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Патент USA US3092758

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June 4, 1963
H. A. HAUS ETAL
3,092,750
TRAVELING WAVE TUBE
Filed OC‘I'.. 22. 1959
œOPmlj 205m
QM2OIE4Q
/NvE/vrons
HERMA/v A. HAI/s
JAMES A. MULLE/v
Afro/mfr
3,092,750
g.
Unit
i
States atet
Patented June 4, l 1 963
1
2
3,092,750
The invention may be best described with the help of
the accompanying FIGURE in which there is shown a
TRAVELING WAVE TUBE
Hermann A. Haus and James A. Mullen, Milton, Mass.,
assignors to Raytheon Company, Lexington, Mass., a
corporation of Delaware
Filed Oct. 22, 1959, Ser. No. 848,071
4 Claims. (Cl. S15-3.6)
schematic diagram of a traveling wave tube utilizing a
particular embodiment of the structure of the invention.
In the figure, there is shown a traveling wave tube 10
having an electron gun system 11 which includes a cathode
12 and an accelerating beam forming anode 13. The
beam as shown in this iigure travels down the tube sub
stantially in a straight line as shown by dashed line 20.
This invention relates generally to traveling wave
tubes and, more particularly, to means for reducing noise 10 The traveling wave tube further includes a first
helical section 14 and a second helical section 15,
Within said traveling wave tubes.
the latter including an attenuation means 16 the
In traveling wave tubes, it is well known that noise gen
function of which is explained subsequently. ‘It is ad
erated in the tube may be excessive for some applications,
vantageous to make the diameters of the first Áand second
especially when the tube is used in receiver operation with
low signal inputs. -Noise in traveling wave tubes general 15 helical sections substantially equal, as shown in the iigure,
ly arises because electrons are emitted from the electron
gun at random velocities and at random times. Such ran
dom emission gives rise to random currents and voltages
although it is understood that such a construction is not
necessarily required. There is also included in the tube
a collector anode 17.
The cathode and anodes lare con
nected to appropriate power supplies shown in the figure
in the tube.
It has been conventional in prior art systems to reduce 20 by block 18. The R-F signal from input source 21 is fed
to one end of ñrst helical section 14 and R-F output is
this noise by providing a series of auxiliary electrodes in
taken from one end of helical section 15.
the region following the electron gun. These electrodes
`First helical section 14 is arranged so that its pitch,
provide additional accelerative forces for the electron
defined as the reciprocal of the number of turns per unit
beam as it travels down the tube. The auxiliary elec
trodes may be arranged to provide discreet jumps of ac 25 length, is such as to cause the R-F input signal to inter
act with the electron beam to cause an interchange of
celeration or a substantially continuous acceleration of the
energy between the R-F signal and the fast space charge
beam before it moves along the path adjacent the delay
‘beam wave associated with the electron beam. In this
line. Although such a structure reduces noise eíïects in
Way, a portion of the noise associated with the fast space
the tube, the use of such accelerating regions is undesirable
charge wave of the electron beam is coupled to the iirst
because the beam becomes defocussed and additional
helical section. The pitch of the helix of second helical
focusing ñelds are required to cause the beam to travel
down through the tube in the correct path.
>section 1S is arranged so as to provide -an interaction be
tween the R-F signal and the slow space charge Wave as
This invention, however, provides a system which re
sociated with the electron beam. Similarly, a portion of
duces the noise to a minimum without the requirement of
additional focusing fields to obtain correct beam travel. 35 the noise associated with the slow space charge wave is
coupled to the second helical section. Since there is a
The invention makes use of the fact that two space charge
correlation between the noise associated with the fast space
waves exist in the electron beam, one of which travels
charge wave and the noise associated with the slow space
faster than the electrons and the other of which travels
charge wave, there is a substantial cancellation of the
more slowly than the electrons. The noise which ac
latter noise by the former noise. To achieve maximum
companies the fast space charge wave is, in general, par
noise reduction, the length of first helical section 14 is
tially correlated with the noise associated with the slow
adjusted until a minimum noise can be measured on the
space charge wave. The tube gain is obtained by the
R-F output signal removed at the output end of second
interaction of the R-F signal and the slow space charge
helical section Y15.
beam wave.
A conventional attenuation means 16 is placed in slow
In one embodiment of the invention wherein a traveling
wave tube utilizes a helical delay line structure for pro
wave helical structure 15 to suppress backward wave re
viding interaction between lan electromagnetic wave, or
Alll-F input signal, and the beam, the helical structure is
divided into two sections connected together. The »first
helical section is arranged to provide interaction between
the R-F signal and tbe fast space charge beam wave. The
flections so that the possibility of backward wave oscilla
second helical section is arranged to provide interaction
between the R-F signal and the slow space charge beam
wave. In this way, a portion of the fast >space charge
power is coupled to the ñrst helical section.
tions is eliminated.
Although one speciiic embodiment of the invention uti
lizes an adjustment of pitch and length to obtain inter
action between the electromagnetic wave and the fast
space charge wave in helical structure 14, it is obvious
that any other means which provides interaction with the
fast space charge wave vfollowed by subsequent interac
tion with the slow space charge wave would bring about
the same noise reduction effect. Such a system essentially
requires an adjustment of the well-known Pierce’s b
Noise asso
ciated with the fast space charge wave is, thus, transferred
to the `first helical section and is propagated with the R-F
signal along the helical structure. Since the noise in the
parameter. The fast space charge wave is a wave which
fast and slow space charge waves is partially correlated, 60
travels faster than the speed of the electrons and the
the noise due to the fast space charge wave partially can
cels the noise transferred to the »R-F signal due to inter
action with the slow space charge -wave in the second
helical section. Some uncorrelated noise is also present,
but the over-all noise reduction is effective enough to pro-
vide theoretically the minimum noise of which the system
is capable. Although some of the input power from the
R-F signal is transferred to the fast space charge wave
and lost as far as the output circuit is concerned, it is pos
sible to make up this power by extending the length of
the second helical section and, thus, increase the gain
due to the slow space charge wave interaction.
