An Ultra-thin Polarization Independent Quad-band Metamaterial-Inspired Absorber for X-and Ku-band Applications

In this paper, a compact polarization independent quad-band metamaterial (MTM) structure for unity absorption characteristics has been proposed. The proposed unit cell consists of two resonators designed on top of FR4 glass epoxy dielectric substrate completely laminated by copper on the bottom side. The absorber has been designed and developed in such a way that four different absorption peaks occurs in X- and Ku-band having absorptivity of 96.18, 98.51, 96.54, and 98.22% at 8, 10.5, 14.4, and 16.6 GHz under normal incidence, respectively. The main advantage of this structure is its high absorption bandwidth. The full width at half maximum (FWHM) bandwidth is 330 MHz (7.86-8.19 GHz), 450 MHz (10.27-10.72 GHz), 460 MHz (14.20-14.66 GHz), and 780 MHz (16.23-17.01 GHz) at the four frequency bands. The presented absorber also shows compactness property with electrical dimensions of 0.26 λ0 × 0.26 λ0 and thickness of 0.026 λ0, which can be considered as ultrathin. λ0 is the corresponding free space wavelength with respect to the lowest absorption frequency i.e. 8 GHz. The proposed absorber structure exhibits polarization independent behavior due to its four-fold symmetrical unit cell. In addition, absorption characteristics have been investigated and found intact under different angles of incidence for both TE- and TM-polarized waves.