Design of Ultra-miniaturised Frequency Selective Surfaces Based on 2.5-Dimensional Closed Loop

A novel approach for designing ultra-miniaturised frequency selective surfaces (UMFSSs) based on 2.5-dimensional closed loop (2.5DCL) is proposed. Segregated by a substrate and connected by metallic vias, two sets of parallel metallic lines are arranged compactly along two orthogonal directions. The proposed approach extends the total length of 2.5DCL efficiently, thus the unit cell can achieve a superior miniaturization. Single-band and dual-band FSSs are designed and simulated to verify this method. The single-band FSS operates at 1.98GHz with a unit cell size of merely 0.029λ₀×0.029λ₀, and element size of the dual-band FSS is about 0.036λ₀. Both the proposed FSSs provide stable frequency responses under various incident angles and polarisations.