Agilent Technologies 8753ET User Manual page 343

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.
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