User Calibration

A user calibration is accomplished with a set of calibration standards from a network analyzer calibration kit or user-fabricated, user-defined standards. By comparing the standard values, stored in the network analyzer, against the measured values of the calibration standards, a set of correction factors is created. These correction factors are applied to the data during the post-calibration measurements to compensate for the sources of error. User calibration removes uncertainty by applying the 12-term error model.

There are various types of user calibration to perform. RF Calibration refers to the standard calibration family types that calibrate for the accuracy of S-parameter measurements. Power Calibration refers to calibration methods that improve power accuracy delivered to and received from the device under test (DUT), specifically when you need accurate power levels at some point along the measurement path between the DUT and VNA test ports.

The following user calibration types are referenced in this help file:

RF Calibration:

• Automatic Calibration (AutoCal)
• Short-Open-Load-Through (SOLT) Calibration
• Short-Open-Load-Reciprocal (SOLR) Calibration
• Through-Reflect-Line (TRL) Calibration

Power Calibration:

• Source Power Calibration
• Test Receiver Calibration
• Reference Receiver Calibration

Many factors determine how often user calibration is performed, such as the required measurement accuracy, environmental conditions, and the repeatability of the DUT connection. For accurate results, your NI-VNA device must be calibrated at the ambient temperature after at least 30 minutes of warm-up time and before making any measurements. The NI-VNA should be recalibrated whenever the instrument setup changes or whenever a test port extension cable is added, removed, or replaced. Typically, network analyzers need user calibration every few hours to every few days. You should use verification standards, identification of the sources of measurement uncertainty, and personal experience to determine how often to calibrate. The remainder of this section uses the term calibration to describe user calibration, not the recommended yearly certified factory calibration.

Using a User-Defined Calibration Kit

NI-VNA allows you to use a third-party calibration kit with your VNA; however, you must specify all the calibration coefficients into the software for the equipment to be properly calibrated.

To specify the coefficients, complete the following steps:

1. Launch the NI-VNA Soft Front Panel.
2. Select Calibration»Cal Kit/AutoCal Characterization»Create/Edit Kit from the NI-VNA Settings Panel to launch the Cal Kit Info dialog box.
3. Select the Cal Kit option.
4. Enter a name for the new calibration kit in the Define New Cal Kit control, and specify the gender.
5. Click OK to launch the User Defined Standard dialog box, shown in the following image.
   
   
6. Enter the coefficients in the appropriate controls.
7. Click Save To Disk and specify the location to save the calibration file.

After you enter the information about your user-defined calibration kit, you can then save the information and load it again for later measurements. To load the data at a later time, use the niVNA Load User Defined Calibration Kit Data From File VI or the niVNA_LoadUserDefinedManualCalibrationKitDataFromFile function.

Calibration Tips

During user calibration, observe the following guidelines:

• To change the gender of a connector to make a through connection, use phase-equal adapters during all steps of calibration to keep the reference plane constant.
• Perform calibration under the lowest noise scenario (when you have a low IF bandwidth configured, high power, and averaging is enabled).
• Keep setup parameters (start frequency, stop frequency, and so on) constant for the most accurate calibration results.