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Патент USA US3038114

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June 5, 1962
R. I. HARRISON
3,038,100
TRAVELLING WAVE TUBE
Filed Feb. 26, 1957
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June 5, 1962
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R. 1. HARRISON
3,038,100
TRAVELLING WAVE TUBE
Filed Feb. 26, 1957
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INVENTOR
RICHARD J. HARRISON
BY 3%?‘
A'ITORN
United States Patent ()?ice
3,%8,i@®
Fa’tented June 5, 1962
2
i
the same given frequency.
Each of the powers as
sociated with each component flows in said given direc
TRAVELLING WAVE TUBE
tion and can be added together to produce the total
Richard I. Harrison, Mineola, N.Y., assignor, by mesne
power. However, the direction of propagation for these
assignments, to Sylvania Electric Products Inc, Wil
components varies such that the phase velocity vector
mington, Deh, a corporation of Delaware
of each component points either in the given direction
Filed Feb. 26, 1957, Ser. No. 642,394
or an opposite direction; in general, at any given fre
3 Claims. (til. 315-345)
quency, each component has a different phase velocity.
My invention relates to travelling wave tubes.
The fraction of the total power carried by each com
The conventional travelling wave tube depends for its 10 ponent is a constant determined by the characteristics of
characteristics upon the interaction between the ?eld of
the particular slow wave structure used. \In particular,
an electromagnetic wave propagated along a slow wave
the component of highest power level which has its phase
velocity vector pointing in the direction of power ?ow
structure, such as a helix, and a beam of electrons travel
ling with the wave, as for example, by travelling axially
is denoted as the htogund) or fundamental component,
within the helix. The slow wave structure is periodic in 15 and the component of highest power which has its velocity
the direction of beam travel. The velocity of ?eld prop
vector pointing in a direction opposite to that of the
3,038,1itltl
agation along the structure (the synchronous velocity)
power ?ow is denoted as h(_1) or backward wave com—
is adjusted to be slightly less than the velocity of the beam.
ponent.
Due to the resultant periodic electromagnetic interaction
Travelling wave tubes can be segregated into two main
between the beam and the helix, the power is transferred 20 types; the forward wave type in which the electrons travel
from the beam to the hel'm. The travelling wave tube
in the direction of wave energy propagation; and the
can be used as an ampli?er or as an oscillator.
backward wave type in which the electrons travel in a
It is known to the art that an electron beam can func
direction opposite to the direction of wave energy propa
tion as a special type of transmission line capable of
gation.
propagating slow electromagnetic ?elds, (A detailed 25 The gain of a forward wave tube remains essentially
constant over a wide frequency range, and hence it is
analysis of this type of beam function can be found, for
example, in an ‘article written by R. Kompfner entitled
extremely useful as a broad band ampli?er. However,
“Travelling Wave Tubes” and published in 1952 as Repts.
because of this gain-frequency characteristic, the forward
Progr. Phys. 15,275.)
wave tube is notpwell adapted for use as an oscillator or
I have discovered that when a slow electromagnetic 30 as a narrow band ampli?er.
?eld propagating along a ?rst electron beam is periodi
In contradistinction, the gain of backward wave tubes‘
cally shielded from a second electron beam travelling
‘ is only constant over a narrow frequency range. Further,‘
while the backward wave tube will amplify low level
in a direction parallel tothe ?rst beam, or stated dif—
signals over this narrow range, since it inherently is ‘a
ferently, when the two beams are periodically coupled
to each other, these two beams interact in the same man: 35 regenerative type device, it presently ?nds its principal
application as an oscillator.
nor as if the ?rst beam were replaced by a conventional
In the conventional forward wave tube, the beam
slow wave structure. Thus, I have invented a new type
velocity is made approximately equal to the phase veloc
ity of the fundamental component. The interaction of
of travelling wave tube which, instead of requiring the
combination of a slow Wave structure and a single elec
tron beam, only requires two periodically coupled elec
the beam and the fundamental component (since the
beam and this component travel in the same direction)
tron beams.
My rtube can be produced more rapidly and less ex
pensively than conventional travelling wave tubes. More
results in a growing Wave (i.e. increased wave amplitude)
in the direction of the beam thereby producing the de
over, my tube can be used either as a forward wave
tube or as a backward wave tube and, further, can be 45
used either as an ampli?er or as an oscillator.
Accordingly, it is an object of the present invention
to substitute, for the conventional travelling wave tube
combination of slow wave structure and single electron
beam, two periodically coupled electron beams.
