Broadband Polarization Reconfigurable Frequency-Selective Surface Design

Objective A frequency- selective surface (FSS), an artificial electromagnetic metamaterial, is a planar periodic structure extensively studied in various fields such as filters, absorbers, and polarization converters. However, most metasurfaces focus solely on single- function realization and cannot switch between harmonic functions. With the development of multifunction and intelligent devices, the static nature and narrow bandwidth of single- function FSS are inadequate for complex operational scenarios. Recently, attention has turned towards multifunctional switching FSS capable of dynamically altering their states. However, these FSSs can only switch between transmission and shielding, lacking the capability to regulate electromagnetic polarization characteristics and achieve independent polarization control. Therefore, we propose a multifunctional, reconfigurable wideband FSS. Compared to traditional frequency- selective surface structures, this design enables switching between second- order filtering and polarization rotation functions while independently controlling transverse electric (TE) and transverse magnetic (TM) waves polarization. These features render the technology promising for applications such as multi- mode radomes requiring high transmittance and broadband, and for meeting specific polarization signal requirements during antenna transmission and reception. Methods We introduce an electromagnetic metasurface capable of independent polarization control, enabling the switching between second- order filtering and polarization rotation. Based on the traditional FSS model, the structure employs mutually orthogonal feeding designs on its top and bottom layers, with a PIN diode constructing the conversion layer in the middle. When the top and bottom layer diodes align in the same direction and the middle layer diode is activated, the FSS structure generates C- L- C resonance to achieve second- order filtering. To enhance structural understanding, an equivalent circuit model based on the FSS structure validates the design's accuracy. By configuring the top and bottom diodes in opposite directions and deactivating the middle layer diode, the structure forms a Fabry-Perot- Perot (FP) cavity, facilitating polarization conversion. Detailed analysis of the electromagnetic wave propagation path within the structure using the FP cavity model elucidates changes in electromagnetic wave polarization. Results and Discussions The structure effectively adjusts electromagnetic wave polarization, achieving second- order filtering and polarization conversion functions. It exhibits excellent shielding properties for one polarized wave while modulating another. Control over PIN diode activation and deactivation provides four independent operational modes (Fig. 1), meeting modern communication requirements for functionality and adaptability. Each structural function demonstrates superior electromagnetic properties with high transmission efficiency, wide operating frequency bands (Fig. 6), and robust angular stability. These attributes position, the proposed structure favorably for applications in spatial filtering, radomes, and other related fields. Conclusions In this paper, we propose a multifunctional, reconfigurable wideband FSS capable of switching between second- order filtering and polarization rotation functions while independently controlling TE and TM waves. Utilizing an equivalent circuit model, the design achieves wideband second- order filtering through a three- layer metal surface, employing PIN diodes to control TE and TM polarized wave transmission and shielding for independent polarization control. Building upon the second- order filter structure, a conversion layer in the middle layer facilitates polarization rotation based on FP cavity principles. Under second- order filtering, the structure achieves passband transmission from 2.29 - 4.21 GHz with a 59.1 degrees o relative bandwidth. For polarization rotation, linear to cross- polarization conversion spans 1.87-4.48 GHz, achieving an 82.2 degrees o relative bandwidth with polarization conversion rates exceeding 90 degrees o. These capabilities highlight the technology's potential for multi- mode radomes with high transmittance and broadband needs, catering to specific polarized signal requirements during the antenna transmission and reception.