Dual-polarized angle-selective surface with ultra-narrow angular selectivity and broadband characteristics

This paper designs an angle-selective surface (ASS) composed of two identical layers of frequency-selective surfaces (FSS) with regular hexagonal structures. By leveraging the equivalent circuit model (ECM) theory and the modal interaction poles (MIPs) principle, the interlayer height is optimized to modulate electromagnetic coupling between layers, thereby achieving angular selectivity. The structure exhibits excellent ultra-narrow angular domain transmission characteristics, with the width of the transmission angle domain where |S₂₁| > -1dB is less than 0.1° under TE polarization and only 0.7° under TM polarization. Yet also has the characteristic of a narrow transition angular domain, where the widths of the transition angle domains on both sides, where 1dB ≤ |S₂₁| ≤ ~ - 20dB, are both 2.6° under TE polarization, and 16° and 9.3° under TM polarization. Meanwhile, the proposed structure also exhibits angular selectivity with broadband characteristics that it maintains angular selectivity over a 4.1 GHz bandwidth from 17.6GHz to 21.7GHz under TE polarization, and the angular selectivity spans a 5.4 GHz bandwidth from 17.6GHz to 23GHz under TM polarization. Finally, a prototype of this structure was fabricated, and the actual measurement results are in good agreement with the simulation results. This paper is the first to propose the concept of broadband characteristics for ASS, and the structure integrates the three advantages of narrow-angle domain transition, ultra-narrow-angle domain transmission, and dual polarization. With superior angle-selective performance compared to existing solutions, this structure offers important application potential, especially for applications in the front end of telescope imaging systems, optical coupling in AR waveguides, enhancing the signal-to-noise ratio (SNR) of signal detection in optical communications, and offering privacy protection for transmitters.