5 CALIBRATION AND CALIBRATION KIT
133
5.2.13 Port Extension
The port extension function enables you to eliminate the fixture (with or without losses)
effects on the measurement results. The function virtually extends the test ports moving
the calibration plane to the terminals of the DUT (by the length of the fixture). The
fixture parameters are defined by the user for each port individually (See figure 5.14).
Figure 5.14 Port extension
The phase incursion caused by electrical delay is compensated for, when a lossless
fixture needs to be removed:
tfj
e×××
p
2
,where
f – frequency, Hz,
t – electrical delay, sec.
The feature of removing a lossless fixture is similar to the feature of electrical delay
setting for a trace (See section 4.9.7), but unlike the latter it applies to all the traces of
the channel. It compensates for a fixture length in transmission measurements and for a
double fixture length in reflection measurements.
To remove a fixture with losses, the following methods of loss defining (in one, two or
three frequency points) are applied:
1. Frequency-independent loss at DC - L0
0
)( LfL
=
2. Frequency-dependent loss determined by the losses in two frequency points: L
0
at
DC, and L1at frequency F1
Port
1
Port
2
Calibration
plane
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