Characterizing Microwave Systematic Errors - Agilent Technologies 8753ET User Manual

Operating Concepts
Measurement Calibration

Characterizing Microwave Systematic Errors

One-Port Error Model
In a measurement of the reflection coefficient (magnitude and phase) of a test device, the
measured data differs from the actual, no matter how carefully the measurement is made.
Directivity, source match, and reflection signal path frequency response (tracking) are the
major sources of error. See Figure 7-24.
Figure 7-24 Sources of Error in a Reflection Measurement
To characterize the errors, the reflection coefficient is measured by first separating the
incident signal (I) from the reflected signal (R), then taking the ratio of the two values. See
Figure 7-25. Ideally, (R) consists only of the signal reflected by the test device (S , for S
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actual).
Figure 7-25 Reflection Coefficient
However, all of the incident signal does not always reach the unknown. Refer to Figure
7-26. Some of (I) may appear at the measurement system input due to leakage through the
test set or through a signal separation device. Also, some of (I) may be reflected by
imperfect adapters between a signal separation device and the measurement plane. The
vector sum of the leakage and the miscellaneous reflections is the effective directivity, E .
DF
Understandably, the measurement is distorted when the directivity signal combines
vectorally with the actual reflected signal from the unknown, S .
11A
7-42