Polarization independent metal–insulator–metal layered wide-band absorber with large angular stability for radar cross section reduction application

Abstract

A wide-band polarization independent microwave absorber has been proposed using two cross dipole resonators and square nodes with an unit cell size of $0.18{\lambda }_L\times 0.18{\lambda }_L$, where ${\lambda }_L$ represents the wavelength at the lowest operating frequency. The cross-dipole based resonating patterns with four nodes are designed on the FR4 dielectric layer. Lumped resistors are employed on the top layer to achieve the wide bandwidth. The bottom-most layer of the proposed absorber structure is made of copper. An air-spacer layer has been deployed between the substrate and the metallic ground layer to extend the low frequency absorption. The fractional bandwidth of the absorber is 93% with the absorption greater than 90% in the operating frequency range of 2.76 GHz-7.56 GHz. The profile of the proposed absorber is 0.08${\lambda }_L$. The unique characteristic of the proposed absorber structure is that the polarization conversion ratio of the structure is less than 0.1. The absorptivity of the proposed structure is more than 80% for a wide range of incident angles up to 60°. The absorption characteristics are found to be stable for both transverse electric and transverse magnetic polarized incident waves under normal incidence. Further, the mono-static radar cross section reduction of the proposed absorber structure has been verified to be greater than 20 $\text{dB}\text{m}{}^2$ in the operating bandwidth.