User`s guide
7-48
Operating Concepts
Measurement Calibration
Figure 7-36 Load Match E
LF
The measured value, S
21M
, consists of signal components that vary as a function of the
relationship 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 7-37. 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 softkey under the 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.
RESUME CAL SEQUENCE
Cal