Technical data

5-32
Operating Concepts
Measurement Calibration
Figure 5-26. Source Match E
SF
Frequency response (tracking) error is caused by variations in magnitude and phase flatness versus
frequency between the test and reference signal paths. These are due mainly to coupler roll off,
imperfectly matched samplers, and differences in length and loss between the incident and test signal
paths. The vector sum of these variations is the reflection signal path tracking error, E
RF
as shown in
Figure 5-27 on page 5-32.
Figure 5-27. Reflection Tracking E
RF
These three errors are mathematically related to the actual data, S
11A
, and measured data, S
11M
, by the
following equation:
If the value of these three "E" errors and the measured test device response were known for each
frequency, this equation could be solved for S
11A
to obtain the actual test device response. Because each of
these errors changes with frequency, their values must be known at each test frequency. These values are
found by measuring the system at the measurement plane using three independent standards whose S
11A
is known at all frequencies. The first standard applied is a "perfect load," which makes S
11A
= 0 and
essentially measures directivity. See Figure 5-28 on page 5-33. "Perfect load" implies a reflectionless
S
11M
E
DF
S
11A
E
RF


1
E
SF
S
11A
–


-----------------------------------------+=