Agilent Technologies 4395A - Calibration for Network Measurement

Calibration
for
Network
Measurement
Calibration for
Network Measurement
Introduction
Network
measurement
calibration is
an accuracy
enhancement procedure
that eectively
reduces
the
system
errors
that
cause
uncertainty in
measuring a
DUT.
It measures
known
standard
devices
,
and
uses
the
results of
these measurements
to characterize
the system.
This
section
explains
the
theoretical
fundamentals
of accuracy
enhancement and
the sources
of
measurement
errors
.It
describes the
dierent measurement
calibration procedures
available
in
the
analyzer
, which
errors they
correct, and
the measurements
for
which
each
should
be
used.
The
later
part of
this section
provides further
information on
characterizing
systematic
errors
and
using
error
models
to analyze
the overall
measurement performance
.
A
ccuracy
Enhancement
If
it
were
possible
for
a
perfect
measurement
system
to
exist,
it
would
have
innite
dynamic
range
,
isolation,
and
directivity
characteristics
,
no
impedance
mismatches
in
any
part
of
the
test
setup
,
and
at
frequency
response
.
V
ector
accuracy
enhancement,
also
known
as
measurement
calibration
or
error
correction,
provides
the
means
to
simulate
a
perfect
measurement
system.
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
DUT.
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
.
For
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
DUT
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.
Measurement
calibration simulates
a perfect
analyzer
system.
It
measures
the
magnitude
and
phase
responses of
known standard
devices
,
and
compares
the
measurement
with
actual
device
data.
It uses
the results
to characterize
the
system
and
eectively
remove
the
system
errors
from
the measurement
data of
atest
device
,
using
vector
math
capabilities
internal
to
the
analyzer
.
When
measurement calibration is used, 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.
Sources of Measurement Errors
Network analysis measurement errors can be separated into systematic
, random, and drift
errors.
Correctable systematic errors are the repeatable errors that the system can measure. These are
errors due to mismatch and leakage in the test setup, isolation between the reference and test
signal paths, and system frequency response.
The system cannot measure and correct for the non-repeatable random and drift errors. These
errors aect both reection and transmission measurements. Random errors are measurement
variations due to noise and connector repeatability. Drift errors include frequency drift,
A-40 Basic Measurement Theory