Streamlined Permittivity Lossy Dielectric Design for Wide-Angle Frequency-Selective Surface Composite Absorbers

Design of wide-angle frequency-selective surface (FSS) absorbers is significantly challenging as the impedance in free space varies substantially with the incidence angle. To enhance the angular coverage of FSS absorbers and improve their performance under oblique incidence, a streamlined permittivity lossy dielectric (SPLD) model was constructed. The Riccati equation relating the input impedance to different streamlined permittivity functions was derived and solved. The computational results indicate that the exponential decay streamline yields the best wide-angle performance. Streamlined permittivity exhibiting exponential decay with distance was approximated using a layered gradient honeycomb. Under normal incidence, the absorber achieved a −10-dB fractional bandwidth of 158.0%. Under transverse electric (TE) polarization at 60° oblique incidence, it achieved an approximately 153.3% fractional bandwidth, while under transverse magnetic (TM) polarization, a 148.7% fractional bandwidth was obtained. The fabricated samples were tested in an anechoic chamber, and the experimental results aligned with the full-wave simulation results, thereby validating the effectiveness of our design.