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Патент USA US3020454

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Feb- 6, 1962
H. J. WOLKSTEIN ETAL
3,020,444
TRAVELLING WAVE TUBE COUPLER
Filed May 5, 1959
2 Sheets-Sheet 1
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3,020,444
Patented Feb. 6, 1962‘
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1
loading at high frequency reduces the wave velocity dis- _
3,020,444
TRAVELLING WA‘VE TUBE COUPLER
Herbert J. Wolkstein, Newark, and Ralph E. Bridge,
South Bound Brook, N.J., assignors to Radio Corpora
tion of America, a corporation of Delaware
Filed May 5, 1959, Ser. No. 811,180
5 Claims. (Cl. SIS-3&3)
The present invention relates to an improved ?uted
persion in the coupler. This is accomplished by the rows
of ridges which preferentially load the low ends of the
frequency band. In this manner, the coupler support
provides a minimum of lossy material and a maximum
of energy transfer between the wire mounted on the sup
port and the helix of the travelling wave tube which it
surrounds. The coupler of the invention thus meets the
need of a low noise traveling wave tube Where a decrease
microwave helical coupler support useful in coupling 10 in insertion loss is signi?cant.
A more detailed description of the invention follows
radio frequency energy to or from the helix of a travel
in conjunction with a drawing, wherein:
FIGURE 1 illustrates an embodiment of the low loss
Known helical coupler supports comprise a hollow
helical coupler support of the invention mounted upon
relatively short cylindrical tube of insulation having a
pro-formed helical groove completely embedded in the 15 the envelope of a traveling wave tube. Only a portion
of the traveling wave tube is shown.
insulation.
his groove accommodates a wire adapted
ling wave tube.
to carry radio frequency energy. Because of the 'arrange- -
FIGURE 2 is a cross-section of FIGURE 1 taken
along line 2-2; and
ment of the pre-formed embedded helical groove in the
FIGURE 3 is a fragmentary view of a longitudinal
insulation of the coupler, the Wire in the coupler sup
port is also completely embedded in the insulation. As a 20 section of the ?uted hollow tube of insulation of the
coupler support, showing the parallel rows of ridges of
result, there is a very appreciable loss in the transfer of
insulation material on the interior surface of the hollow
energy between the coupler and the medium with which
tube.
1
the coupler is in energy transfer relation. In using such
FIGURES 4 and 5 are graphs relating insertion loss to
known coupler supports with travelling wave tubes, it has
distance for a known type of helical coupler support
been found that each db of loss inserted into the system
(FIGURE 4) mounted externally of a traveling wave
by the input coupler support results in a db of noise
tube as compared to the helical coupler support of the in
?gure. Since travelling wave tubes are designed to carry
a wide band of very high frequencies, each added db
vention (FIGURE 5).
FIGURE 1 shows a portion of a traveling wave tube
of noise ?gure resulting from loss in the coupler sup
port reduces the ei?ciency and effectiveness of the travel 30 having an evacuated glass, envelope 10 of cylindrical
cross-section surrounding, an internal helical conductor
ling wave tube.
An object of the present invention is to enable the '4 12 through the interior of which an electron beam is
adapted to be projected. Since the traveling wave tube
ef?cient transfer of energy between the helix of a travel
is ‘well known in the art, and no claim is made herein
the tube envelope, with a minimum of loss.
35 to it per se, the details thereof including the source of
electrons, the collector electrode, and the means for ap
Another object is to provide an improved helical
_ ling wave tube and a helical coupler support external of
coupler support which is relatively rigid and reduces to a ‘ ‘
plying the magnetic fieid have not been vshown in the in
spaced rows of ridges arranged parallel to the longitu
FIGURE 2.
terests of simplicity of illustration.
minimum the loss encountered in transferring energy be
Surrounding the glass envelope 10 of the traveling
tween the external coupler and an internal helix adapted
to carry high frequency currents.
