Broadband Angularly Stable Metasurface Absorber via Coupling‐Based Modal Analysis of an Interconnected Rotated Resonator Array

Abstract

A compact metasurface absorber is presented, using four square ring resonators connected in a 2 × 2 configuration, with 90° rotation between the rings, where each ring has symmetric slots and one resistor. First, a quasi‐modal analysis of the slot‐loaded single‐resistor ring shows control of the main modes and absorption resonances without lumped elements. Then, using a quasimodal analysis of the array evolution from two diagonal elements to a fully connected four‐element configuration, it is shown that introducing multiple coupling paths, adjusting the resonator orientations and interconnecting them can provide increased design freedom for a thin, single‐layer absorber without an air gap, while enhancing the absorption bandwidth for both TE‐TM polarisations and larger incidence angles. Moreover, an extended circuit model with a matrix formulation based on characteristic‐mode analysis is proposed to derive closed‐form relations for the dominant absorption resonances and to clarify the physical mechanisms, enabling practical redesign from microwave up to mm‐wave and terahertz. For validation, a 10 × 10 array of the optimised cell with a thickness of only 0.1 λm is fabricated, showing over 65% absorption bandwidth and angular stability beyond 50°, with good agreement between simulations and measurements for different angles and two polarisations.