Optimal design of Dallenbach absorbers under broadband broad-angle illumination

The classical scenario where a single-plane-wave field impinges a Dallenbach absorber is well studied both theoretically and experimentally. However, occasionally a 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 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 perfect-electric-conductor plane in the 6G frequency range. In the absence of the absorbing layer covering the perfect-electric-conductor 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.