5. Math Functions
7. Select S
11
Calibration. After going through an informational message box, the S
11
Calibration menu will appear and the CT100B will ask for the open terminator. Attach the
open terminator and press Scan Open, or alternatively press Use Selected to use the currently
selected trace as the open calibration standard. For the best results when using type SMA
terminators, use a calibrated 3.5 in.-lb. (0.4 Nm) torque wrench (pn: CT100-TL-TORX7) to
tighten the test standards as well as the DUT.
8. Follow the same process as instructed to scan or use the selected trace for the short and
50 ohm load calibration standards.
9. The instrument will now ask for the Measured “Device Under Test” (DUT). Press Use Live
to create a live S
11
trace, Use Selected to create a static S
11
trace from the currently selected
trace, or Scan Measured to scan the current live TDR trace.
10. Select the S
11
return loss trace. Use the cursors to measure return loss at cursor and average
return loss between cursors.
Figure 5.4 shows an S
11
return loss plot and TDR trace for a 2.4 GHz WiFi antenna. The return
loss at 2.4 GHz (2400 MHz) is 20.9 dB.
Figure 5.4. S
11
return loss plot (orange) and TDR trace (red) of a 2.4 GHz WiFi antenna.
The return loss is calculated on the portion of the TDR trace between the cursors.
5.5. Return Loss (S
11
) Options
There are several mathematical transforms to apply to the S
11
trace and its input traces that can,
in some cases, help reduce irregularities in the final Return Loss plot. These options can be found
under SCAN → Math → SParam & Normalize Tools → S
11
Options. If the options are changed
when no S
11
traces exist, then they will be applied to the next S
11
trace created. Otherwise, they
are applied to the last S
11
trace that was selected using the SELECT button. The options can be
combined as necessary, and will change the last selected S
11
trace in real time.
CT100B TDR Cable Analyzers Operator’s Manual 81
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