Agilent Technologies 8719D, Руководство пользователя

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Source match and load match
A TRL* calibration assumes a perfectly balanced test set architecture as shown by the term
which represents both the forward source match and reverse load match and by the
term which represents both the reverse source match and forward load match (E
LF
).
However, in any switching test set, the source and load match terms are not equal because the
transfer switch presents a different terminating impedance as it is changed between port 1 and
port 2.
Because the standard HP
network analyzer is based on a three-sampler
receiver architecture, it is not possible to differentiate the source match from the load match
terms The terminating impedance of the switch is assumed to be
the in
either direction.
Therefore, the test port mismatch cannot be fully corrected. An assumption is made that:
forward source match
= reverse load match =
reverse source match = forward load match =
For a can eliminate the effects of the fixture’s loss and length, but does not
completely remove the effects due to the mismatch of the This is in contrast to the
‘pure” TRL technique used by instruments equipped with Option 400.
Note
Because the TRL technique relies on the characteristic impedance of
transmission lines, the mathematically equivalent method (for
line-reflect-match) may be substituted for Since a well matched
termination is, in essence, an long transmission line, it is well suited
for low (RF) frequency calibrations. Achieving a long line standard for low
frequencies is often times physically impossible.
How True Works (Option 400 Only)
The implementation with Option 400 requires a of fourteen measurements to
quantify ten unknowns as opposed to only a total of twelve measurements for (Both
include the two isolation error terms)
Because of the four-sampler receiver architecture of Option 400, additional correction of the
source match and load match terms is achieved by measuring the ratio of the two “reference”
receivers during the thru and line steps. These measurements characterize the impedance
of the switch and associated hardware in both the forward and reverse measurement
configurations. They are then used to modify the corresponding source and load match terms
(for both forward and reverse).
Option 400 with TRL establishes a higher performance calibration method
over when making measurements, because all significant error terms are
systematically reduced. With the source and load match terms are essentially that of the
raw, “uncorrected” performance of the hardware.