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Calibrating for Increased Measurement Accuracy
Making Non-Coaxial Measurements
If You Want to Design Your Own Fixture
Ideally, a fixture should provide a transparent connection between the test instrument and
the test device. This means it should have no loss or electrical length and a flat frequency
response, to prevent distortion of the actual signal. A perfect match to both the instrument
and the test device eliminates reflected test signals. The signal should be effectively
coupled into the test device, rather than leaking around the device and resulting in
crosstalk from input to output. Repeatable connections are necessary to ensure consistent
data.
Realistically, it is impossible to build an ideal fixture, especially at high frequencies.
However, it is possible to optimize the performance of the test fixture relative to the
performance of the test device. If the fixture’s effects on the test signal are relatively small
compared to the device’s parameters, then the fixture’s effects can be assumed to be
negligible.
For example, if the fixture’s loss is much less than the acceptable measurement
uncertainty at the test frequency, then it can be ignored.
For additional information about fixtures, refer to Agilent Technologies Application Note
1287-9, “In-Fixture Measurements Using Vector Network Analyzers,” literature number
5968-5329E.