H26-8414A Polar Display; Locus Of Measured Reflection When Load Is Moved; Locus Of Measured Reflection With Directivity Cancelled - HP 8414A Operating And Service Manual

Model 8414A
Figure 3-6. Measured Reflection Coefficient
cies. The measured reflection is the vector sum of
the directivity vector plus the reflection coefficient
of the device under test, or a sliding load (see Fig¬
ure 3-6). The error can be calibrated out with a
sliding load. Figure 3-7 depicts the sliding load in
one position at a single frequency. As the sliding
load is moved, the magnitude of its reflection coef¬
ficient remains constant but the phase of the coef¬
ficient changes. As the load is moved its reflection
coefficient indication rotates in a circle of constant
magnitude about the directivity vector. The center
of this circle is the tip of therdirectivity vector.
When the magnitude of the directivity vector is
zero, the locus circle is centered about the origin as
shown in Figure 3-8. When the location of the cen¬
ter of the circle is known, the directivity vector can,
be subtracted from the measured reflection. The
Figure 3-7. Locus of Measured Reflection when
Load is Moved
Section III
Operation
resultant is the reflection coefficient of the device
under test.
3-35. The vector subtraction can be performed
directly with the horizontal and vertical controls
on the 8414A Polar Display. Increase the Network
Analyzer test channel gain1 so full scale reflection
on the polar display is suitable for the component
you wish to measure. Attach a sliding load such as
the HP 905A in place of the device under test.
Slide the load and adjust the horizontal and verti¬
cal controls until the circle rotates about the center
of the CRT. The effect of directivity is now can¬
celled for this frequency and this test channel
gain1 on the Network Analyzer. Remove the slid¬
ing load and connect the device under test. The
8414A display is now the reflection coefficient of
the device under test.
3-36. H26-8414A POLAR DISPLAY.
3-37. The H26 modification to the standard
8414A Polar Display controls the display of magni¬
tude and phase data in the Hewlett-Packard 8542
series Automatic Network Analyzer systems. The
H26-8414A contains circuits to achieve compati¬
bility with the automatic system. The H26-8414A
is also compatible with the standard Network Ana¬
lyzer except for the test channel amplitude signal.
For the standard Network Analyzer and 8414A the
test channel amplitude signal is fed to the 8414A
through a 24-contact rear-panel connector. For the
H26-8414A the test channel amplitude signal input
is through a rear-panel BNC connector (TEST IN).
To use the H26-8414A in a standard Network
Analyzer mainframe connect the Network Ana¬
lyzer rear-panel test output to the H26-8414A
TEST IN. See Figure 3-12 on page 3-12.
^Display reference for 8407A
Figure 3-8. Locus of Measured Reflection with
Directivity Cancelled
3-7