Apparent discrepancy between S11 from "source data" and S-parameters in POSTFEKO
Altair EmployeeAnswers
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When FEKO processes the S-parameter request each port is automatically loaded (as required by the definition of S-parameters) with the specified reference resistance (usually 50 Ohm).
Consider a wire dipole array in free space where each dipole has a port with S-parameters requested. If we post-process the antenna array in POSTFEKO we can plot the source data and the S-matrix (or S-parameters) on a Cartesian graph.
The S-parameters will be correct, however, although not intended, users can still plot the source data since sources are used on each port for which S-parameters are requested. For the source data the reported source impedance will include the reference resistance (added by the S-parameter request) in series with the impedance of the antenna - often then it would appear that the antenna's input impedance is 50 Ohm higher than expected.
Given a 1-port model such as a single dipole antenna, if the a wire port and voltage source is specified FEKO will compute parameters such as impedance, S11 and VSWR which can be obtained from the source data. If a S-parameter request is made in addition to the voltage source, then in this case FEKO will ignore it and give a note in the standard output.
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