VNA Measurement Best Practices

When making precise measurements with network analyzers, use the following practices to ensure the best results:

• Use quality components and sound measurement practices.
• Use high-quality connectors, adapters, and cables to achieve the highest measurement quality and precision from a VNA.
• Provide proper care for the components, connectors, adapters, and cables and clean them periodically.
• Use a calibrated torque wrench to ensure consistent connections between the VNA and DUT, or the VNA and calibration standards.

Making Measurements with the NI Vector Network Analyzer

When making precise measurements with network analyzers, you must correctly implement each step in the process for best results. Complete the following steps to make a calibrated measurement with the NI vector network analyzer:

1. Prepare for the measurement.
   1. Warm up the NI vector network analyzer and the DUT as specified in the device specifications.
   2. Clean and inspect all connectors, and ensure all connectors are of the appropriate pin depth.
   3. Use phase-equal adapters to handle a non-insertable connection if you are using SOLT calibration.
   4. Connect cables and adapters to the VNA, following the guidelines in the Connector Care topic.
   5. Verify that the device is within the factory calibration interval.
2. Set up an initial, uncalibrated measurement.
   1. Preset the VNA.
   2. Set up source parameters, including reference frequency, output power, and IF bandwidth.

      Tip  Increasing the IF bandwidth improves the speed of the sweep measurement, but it introduces more noise. Decreasing the IF bandwidth yields more accurate measurements but at a lower speed. Higher power on the output port improves measurement accuracy, but amplifiers or sensitive devices may require lower output power.

   3. Connect the DUT to verify setup, cables, adapters, and operation.
   4. Select which S-parameter(s) to measure, and choose the display format.
3. Start the measurement.
4. Observe the uncalibrated response.
5. Remove the DUT.
6. Calibrate the device.
   1. Choose whether you want to perform a new calibration or load a previously performed calibration.
   2. To perform a new calibration, complete the following steps:
      1. Set the measurement parameters such as power, frequency, and number of points.
      2. Set IF bandwidth and averaging to minimize noise during calibration.
      3. Choose the proper calibration kit or input calibration standard definitions.

         Tip  Keep the reference plane constant between your initial, uncalibrated measurement and your calibration setup. The reference plane is established at the location where the VNA connects to the AutoCal module or to the calibration standard. For example, your reference plane may be located at the end of an adapter connected to the end of a precision cable.

      4. Calibrate manually or use automatic calibration.
      5. Verify calibration quality using a known verification standard.

      Note  Do not use the same calibration standards that you used for calibration to perform the verification.

      6. Save the instrument state and calibration.
   3. To load a saved calibration, complete the following steps:
      1. Select the calibration file.
      2. Ensure that the source parameters you specified in the step 2b match those that were used in the calibration. Perform a new calibration if the settings do not match.
7. Perform the calibrated measurement.
   1. Measure the DUT.
   2. Ensure the proper correction from the calibrate step is still being applied.
   3. Measure and save DUT parameters.
8. Verify that the calibrated measurement falls within your expected range.