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Spurious
Signal F
~·
-
This
er
ro
r signal a rrive
s
at
the
forwa
r
d
de te
etor
because oi the
impedect
·
~~
ire
c
tivity
of
the forward (incident)
directional
coupler.
A sample of the
v
oha.ge
component
of the
refl
e
cted wave
[(
p
LH
EJ]
-[s
coupled
(
af}
into the se
c0Eda17
a
rm
of
the
forward
directional c
ouple
r"
1
B
ecause
of the
imperfect
directi
v
ity (df)
of
th
e c
ouple
r,
some
(a
small
part} of the reflected-
wave voltage will
reach the
forward dete ctor.
where pL
E.
1
::
reflection coefficient
of
load
:
worst
possible
di
rectivity of
forward coup
ler
(. 01)
=
voltage coup.
ing
coefficient
of forward (20 db}
coupler
(.
1)
:
voltage
component of
incident
wa
ve
,
in ma
in
gui
de
Substituting
approxi
mate va
l
ues,
F 1 ha
s a typic
al
value of:
pL
(.
01)(.l}Ei
::
l
xl0-
3
pLEi
_S"' " ' p _u_r..,.·1_·
o_u_s...,.S,,__ig""--n_a_l.,_..F:
. z
-
T
his
error signal
results
from
discontinuities
in the
system,
primarily
at
the fla
nge
joi
nt
betwee
n forward a
nd
reverse couplers.
T
he
discontinuity
reflection [(Pc)
(Ei)]
is
re
~re
fle
c
ted
(pg) at
the generator,
coupled
(of} into the secondary
arm
of
the
di
rectional coupler,
and
then
applied
to the
forward detector.
The
value
of
F 2
is:
F 2
=
Pc Pg a.f Ei
where
Pc
:: I.umped
refle ction
c
oefficient
of discontinuiti
e
s
pg
::::
lumpe
d
reflection coeffic
ient
of
ge
ne
r
ator
Assuming
that
dis
c
ontinuities may have a reflection coefficient
of
•
01, and
the
generator a
reflection
coefficient
of
.1,
F 2 n1ay have
a
typical value of:
(.
01) (.1) (.1)
Ei
:
1x10- 4 Ei
Spurious
Signal
F3
-
This
error
signal results from reflections from
the
forward
(incident)
detector.
The
incident
voltage {Ei)
is
coupled (of)
by
the for-
ward directional
coupler
to the
forward
detector, and the reflection (pd) from the
detector is coupled
(af) back through
the
coupler to
the generator
,
re-reflected
(pg) by the generator
,
and coupled (af) again by the
coupler to
the
forward detector.
3
The value
of
F3
is: F3
=
Pd
Pg
Uf
Ei
where
Pd :: reflection coefficient
of forward
detect.or (assumed value,
•
2)
-34-
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