Fig. 1. (a) The new spoof SPP TL with zigzag grooves, in which the width of the TL is w₁, the period of the TL is p₁, the width of the grooves is a₁ and the depth of the grooves is d₁, the folding extent parameters are X and Y. (b) The conventional spoof SPP TL with straight grooves, in which the width of the TL is w₂, the period of the TL is p₂, the width of the grooves is a₂, the vertical depth of the grooves is d₂.

Fig. 2. (a) Dispersion diagrams of the new spoof SPP TLs with different X, where Y is set as 1 mm. (b) Dispersion diagrams of the new spoof SPP TLs with different Y, where X is set as 1 mm. (c) Dispersion diagrams of the conventional spoof SPP TLs with different d₂. (d) The plot of the relationship between depth of straight grooves and cutoff frequency.

Fig. 3. [in Chinese]

Fig. 4. The simulated (a) S21 and (b) S11 of the whole structures with different X, in which Y is fixed as 1 mm. From (a) and (b), it can be concluded that larger X implies larger equivalent depth. The simulated (c) S12 and (d) S11 of the whole structures with different Y, in which X is fixed as 1 mm. From (c) and (d), it can be concluded that larger Y implies smaller equivalent depth.

Fig. 5. [in Chinese]

Fig. 6. The two plots of field distribution are normalized on the same dimension. (a) The simulated amplitude distributions of electric field near the conventional spoof SPP TL with straight grooves where w₂=5 mm, d₂=4.6 mm, p₂=5 mm and a₂=0.4 mm. (b) The simulated amplitude distributions of electric field near the new spoof SPP TL with zigzag grooves where w₁=5 mm, d₁=4.6 mm, p₁=5 mm, a₁=0.4 mm, X=1.5 mm and Y=1 mm. From this figure, strong field confinement of the new spoof SPP TL with undulant grooves can be observed.

Fig. 7. (a) The sample of the typical spoof SPP TL with straight grooves, in which t₁=0.508 mm, w₁=5 mm, a₁=0.4 mm, p₁=5 mm and d=4.6 mm. (b) The sample of the new spoof SPPs TL with undulant grooves, in which t₂=0.508 mm, w₂=5 mm, a₂=0.4 mm, p₂=5 mm, X=1.5 mm and Y=1 mm.

Fig. 8. [in Chinese]

Fig. 9. [in Chinese]

Fig. 10. [in Chinese]

Table 1. Geometrical equivalent depths and simulated equivalent depths of zigzag grooves (unit: mm)]]>