Broadband Frequency Selective Surface Absorber With Dual-Section Step-Impedance Matching for Oblique Incidence Applications

A method for designing and fabricating a dual-section step-impedance frequency selective surface (DSSI-FSS) absorber for oblique incidence applications is proposed. The features of dual-section and step-impedance are realized by using two dielectric layers, which show better impedance matching characteristics compared with a single-section matching layer. We also propose a transmission line model that can be used for a DSSI-FSS absorber at different incidence angles. The model can be especially helpful for the rapid design of broadband and wide-angle absorbers. The proposed absorber structure has a -10 dB bandwidth in the range of 2.3-13.3 GHz at normal incidence (144.0% in fractional bandwidth), 2.5-14 GHz (139.4%) at transverse electric (TE) 45 degrees, and 3.1-14 GHz (127.5%) at transverse magnetic (TM) 45 degrees. In view of the difficulty in obtaining low-permittivity materials, the dielectric layers were fabricated with a honeycomb structure, which ensures high structural strength and low weight. Reflectivity simulation results were in good agreement with measurement results, which validated the design principle and fabrication process. The proposed absorber has a wide absorption band and a wide scan angle, which render it competitive in practical applications.