Test fixtures are necessary for mounting the device so that it can be
measured in our coaxial (or waveguide) measuring system
(Figure 8-21).
Now we have an interesting situation. While we can measure the per-
formance at the connector—which is the calibration plane—what we
really want to know is how our device performs (Figure 8-22).
You can consider the device embedded in the fixture and can measure
the S-parameters of the fixture with the device installed.
The most elementary situation is a system in which the test fixture is
electrically ideal or transparent. In this case, the solution is sim-
ple—merely move the reference plane out to the device (Figure 8-23).

37xxxE OM 8-25

MEASUREMENTS ACTIVE DEVICE

Figure 8-21. Active Device Test Fixture

F E T

G P C - 7

S
1 1 M

G P C - 7

S
1 1
Figure 8-22. View of a Test Device