig holding the, device under test. The permittivity profile is achieved by boring circular cones from the front and the back surfaces of a lossy dielectric slab in a way that achieves near-optimum packing of the cones on both surfaces. The resulting geometry is reminiscent of a honeycomb structure, and is modeled as a uniaxial medium with the optic axis parallel to the normal of the plate. A modified scattering matrix propagator scheme was developed to predict the reflection and the transmission coefficients for both the TEz and TMx polarizations in a way that takes into account explicitly both the effect of the non-uniform wave propagation incurred by the presence of material losses, and the effect of the longitudinal anisotropy incurred by the geometry of the machined plate. A choice of parameters that yields a predicted reflection tevel of less than about -22 dB over an angular range of 0 degrees to about 50 degrees is presented.