Smith Chart |
| A smith chart maps part of the impedance
plane (usually the right or positive real half) onto a unit circle. The center of the
smith chart represents the normalizing impedance, typically 50 ohms. As you pass the cursor over a smith chart, the status bar at the bottom of the program displays the corresponding reflection coefficient under the cursor rather than impedance. This is because Eclipse allows an arbitrary terminating impedance at each port and therefore a different impedance would have to be displayed in the status bar for each unique termination. Individual markers, however, can be customized to display reflection coefficient, impedance, VSWR or Q. If a marker is customized to read impedance, Eclipse attempts to determine which termination should be used as the de-normalizing impedance for the expression associated with the marker. If the expression is simply Sii (where i = 1, 2, 3 … 9) then the impedance at port i will be used. If the expression is more elaborate then the marker will display the reflection coefficient since the de-normalizing impedance is unknown. The TERM statement establishes the reference impedance used at the associated port. When a complex impedance is specified in the TERM statement (via ZR-ZI, GM-GA, or DATA file parameters) then the complex conjugate of that impedance becomes the reference impedance. This approach correctly displays the reflection between the network and terminating impedance; thus, a perfect match between termination and network is represented by the center of the smith chart. |