Abstract
Spoof surface plasmon polaritons (SSPPs) exhibit strong field confinement and slow-wave characteristics for microwave and terahertz applications. However, existing multiband SSPP structures generally lack independent control of cutoff frequencies and often suffer from radiation losses. Here, a multilayer substrate-integrated waveguide (SIW) supporting multi-order effective SSPP (ESSPP) modes is proposed for independently controllable multiband transmission. By exploiting structural dispersion in rectangular waveguides, multiple equivalent epsilon-negative/epsilon-positive interfaces are created to excite different-order ESSPP modes in distinct frequency regions. Analytical dispersion relations and closed-form expressions for the cutoff frequencies are derived, showing that each passband is controlled by a single layer, thereby enabling independent frequency tuning and analytical filter design. A tri-band ESSPPs filter is designed, fabricated, and experimentally validated. The measured results agree well with theory and simulations, demonstrating three passbands at 5–5.7 GHz, 6.3–6.7 GHz, and 8.3–8.8 GHz with low insertion losses. The proposed structure provides a compact and low-radiation platform for multiband microwave and millimeter-wave applications.