HP 8753D - Page 347

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ARBITRARY
IMPEDANCE denes
the standard
type to
be a
load, but
with an
arbitrary
impedance
(dierent
from
system
Z0).
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TERMINAL
IMPEDANCE allows
you
to
specify
the
(arbitrary)
impedance
of
the
standard,
in
ohms
.
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FIXED
denes the
load as
a xed
(not sliding)
load.
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SLIDING
denes
the
load
as
a
sliding
load.
When
such
a
load
is
measured
during
calibration,
the
analyzer
will prompt
for several
load positions
,
and
calculate
the
ideal
load
value
from
it.
Any
standard
type
can be
further dened
with osets
in delay
,
loss
,
and
standard
impedance;
assigned
minimum
or
maximum frequencies
over which
the standard
applies; and
dened
as
coax
or
waveguide
.
The
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SPECIFY
OFFSET
softkey
provides
access
to
the specify
oset menu
(described
next).
The
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LABEL STD
softkey allows
you
to
dene
a
distinct
label
for
each
standard,
so
that
the
analyzer
can
prompt
the
user
with explicit
standard labels
during
calibration
(such
as
SHORT
).
The
function
is
similar
to
dening
a
display
title
,
except that
the
label
is
limited
to
ten
characters
.
After
each
standard
is dened,
including osets
, the
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STD
DONE
(DEFINED)
softkey will
terminate the
standard
denition.
Specify
Oset
Menu
The
specify
oset
menu
allows
additional
specications
for
a
user-dened
standard.
F
eatures
specied
in
this
menu
are
common
to
all
ve
types
of
standards
.
Osets
may
be
specied
with
any
standard
type
.
This
means
dening
a
uniform
length
of
transmission
line
to
exist
between
the
standard
being
dened
and
the
actual
measurement
plane
.
(Example:
a
waveguide
short
circuit
terminator
,
oset
by
a
short
length
of
waveguide
.)
F
or
reection
standards
,
the
oset
is
assumed
to be
between the
measurement
plane
and
the
standard
(one-way
only).
F
or
transmission
standards
,
the
oset is
assumed to
exist
between
the
two
reference
planes
(in
eect,
the
oset
is the
thru). Three
characteristics of
the oset
can
be
dened:
its
delay
(length),
loss
,
and impedance
.
In
addition,
the
frequency
range
over
which
a
particular
standard is
valid can
be dened
with
a
minimum and
maximum frequency
. This
is particularly
important
for
a
waveguide
standard,
since
its behavior
changes rapidly
beyond its
cuto frequency
.
Note
that
several
band-limited
standards
can together
be dened
as the
same \class"
(see specify
class menu).
Then,
if
a
measurement
calibration
is
performed
over
a
frequency
range
exceeding
a
single
standard,
additional standards can be used for each portion of the range
.
Lastly,the
standard must be dened as either coaxial or waveguide
. If it is waveguide
,
dispersion eects are
calculated automatically and included in the standard model.
The following is a
description of the softkeys located within the specify oset menu:
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OFFSET DELAY
allows you to specify the one-way electrical delay from the measurement
(reference) plane to the standard, in seconds (s). (In a transmission standard, oset delay is
the delay from plane to plane.) Delay can be calculated from the precise physical length of
the oset, the permittivity constant of the medium, and the speed of light.
In coax, group delay is considered constant. In waveguide, however, group delay is
dispersive,thatis, it changes signicantly as a function of frequency. Hence, for a waveguide
standard, oset delay must be dened as though it were a TEM wave (without dispersion).
6-80 Application and Operation Concepts