A transparent ultra-wideband absorber with wide-angle stability for applications based on characteristic mode analysis

Abstract The escalating demands for electromagnetic compatibility and radar stealth in transparent electronics drive the need for high-performance microwave absorbers that integrate optical transparency, ultra-wide bandwidth, low profile, and angular stability. Tackling this challenge, we propose a transparent metamaterial absorber designed via a synergistic approach combining the antenna reciprocity theorem and characteristic mode analysis (CMA). This methodology transforms the absorption problem into targeted excitation and coupling of structural radiation modes. We first designed low-frequency resonant elements by identifying key narrowband modes via CMA, then introduced and optimized broadband elements for enhanced modal bandwidth. Spatial integration of these elements through a multi-mode coupling strategy yielded an ultra-wideband absorber. The proposed structure achieves over 90% absorption from 1.96 to 6.68 GHz (110% fractional bandwidth) with a minimal thickness of 0.047 λ L. It maintains stability for incidence angles up to 40° (TE) and 60° (TM). The absorption mechanism, validated by characteristic current analysis and an equivalent circuit model, demonstrates effective multi-mode resonance. Measured results confirm excellent performance, offering a promising solution for stealth and compatibility applications.