Another object is to provide a new and improved
travelling wave tube characterized by the absence of a
slow wave structure.
Still another object is to provide a new and improved‘
travelling wave tube wherein gain is obtained by the
transfer of energy between two periodically coupled
electron
beams.
.
_
.
Yet another object is to provide a new and improved
travelling wave tube employing, two periodically coupled
electron beams, the direct current power associated with,
one of said beams propagating in the same or opposite
direction with respect to the propagation direction of the
direct current power associated'with the other beam.
sired gain.
On the other hand, in the backward wave tube the
beam velocity is made approximately equal to the phase
velocity of the backward wave component.
The re
sultant beam-component interaction is regenerative in
nature, since the beam carries energy in a direction op
50 posite to the direction of power flow of the backward
wave component while the phase velocity of the beam
and the backward wave component point in the same
direction and are approximately equal (or synchronous).
Therefore, positive or regenerative feedback takes place
55 over each differential length of the beam.
In accordance with the principles of my invention,
?rst and second electron beams are caused to travel in
essentially parallel paths. An electromagnetic wave of
given frequency propagates along the ?rst beam. Means
associated with said beams periodically shields the second
beam from the ?eld produced by this wave, or, stated
differently, periodically couples this ?eld to the second
beam. The interaction between the second beam and the
?eld is equivalent to the interaction between a beam and
These and other objects of my invention will either
65 the ?eld propagating along a helix as displayed in a con
be explained or will become apparent hereinafter.
As is well known to the travelling wave tube art, when’
an electromagnetic ?eld of given frequency and given.
mode propagates in a given direction along a slow wave
ventional travelling wave tube.
Consequently, the periodically coupled ?eld can be de
composed into an in?nite number of spacial harmonic
structure which is periodic in the direction of beam
wave components, all components carrying power in the
70
travel, the ?eld can be ‘decomposed into an in?nite num
same direction (the direction in which the ?eld propa
ber of spacial harmonic wave components which have
gates’ along the ?rst beam), the phase velocity vectors
3,038,100
3
of all components in a ?rst set pointing in this direction,
the phase velocity vectors of all components in a second
set pointing in an opposite direction. Each component
The resultant action With respect to beam 20 is the
same as if beam 18, cylinder 35 and members 44 were
replaced by a conventional periodic slow wave structure.
As indicated previously, the periodically coupled ?eld
is contained in one of these ?rst and second sets. The
?eld and all of its components have the same frequency.
can be decomposed into an in?nite number of spacial
harmonic wave components having ‘the same frequency
as the incoming wave. The phase velocity vectors of a
?rst set of these components point in the direction of
beam 18; the phase velocity vectors of a second set point
The component of the ?rst set having the lowest phase
velocity is known as the fundamental component. The
phase velocity of each other component has some ?xed
ratio to the velocity of the fundamental component.
For any given frequency, the Velocity of the ?rst beam 10 in the direction of beam 24}. Each component is con
will be approximately equal to the phase velocity of the
tained in one or the other of these two sets.
fundamental component, and thus the velocity of the
The velocity VA of beam 18 establishes the phase ve
?rst beam establishes the phase velocities of all the wave
locity of the fundamental component of the ?rst set and,
components.
as previously discussed, ‘thus determines the phase veloci
Hence, in my invention, when both ?rst and second 15 ties of all other components. The velocity VB of beam
beams travel in the same direction, and the velocity of
26 is then adjusted to be approximately equal to the
the second beam is adjusted to be approximately equal
phase velocity of a selected component in the second
to the phase velocity of a selected component in the ?rst
set, as for example the backward wave component, and
set, as, for example, the fundamental component, a for
the tube then functions as a backward wave ampli?er,
ward wave tube interaction ensues. Conversely, if the
the output signal appearing at element 42.
?rst and second beams travel in opposite directions, and
It will be apparent that by applying the incoming
the velocity of the second beam is adjusted to be equal
wave to element 42 and interchanging the velocities of
to the phase velocity of a selected component in the
beams 18 and 20, the tube will function in the same
second set, as, for example, the backward wave compo
nent, a backward wave tube interaction ensues.
Illustrative embodiments of my invention will now be
described in detail with reference to the accompanying
drawings wherein
FIGS. 1 and la illustrate one embodiment of my in
vention;
25
manner but the output signal will appear at element 40.
