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Circuit
Des
cri
ption
Introduction
-
-
The Model 416A
Ratio
Meter
is
designed to
accept any
two 1
-
kc
volt-
ages, and
to
conver
t
and combine them electronically in
such manner that
the
square root
of
their ratio is indicated
directly by the meter on the instru-
ment.
Reflection coefficient
may be defined as the
ratio
of the
v
oltage of the
reflected
wa
ve
to
the
vo
ltage of the
incident wave
,
and
~herefore
the Model
416A is
par
tic
ul
ar
l
y adapted for
use
in
a reflectometer
system to measure
the magnitude
of
the reflection coefficient
of
components in a
microwave
transmission system
,
A
reflectometer sys
t
e
m
contains
a
m
i crowave
oscillator modulated
at an audio rate (usually a
1
-
kc
square
wave
),
By means of two directional
couplers
in the line
,
between
the source
and the
load,
the incident
and re
-
flec
te
d powers
are
sampled
and subsequently
detected
hy
crystal usually
operated as
s qua
re
-
l
aw
devices
,
Thus
,
two 1
-
kc
voltages
,
one proportional
to the
i
nc
i
dent pow
er
and the
other to the
reflected
power
,
are
derived
,
When
the
detectors used
are square
-
law
devices
,
the
magnitude of the reflection
coefficient is
equal
to
the
square root
of
the ratio
of these two
voltages
.·
While
the
Model 416A
a
lso may be used
i
n
the
measurement of the
rati
o b
etween
any
tw
o
l
··
kc
volta
ges o
r
to
measure
a
standing
wave
ratio
,
.
many of
the
consi
de
rations
concerning its
design
were
determined by the re
-
quirements governing
th
e
measurement
of the
m
a
gnitudes of
reflection
coef
-
fi
c
ie
n
ts
,
and
therefore the
circuit will
be
described in terms
of the measure
-
ment of the magnitude of
reflecti
on coefficients,
Theory
-~
The
ratio of
the amplitudes of
two
sinusoids
which are in
phase can be
formed simply
by using an
oscillo
s
cope
.
If
one
s
i nusoi
d
is
applied across
the horizontal deflection
pla
tes and
the
other sinus
o
id
i
s
applied across
the
ver
t
ical
defl
ection
plates
,
the well
-
known
straigh
t-
l
ine
L issajous pattern
results
.
The pattern
has the
property
tha
t the s
lope
of
the
line is a
function
of
the ratio of the
two
voltages
,
In a geometrica
l
representation
,
the
rati
o
is
the
s
lop
e
of
the
lo
cus formed by rotating
one
vector by
a
n
angle
of·
7f
/
2
and addi
ng
the two
v
ectors vectorially
.
In the
time domain
there are
operations which correspond
to those
in the space
doma
in
.
That
is, shift the
phase
of one sinusoid (E2
)
by an
angle
of
'IT
/2
relative to the
other (E1)
,
the
n sum
them
(E3),
,
and
measure
the
phase angle
(e)
between
this
sum
and the
other sinusoid (E1) (see
Fig.
2).
Tan
(
8
)
is the ratio
of
E
2
,
E1
Phys
ical
realizati
on
of
t
hese
operations
i
s
achieved
by
combining
the outputs
of
two filters
which are
tuned
to
the
same
frequency.
One filter
(Filter
1)
includes
a ser
i
es
-
reso
n
ant circ
uit coupled to
a
parallel
-
resonant
-
6-
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