  Spoof surface plasmon meta-couplers are compact antennas which link
propagating waves and surface waves. However, most of them are designed with a
fixed phase gradient and channel for the incident waves with specific
polarization, which limits their further applications in multichannel
scenarios. In this Letter, we propose, to the best of our knowledge, a new
method that combines the Brillouin folds theory with the Generalized Snell Law.
We demonstrate that when the phase gradient of the metasurface is large enough,
Brillouin folds effect will occur, which will create dual phase gradient space
in a single metasurface. With this method, we design two novel terahertz
meta-couplers with functionalities of symmetrical and asymmetrical
binary-channel/bidirectional SSP excitation. Furthermore, finite element method
(FEM) simulations are performed to demonstrate their functionalities.
Considering the orthogonality of the incident waves, there can be a total of
four independent space channels to excite SSP on one metasurface. This work may
open up new routes in multi-channel SSP meta-couplers and multi-beam surface
wave antennas.
