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Accuracy problems calibrating VNA at high IFBW
Background: When using the VNA for pulsed measurements the classic configuration is to increase the VNA IFBW setting such that the data acquisition time is less than the pulse width (based on a 1/IFBW calculation). For example, 600 kHz corresponds to 1.67 us data acquisition time. This setting would be suitable for a 3 us pulse width. Additionally, this type of configuration requires the VNA to be externally triggered (with a pulse generator).
Symptoms: When calibrating the VNA on progressively higher IFBW settings (as described above). The VNA calibration accuracy/verification will degrade. This is typically partially compensated by increasing the VNA averaging. However, in many cases (with small pulse widths and high IFBW settings) this degradation becomes unavoidable and the VNA accuracy suffers greatly.
Solution: When calibrating the VNA the user should select a relatively low IFBW setting (as would typically be done for non-pulsed applications). This will result in a higher quality VNA calibration & verification. Post calibration the VNA IFBW can be increased. After changing the IFBW, the VNA calibration should be re-verified (and averaging enabled if necessary) to maintain the accuracy of the VNA measurement (as observed by the VNA verification).
Keywords: VNA, Calibration, Pulse, Pulsed, Accuracy, Verification
Last date modified: March 23rd 2017
