HP 8753D - Page 333

The
Calibration
Standards
During
measurement
calibration,
the
analyzer
measures
actual,
well-dened
standards
and
mathematically
compares
the
results
with
ideal
\models"
of
those standards
.The
dierences
are
separated
into
error
terms
which
are
later
removed during
error-correction. Most
of the
dierences
are
due
to
systematic
errors
-
repeatable
errors introduced
by the
analyzer,
test set,
and
cables
-
which
are
correctable
.
The
standard
devices
required
for
system
calibration
are
available in
compatible calibration
kits
with
dierent
connector
types
.
Each
kit
contains at
least one
short circuit,
one
open
circuit,
and
an
impedance-matched
load.
In
kits
that
require adapters
for interface
to
the
test
set
ports
,
the
adapters
are
phase-matched for
calibration prior
to measurement
of
non-insertable
and
non-reversible
devices
.
Other
standard
devices
can be
used by
specifying
their
characteristics
in
a
user-dened
kit,
as
described
later in
this section
under \Modifying
Calibration
Kits
."
The
accuracy
improvement
of
the correction
is limited
by the
quality of
the
standard
devices
,
and
by
the
connection
techniques used.
For
maximum accuracy
, use
a
torque
wrench
for
nal
connections
.
Frequency Response
of
Calibration
Standards
In
order
for
the
response
of
a
reference
standard
to
show
as
a
dot on
the smith
chart display
format,
it
must
have
no
phase
shift
with
respect
to
frequency
.
Standards
that
exhibit
such
\perfect"
response
are
the
following:
7-mm
short
(with
no
oset)
type-N
male
short
(with
no
oset)
There
are
two
reasons
why
other
types
of
reference
standards
show phase
shift
after
calibration:
The
reference
plane
of
the
standard
is
electrically
oset
from
the
mating plane
of the
test
port.
Such
devices
exhibit
the
properties
of
a
small
length
of
transmission line
, including
a
certain
amount
of
phase shift.
The
standard is
an open
termination, which
by denition
exhibits
a
certain
amount
of
fringe
capacitance
(and
therefore
phase shift).
Open terminations
which are
oset
from
the
mating
plane
will
exhibit
a phase
shift due
to the
oset
in
addition
to
the
phase
shift
caused
by
the
fringe
capacitance
.
The
most important
point to
remember
is
that
these
properties
will
not
aect
your
measurements
.
The
analyzer
compensates
for them
during
measurement.
As
a
result,
if
these
standards are measured after a
calibration, they will not appear to be \perfect" shorts or
opens. This is an indication
that your analyzer is working properly
and that it has successfully
performed a calibration. Figure 6-47 shows sample displays of various calibration standards
after calibration.
6-66 Application and Operation Concepts