Design of an absorbing mounting plate for a low reflection level

This paper presents the design of a mounting plate with a complex permittivity profile that minimizes the reflection from the mounting plate over a broad range of incidence angles while providing the mechanical rigidity necessary for mounting a styrofoam jig holding the device under test. The 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 TE/sup z/ and TM/sup z/ polarizations in a way that takes into account explicitly both the non-uniform wave propagation resulting from the presence of material losses, and the longitudinal anisotropy resulting from the geometry of the machined plate. A choice of parameters that yields a predicted reflection level of less than -20 dB from 0/spl deg/ to 55/spl deg/ is presented.