Long-metallic-strip array with parasitic rings: an efficient metasurface for dual-broadband electromagnetic window at large angles.

The long-metallic-strip (LMS) array proposed by J. B. Pendry has been widely studied in electromagnetic windows. However, it could only work for the single-band window, not the dual-band one, due to the plasma-like oscillation attenuating with increasing frequency. To solve the problem, we have analyzed the condition of EM windows and then proposed to introduce "parasitic" rings (PRs) into the LMS array. The design is called the LPR metasurface, which could open the dual-broadband window at large incident angles (60°-85°). In C band, the LPR metasurface could conserve the LMSs' plasma-like oscillation, thus opening a broadband window for transverse-electric polarization. In K band, where the plasma-like oscillation has almost disappeared, the PR generates a capacitive resonance. It could open an additional window at large angles and provide a great out-of-band suppression concurrently. Unlike related studies, the PRs here are structurally easy and integrated into the LMSs. It has conserved the LMSs' simplicity and continuity, thus could better meet processing and protective materials. Additionally, with the great performance at large angles, the LPR metasurface may find wide applications in hypersonic aircraft radars, 5G/6G base stations, and others.