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HFSS15: Calculating the PI Impedance
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Calculating the PI Impedance
The Zpi impedance is the impedance calculated from values of power (P) and current (I):
| 
| (1) |
The power and current are computed directly from the simulated fields. The power passing through a port is equal to the following:
| 
| (2) |
where the surface integral is over the surface of the port.
The current is computed by applying Ampere’s law to a path around the port:
.
| 
| (3) |
While the net current computed in this way will be near zero, the current of interest is that flowing into the structure, I-, or that flowing out of the structure, I+. In integrating around the port, HFSS keeps a running total of the contributions to each and uses the average of the two in the computation of impedances.
Note | Zpi calculation is modified when a symmetry E plane touches a port. The current on the symmetry E plane is included in the Zpi calculation for a port with more than one conductor, where as for a single conductor port, such as a waveguide, the current on the symmetry E plane is not included in the Zpi calculation. |
