Polarization-Insensitive Time-Modulated Frequency Selective Surface with Asymmetric Geometry for Radar Countermeasures

Abstract

This work presents a time-modulated switchable frequency-selective surface (FSS) for radar-countermeasure applications operating across 2.3-3.76 GHz. The proposed unit cell employs a compact, three-layer geometry incorporating only two PIN diodes, where an offset diode placement combined with a tailored capacitive layout is utilized to exhibit polarization-insensitive operation without requiring conventional four-fold symmetry. By appropriately biasing the diodes, the structure achieves two reflection states under both ON and OFF conditions with nearly identical magnitudes but a stable phase difference ranging from 115.04° to 244.96° required for effective time modulation. This results in the suppression of the primary reflected beam and a 24.73 dB enhancement of the first-order sidebands, thereby achieving broadband radar-countermeasure behavior. The full-wave simulations and surface current analyses further verify the desired response under orthogonal polarizations, ensuring its polarization-independent behavior and angular stability up to 45°. With its compact topology, parallel biasing scheme, and robust electromagnetic (EM) characteristics, the proposed design offers strong potential for efficient and practical radar-evasive surfaces. © 2026 IEEE.