User`s guide

7-47
Operating Concepts
Measurement Calibration
Figure 7-34 Major Sources of Error
The transmission coefficient is measured by taking the ratio of the incident signal (I) and
the transmitted signal (T). Refer to Figure 7-35. Ideally, (I) consists only of power delivered
by the source, and (T) consists only of power emerging at the test device output.
Figure 7-35 Transmission Coefficient
As in the reflection model, source match can cause the incident signal to vary as a function
of test device S
11A
. Also, since the test setup transmission return port is never exactly the
characteristic impedance, some of the transmitted signal is reflected from the test set
port 2, and from other mismatches between the test device output and the receiver input,
to return to the test device. A portion of this signal may be re-reflected at port 2, thus
affecting S
21M
, or part may be transmitted through the device in the reverse direction to
appear at port 1, thus affecting S
11M
. This error term, which causes the magnitude and
phase of the transmitted signal to vary as a function of S
22A
, is called load match, E
LF
. See
Figure 7-36.