When a periodic structure is excited using a plane wave source, it acts as a periodic surface that reflects or transmits the incident wave. You can model frequency selective surfaces, electromagnetic band-gap structures and metamaterials in this way. EM.Cube calculates the reflection and transmission coefficients of periodic surfaces or planar structures. If you run a single plane wave simulation, the reflection and transmission coefficients are reported in the Output Window at the end of the simulation. Note that these periodic characteristics depend on the polarization of the incident plane wave. You set the polarization (TMz or TEz) in the '''Plane Wave Dialog''' when defining your excitation source. In this dialog you also set the values of the incident '''Theta''' and '''Phi''' angles.
At the end of the planar MoM simulation of a periodic structure with plane wave excitation, the reflection and transmission coefficients of the structure are calculated and saved into two complex data files called "reflection.CPX" and "transmission.CPX". These coefficients behave like the S<sub>11</sub> and S<sub>21</sub> parameters of a two-port network. You can think of the upper half-space as Port 1 and the lower half-space as Port 2 of this network. '''As a result, you can run an adaptive sweep of periodic structures with a plane wave source just like projects with gap or probe sources.''' The reflection and transmission (R/T) coefficients can be plotted in EM.Grid on 2D graphs similar to the S parameters. You can plot them from the Navigation Tree. To do so, right click on the '''Periodic Characteristics''' item in the '''Observables''' section of the Navigation Tree and select '''Plot Reflection Coefficients''' or '''Plot Transmission Coefficients'''. The complex data files are also listed in EM.Cube's '''Data Manager''', where you can view or plot them. '''Â {{Note that in |In the absence of any finite traces or embedded objects in the project workspace, EM.Cube computes the reflection and transmission coefficients of the layered background structure of your project.'''}}
[[File:PMOM102.png]]
Figure 1: A periodic planar layered structure with slot traces excited by a normally incident plane wave source.
=== Characterizing Periodic Surfaces Using Angular Sweeps ===