HP 8753D - Page 317

Measurement Calibration
Measurement
calibration
is
an
accuracy enhancement
procedure that
eectively removes
the
system
errors
that
cause
uncertainty
in
measuring a
test device
.It
measures known
standard
devices
,
and
uses
the
results
of these
measurements to
characterize the
system.
This
section
discusses
the
following
topics:
denition
of
accuracy
enhancement
causes
of
measurement
errors
characterization
of
microwave
systematic
errors
calibration
considerations
eectiveness
of
accuracy enhancement
correcting
for
measurement errors
ensuring
a
valid calibration
modifying
calibration
kits
TRL*/LRM*
calibration
power
meter
calibration
calibrating
for
non-insertable
devices
What
is
A
ccuracy
Enhancement?
A
perfect
measurement
system
would
have
innite
dynamic
range
,
isolation,
and directivity
characteristics
,
no
impedance
mismatches
in
any
part
of
the
test
setup
, and
at
frequency
response
.
In
any
high
frequency
measurement
there
are
measurement
errors
associated
with
the
system
that
contribute
uncertainty
to
the
results
.
P
arts
of
the
measurement setup
such
as
interconnecting
cables
and
signal-separation
devices
(as
well
as
the
analyzer
itself)
all
introduce
variations
in
magnitude
and
phase
that can
mask the
actual
performance
of
the
test
device
.
V
ector
accuracy
enhancement,
also
known as
measurement calibration
or
error-correction,
provides
the
means
to simulate
a nearly
perfect measurement
system.
F
or
example
,
crosstalk
due to
the channel
isolation characteristics
of
the
analyzer
can
contribute
an
error
equal
to
the transmission
signal of
a high-loss
test device
.
F
or
reection
measurements
,the
primary limitation
of
dynamic
range
is
the
directivity
of
the
test
setup
.
The
measurement system
cannot distinguish
the
true
value
of
the
signal
reected
by
the
test
device
from the
signal arriving
at the
receiver input
due
to
leakage
in
the
system.
F
or
both
transmission and reection measurements
, impedance mismatches within the
test setup cause
measurement uncertainties that appear as ripples superimposed on the measured
data.
Error-correction simulates an improved analyzer system. During the measurement calibration
process, the analyzer measures the magnitude and phase responses of known standard devices
,
and compares the measurement with actual device data. The analyzer uses the results to
characterize the system and eectively remove the system errors from the measurement data
of a test device
, using vector math capabilities internal to the network analyzer
.
When you use a measurement calibration, the dynamic range and accuracy of the measurement
are limited only by system noise and stability, connector repeatability, and the accuracy to
which the characteristics of the calibration standards are known.
6-50 Application and Operation Concepts