A full wave EM simulation has been performed
based on the standard finite-difference time domain
(FDTD) method by CST Microwave Studio software.
In simulations, we set periodic boundary conditions
with the wave vector k parallel to the double U-shaped
structure plane and the electric field paralleling the x
axis and the magnetic field paralleling the y axis (see
the inset of Fig. 1(a)). There is no transmission to be
examined for a normal incident TEM plane wave, as it
is blocked by the backing metal plate. Thus, only the
reflectance needs to be measured in our simulations
and experiments.