Highly Angular-Stable Optically Transparent Microwave Absorber With Wide Absorption Bandwidth

This work presents an optically transparent frequency-selective surface (FSS)-based electromagnetic (EM) wave absorber that is polarization insensitive and offers a wide-band absorption bandwidth of 9 GHz within the C, X, and Ku bands. A slotted unit cell of an annular ring integrated with a cross exhibits fourfold symmetry, which makes it polarization insensitive. The proposed absorber is compact as the surface area of the unit cell is $0.25 {\mathrm {\lambda }} _{c}\,\, {\times }\,\,0.25 {\mathrm {\lambda }} _{c}$ with a thickness of $0.015 {\mathrm {\lambda }} _{c}~( {\mathrm {\lambda }} _{c}$ is the wavelength at 10.95 GHz). In this work, the absorbance mechanism is presented using an electric and magnetic coupling, along with an effective input impedance plot of the unit cell. The theoretical analysis indicates that the proposed EM-wave absorber provides an absorption bandwidth of 9 GHz for normal incidence with 90% absorption. Theoretical results presented here further suggests that the proposed EM-wave absorber is polarization insensitive and angular stable up to 50° and 70° for TE and TM polarization, respectively. A prototype of the proposed EM-wave absorber is experimentally tested for its absorbance at different polarization angles. It is observed that the experimental results match well with the theoretical analysis.