A Multi-Coupling 3D Frequency-Selective Surface with High Selectivity and Wide Dual Passband

A novel single-layer multi-coupling 3D frequency-selective surface featuring high selectivity and a 3D dual-band frequency-selective surface (3D-DBFSS) is presented in this paper. By incorporating three different coupling gaps within each unit cell, the design achieves two distinct passbands with wide bandwidths and steep transition edges. For the first passband, the −3 dB bandwidth ranges from the lower cutoff frequency of 9.9 GHz to the upper cutoff frequency of 15.2 GHz, yielding a bandwidth (BWL3dB) of 5.3 GHz. For the second passband, the −3 dB bandwidth extends from 22 GHz to 26 GHz, providing a bandwidth (BWU3dB) of 4 GHz. The structure exhibits eight transmission poles and four transmission zeros within a single layer, enhancing its selectivity. The simulation results indicate that the dual passbands are centered at 12 GHz and 24 GHz, respectively, with bandwidths sufficient for practical applications. The proposed frequency-selective surface demonstrates a low insertion loss of just 0.8 dB, which is significantly lower compared to most reported dual-band FSS designs. Furthermore, the thickness of the 3D-DBFSS is only one-third of the wavelength in free space, making it considerably thinner than other 3D-FSS structures operating in the same frequency range. The proposed design also ensures stable performance over a wide range of incident angles, which is crucial for practical deployment. Additionally, the overall size of the unit cell of the frequency-selective surface is 4 × 4 × 10.8 m³. The structure is easy to fabricate, which contributes to its potential for cost-effective mass production. Overall, the 3D-DBFSS offers high frequency selectivity, effective bandpass performance, and strong suppression in the stopband region.