A dual-band frequency-selective surface with rectangular filtering characteristic for the second band enabled by harmonics resonance

In this article, a dual-band frequency-selective surface is proposed, which the second band is realized utilizing higher harmonics. First, source of harmonics from a traditional single-layer X-shaped slot FSS is analyzed. Second, based on the equivalent circuit model (ECM) method, a dual-band FSS is proposed by loading a cross-dipole patch as band-stop filtering circuit, which the second band is designed close to the higher harmonics. Then, to utilize the higher harmonics, an ECM with odd- and even-mode analysis is proposed to guide the synthesis of the FSS. Cascading the top and bottom layers of the modified X-shaped slot layers and the middle cross-dipole patch layer, harmonic coupling is achieved, resulting in good rectangular filtering characteristic of the second passband is obtained. The simulated results indicate that the 3 dB relative bandwidth of the two passbands are 24.2% and 14.4%, and the roll-off rates at the left and right edges of the second passband are 233 dB/GHz and 47 dB/GHz, respectively. Finally, the prototype is fabricated and measured, showing good agreement with simulation results and angular stability up to 45°under TE polarization. • Breaking through the inherent idea of traditional FSS to suppress higher harmonics, the proposed FSS provides a unique method for the design of multi-band FSS. • Improved rectangular filtering characteristic in the passband after coupling harmonics, The roll-off rates at the left and right edges of the second passband are 233 dB/GHz and 47 dB/GHz, respectively. • The isolation between passbands is higher, avoiding the interference of signals between passbands. • The bandwidth is better than the bandwidth of the compared literature.