Technical data

5-37
Operating Concepts
Measurement Calibration
between E
SF
and S
11A
as well as E
LF
and S
22A
, so the input and output reflection coefficients of the test
device must be measured and stored for use in the S
21A
error-correction computation. Thus, the test setup
is calibrated as described for reflection to establish the directivity, E
DF
, source match, E
SF
, and reflection
frequency response, E
RF
, terms for reflection measurements on both ports.
Now that a calibrated port is available for reflection measurements, the thru is connected and load match,
E
LF
, is determined by measuring the reflection coefficient of the thru connection. Transmission signal path
frequency response is then measured with the thru connected. The data is corrected for source and load
match effects, then stored as transmission frequency response, E
TF
.
NOTE It is very important that the exact electrical length of the thru be known. Most calibration
kits assume a zero length thru. For some connection types such as Type-N, this implies one
male and one female port. If the test system requires a non-zero length thru, for example,
one with two male test ports, the exact electrical delay of the thru adapter must be used to
modify the built-in calibration kit definition of the thru.
Isolation, E
XF
, represents the part of the incident signal that appears at the receiver without actually
passing through the test device. See Figure 5-36 on page 5-37. Isolation is measured with the test set in the
transmission configuration and with terminations installed at the points where the test device will be
connected. Since isolation can be lower than the noise floor, it is best to increase averaging by at least a
factor of four during the isolation portion of the calibration. The RESUME CAL SEQUENCE, softkey
under the Cal, menu allows a calibration sequence to resume after a change to the averaging factor. If the
leakage falls below the noise floor, it is best to increase averaging before calibration. In this case, omitting
isolation is better than measuring the isolation standards without increasing the averaging factor.
Figure 5-36. Isolation E
XF
Thus there are two sets of error terms, forward and reverse, with each set consisting of six error terms, as
follows:
• Directivity, E
DF
(forward) and E
DR
(reverse)
• Isolation, E
XF
and E
XR
•Source Match, E
SF
and E
SR
• Load Match, E
LF
and E
LR