HP 8753D - Page 321

Figure
6-31.
Sources
of
Error
in
a Reection
Measurement
T
o
characterize
the
errors,
the reection
coecient is
measured by
rst
separating
the
incident
signal
(I)
from
the
reected
signal
(R), then
taking the
ratio
of
the
two
values
(see
Figure
6-32
).
Ideally
,
(R)
consists
only
of
the
signal
reected by
the
test
device
(S
11A
,
for
S
11
actual).
Figure
6-32.
Reection
Coecient
However
,
all
of
the
incident
signal
does
not
always
reach
the
unknown
(see
Figure
6-33).
Some
of
(I)
may
appear
at
the
measurement
system
input
due
to
leakage
through
the
test
set
or
through
a
signal
separation
device
.
Also
,
some
of
(I)
may
be
reected by
imperfect
adapters
between
a
signal
separation
device and
the measurement
plane.
The vector
sum of
the leakage and the
miscellaneous reections is the eective directivity
,E
DF
. Understandably
,
the measurement is distorted when
the directivity signal combines vectorally with the actual
reected signal from the unknown, S
11A
.
6-54 Application and Operation Concepts