Abstract
In this paper, a wide bandwidth angle- and polarization-insensitive symmetric metamaterial (MM) absorber for X and Ku band is proposed. For both normal and oblique incidence in TEM mode, the proposed unit cell shows high absorption at different polarizing angles due to structural symmetry. A four-fold resonator was introduced in the unit cell to enhance the bandwidth. The performance of the proposed absorber is determined by both full-wave simulations and measurements. The simulated and measured absorptions are almost similar at normal incidence with 94.63%, 95.58%, 97% and 75.58% at 11.31 GHz, 14.11 GHz, 14.23 GHz, and 17.79 GHz respectively. At 45° for these frequencies, the absorptions are 95.47%, 97.2%, 97.12% and 75.29% respectively. For 90°, the absorptions are similar to those for 45° except 98.15% for 14.21 GHz. At all these angles and resonance frequencies, either permittivity or permeability was found negative, as a result, the refractive index was negative revealing metamaterial characteristics of the unit cell. Along with high absorptivity and wide incidence angle insensitivity up to 90°, a total of 1.42 GHz of absorption bandwidth was achieved, which is better than recent similar works with FR4 substrate.
Highlights
The absorption capability of an MM absorber depends on the unit cell design and on the angle of incidence of the incident EM wave and their polarization types
We propose an MM absorber which satisfies all these properties for X and Ku band applications
The most popular FR4 substrate is used as the dielectric barrier for the unit cell, where the copper patch is backed up by a copper ground with the substrate in between them
Summary
Saif Hannan1 ✉, Mohammad Tariqul Islam1 ✉, Ali F. The unit cell should be symmetrically shaped like a split-ring cross resonator, circular sector, Jerusalem cross-section, four-fold symmetric and so on[14,15,16,17,18,19] These absorbers can absorb EM waves with high efficiency at some certain frequencies with very low bandwidth. Into places for wide bandwidth absorption like radar cross-section reduction, remote sensing, unwanted frequency absorption in antennae, stealth capability in modern military airplanes and so on To overcome all these challenges in this modern age, the MM absorbers should be designed with such precision that, they will be polarization and wide-angle insensitive, symmetric in structural design, capable of high absorption and most importantly, they must have broad bandwidth of absorption efficiency. Each quadrant with the center square and the perimeter lines act as inductive loads with
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