You can use Floquet ports with periodic boundary conditions to simulate S11 and S21 of an infinite array of the unit cells. By controlling the phase across the primary and secondary periodic boundaries you can control the incident angle of the excitation from the Floquet ports.
Mohamed K. Emara Thank you for sharing your knowledge. I've done it before using the incPlanewave excitation mode and had similar results. I also considered using the floquet ports excitation mode, but I'm not sure if it's limited for periodic structures. Anyway, if you don't mind, can I ask for your email address?