Broadband low-pass filter based on trapezoidal spoof surface plasmon polaritons structure

A novel broadband low-pass filter is proposed, utilizes the dispersion characteristics of surface-bound modes supported by spoof surface plasmon polaritons (SSPPs). The trapezoidal SSPP structure improves broadband performance by adjusting the dispersion of surface modes, withthe integration of bent transmission lines providing ultra-broadband suppression. Compared to traditional SSPP units, the trapezoidal design shows enhanced slow-wave effects. A folded microstrip dual-port coupling mechanism enables excellent high-frequency out-of-band suppression. Simulations demonstrate an ultra-broad passband up to 20.5 GHz with in-band return loss below – 10 dB, and the results align closely with experimental measurements. This design achieves −45 dB out-of-band suppression within 2.5f0 to 3.5f0(f0 is the center frequency), making it promising for microwave integrated systems.