Negative group delay SSPP mode based on coupled periodic cells

Abstract

To realize negative group delay (NGD) of spoof surface plasmon polaritons (SSPPs), two coupling strips are introduced within the U-shaped cell for SSPP waveguide. Furthermore, two such cells are coupled to form a double-structured NGD unit. At lower frequencies, the constructed unit can implement both TE and TM modes with the NGD feature, and the maximum NGD values of – 0.42 ns for TE mode is achieved at 1.83 GHz. Since the TM mode is alongside the stopband, a wide NGD band of 2.01–3.25 GHz is yielded, with a small NGD value. However, as this unit is applied to SSPP waveguides to compensate for positive delays, the measured NGD maximum is 2.81 ns at 1.93 GHz and 9.65 ns at 2.42 GHz, due to the influence of waveguide structure on the NGD unit. The proposed unit structure exhibits promising applications in delay equalization and dispersion compensation for microwave system.