If your planar structure is excited by gap sources or probe sources or de-embedded sources, and one or more ports have been defined, the planar MoM engine calculates the scattering, impedance and admittance (S/Z/Y) parameters of the designated ports. The scattering parameters are defined based on the port impedances specified in the project's Port Definition dialog. If more than one port has been defined in the project, the S/Z/Y matrices of the multiport network are calculated. Note that the S/Z/Y matrices of an N-port structure are related to each other through the following equations:
:<math>\mathbf{ [S] = [File:PMOM121.pngY_0]\cdot ([Z]-[Z_0]) \cdot ([Z]+[Z_0])^{-1} \cdot [Z_0]}</math>
where ['''U'''] is the identity matrix of order N, ['''Z:<submath>0</sub>'''] and \mathbf{ ['''Y<sub>0</sub>'''] are diagonal matrices whose diagonal elements are the port characteristic impedances and admittances, respectively, and = ['''vZ<sub>0Z]^{-1} } </submath>'''] is a diagonal matrix whose diagonal elements are the square roots of port characteristic impedances. The voltage standing wave ratio (VSWR) of the structure at the first port is also computed:
:<math>\mathbf{ [Z] = [\sqrt{Z_0}] \cdot ([U]+[S]) \cdot ([U]-[S])^{-1} \cdot [\sqrt{Z_0}] }</math><!--[[File:PMOM121.png]]--> where <math>\mathbf{[U]}</math> is the identity matrix of order N, <math>\mathbf{[Z_0]}</math> and <math>\mathbf{[Y_0]}</math> are diagonal matrices whose diagonal elements are the port characteristic impedances and admittances, respectively, and <math>\mathbf{[\sqrt{Z_0}]}</math> is a diagonal matrix whose diagonal elements are the square roots of port characteristic impedances. The voltage standing wave ratio (VSWR) of the structure at the first port is also computed: :<math> \text{VSWR} = \frac{|V_{max}|}{|V_{min}|} = \frac{1+|S_{11}|}{1-|S_{11}|}</math><!--[[File:PMOM122.png]]-->
At the end of a planar MoM simulation, the values of S/Z/Y parameters and VSWR data are calculated and reported in the output message window. The S, Z and Y parameters are written into output ASCII data files of complex type with a "'''.CPX'''" extension. Every file begins with a header consisting of a few comment lines that start with the "#" symbol. The complex values are arranged into two columns for the real and imaginary parts. In the case of multiport structures, every single element of the S/Z/Y matrices is written into a separate complex data file. For example, you will have data files like S11.CPX, S21.CPX, ..., Z11.CPX, Z21.CPX, etc. The VSWR data are saved to an ASCII data file of real type with a "'''.DAT'''" extension called, VSWR.DAT.
Figure 3: Changing the graph type by editing a data file's properties.
[[File:PMOM134.png|800px]]
Figure 4: The S<sub>11</sub> parameter plotted on a Smith Chart graph in EM.Grid.