Multimaterial 3-D-Printed FSSs for Ultrawide and Dual Passbands in the K-Ka Spectra

This article presents two 3-D bandpass frequency-selective surfaces (FSSs) featuring ultrawide and dual operating frequency spectra, respectively. Leveraging advanced multimaterial additive manufacturing, the design potential of 3-D meta-atoms can be unlocked. Compared to conventional 2.5-D or quasi-3-D FSSs that incorporate vias or microstrip lines, the proposed centrally loaded geometries facilitate in-depth topological optimization. The assembly of diverse fundamental FSS shapes introduces multiple poles and zeros, contributing to broad in-band transmission, extensive out-of-band rejections, and sharp transitions while still attaining simplicity when using equivalent circuit-transmission line modeling and associated qualitative design aids. The application-oriented FSSs are properly configured to fit the K-Ka spectra, where the ultrawideband FSS covers a fractional bandwidth of approximately 2:1, and the dual-band FSS offers two near-equal absolute bandwidths of 8 GHz. Both designs are inherently polarization insensitive due to unit-cell symmetry, and their robustness against oblique incidences has also been experimentally verified for both TE and TM modes.