40 wave tube is the low loss support for the helical coupler
of the invention. The helical coupler support comprises
Still another object is to provide for use with a travel
a hollow thin tube of insulation 14, such as above-men
ling wave tube a ?uted external helical coupler in the
tioned “Te?on” manufactured by Dupont, having on its
form of a very thin hollow tube of insulation having on
interior surface a plurality of rows 16 of ridges 18 of in
the interior surface thereof a plurality of spaced rows of
ridges arranged to support an exposed wire wound be 45 sulation. The ridges 18 in each row are arranged in
series, as shown, and are made of the same insulation
tween the rows.
material as the thin hollow tube 14. Adjacent ridges 18
In brief the invention comprises a low loss helical cou
in each row are separated by an open space or valley 20.
pler support for use externally of the glass envelope of
The bottom of each open space or valley forms the
a travelling wave tube containing an internal helix. The
smooth interior wall of the tube 14 of insulation. The
coupler support is in the form of a thin hollow tube of
three rows extend parallel to the longitudinal axis of in~
insulating material, such as polytetrafluoroethylene known
sulatio-n tube 14 and are spaced 120° apart, as shown in
as “Te?on,” having on its interior surface a plurality of
dinal axis of the hollow tube of insulation. Each row
The rows of ridges are so arranged that
the coupler wire 22 is threaded in helical fashion be
of ridges is composed of a series of raised portions of 55 tween the ridges of the three rows, as shown in FIGURE
1. The ridges 18 are smaller in height ‘than the diameter
of helical coupler 22 and constitute a minimum of lossy
ridges. These rows, preferably three in number, have
material to hold the wire 22 in position. Hence, the
their ridges so arranged that a coupler wire can be
major portion of the wire 22 is exposed to the interior
threaded in helical fashion through the open valleys or
slots between the ridges, with the major portion of the 60 of tube 14.- for coupling with the internal helix 12 of the
traveling wave tube, which the coupler Wire surrounds.
wire exposed to the interior of the hollow tube of in
It should be noted that the coupler wire 22 is wound
sulation. The coupler wire is thus supported by the sides
in opposite sense to the inner helix of the travelling wave
of adjacent ridges in the respective rows. This arrange
tube.
ment permits a greater extension of the electric ?elds
surrounding the Wire, thereby increasing the coupling co 65 ' In actual practice, in the manufacture of the coupler
support of the invention, the insulation tube 14 is ?rst
e?icient between the helix of the travelling wave tube
threaded and then the ?utes are made to provide the
and the surrounding helical coupler. The total effect is
three spaced parallel rows 16, and then the rows are
seen in the reduced insertion loss. Further, removal of
threaded to cut out the valleys or open spaces 20, thereby
a good portion of the insulation of the hollow tube, as
compared to previously known coupler supports, signi? 70 forming the ridges 18. Because the larger diameter wire
is supported by the sides of the smaller ridges, there is an
cantly reduces the dielectric stored energy and enhances
increase in the. coupling coe?icient between the two
output. In addition to this, the reduction of dielectric
insulation with an open valley or slot between adjacent
3,020,444
3
A.
2. The combination with a low loss, electromagnetic
energy coupler support comprising a hollow tube of insu~
helices 22 and 12, with a consequent appreciable reduc
tion in insertion loss. The removal of a considerable
area of insulation around the wire 22, compared to the
lation having on the interior surface thereof a plurality
embedded type of prior art coupler supports, signi?cantly
of spaced rows of ridges of insulation material with said
ridges each extending inwardly a given distance away
reduces the energy stored in the dielectric and hence en
from said interior surface, adjacent ridges in each row
being spaced apart by an open valley, said rows being
parallel to the longitudinal axis of said tube, of a wire
hances output from or input into the coupler, depending
on whether the coupler is used as an output or input
coupler. The reduction in dielectric loading at the high
wound helically around the interior of said tube in con
frequencies to be passed by the traveling wave tube also
reduces the wave velocity dispersion in the coupler. In 10 tinuous contact with said interior surface and held in posi
tion by the sides of the ridges of said rows, the diameter
practice, the ridge arrangement in the three parallel rows
of said wire being greater than the height of said ridges.
load the low end of the microwave frequency band to a
3. The combination with a low loss, radio frequency
greater extent than the high end of the band.
energy coupler support comprising a hollow tube of insu
Surrounding the insulation tube 14 is a cylindrical
metallic coupler support 24 to which is fastened a coaxial 15 lation having formed on the interior surface thereof a
plurality of spaced rows of ridges with said ridges each
line 26 the inner conductor 28 of which is connected to
extending inwardly a uniform distance above said interior
a point at or near one end of the helical coupler wire 22.
surface, adjacent ridges in each row being spaced apart
The low loss coupler support of the invention may be
used for both feeding input energy to the traveling wave
tube and for abstracting energy therefrom. For this pur
pose, two couplers of the invention surround the enve
by an open valley, said rows being parallel to the longi
tudinal axis of said tube, of a wire wound helically
around and continuously contacting the interior surface
lope 10 as shown in FIGURE 1 and are suitably spaced
of said tube, said wire being held in position by the sides
of the ridges of said rows, the diameter of said wire be
ing greater than the height of said ridges.
