HP 8753D - Page 343

Modifying Calibration
Kits
Modifying
calibration
kits
is
necessary only
if unusual
standards (such
as in
TRL*) are
used
or
the
very
highest
accuracy
is
required. Unless
a calibration
kit model
is provided
with the
calibration
devices
used,
a
solid
understanding
of error-correction
and the
system error
model
are
absolutely
essential
to
making
modications
.Y
ou may
use modications
to a
predened
calibration
kit
by
modifying
the kit
and saving
it as
a user
kit.
The
original
predened
calibration
kit
will
remain
unchanged.
Before
attempting
to
modify
calibration
standard
denitions,
you should
read application
note
8510-5A
to
improve
your
understanding
of
modifying calibration
kits.
The part
number
of
this
application
note
is
5956-4352.
Although
the
application note
is written
for the
HP
8510
family
of
network
analyzers,
it also
applies to
the HP
8753D
.
Several
situations
exist that
may require
a user-dened
calibration kit:
A
calibration
is required
for a
connector interface
dierent from
the
four
default
calibration
kits
.
(Examples: SMA,
TNC, or
waveguide.)
A calibration
with standards
(or
combinations
of
standards)
that
are
dierent
from
the
default
calibration
kits
is
required.
(Example:
Using three
oset
shorts
instead
of
open,
short,
and
load
to
perform
a
1-port
calibration.)
The
built-in
standard
models
for
default
calibration
kits
can
be
improved
or
rened.
Remember
that
the
more
closely
the
model
describes
the
actual
performance
of
the
standard,
the
better
the
calibration.
(Example:
The
7
mm
load
is
determined to
be 50.4
ohms
instead
of
50.0
ohms
.)
Denitions
The
following
are
denitions
of
terms:
A
\standard"
(represented
by
a
number
1-8)
is
a
specic
,
well-dened,
physical
device
used
to
determine
systematic
errors
.
F
or
example
,
standard
1
is
a
short
in
the
3.5
mm
calibration
kit.
Standards
are
assigned
to
the
instrument
softkeys
as
part
of
a
class
.
A
standard
\type"
is
one
of
ve
basic
types
that
dene
the form
or structure
of the
model to
be
used
with
that
standard
(short,
open,
load,
delay/thru,
and
arbitrary
impedance); standard
1
is
of
the
type
short
in
the
3.5
mm
calibration
kit.
Standard
\coecients"
are
numerical
characteristics
of
the
standards
used
in
the
model
selected.
F
or
example
,
the oset
delay of
the short
is 32
ps
in
the
3.5
mm
calibration
kit.
A
standard
\class"
is a
grouping of
one or
more standards
that determines
which of
the eight
standards are used at each step of the calibration. F
or example
, standard number 2 and 8
usually
makes up the S
11
A
reection class
, which for type-N calibration kits are male and
female shorts
.
Procedure
The following steps are used to modify or dene a user kit:
1.
Select the predened kit to be modied. (This is not necessary for dening a new calibration
kit.)
2. Dene the standards:
a. Dene which \type" of standard it is.
b. Dene the electrical characteristics (coecients) of the standard.
3. Specify the class where the standard is to be assigned.
6-76 Application and Operation Concepts