HP 8753D - Page 352

TRL*/LRM* Calibration
The
HP
8753D
RF
network analyzer
has the
capability of
making calibrations
using the
\TRL"
(thru-reect-line)
method.
This
section
contains
information
on the
following subjects:
Why
Use
TRL
Calibration?
TRL
T
erminology
How
TRL*/LRM*
Calibration
W
orks
Improving
Raw
Source
Match
and
Load
Match F
or TRL*/LRM*
Calibration
The
TRL
Calibration
Procedure
Requirements
for
TRL Standards
TRL
Options
Why
Use
TRL
Calibration?
This
method
is
convenient
in
that
calibration
standards
can
be
fabricated
for
a
specic
measurement
environment,
such
as
a
transistor
test
xture
or
microstrip
.
Microstrip
devices
in
the
form
of
chips
,
MMIC's
,
packaged
transistors
,
or
beam-lead
diodes
cannot
be connected
directly
to
the
coaxial
ports
of
the
analyzer
.
The
device
under
test
(DUT)
must
be physically
connected
to
the
network
analyzer
by
some
kind
of
transition
network
or
xture
.
Calibration
for
a
xtured
measurement
in
microstrip
presents
additional
diculties
.
A
calibration
at
the
coaxial
ports
of
the
network
analyzer
removes
the
eects
of
the
network
analyzer
and
any
cables
or
adapters
before
the
xture;
however
,
the eects
of
the
xture
itself
are
not
accounted
for
.
An
in-xture
calibration
is
preferable
,
but high-quality
Short-Open-Load-
Thru
(SOL
T)
standards
are
not
readily
available
to
allow
a
conventional
Full 2-port
calibration
of
the
system
at
the
desired
measurement
plane
of
the
device
.
In
microstrip,
a
short
circuit
is
inductive
,
an
open
circuit
radiates
energy
,
and
a
high-quality
purely
resistive
load is
dicult
to
produce
over
a
broad
frequency
range.
The Thru-Reect-Line
(TRL)
2-port
calibration
is
an
alternative
to
the
traditional
SOL
T Full
2-port calibration
technique
that
utilizes
simpler
,
more
convenient
standards
for
device
measurements
in the
microstrip environment.
F
or
coaxial,
waveguide and
other environments
where high-quality
impedance standards
are
readily
available
,
the
traditional
short, open,
load, thru
(SOLT)
method
provides
the
most
accurate
results since
all of
the
signicant
systematic
errors
are
reduced.
This
method
is
implemented
in the
form of
the
S
11
1-port,
S
22
1-port,
and full
2-port calibration
selections
.
In
all measurement
environments,
the user
must provide
calibration
standards
for
the
desired
calibration
to
be
performed.
The
advantage
of
TRL is
that
only
three
standards
need
to
be characterized as opposed to 4 in the traditional open,
short, load, and thru full 2-port
calibrations. Further, the requirements for characterizing the T
, R, and L standards are less
stringent and these standards are more easily fabricated.
TRL T
erminology
Notice that the letters TRL, LRL, LRM, etc
. are often interchanged, depending on the
standards used. F
or example, \LRL" indicates that two lines and a reect standard are used;
\TRM" indicates that a thru, reection and match standards are used. All of these refer to the
same basic method.
Application and Operation Concepts 6-85