slow space charge wave is one which travels more slowly
than the electrons. When Pierce’s parameter b equals 0,
the R-F signal phase velocity substantially equals the
, velocity of the electrons in the beam. Matching of the
R-F signal phase velocity with the fast space charge wave
requires adjustment of Pierce’s parameter b so that b is
positive. Similarly, in order to match the slow space
ycharge wave, Pierce’s parameter b is made negative. Such
an adjustment of this parameter in each helical section
may be brought about in any convenient manner. The
adjustment is shown in the ñgure as accomplished by ap
3,092,750
4
propriately adjusting the pitch of the helices in each helical
moving said electromagnetic wave from said traveling
section.
wave tube.
n
Although the particular traveling wave tube shown in
the specific embodiment of the invention `described above
ì
,
3. A -traveling wave tube comprising an electron source;
means for directing a 4beam of electrons from said source
utilizes helical :delay linestructures, it is not to 'be con U1 along an extended path, said electron beam having a first
strued as the only embodiment of the invention. Any
space charge wave traveling at a velocity greater than that
type of traveling wave tube delay line structure may be
of said electrons and a second space charge wave travel
utilized, as long as the delay line structure `is divided into
ing at a velocity less than that Vof said electrons; helical
two portions, a first one having the R-F input signal
delay line means being positioned adjacent said extended
matched to the fast space charge wave and the second
path and including first and second interconnected helical
having the R-F signal matched to the slow space charge
delay line sections, said second helical section including
Hence, the invention is not tofbe construed as
attenuation means for preventing backward wave oscilla
limited to the specific embodiments shown and described
herein except as Idefined ‘by the appended claims.
What is claimed is:
l. A traveling wave tube comprising an electron source;
means for directing a Íbeam of electrons from said source
along an extended path, said electron beam having a first
wave.
tions within said traveling wave tube; means for propa
gating an electromagnetic wave along said first and sec
ond helical sections; the pitch of said first helical section
being selected to provide an interaction between said elec
tromagnetic wave and said ñrst space charge wave and
the pitch of said second helical section being selected to
provide an interaction between said electromagnetic wave
and said second space charge wave; output coupling
space charge wave traveling Iat a rate faster than said
electrons and a second space charge wave traveling at a
rate more slowly thanV said electrons; lhelical delay line
means being positioned adjacent said extended path and
including ûrst and second interconnected helical delay
line sections; means for propagating an electromagnetic
means connected to said second helical section for remov
Ying said electromagnetic wave from said traveling wave Y
said electromagnetic wave and said second space charge
helical delay line sections, said ksecond helical section in
cluding attenuation means for preventing backwardewave
tube.
4. A traveling wave tu'be comprising an electron source;
wave along said first and said second helical delay line 25 means for directing a beam of electrons from said source
sections; the pitch of said first helical delay line section
along an extended path, said electron beam having a first
being selected to provide an interaction -between said elec
space charge wave traveling `at a velocity greater than
tromagnetic wave and said first space charge wave as said
that of said electrons and a second space charge wave
beam travels along a path adjacent said first helical delay
traveling at a velocity less than that of said electrons; heli
line section and the pitch of said second helical delay line 30 cal delay line means being positioned »adjacent said eX
section being selected to provide an interaction 4between
tended path and including first and second interconnected
wave as said beam travels along a path adjacent said sec
ond helical `delay line section, said electromagnetic wave
being thereby amplified; output coupling means for re
moving said amplified electromagnetic wave from said
traveling wave tube.
oscillations within said traveling wave tube; means for _
ropagating an electromagnetic wave along said first and
second helical sections, the pitch of said first helical sec
tion being selected to provide an interaction between said
2. A traveling wave tube comprising an electron source;
>electromagnetic wave »and said first »space charge wave and
means for directing a beam of electrons from said source
the pitch of said second helical section being selected to
along an extended path, `said electrom beam having a 40 provide an interaction between said electromagnetic wave
first space `charge wave traveling at a rate faster than said
and sm'd second space charge wave, the length of said first
electrons and a second space charge ywave traveling at a
helical section being adjusted so as to reduce the noise
rate more slowly than said electrons; helical delay line
associated with said electromagnetic wave to a minimum;
means being positioned adjacent said extended path and
output coupling means connected to said second helical
including first and second interconnectedV helical delay
ection for removing said electromagnetic wave from said
-traveling wave tube.
line sections; means for propagating an electromagnetic
wave along said first and said second helical delay line
References 'Cited in the file of this patent
sections, the pitch of said first helical delay line section
being selected to provide an interaction between said elec
vUNITED STATES PATENTS
tromagnetic wave and said first space charge -wave as said 50
beam travels along a path adjacent said first helical `delay
' 2,584,597
Landauer _____ __ ...... __ Peb. 5, 1952
vline section and the pitch of said second helical delay line
` 2,767,259
Peter _____ __ _________ __ Oct. 16, 1956
section being selected to provide an interaction between
said electromagnetic Wave and said second space charge
wave as said beam travels along a path adjacent said sec
ond helical delay line section, the pitch of said first helical
delay line section being less than that of said second
helical delay line section; output coupling means for re
2,908,844
3,009,078»
y'Quate ________________ __ Oct. 13, 1959
Ashkin ______ ________ __ Nov.Y 14, 41961
696,058
-Great Britain _________ __ Aug. 26, 1953
1,041,169
Germany ____________ __ Oct. 16, 1958
55
FOREIGN PATENTS
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