Optimal Design of Dallenbach Absorbers Under Broadband Broad-Angle Illumination

Abstract: The classical scenario where a \emph{single plane-wave} field impinge a Dallenbach absorber is well studied both theoretically and experimentally. However, occasionally a \emph{spectrum of plane-waves} impinges the absorber. Such a scenario occurs for example if an antenna is located adjacent to the absorbing layer. In this paper, for this scenario we obtain the absorbing performance bound and design an \emph{optimized layered absorber} that approaches the bound. In a numerical demonstration, we explore a realistic case where a dipole antenna is placed in the vicinity of a finite, electrically thin, Dallenbach absorber backed by a PEC plane in the 6G frequency range. In the absence of the absorbing layer covering the PEC plane, severe scattering from the plane distorts the radiated fields. These distortions are robustly mitigated by the specifically tailored optimal absorber to yield a more desired radiation pattern. Additionally, we propose a metamaterial realization that emulates the required properties of the absorbing layer for all field polarizations.