Design of Broadband Absorbing Metasurfaces Unit Based on Characteristic Mode Theory

To address the critical challenge of difficult collaborative optimization of bandwidth, oblique incidence stability, and profile thickness in single-layer absorbing metasurfaces design, this paper proposes an innovative design method based on Characteristic Mode Theory (CMT). By deconstructing the distribution characteristics of characteristic current modes and combining the reciprocity theorem with the principle of pattern orthogonality, we systematically analyze the electromagnetic response mechanisms of fundamental modes and high-order modes excited by normally incident waves. It is found that strategically loading lumped resistive elements in the extreme value regions of characteristic currents can effectively regulate mode weight coefficients and enhance energy dissipation efficiency. This method breaks through the limitations of traditional empirical parameter optimization, establishes an internal correlation model between mode orthogonality and broadband absorbing characteristics, and successfully enables a single-layer metasurface unit to maintain an absorption rate of over 90% within the oblique incidence range of 0°–60°.