Efficient phase shift in metamaterial spoof surface plasmon polaritons waveguides.

We propose a novel method for phase shift control in spoof surface plasmon polaritons (SPPs) by systematically loading engineered metallic-dielectric structures. Prior researches examined material effects on spoof SPPs cells dispersion diagrams, But systematic loading different regions of cells remains unaddressed. By tailoring the dielectric loading of bulky U-shaped metallic unit cells using materials with relative permittivities ranging from 3.2 to 9.8 (TMM 3 to TMM 10) in different regions, we precisely investigate the corresponding dispersion's behavior. A measurement setup including a PCB-to-bulky U-shaped spoof SPPs waveguide transition was engineered to feed the U-shaped cells, ensuring they closely match the ideal theoretical performance, defined as a U-shaped cell without any substrate effects. Our theoretical and experimental analyses show that loading the cell's exterior region maximizes the phase shift, with TMM10 achieving up to [Formula: see text] at 3.5 GHz and TMM3 yielding [Formula: see text] at 5 GHz. Near-field measurements using a NEOSCAN optical probe validate these findings across 0.5-6 GHz, demonstrating a clear trade-off between maximum phase shift and bandwidth. This work provides a practical approach for developing compact, high-performance phase shifters for telecommunications and sensing applications.