Figure 1 - The “FSS - Unit Cell (FD)” template simplifies simulation set-up by automatically setting the
unit cell boundary conditions.
The incident angle of the incoming plane wave may be specified by setting angles Theta and Phi, both of which have already been parameterized by the template. The periodicity of the FSS is also freely configurable as shown below. Different periodicities can be assigned in the x- and y-directions, and the use of a skewed lattice is also possible by specifying the grid angle (this can be useful for simulating compact closely coupled arrays).
Figure 2 - The incident plane wave angle and unit cell periodicity of the FSS are freely configurable.
For off-normal incident angles the Floquet port modes ensure that the reflected wave is recorded in the direction of optical reflection, while the transmission is in the same direction as the incident wave. This is elucidated by the figure below.
Figure 3 - Incident and transmitted directions are automatically set by the Floquet modes.
The periodicity can also be specified, as in this example, by setting the size of the substrate to the desired periodicity, then checking the “Fit unit cell to bounding box” checkbox.
Figure 4 - Unit cell boundary conditions can be set to fit the bounding box.
The default Floquet port settings excite two plane waves with orthogonal electric fields as shown below (TE(0,0) and TM(0,0) modes), but higher order modes may also be specified in the port properties dialog (“Details”). Co-polar and cross-polar coupling between the modes, both reflection and transmission, are represented in terms of S-parameters. The co-polarised reflection of mode 1 at port Zmin would thus, for example, be named SZmin(1),Zmin(1), and the cross-polarised transmission between modes 2 and 1 SZmax(1),Zmin(2).
Figure 5 - Two orthogonal Floquet port modes are excited by default.
Figure 6 - Higher order or circularly polarised Floquet modes may be defined.
Once the geometry is constructed, the simulation conditions are set up, and some field monitors have been defined, the frequency solver can be started (with either a hexahedral or tetrahedral mesh).
Simulation results
Of primary interest in this case are the S-parameter results, which represent the reflection from and transmission through the FSS. The co-polar reflections and transmissions of both modes are almost identical due to the symmetrical circular rings (the slight difference is due to the tetrahedral mesh). The transmission is almost completely blocked at 15.02 GHz, as seen from the SZmin(1),Zmax(1) of about -63 dB, and the reflection is almost complete (SZmax(1),Zmax(1) ≈ -0.006 dB).