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In recent years, many kinds of multiband metamaterial absorbers (MMAs) have sprung up. However, most of their dielectric layers were filled with rigid dielectric materials, which has many limitations in practical application. In this paper, an ultra-thin flexible conformal four-band metamaterial absorber (FMMA) is presented based on the dielectric material of polyimide (PI), and its thickness is only 0.0047 of the wavelength at the lowest absorption frequency. The top resonator is adopted a hollow structure, which is different from the common strip and ring structure, providing a novel idea for multiband absorber design. The proposed FMMA achieved four absorption peaks with an absorptivity higher than 90% from S-band to X-band. Meanwhile, in both TE and TM modes, it is insensitive to polarized waves and maintains good absorption under a wide incident angle. The experiment is carried out to demonstrate that the FMMA has satisfactory absorption performance. Due to its flexible conformal characteristic and good absorption performance, the FMMA can be applied in electromagnetic shielding of a curved surface, meteorological satellite, and radar detection.

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Herein, a polarization-insensitive and wide-angle characteristic ultrabroadband metamaterial absorber (UBMMA) is reported, which covers the entire X band and Ku band and parts of the C band and K band. The standard unit cell of the UBMMA is designed based on the frustum of a cone with a through-hole, and it is composed of multiple metal and dielectric layers by cross. The calculation results indicate that the absorptivity of the proposed UBMMA is more than 85% from 6.65 to 23.73 GHz except for the frequency bands 13.10-13.20 and 15.38-15.73 GHz, and the absorptivity is more than 90% in the frequency bands 6. 65-12.25 and 20.33-23.33 GHz. The distributions of the electric field, magnetic field, and surface current are calculated and analyzed, and the absorbing mechanism of the UBMMA is explained. The UBMMA is insensitive to the transverse electric and transverse magnetic polarization, and it displays an agreeable absorption effect under high incident angles. The influence of important geometric parameters on the absorption performance of the UBMMA is studied. Because of the satisfactory ultrabroadband absorption performance of the UBMMA, it can be applied in the fields of satellite radar, broadband antennae, and electromagnetic shielding.