Test Sets; Calibration - Agilent Technologies AN 1287-6 Application Note

Test sets

There are many variations of network analyzers,
but one of the most distinguishing factors of a
network analyzer is its test set. A test set is a
collection of switches and couplers that directs the
source power and separates forward and reverse
traveling signals. Some network analyzers, like the
Agilent 8720E family of vector network analyzers,
have an S-parameter test set with a transfer switch
that directs the source power to either port 1 or
port 2 — allowing the analyzer to make forward
and reverse measurements. Other network analyzers,
like the Agilent 8712C family of network analyzers,
have a transmission/reflection (T/R) test set that
does not have a transfer switch and source power
only goes to port 1 — these test sets allow only
forward measurements to be made (Figure 13).
In the past, test sets were sometimes not included
in the network analyzer, but almost all of today's
network analyzers have a built-in test set.

Calibration

Key to network analyzer measurements is calibra-
tion. Calibration does two things. First, it estab-
lishes a reference amplitude and reference phase
at a point in the system. Second, it determines the
accuracy of the measurement. Network analyzer
calibration corrects for systematic errors (time
invariant instrument and test setup errors) in the
measurement setup. Ideally, calibration corrects
for all errors up to the point where the DUT will
be connected.
Transmission/reflection test set
Source
A
Port 1
Fwd
S-parameter test set
Source
R
A
Port 1
Fwd
DUT
Figure 13. Transmission/reflection versus S-parameter
test set
Figure 13-top
• RF power always comes out of port 1
• Port 2 is always receiver
• Response, one-port cal available
Figure 13-bottom
• RF power comes out of port 1 or port 2
• Forward and reverse measurements
• Two-port calibration possible
R
B
Port 2
DUT
Transfer switch
B
Port 2
Rev
25