A Novel Miniaturized 2.5-D Frequency Selective Structure with Cross-Resonance Design for Enhanced Wide Passband and High Stopband Suppression

This paper introduces an innovative filter circuit by building upon a foundational broadband filter model, incorporating novel resonators and cross-coupling between them to achieve a filter with both a wide passband and high stopband suppression. Leveraging this advanced circuit design, a novel miniaturized 2.5-D Frequency Selective Surface (FSS) is developed, featuring five planar layers and two vertical layers. The planar layers are designed with a unique miniaturization approach, while the vertical layers enable efficient cross-coupling between resonators, significantly improving the overall performance. Simulation results demonstrate that the proposed FSS achieves an average insertion loss of just 0.43 dB within the 1.5–3.7 GHz range, corresponding to a passband fractional bandwidth of 84.6%. Notably, the stopband spans 0.69–1.19 GHz with a suppression of −15 dB at 1.05 GHz, and the high-frequency stopband maintains −10 dB at 4 GHz. Additionally, the FSS maintains excellent passband performance and stopband suppression even under oblique incidence angles ranging from 0° to 60°. A prototype of the FSS was fabricated and experimentally tested, and the results closely match the simulations, confirming that the proposed FSS outperforms conventional broadband FSS designs in terms of stopband suppression, insertion loss, and angular stability. This innovative circuit and structural design provide a significant solution for achieving high-performance electromagnetic shielding, particularly in complex electromagnetic environments.