HP 8753D - Page 320

The
error contributed
by load
match is
dependent
on
the
relationship
between
the
actual
output
impedance of
the
test
device
and
the
eective
match
of
the
return
port
(port 2).
It is
a
factor in
all
transmission
measurements
and
in
reection
measurements
of
two-port
devices
.
The
interaction between
load
match
and
source
match
is
less
signicant
when
the
test
device
insertion
loss is
greater
than
about
6
dB
.
However
,
source
match
and
load
match
still interact
with
the input
and
output
matches
of
the
DUT
,
which
contributes
to
transmission
measurement
errors
.
(These
errors
are
largest
for
devices
with
highly
reective
output
ports
.)
Isolation
(Crosstalk)
Leakage
of
energy
between
analyzer
signal
paths
contributes
to
error
in
a
transmission
measurement,
much
like
directivity
does
in
a
reection
measurement.
Isolation
is
the
vector
sum
of
signals
appearing
at
the
analyzer
samplers
due
to
crosstalk
between
the reference
and
test
signal
paths
.
This
includes
signal
leakage
within
the
test
set
and in
both the
RF and
IF
sections
of
the
receiver
.
The
error
contributed
by
isolation
depends
on
the
characteristics
of
the
test
device.
Isolation
is
a
factor
in
high-loss
transmission
measurements
.
However
,
analyzer
system
isolation is
more
than
sucient
for
most
measurements
,
and
correction
for
it
may be
unnecessary.
F
or
measuring
devices
with
high
dynamic
range
,
accuracy
enhancement
can
provide
improvements
in
isolation
that
are
limited
only
by
the
noise
oor
. Generally
, the
isolation falls
below
the
noise
oor
,
therefore
,
when
performing
an
isolation
calibration you
should use
a
noise
reduction
function
such
as
averaging
or
reduce
the
IF
bandwidth.
Frequency
Response
(Tracking)
This
is
the
vector
sum
of
all
test setup
variations
in
which
magnitude
and
phase
change
as
a
function
of
frequency
.
This
includes
variations
contributed by
signal-separation
devices
,
test
cables,
adapters
,
and
variations
between
the
reference
and
test
signal
paths
.
This
error
is
a
factor
in both
transmission
and
reection
measurements
.
F
or further
explanation
of
systematic
error
terms
and
the
way
they
are
combined
and
represented
graphically in
error models
,
refer
to
the
\Characterizing
Microwave
Systematic
Errors"
next.
Characterizing
Microwave
Systematic
Errors
One-P
ort
Error Model
In
a
measurement of
the reection
coecient (magnitude
and phase)
of
a
test
device
,
the
measured data
diers from
the actual,
no matter
how carefully
the measurement
is made
.
Directivity,
source
match,
and
reection
signal
path
frequency
response
(tracking)
are
the
major sources of error (see Figure 6-31).
Application and Operation Concepts 6-53