Miniaturized Dual-Band Bandpass Filter Based on High-Order Mode of Spoof Surface Plasmon Polaritons with Triangular Notch Structure

This paper proposes a novel triangularly notched spoof surface plasmon polariton (SSPP) unit for designing dual-band bandpass filters (DPF). Compared with rectangular SSPP units, the proposed triangularly notched SSPP unit exhibits a superior slow-wave effect and enables the simultaneous excitation of multiple higher-order SSPP modes through a simple structure with compact transverse and longitudinal dimensions. The designed filter optimizes the need for conventional mode-conversion transition structures, significantly reducing the overall size. By adjusting the geometric parameters of the proposed triangularly notched SSPP unit, the upper and lower cutoff frequencies of the passbands can be flexibly tailored with fewer adjusting parameters. The final filter achieves two operating passbands covering 4.85 GHz to 9.3 GHz and 10.4 GHz to 15.3 GHz, with the return loss maintained better than 12 dB within both bands. For validation, the designed filter was fabricated and measured. The measured results show good agreement with the simulations, verifying the effectiveness of the proposed structure and design methodology.