In the event that forward wave operation is desired,
beams 18 and 20 are caused to travel in the same direc
tion rather than opposed directions as shown here. The
velocity VA of beam 18 then establishes the phase veloc
ities of the various components as before. In this case,
30 however, the velocity VB of beam 20 must be adjusted
to be approximately equal to the phase velocity of a
selected component in the ?rst set, as, for example, the
FIGS. 3 and 3a illustrate a third embodiment of my
fundamental component, and the tube will function as
invention; and
a forward wave ampli?er. (Note that in this example
FIGS. 4 and 4a illustrate a fourth embodiment of my 35 both beams have the same velocity VA.)
invention.
When the tube shown in FIG. 1 is to be used as a
Referring now to FIG. 1, there is provided a travelling
backward wave oscillator, no incoming wave is applied
wave tube structure having an evacuated envelope (not
to either coupling element 40 or 42. However, as is
shown) and- an electrically conductive cylinder 35 dis
known to the art, all wave guides and beams generate a
posed within the envelope. First and second separate
noise spectra. Due to the regenerative action of the
FIGS. 2 and 2a illustrate a second embodiment of my
invention;
coupling means or transition elements 40 and 42 are con
nected to cylinder 35. A ?rst electron beam 18 is gen
erated at electron gun 14 and travels within cylinder 35
tube, the frequency component of the noise spectra equal
to the selected frequency is selectively ampli?ed. The
toward collector 10 mounted within element 42 at a
gain is in general a function of the combined beam cur
rents; when both beam currents are increased to a point
velocity VA. A second electron beam 26 is generated
such that the gain becomes in?nite, the tube of FIG. 1
at electron gun 16 and travels within cylinder 35 in a 45 oscillates.
direction opposite to beam 18 toward collector 12 within
It will be apparent to those skilled in the art that many
cylinder 35 in a direction opposite to beam 18 toward
other arrangements for periodically coupling or shielding
collector 12 mounted within element 40 with velocity
the two beams from each other can readily be used. For
example, the round members can be replaced by an elec
VB‘
A plurality of parallel, electrically conductive mem 50 trically conductive plate having equidistantly spaced cir
bers 44 equidistantly spaced apart from each other are
cular or elliptical holes through which the beams can be
connected at both ends to the cylinder 35 and are inter
coupled together, or a series of equidistantly spacial di
posed between the two beams, each member extending
electric obstacles can be used to periodically shield the two
in a direction perpendicular to the directions of beam
beams from each other.
55
travel, as shown in more detail in FIG. 1a.
FIG. 2 shows an arrangement in which the beam 18
The voltages of batteries 26 and 28 determine the
is a hollow beam and beam 20 is a “solid” beam which
beam velocities VA and VB respectively. Similarly, the
travels along the axis of beam 18. "In this example, the
voltages of batteries 30 and 32 respectively determine
periodic coupling is obtained by equidistantly separated,
the beam currents of beams 18 and 20. Note that cyl
electrically conductive rings 50. The operation of the de
inder 35 is coupled to the junction of batteries 26 and 60 vice of FIG. 2 is substantially identical with the device of
28 and hence is maintained at a positive potential with
FIG. 1.
respect to the two electron guns.
In the device of FIG. 3, the two electron beams are
As is conventional, these beams are columnated by
intermingled in the main portion of their path, these beams
an axial magnetic ?eld. For the purposes of clarity, the
being separated at points adjacent the guns and collectors
external magnets for producing this ?eld, as well as in 65 by the action of magnetic ?eld beam separation devices
ternal gun mounting structures and the like, which are
36 and 38. The magnetic ?ux lines established by these
common both to my tube and conventional tubes, have
devices are directed along a line extending perpendicular
been omitted from all the ?gures of this application.
ly
into the paper, and because of the opposed directions of
An electromagnetic wave of given frequency and mode
is supplied to coupling element 40 and thereafter propa~ 70 travel of the beams in the region where these ?elds are
effective, the separation occurs in the manner indicated.
gates along beam 18.
A plurality of equidistantly spaced magnetic lenses 52
At each member 44 the ?eld produced by the propa
are used in place of the members 44 of FIG. 1. In regions
gating wave is periodically shielded from beam 20. At
where these lenses have no appreciable effect upon the
positions intermediate the member, the ?eld is periodi
cally coupled to beam 20,
75 intermingled beams, i.e. at regions intermediate the lenses,
M.
aoasnoo
5
6
the intermingled beam cross section is relatively large (as
shown in more detail in FIG. 3a), and there is essentially
no coupling between the two beams. However, in regions
said conductive cylinder, said magnetic lenses periodically
where the lenses are effective, the intermingled beam cross
coupling said ?rst electron beam to said second electron
beam.
