5 CALIBRATION AND CALIBRATION KIT
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5.1.3 Error Modeling
Error modeling and method of signal flow graphs are applied to vector network
analyzers for analysis of its systematic errors.
5.1.3.1 One-Port Error Model
In reflection measurement only one port of the Analyzer is used. The signal flow graph
of errors for the port 1 is represented in figure 5.1. For port 2 the signal flow graph of
the errors will be similar.
Figure 5.1 One-port error model
Where:
§S11a – reflection coefficient true value;
§S11m – reflection coefficient measured value.
The measurement result at port 1 is affected by the following three systematic error
terms:
§Ed1 – directivity;
§Es1 – source match;
§Er1 – reflection tracking.
For normalization the stimulus value is taken equal to 1. All the values used in the
model are complex.
After determining all the three error terms Ed1, Es1, Er1 for each measurement frequency
by means of a full 1-port calibration, it is possible to calculate (mathematically
subtract the errors from the measured value S11m) the true value of the reflection
coefficient S11a.
There are simplified methods, which eliminate the effect of only one or two out of the
three systematic errors.
S11a
Er1
Ed1 Es1
Port 1
S11m
1
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