HP 8510, Руководство пользователя

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Ho w ev er, there are applications in whic h the 2-P ort error mo del cannot b e used. There are
others in whic h b etter results are pro duced using other calibration tec hniques describ ed later.
These are the reasons that 2-P ort correction cannot b e used eectively:
1. V ery low signal lev els of the S
22
and S
12
measuremen t will probably reduce the accuracy of
the S
11
and S
21
measuremen ts.
Using 2-P ort correction, the v alues of all four parameters are used to nd the corrected
v alue for the display ed parameter. If, for example, the rev erse parameters are not
represen tativ e of their actual v alues due to insucien t signal lev els, then their
con tribution to the accuracy enhancemen t algorithm will cause errors. This leads to noisy ,
nonrep eatable data for the other parameters, ev en if their measured data is represen tativ e.
2. Equipmen t external to the HP test set m ust b e switched dep ending up on the parameter
b eing measured.
There is no means of automatically switching equipmen t external to the test set dep ending
up on the S-parameter b eing measured.
Using 2-P ort correction, all four S-parameters are automatically selected in sequence,
and there is no signal a v ailable to indicate whic h parameter is b eing measured. If
dynamic range considerations make it necessary to c hange the test set conguration for
measuremen t of dieren t parameters, the automatic switching used in the 2-P ort error
mo del cannot b e used.
3. T est set conguration c hanges error terms other than frequency resp onse b et w een
calibration and measuremen t.
If c hanges to the test set b et w een calibration and measuremen t signicantly c hange
the directivit y , isolation, source or load match, or frequency resp onse error co ecien ts
measured during the calibration, then the corrected data will b e in error. If only the
frequency resp onse c haracteristics of the test set c hange, comp ensation can b e pro vided
using the display memory features of the HP 8510B. (See the Changing Signal P ath After
Calibration section in this c hapter.)
In all of these situations the b est c hoice will b e to use a separate error mo del for eac h
parameter. F or example, use the Resp onse or the Resp onse & Isolation calibration for the
S
21
and S
12
parameters, and 1-P ort calibrations for the S
11
and S
22
parameters. Combining
error mo dels like this allo ws setup, calibration, and measuremen t for eac h parameter
to b e accomplished indep enden tly . After separate calibration for eac h parameter, the
forward/rev erse switch in the test set will resp ond to fron t panel parameter selections, and
the cal set for the selected parameter will b e recalled.
Combining error mo dels is describ ed in the HP 8510 Op erating and Programming man ual,
Basic Net w ork Measuremen ts p ortion, with the Cal men u in the S-P arameter T est Set
Calibration Error Mo dels section.
10-8 High P o w er Measurements