# Transmission and Reflection Coefficients

Calculate the properties of frequency selective surfaces (FSS) in a multilayer scattering scenario by using transmission and reflection coefficients for plane waves. Use in conjunction with periodic boundary conditions (PBC), multilayer planar Green's functions or infinite planes for a more efficient solution.

Note: Only a single plane wave is supported (no additional sources are allowed) when requesting transmission / reflection coefficients. The plane wave is allowed to have (loop over) multiple incident angles.
The model must either contain:
• planar multilayer substrate without any other geometry / mesh in the model
or
• a 2D periodic boundary condition (PBC).

The transmission coefficient is defined as:

(1) $\tau =\frac{{E}_{t}}{{E}_{i}}$
and the reflection coefficient:
(2) $\rho =\frac{{E}_{r}}{{E}_{i}}$