Specifications

frequency (IF). This signal can then be measured
directly by a tuned receiver. The tuned receiver
approach gives the system greater dynamic range.
The system is also much less sensitive to interfering
signals, including harmonics.
Vector Network
Measurement
System Basics
The network measurement system is a tuned re
-
ceiver (Figure 3-5, left). The microwave signal is
down converted into the passband of the IF.
This phase reference can be obtained by splitting off
some of the microwave signal before the measure
-
ment (Figure 3-4, below).
The phase of the microwave signal after it has
passed through the device under test (DUT) is then
compared with the reference signal. The network
analyzer automatically samples the reference sig
-
nal, so no external hardware is needed.
Let us consider for a moment that you remove the
DUT and substitute a length of transmission line
(Figure 3-7, left). Note that the path length of the
test signal is longer than that of the reference sig
-
nal. Now let us see how this affects our measure
-
ment.
Assume that we are making a measurement at
1 GHz and that the difference in path-length be
-
tween the two signals is exactly 1 wavelength. This
means that test signal is lagging the reference sig
-
nal by 360 degrees (Figure 3-8). We cannot really
tell the difference between one sine wave maxima
and the next (they are all identical), so the network
NETWORK NETWORK ANALYZERS,
ANALYZERS A PRIMER
3-6 MS462XX OM
DUT
PHASE
DETECTOR
REFERENCE
SIGNAL
SPLITTER
TEST
SIGNAL
MICROWAVE
SOURCE
Figure 3-4. Splitting the Microwave Signal
PHASE MEASUREMENT
TIME
TEST
SIGNAL
REFERENCE
SIGNAL
90
Figure 3-6. Signals with a
90 Degree Phase Difference
REFERENCE
SIGNAL
SPLITTER
TEST
SIGNAL
MICROWAVE
SOURCE
LONGER
PATH
LENGTH
PHASE
DETECTOR
Figure 3-7. Split Signal where a
Length of Line Replaces the DUT
A NETWORK ANALYZER IS A TUNED RECEIVER
TUNABLE
LOCAL
OSCILLATOR
INTERMEDIATE
FREQUENCY (IF)
MICROWAVE
SIGNAL
• GREATER DYNAMIC RANGE
• LESS SENSIVITY TO INTERFERING SIGNALS
Figure 3-5. Network Analyzer is a
Tuned Receiver