2. A travelling wave tube comprising a hollow electri
section is relatively small, and a high degree of coupling
is obtained. Since the coupling is periodic, the device of
cally conductive cylinder provided with spaced input and
FIG. 3 functions in essentially the same manner as that
of FIG. 1.
FIG. 4 shows a variation of the device shown in FIG. 3,
wherein the beams are introduced into the metal cylinder
35 at an acute angle with respect to the axis of the cyl
and second beam separation means affixed to the ?rst and
second ends respectively of said conductive cylinder; a ?rst
electric beam travelling with a ?rst velocity from said in
put connection to said output connection along a given path
inder. A plurality of equidistantly spaced pairs of mag
frequency propagating on said ?rst beam; a second elec—
tron beam travelling with a second velocity from said out
put connection to said input connection along a path essen
nets 100 are placed along the cylinder in the manner shown
in FIG. 4a., the two magnets 102 and 104 in each pair
output connections and having ?rst and second ends; ?rst
through said cylinder; an electromagnetic ?eld of given
having opposite polarities, and ‘any two corresponding 15 tially parallel to said given path; said ?rst and second elec
magnets 102 and 104 in any two adjacent pairs 100‘ hav
ing opposite polarities. The two beams then travel in the
paths shown in FIG. 4 and snake or wiggle past each
tron beams being separated at said ?rst and second ends
by said ?rst and second beam separation means; and a plu
rality of magnetic lenses spaced along said conductive cyl
inder, said magnetic lenses producing an axially magnetic
points 106 where the two beams are intermingled, the in 20 ?eld for periodically coupling said ?rst electron beam to
termingled beam cross section at these points being small.
said second electron beam.
other, coupling being obtained at the periodically spaced
The tube of FIG. 4 functions in essentially the same man
ner as that of FIG. 1.
The paths of the two beams as shown in FIGS. 3 and 4
3. A travelling wave tube comprising a hollow elec
trically conductive cylinder having ?rst and second ends,
means for injecting ?rst and second electron beams at ?rst
are not precisely parallel. However, since the amplitude 25 and second velocities into the ?rst and second ends of said
cylinder respectively; each of said beams being injected
of the beam snaking action is relatively small compared
at an acute angle with the longitudinal axis of said cyl
to the length of the path between gun and collector, these
inder, an electromagnetic ?eld of given frequency prop
paths are essentially parallel to each other.
agating on said ?rst beam, and a plurality of magnets
It Will be apparent to those skilled in the art that utiliz
ing the principles of my invention, the two beams can flow 30 spaced along said conductive cylinder, said ‘magnets pro
ducing a transverse magnetic ?eld for periodically cou
in curved rather than straight paths as used for example
pling said ?rst electron beam to said second electron beam.
in magnetrons and in the particular types of backward
wave tubes known as Matype carcinotrons.
While I have shown and pointed out my invention as
applied above, it vw'll be apparent to those skilled in the
art that many modi?cations can be made within the scope
and sphere of my invention as de?ned in the claims which
follow.
What is claimed is:
1. A travelling wave tube comprising a hollow elec 40
trically conductive cylinder provided with spaced input and
output connections; a ?rst electron beam travelling from
said input connection to said output connection along a
given path through said cylinder with a ?rst velocity; an
electromagnetic ?eld of given frequency propagating on 45
said ?rst beam; a second electron beam travelling from
said output connection to said input connection along a
path essentially parallel to said given path with a second
velocity, and a plurality of magnetic lenses spaced along
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,683,238
2,684,453
2,730,647
Milhnan ______________ __ July 6, 1954
Hansell ______________ __ July 20, 1954
IP-ierce _______________ __ Jan. 10, 1956
2,741,718
2,757,311
2,794,146
2,830,271
2,911,556
Wang _______________ __ Apr. 10,
Huber et 'al. _________ __ July 31,
Warnecke et a1 _________ __ ‘May 28,
Pierce _______________ __ Apr. 8,
Charles et a1 ___________ __ Nov. 3,
1956
1956
1957
2,926,281
1958
1959
Ashkin ______________ __ Feb. 23, 1960
1,080,230
1,106,301
706,094
France ______________ __ May 26, 1954
France _______________ __ July 20, 1955
Great Britain ________ __ Mar. 24, 1954
FOREIGN PATENTS
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