Specifications

There are two ways of accomplishing this. The most
obvious way is to insert a length of line into the ref
-
erence signal path to make both paths of equal
length (Figure 3-11, below). With perfect transmis
-
sion lines and a perfect splitter, we would then mea
-
sure a constant phase as we change the frequency.
The problem using this approach is that we must
change the line length with each measurement
setup.
Another approach is to handle the path length dif-
ference in software. Figure 3-12 (left) displays the
phase-vs.-frequency of a device. This device has dif
-
ferent effects on the output phase at different fre
-
quencies. Because of these differences, we do not
have a perfectly linear phase response. We can eas
-
ily detect this phase deviation by compensating for
the linear phase. The size of the phase difference in
-
creases linearly with frequency so we can modify the
phase display to eliminate this delay.
The MS462XX offers automatic reference delay
compensation with the push of a button. Figure 3-13
(left) shows the resultant measurement when we
compensate path length. In a system application you
can usually correct for length differences; however,
the residual phase characteristics are critical.
NETWORK NETWORK ANALYZERS,
ANALYZERS A PRIMER
3-8 MS462XX OM
PHASE
DETECTOR
REFERENCE
SIGNAL
SPLITTER
TEST
SIGNAL
MICROWAVE
SOURCE
BOTH LINE
LENGTHS
NOW EQUAL
Figure 3-11. Split Signal where Paths are of Equal Length
+180
+90
0
-90
-180
1.1
1.2
1.3
1.4
FREQUENCY,
GHz
MEASURED PHASE
SUBTRACT LINEAR
PHASE FROM
MEASURED PHASE
Figure 3-12. Phase Difference
Increases Linearly with Frequency
0
1.1
1.2
1.3
1.4
FREQUENCY,
GHz
+2
+1
-1
-2
RESULTANT PHASE
Figure 3-13. Resultant Phase
with Path Length Compensation
in Place