Broadband low-dispersion waveguide-integrated spoof surface plasmon polariton delay lines

The inherent dispersion of spoof surface plasmon polariton (SSPP) transmission lines-where group velocity decreases monotonically with frequency-constrains their deployment in applications demanding constant group delay. Here, we propose a waveguide-integrated SSPP (WISSPP) structure that achieves broadband low-dispersion characteristics through intrinsic dispersion engineering. The unit exhibits a transition from anomalous to normal dispersion, yielding a U-shaped group delay profile with near-zero group delay dispersion at the design frequency. Experimental validation demonstrates group delay variations within 7% across the 8-12 GHz band. The proposed structure preserves the miniaturization advantages of SSPP circuits while enabling customizable center frequency and unit-length delay time through simple parameter adjustment, thereby expanding the application prospects of SSPP technology in integrated microwave systems.