Calibrations using a match or sliding match
If the calibration kit contains a sliding match standard, the Sliding Match appears in the Measured
Standards list whenever the selected calibration type requires a Match. A click on the node
expands the check boxes for the different positions of the load element. The number of different
positions is defined in the User Interface tab of the System Configuration dialog.
The sliding match is a one-port standard consisting of an air line with a movable, low-reflection load
element (sliding load). This standard is used because a no perfect match is available over a wide
frequency range. However, a series of measurements at a given frequency with equal mismatch
and varying phase yields reflection factors that are located on a circle in the Smith chart. The
center of this circle corresponds to perfect match. The network analyzer determines and further
corrects this match point following I. Kása's circle-fitting algorithm.
To obtain the reflection coefficient for a perfectly matched calibration standard, the sliding load
must be measured at least at 3 positions which should be unequally spaced to avoid overlapping
data points. Increasing the number of positions to 4 – 6 can improve the accuracy. Moreover it is
recommended to use the predefined load positions of the standard.
The calibration is valid (Apply is available) if either the match or three positions of the sliding match
have been measured. However, it is often desirable to acquire calibration data from both standards.
The analyzer combines the data in an appropriate manner:
The match results are used up to the lower edge of the specified frequency range of the
sliding match (Min Freq).
The sliding match results are used for frequencies above the Min Freq. In general, the
sliding match will provide better results than the match within its specified frequency range.
Isolation measurement (optional)
For two or multiport normalizations, the Measured Standards list contains an Isolation (optional)
standard in addition to each through standard. Measurement of the isolation is optional; the
normalization correction is calculated as:
Correction value = (Transmission coefficient DUT – Isolation) / (Transmission coefficient Through –
Isolation).
The isolation term accounts for a possible crosstalk between a pair of analyzer ports. The isolation
standard is not a physical standard; it is recommended to terminate the analyzer ports with 50 Ω to
measure the isolation.
Waveguide calibration
When calibrating waveguide ports, ensure that the calibration standards are connected correctly.
The electric fields at each of the waveguide transitions must be parallel. For example, if you use a
frequency converter and a waveguide calibration kit, the rectangular waveguide cross sections of
To Next Page
Loading...