FIGURE 4 is a graph relating insertion loss to distance
4. In combination, a helix adapted to carry radio fre
between a pair of helical coupler supports of the type 25
apart along the length of the envelope 10.
quency energy and positioned within an evacuated non~
known in the art, mounted on a traveling wave tube. As
indicated on the drawing, the loss per coupler varied
electrically conducting envelope, a coupler unit in energy
from 3 db at 4800 megacycles to 4.8 db at 7000 mega
transfer relation to said helix comprising a hollow tube
of insulation having the same general cross-sectional
FIGURE 5 is another graph relating insertion loss to 30 shape as that of and surrounding said envelope, a metal
lie cylinder surrounding said tube of insulation, said tube
distance between a pair of helical coupler supports of
having on the interior surface thereof three parallel rows
the present invention, mounted on a traveling wave tube.
of ridges of insulation material spaced 120° apart, said
The improvement, as summarized in the legend on this
ridges and tube being made of the same material, adja
?gure, shows that the loss per coupler varied from .9 db
at 4000 megacycles to 2.5 db at 7000 megacycles. The 35 cent ridges in each row being spaced apart by an open
valley, said rows being parallel to the longitudinal axis
reduction in loss by the use of the invention compared
of said tube, a wire wound helically around and contact
to the prior art coupler supports is highly signi?cant, and
ing the interior surface of said tube, said wire being held
now permits e?icient use of low noise traveling Wave tubes
in position by the sides of the ridges of said rows, the
where a decrease in insertion loss is very important.
The slanted dotted line curves in FIGURES 4 and 5 40 diameter of said wire being greater than the height of
said ridges, and a coaxial line having an inner conductor
are continuations or projections of the solid line curves.
coupled to one end of said wire.
The solid line curves are the results of measurements.
cycles.
5. The combination with an electromagnetic wave
carrying medium, of a pair of coupler units in energy
area because the two couplers could not be brought suf
?ciently close to each other on the envelope of the 45 transfer relation to said medium, said units being spaced
apart along the length of said unit, each of said units
traveling wave tube to obtain measurements in this area.
comprising a hollow tube of insulation having on the in
In one embodiment of the invention successfully built
terior surface thereof a plurality of spaced ridges of the
and tested, the ridges of the ?uted rows had a height of
approximately 4 mils, While the diameter of the wire of 50 same insulation material as said tube, adjacent ridges in
each row being spaced apart by an open valley, said rows
the coupler coil held in position by the ridges was 11
being parallel to the longitudinal axis of said tube, of a
mils. Obviously, the low loss coupler support of the in
wire wound helically around and contacting the interior
vention is not limited to these dimensions. Similarly,
surface of said tube, said wire being held in position by
insulation material other than Te?on can be used and of
various thicknesses depending upon the performance 55 the sides of the ridges of said rows, the diameter of said
wire being greater than the height of said ridges.
characteristics desired.
What is claimed is:
References Cited in the ?le of this patent
1. Traveling wave tube apparatus comprising a travel
ing wave tube of the kind ‘having a wave propagating
UNITED STATES PATENTS
helix inside the envelope, and a helical coupler coil ex
2,531,972
Dohler et a1 __________ .._ Nov. 28, 1950
No measurements were made in the dotted line curve
ternal to the envelope and adapted to provide for the 60
coupling of radio frequency energy to said helix, a sup
port for said helical coupler coil comprising a hollow
tube of insulation having on the interior surface thereof
a plurality of spaced rows of ridges of insulation ma
terial, adjacent ridges in each row being spaced apart by
Kompfner ____________ .. Sept. 22, 1953
Goodall _____________ __ June 26, 1956
2,849,651
2,894,168
Robertson ___________ __ Aug. 26, 1958
Wing et a1 _____________ .._ July 7, 1959
984,595
767,563
France ______________ __ Feb. 28, 1951
Great Britain __________ __ Feb. 6, 1957
65
an open valley, said rows being parallel to the longitudi
nal axis of said insulation tube, said helical coupler coil
being held in place by the sides of the ridges in the dif
ferent rows, the diameter of the wire of said helical
coupler coil being greater than the height of said ridges 70
and exposed to the envelope of the traveling wave tube
which it surrounds.
2,653,270
2,752,523
FOREIGN PATENTS
OTHER REFERENCES
Magid et al.: “Helix Coupling for Traveling Wave
Tube,” RCA Technical Notes No. 197. Received Aug.
18, 1958.
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