Agilent Technologies 4395A - Page 389

Network
Measurement
Basics
Network Measurement
Basics
S-parameters
S-parameters
(
scattering parameters
)are
a convention
that characterizes
the way
a device
modies
signal
ow
.
A
brief
explanation is
provided here
of the
S-parameters of
a
two-port
device
.
F
or
additional
details
see Agilent
Technologies
Application Notes
A/N 95-1
and
A/N
154
.
S-parameters
are
always
a
ratio
of
two complex
(magnitude and
phase) quantities
. S-parameter
notation
identies
these quantities
using the
numbering convention:
S
out
in
Where
the
rst
number
(
out
)
refers
to
the
port
where
the
signal
is
emerging
and
the second
number
(
in
)
is
the
port
where
the
signal
is
incident.
F
or
example
,
the
S-parameter S
21
identies
the
measurement
as
the
complex
ratio
of
the
signal
emerging
at
port
2
to
the
signal
incident
at
port
1.
Figure
A
-5
is
a
representation
of
the
S-parameters
of
a
two-port
device
,
together
with
an
equivalent
ow
graph.
In
the
illustration,
\a"
represents
the
signal
entering
the
device
and
\b"
represents the
signal
emerging.
Note
that
a
and
b
are
not
related
to
the
A
and
B
input
ports
on
the analyzer
.
Figure A-5. S-Parameters of a Two-Port Device
S-parameters are exactly equivalent to the more common description terms below, requiring
only that the measurements are taken with all DUT ports properly terminated.
Basic Measurement Theory A-13