Agilent Technologies 4395A, Manual Change

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Calibration for Network Measurement
A ccuracy Enhancement Fundamentals-Characterizing Systematic Errors
One-P ort Error Model
In a measurement of the reection coecient (magnitude and phase) of an unknown device ,
the measured data diers from the actual, no matter how carefully the measurement is made .
Directivity , source match, and reection signal path frequency response (tracking) are the
major sources of error (Figure A -26 ).
Figure A -26. Sources of Error in a Reection Measurement
Measuring reection coecient. The reection coecient is measured by rst separating
the incident signal (I) from the reected signal (R), then taking the ratio of the two values
(Figure A -27). Ideally , (R) consists only of the signal reected by the test device (S
11A
).
Figure A -27. Reection Coecient
Directivity Error . However , all of the incident signal does not always reach the unknown (see
Figure A -28). Some of (I) may appear at the measurement system input due to leakage through
the test set or other signal separation device . Also , some of (I) may be reected by imperfect
adapters between signal separation and the measurement plane . The vector sum of the leakage
and miscellaneous reections is directivity , E
DF
. Understandably , the measurement is distorted
when the directivity signal combines vectorally with the actual reected signal from the
unknown, S
11A
.
Basic Measurement Theory A-49