Skip to content

S-parameters and Smith chart

The S-Parameters tab plots the network response of a finished run: magnitude in dB against frequency, and the same data on a Smith chart. It also carries the markers, reference overlays, imports, and exports for that data.

After a run, each active port contributes a column of traces. The tab shows the reflection Sii for every active port, and both Sij and Sji for every active pair. The reflection trace of the port that was driven this run is the one that carries impedance, so it also appears on the Smith chart.

Traces and parameter chips

The toolbar starts with a chip for S11 and S21 and a More Parameters popover. A chip toggles that trace on the plot and colours itself to match it. More Parameters lists every remaining Sij for the port count, plus S12 and S22 even for a one-port run, and holds one checkbox per imported overlay. Each trace keeps a fixed colour so a port reads as the same hue across the plot, the chart, and the editor canvas.

Which traces start visible follows the active ports, and changing the active port set resets the selection to that default. Missing data never disables a chip: a checked but empty trace means the run did not produce it, so re-run rather than read a blank plot as a broken control.

The freshness badge in the corner reads Latest results when the plot matches the current project. It switches to a stale warning ("Geometry changed since this run", "Config changed since this run", or both) once you edit the project after the run, and to "Running, results shown reflect last run" during a solve. A stale badge means re-run before trusting the numbers.

The two views

Split View is on by default and shows the dB magnitude plot and the Smith chart side by side, divided by a draggable splitter. Uncheck it to show one view at a time. The dB Magnitude and Smith Chart buttons then switch between them. In split view those buttons only pick which plot is active for marker placement and export.

The dB plot has frequency in GHz on the x-axis and magnitude in dB on the y-axis. Drag to pan, scroll to zoom both axes, Ctrl+scroll to zoom frequency only, Shift+scroll to zoom magnitude only.

The Smith chart is normalized to 50 Ω. Constant-resistance circles and constant-reactance arcs are labelled in ohms, the centre is the matched load, the left real-axis endpoint is a short and the right is an open, and inductive (+jX) reactance is the upper half. It stays square and aspect-locked, so it never stretches. Only reflection traces carry the complex impedance the chart needs, so a magnitude-only transmission trace does not draw here.

Range and Home

Range opens a popover to set the frequency and magnitude axis limits. Leave a bound on Auto to fit the data. The popover reflects the plot's true current extent: a manual bound shows its value, and an Auto bound shows the value it resolves to in the grey caption beneath. Home clears every bound back to Auto and refits both views. Range applies to the dB plot only.

Markers

Marker (shortcut M) arms placement. Click the plot to drop a marker on the nearest trace point, and placement disarms after one marker. A marker reads out its frequency and magnitude, the impedance where the trace carries it, and, on a reflection trace, the bandwidth of the dip it sits in. On the Smith chart the readout is frequency, |Gamma|, angle of Gamma, and impedance.

Drag a marker to slide it along the trace, or to another trace. Esc cancels placement, Delete removes the selected marker, and Ctrl+Z undoes the last marker edit.

Right-click a marker for Rename, Hide, Delete, and, on the dB plot, Properties. The properties dialog:

  • Sets the source trace and renames the marker.
  • Follows a chosen dip. Pick the rank N and the ordering (deepest, shallowest, lowest frequency, highest frequency). A tracked marker re-snaps to that dip on every replot, including each Live-mode rerun, so a linked surface-current or radiation viewer stays on the resonance as it moves. If the dip is gone the marker shows (no match) and holds its last frequency.
  • Draws a vertical line at the centre frequency, shades the bandwidth band below a dB threshold (default -10 dB, reflection traces only), and shows a centre-frequency and bandwidth readout on the plot.

Set as Reference

Set as Reference freezes the traces currently on screen as grey dashed overlays, so you can change the design and watch each trace shift against the frozen one. The baseline is stored in the project, and one is kept at a time: setting a new reference replaces the old one.

The reference is view-neutral. Reflection traces keep their complex impedance and phase, so the baseline shows on both the dB plot and the Smith chart, while transmission traces keep magnitude and show on the dB plot only. Setting a reference does not move the axes. In live mode the button moves into the More Parameters popover.

Importing reference traces

Import a measured or external sweep to overlay it on the run. Both live in the Import / Export dropdown, render as dashed traces in distinct colours, and are stored in the project so the source file can be deleted afterward. Importing requires a signed-in license.

  • Touchstone reads .s1p through .s8p and .sNp. Each S-parameter in the file becomes one overlay trace.
  • CSV opens a column-mapping dialog, because a plain CSV is not self-describing. Choose the frequency column and one of three data types: an S-parameter as dB magnitude plus phase in degrees, an S-parameter as real plus imaginary, or an impedance Z as real plus imaginary in ohms. The second value column is optional. The frequency unit is taken from an explicit choice, then from the column header, then guessed from the values, with the guess confirmed before import. The reference Z0 you set converts an imported impedance to S and is stored with the trace so the Smith chart renders it correctly.

Exporting

Every export is in the Import / Export dropdown. Exact file layouts are on File formats and outputs.

  • CSV writes one row per frequency, with each trace interpolated onto the first parameter's frequency grid and points outside a trace's own band left blank. In split view, when reflection data is present, a dialog offers the dB magnitude, the reflection coefficient, or both.
  • Touchstone writes all S-parameters as one network file, labelled by port count (.s2p for two ports). Filled values are disclosed in the export dialog and in file comments. The fill rules are on File formats and outputs. Touchstone export is a Pro feature and shows a lock badge otherwise.
  • PNG saves the plot as an image. In split view a dialog offers the active plot, both plots as two files, or both stitched into one wide image. Marker and curve legends are drawn into the saved image.