This module automatically generates variables for the S-parameters. The port names (use numbers for sweeps to work correctly) determine the variable names. If, for example, there are two ports with the numbers 1 and 2 and Port 1 is the inport, the software generates the variables S11 and S21. S11 is the S-parameter for the reflected wave and S21 is the S-parameter for the transmitted wave. For convenience, two variables for the S-parameters on a dB scale, S11dB and S21dB, are also defined using the following relation:

In addition to the S-parameter variables, variables are also added for reflectances, transmittances, and absorptance, as shown in the table below:

In the table above, ewfd is the tag for the physics interface. This tag can be different for different physics interface instances. N is the name of the port (a number).

In the expressions for the reflectance and the transmittance, it is assumed that the excitation port has the name 1.

The definition of ewfd.Atotal is actually the sum of all the volume and surface losses in the physics. It is only when Activate slit condition on interior port is disabled or Slit type is set to PEC-backed that ewfd.Atotal = 1-ewfd.RTtotal. Otherwise, when Activate slit condition on interior port is enabled and Slit type is set to Domain-backed, some of the radiation that reaches the port might not match any of the port mode fields. Thus, in this case you have the following power conservation relation,

ewfd.RTtotal + ewfd.Atotal + ewfd.Lsca = 1,

where ewfd.Lsca represents scattering loss — radiation that does not match any of the port mode fields.

Periodic ports and diffraction order ports represent the plane-wave radiation propagating in certain directions, defined by diffraction order mode numbers. In 3D, two mode numbers are used, for example m and n, whereas in 2D only one mode number, n, is needed. Each periodic port (or diffraction order port) represent one of two possible polarization directions. Thus, for 3D ports and diffraction order ports, the following variables are available:

In the table above, the variables with the suffix 0_0 represents the mode of the excitation periodic port. The variables with the suffix 0_0_orth represent the reflectance/transmittance for the zero-order mode with a polarization that is orthogonal to the exciting periodic port mode. The suffix M_N_ip represents the mode [M,N] with in-plane polarization. Here, M and N are written p1 for the positive +1 mode number and n1 for the negative −1 mode number, and so on. Variables with the suffix op represent diffraction orders with out-of-plane polarization. In-plane modes have the polarization in the plane spanned by the mode wave vector and port normal, whereas out-of-plane modes are orthogonal to this plane.

Notice that the port mode numbers M and N are completely unrelated to the port name K.