Direction independent broad-band wide angle metamaterial absorber for "K" band applications

In this work, the design of broadband, wide-angle, direction-independent metamaterial (MM) electromagnetic wave (EM) absorber for K-band frequency application is investigated and validated experimentally. The unit cell of the metamaterial absorber consists of four 90 degrees rotated L-shaped metallic patches imprinted on a dielectric substrate backed by a metallic sheet. The structure yield absorption in the broad frequency ranges from 22.5 to 29.3 GHz for both TE and TM polarized waves with more than 90 % absorptivity having a wide fractional bandwidth of (6.8 GHz) 25.8 %. The structure is four-fold symmetric and hence yields polarization insensitivity for different angles of polarization under both TE and TM polarized waves. The structure is also investigated under oblique incidence where the 80 % absorptivity holds up to 45 degrees incident angles for both TE and TM waves. The absorption mechanism is explained with the help of top and bottom surface current distribution, induced electric field, and parametric analysis. To verify the resonance in the structure, characteristic mode, and equivalent circuit analysis have been carried out and presented. A prototype of the absorber has been fabricated and simulated results are validated with measured results. Measured results are showing good agreement with the simulated responses. The novelty of the proposed absorber lies in its unique metallic pattern on a lambda(0)/8 (concerning the canter frequency of absorption bandwidth) thin FR-4 substrate while showing the wide absorption bandwidth and direction independence to normal and oblique incidence. The compact nature of the absorber and broadband response with good polarization insensitivity at normal and oblique incidence makes it commercially suitable for the reduction of radar cross section (RCS) in stealth applications at the K-band.