What are "standard classes" in a calibration kit definition?
A standard class is a group of from zero to seven standards that are
organized according to the calibration of the VNA error model.
The number of classes needed for a particular calibration type is equal
to the number of error terms being calibrated.
For example, a one-port calibration has three error terms in its
error model - directivity, source match, and reflection tracking.
This calibration would require three standard classes, which might be
labeled OPEN, SHORT, and LOADS.
The OPEN class could contain a single open circuit standard, the
SHORT class a short circuit standard, and the LOADS class might
contain two load standards, one for low frequencies and one for
When the VNA is being calibrated, the order of measuring the standards
in a class is not important; however, one class must be completed before
going on to the next.
If two standards within a class overlap in frequency range, the last
one measured will be used for the overlapping range.
It is not always necessary to measure every standard in a class.
In the example above, if the VNA was only being used at low frequencies,
it would not be necessary to measure the high-frequency load in the
The classes needed for each calibration type are as follows:
- Response cal - uses the response class.
- Response & Isolation cal - uses the response & isolation
and one isolation class.
- One-port cal - uses three reflection classes, either S11A, B, and C
or S22A, B, and C.
- Enhanced Response cal – uses three reflection classes, two
transmission classes, and one isolation class, all in either the
forward or reverse direction.
- Full Two-port cal - uses the six reflection classes, four
transmission classes (forward transmission, forward match, reverse
transmission, reverse match), and two isolation classes.
Note that the 8753/8720 network analyzer models do not explicitly
define the isolation classes in the cal kit; the isolation standards
are assumed to be loads.
- TRL Two-port cal - uses the TRL thru, TRL reflect, TRL line, and
two isolation classes.