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Oct. 15,1946.
R. c. SANDERS, JR., er AL
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2,409,449
PHASE IODULATOR
Filed Dec. 30, 1943A
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R. c. SANDERS, JR., ETAL
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Any number of coupling points may be intro
duced simultaneously. If these points are spaced
multiples of 180 degrees apart, they will add sig
23. The shield member 21 (Figure 5) is shaped
like a rotary shutter, with gaps 90 electrical de
grees wide, spaced 180 electrical degrees apart.
nal components at the receiver which are all in
phase with each other. If the coupling of any
The shield 21 serves to prevent coupling be
tween the parallel lines except at the gaps.
point is broadened over a. length of line to in
The
open wire lines 2|
are each made an
clude, for example, everything between plus 45
integral number of wavelengths long, so that the
degrees and minus 45 degrees from its center,
couplings at the two gaps are additive, as ex
the received signal will contain components of all
plained above in connection with Figure 1 of the
phases between plus 90 degrees and minus 90 de 10 drawings. In the structure illustrated in Fig
grees. These components will add vectorially to
ure 5, the lines are one wavelength long.
produce a signal of the same phase as would re
The spacing between the two open lines 2l is
sult from coupling only at the mean point, but
a compromise between the considerations of vari
of much larger amplitude.
.
ations in characteristic impedance resulting
Referring to Figure 2, the parallel lines 3 and
from close proximity of the shutter blades to the
9 are curved into a circle having a circumference
lines, and incomplete coupling because of dis
an integral number of wavelengths long. The
tance between the lines. Variations of line im
signal at the point i1 at the beginning of the circle
pedance cause reflections, which make the phase
is in phase with that at the point I9 at the end
shift non-linear with respect to angle of shutter
of the circle, and the point of coupling may be
rotation and change the amplitude of the re
moved across the gap without discontinuity in
ceived signal with change in phase. Low cou
phase of the‘ received signal. If the point of cou
pling between the two lines results in high at
pling is revolved about the center of the circle
tenuation.
so as to sweep along the lines 3 and 9 the signal
High shutter rotation speeds may be required
phase at the receiver 1 is uniformly and contin
under certain conditions, involving undesirably
uously advanced or retarded by an angle:
large centrifugal forces, with consequent vibra
tion and bearing load problems. To avoid this
difficulty, the diameter required for a given fre
Where A0 is the change in angle in radians, n
quency of operation may be reduced by provid
is the circumference of the circle in wavelengths, 30 ing dielectric material between the lines and their
and T is the number of turns made by the cou
ground planes, thus lowering the propagation
pling point. If the coupling point is continu
velocity through the lines and hence reducing
ously moved in one direction at s revolutions per
second for a period of t seconds,
The instantaneous signal voltage at the re
ceiver is proportional to
sin 21rfrt=sin (21rfLt-l-0l)
where fr is the received frequency, ft is the trans
mitted frequency, and @t is the total phase differ
ence between the transmitter and the receiver.
Assuming an initial angle a between the trans
mitter and receiver,
the wavelength.
Figures 6 and 7 show a structure of this type.
Reference numerals in Figures 6 and '1 corre
spond to those used to designate correspondingr
parts of Figures 3, 4 and 5. The lines 2| are
supported in circular grooves cut in the faces of
boards 3i of insulating material such as “Bake
40 lite” or the like, backed by the conducting sur
faces 23. To prevent transmission of energy
across the shutter member 21, the two blades 33
are insulated from each other by means of a
“Bakelite” block 35 which is secured to the shaft
45 29 by a bushing 31. The open sections into which
signal is introduced should be placed 90 elec
trical degrees apart to reduce the effect of any
discontinuity caused by incorrect line length.
The invention has been described as a phase
modulator system including two transmission lines
disposed parallel to each other and shielded from
each other except at certain coupling points. The
lines are curved to circular formation and the
55 coupling points are continuously swept over the
lengths of the lines, by rotation of the shield.
One end of each line is connected to the circuit
in which the modulation is to be produced. Mo
In reflection type speed measuring systems, a
tion of the coupling points varies the effective
reflecting object wth a velocity V relative to a
source of signal of wavelength A returns an echo 60 length of line included in the circuit, causing cor
signal differing in frequency from the transmit
responding variations in the transmission delay
ted signal by 2V/>\. The same difference in fre
and hence phase modulation.
quency may be obtained by revolving the coupling
point of the system of Figure 2 at a speed
We claim as our invention:
1. A phase modulator system including two
65 spaced parallel transmission lines, means for ap
plying radio frequency energy to one end of one
of said lines, means for absorbing radio fre
mission lines may be an open wire 2| supported
quency energy from the corresponding end of
above a conductive ground plane 23 on standoff
the other of said lines, movable shield means dis
insulators 25. The two curved lines are placed 70 posed between said lìnes, said shield means pro
with their planes parallel to each other with the
vided with at least one gap whereby coupling
open sides facing each other as shown in Figure
between said lines is prevented except at said
4. A conductive shield member 21 is supported
gap, and motion of said shield means moves said
between the two lines on a shaft 29 extending
coupling longitudinally with respect to said lines
through the center of the lower ground plane 75 to vary the effective length of the transmission
Referring to Figure 3 each of the curved trans
2,409,449
5
path between said means for applying energy and
said means for absorbing energy.
2. The invention as set forth in claim 1 where
in said transmission lines are curved to substan
tially a circular outline an integral number of
6
ly circular form, a rotary shield member lying
between said conductors and provided with at
least one gap in its periphery, and two ground
planes, each disposed adjacent to one of said
conductors and on the opposite side thereof fram
wavelengths in circumference at the frequency
at which the system is to operate.
3. The invention as set forth in claim 1 where
cluding two plates of insulating material, each
in each of said lines is terminated in a load of
such impedance as to match the impedance pre
spective adjacent ground plane.
sented by said line.
4. The invention as set forth in claim 1 where
in said lines are curved to substantially circu
lar outline and said shield means comprises a ro
15
tary shutter-like structure.
5. A phase modulator structure comprising two
spaced parallel conductors curved to substantial
said shield member.
-
6. The invention as set forth in claim 5, in
lying between one of said conductors and the re
7. The invention as set forth in claim 5 where
in said shield’member is in theíorm of a rotary
shutter comprising at least two blades, and means
for insulating said blades from each other.
ROYDEN C. SANDERS, JR.
WILLIAM R. MERCER.
DANIEL BLITZ.
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