(a) The schematic diagram of the prototype of the digital SSPP waveguide, which is supported by the direct interaction between the incident wave and digital coding. (b) The schematic diagram of a single digital SSPP unit, which is described by the period p = 3.2 mm, strip width w = 0.5 mm, slit width s = 0.45 mm, height of below metallic bar h1 = 3 mm, and height of upper metallic bar h2 = 2.8 mm. (c) The simulated dispersion curves of the digital SSPP unit with different states. (d-f) The Eigen-mode field distributions of the digital SSPP units with '1' state (d & e) and '0' state (f) at 7.2 GHz (d & f) and 10 GHz (e).