Ultra-thin, polarization-insensitive, deca-band metasurface absorber based on a plus-shaped resonator with concentric circular arc elements

This article presents an ultra-thin, polarization-insensitive, and high-performance deca-band metasurface absorber designed on a low-cost FR-4 substrate. The proposed structure consists of unit cells with dimensions of 20×20×1mm3. When the free-space wavelength (λo) at the lowest operating frequency of 3.8 GHz is considered, the unit cell periodicity is approximately 0.25λo and the total structure thickness is 0.012λo (≈λo/77), which is well below λo/10, thereby confirming the ultra-thin nature of the proposed structure. The metasurface absorber achieves absorption levels exceeding 90% at 3.8, 5.4, 8, 9.7, 14.7, 17.6, 18.8, 20.6, 21.2, and 24.35 GHz in the S,C,X,Ku, and K bands. The maximum absorption occurs at 24.35 GHz with a quality factor of 243.5, indicating suitability for both radar cross-section (RCS) reduction and sensing applications. Monostatic RCS analysis demonstrates more than 7 dBsm reduction at the absorption frequencies. The structure exhibits polarization-insensitive behavior under normal incidence and maintains absorption above 80% for oblique incidence angles up to 45 degrees. An equivalent circuit model developed in Advanced Design System (ADS), along with experimental validation using a fabricated prototype and Vector Network Analyzer (VNA) measurements, shows strong agreement with simulation results, confirming the accuracy and validity of the proposed metasurface absorber.