Calibration is the process of eliminating systematic, reproducible errors from the measurement results (system error correction). The process involves the following stages:
A set of calibration standards is selected and measured over the required sweep range. For many calibration types the magnitude and phase response of each calibration standard (i.e. its S-parameters if no system errors occur) must be known within the entire sweep range. In some calibration procedures (TRL, TNA, TRM), part of the characteristics of the standards can be auto-determined due to implicit redundancy (self-calibration).
The analyzer compares the measurement data of the standards with their known, ideal response. The difference is used to calculate the system errors using a particular error model (calibration type) and derive a set of system error correction data.
The system error correction data is used to correct the measurement results of a DUT that is measured instead of the standards.
Calibration is always channel-specific because it depends on the hardware settings, in particular on the sweep range. The means that a system error correction data set is stored with the calibrated channel.
The analyzer provides a wide range of sophisticated calibration methods for all types of measurements. Which calibration method is selected depends on the expected system errors, the accuracy requirements of the measurement, on the test setup and on the types of calibration standards available.
Due to the analyzer's calibration wizard, calibration is a straightforward, menu-guided process. Moreover, it is possible to perform the entire calibration process automatically using a Calibration Unit (accessories R&S ZV-Z5x).
The system error correction data determined in a calibration procedure are stored on the analyzer. You can read these correction data using the remote control command [SENSe<Ch>:]CORRection:CDATa. You can also replace the correction data of the analyzer by your own correction data sets.
A red label Cal Off ! appears behind the trace list if the system error correction no longer applies to one or more traces: This may happen for one of the following reasons: – The sweep range is outside the calibrated frequency range. – The channel calibration is not sufficient for the measured quantity (e.g. a one-port calibration has been performed, but the measured quantity is a transmission parameter). – The system error correction has been switched off deliberately (Correction Off). The analyzer provides other labels to indicate the status of the current calibration; see Calibration Labels.