Miniaturized broadband lowpass filter based on the integrated square dumbbell and meander structure spoof surface plasmon polaritons

A novel miniaturized broadband low-pass filter (LPF) is proposed based on the integrated square dumbbell and meander (SDBM) structure spoof surface plasmon polaritons (SSPPs). Compared with the conventional H-shaped and square dumbbell structure SSPP unit-cells, the integrated SDBM structure can effectively reduce its asymptotic frequency, revealing much better slow-wave characteristics. A broadband LPF is designed by integrating two types of SDBM structure SSPP unit-cell to enhance out-of-band suppression. Finite element method (FEM) simulations demonstrate that the SDBM structure SSPPs-based LPF exhibits excellent lowpass characteristics across a broadband range of 0-2.24 GHz, achieving a remarkably high out-of-band rejection level of - 27 dB in a broadband range of 2.39-8.7 GHz. An equivalent LC circuit model is established for the proposed SDBM-structured SSPPs-based LPF, exhibiting a reasonable consistency with the FEM results. The designed LPF is skillfully realized utilizing conventional PCB manufacturing techniques, achieving with a size of only 0.238λ_c × 0.12λ_c (λ_c is the wavelength at cut-off frequency). The experimental results exhibit a remarkable consistency with the simulated data, thereby validating the soundness and practicality of the proposed design. The proposed broadband LPF featuring robust out-of-band rejection, demonstrates significant potential for integration into compact microwave and terahertz (THz) circuits, paving the way for advanced applications in these frequency bands.