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Патент USA US3084290

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April 2, 1963
J. w. MGLAUGHLIN
3,084,280
INTERDIGITAL LINE MAGNETRON
Filed Oct. 24. 1960
INVEN TOR.
JOHN W. MCLAUGHL IN
ATTORNEYS
3,0842%
Patented Apr. 2, 1963
H
3,1981%,230
H?TERDiG-ITAL KNEE MAGNETRQN
John W. McLaughlin, San Jose, Qaliil, assignor to Eitel
McCullough, 1112., 5am Carlos, tl‘alii, a corporation of
California
Filed Oct. 24, 1963, Ser. No. 64,663
17 iClaims. (Cl. 3l5—39.73)
This invention relates to magnetrons and, particularly,
to magnetrons having an interdigital line forming the
radio frequency (RF) interaction means.
One of the types of magnetrons made according to the
present state of the art is known as a voltage tunable
2
FIGURE ‘2 shows a perspective view of the novel inter-v
digital line of the magnetron with the other parts re
moved.
Referring to the drawing in greater detail and to FIG
URE 1, in particular, the magnetron has a cathode sup
port 10 at one end, a collector 12 at the other end, and
between the two a cylindrical interaction space 14 formed
by the novel interdigital line. The interdigital line is
formed by a plurality of thin, elongated segments‘lS
disposed in a circular array. A hot electron-emitting
cathode 16 emits electrons which are guided into the in
teraction space 14 by a control electrode 18. A magnetic
?eld axially aligned with the interaction space 14 causes
the electrons to spiral around a cold non-emitting cathode
magnetron, that is, the frequency of the device is con
trolled by the voltage between the cathode and the inter 15 or electrode 2:’), which is at the same potential as the
digital line. Such magnetrons have a construction known
hot cathode 16. The electrons thus travel in an essen
as the interidigital line construction, as shown for ex
tially helical path axially along the tube until they are
ample in US. Patent No. 2,810,095. This interdigital
collected on the collector 12 at the other end of the tube.
line consists of an even number of parallel segments dis
posed in a circular array. According to the prior art the
terminals for the segments were limited to two rings
The electrons travel this spirally-helical path because the
disposed around the segments, with every other segment
control electrode 18 is at a positive potential relative to
the hot cathode, thereby attracting the electrons radially
outward, because the electrons are affected by a force
connected to one of the terminal rings and the alternate
segments connected to the other terminal ring. The two
terminal rings are disposed one at each end of the inter
digital line. Since only one of the rings can be at radio
?eld, and because they are attracted into the interaction
space 14 by a positive potential on the segments 15, which
potential is more positive than the potential of control
frequency ground potential and the other ring is not, a
electrode 18.
which is perpendicular to the axially aligned magnetic
relatively high capacitance by-pass is formed between said
The cathode 16 is preferably a porous sintered-nickel
other ring and another closely spaced electrode in the
body with barium, strontium, or calcium oxides inter
magnetron. ‘inherently this closely spaced electrode is 30 posed within the pores and is known as a matrix-type
at the radio frequency ground potential and, the high
cathode. Other types of cathodes such as a hot emitting
capacitance between one of the rings and the closely
?lament or a coated oxide cathode may be used instead of
spaced electrode will tap-oif radio—frequency power and
a matrix~type cathode. The preferred cathode 16 is
return the power to the other terminal ring through the
mounted between a tubular metallic sleeve 28 and a non—
intra-electrode capacitance within the magnetron. There 35 emitting metallic radial ?ange 29, which are in turn
fore the available radio-frequency power is less than it
mounted on an axial metallic sleeve 30 extending almost
should be if there were no losses through the intra-elec
the length of the magnetron. Between the axial sleeve
trode capacitance within the magnetron.
30 and the tubular sleeve 28 is disposed a heating ?lament
An object of the present invention is to increase the
32. The heating ?lament 32 is preferably a double
amount of available radio frequency power of a mag 40 helically wound type which has its leads connected to a
netron with an interdigital line.
terminal ring 34 and metallic vacuum wall 35, insulated
Another object of the present invention is to reduce
from each other by a ceramic insulator 36. A ceramic
the capacitance between at least one terminal of the inter
backing ring 3"] backs up the metal-ceramic seal at the
digital line and the other electrodes within the magnetron.
terminal ring 34, and a ceramic backing ring 38 backs
Still another object of the present invention is to pro 45 up the metal-ceramic seal at the end wall 35. The ter
vide a magnetron with three terminals for the interdigital
minal ring 34 is also a sealing ring which has a ?ange
line wherein one terminal is shielded by the other two
39 turned parallel to the axis of the tube. The axial
terminals.
sleeve 3%, on which the hot cathode 16 is mounted, is
A further object of the present invention is to provide
preferably of thin-wall construction which acts as a heat
a means for extending the ground plane of a coaxial line
into the magnetron.
A still further object of the present invention is to pro
vide direct connection of a coaxial line to the inter
digital line.
Yet another object of the present invention is to provide
an improved voltage tunable magnetron.
Briefly described, one embodiment of the invention
comprises a magnetron in which the interdigital line has
three terminal rings disposed around parallel elongated
dam on one side of the cathode holding the heat of the
?lament 32 in the region of the cathode 16. The thin
wall axial sleeve 30 is mounted at one end on a thin-wall
conical support 41 which acts as a heat dam on the other
side of the cathode. An aperture '42 is provided in sup
port 41 for easy evacuation. The conical support 41 in
turn is mounted on the metallic end wall 35. The other
end of the axial sleeve ?ts over a ceramic rod 43 which
in turn ?ts into a well 44 formed in the collector 12.
The cold electrode 20 is concentrically supported on the
segments disposed in a circular array with some of the 60 axial sleeve 39 by two metal rings 46 having apertures 47
for easy evacuation. Thus, the cathode support it), which
segments connected to the middle terminal ring and the
is one sub-assembly of the magnetron, is formed.
remaining segments connected to the other two.
The other assembly of the magnetron comprises the
The invention possesses other objects and features of
control electrode 18 which is preferably made cylindrical
advantage some of which, with the foregoing, will be set
forth in the following description of the invention. The 65 with an inner diameter equal to the outer diameter of the
interaction space 14 formed by the segments 15. The
invention is not limited to the disclosed embodiment, as
control electrode 18 has a terminal ring 48 with a ce
variant embodiments thereof are contemplated and may
ramic insulator 51 separating the ring 48 ‘from a metal
be adopted within the scope of the claims.
sealing ring 52. A ceramic backing member 53 is dis
Referring to the drawing:
70 posed on the opposite side of the sealing ring 52. The
FIGURE 1 shows in cross-section the voltage tunable
segments 15 are mounted so that they form the novel
magnetron; and
interdigit-al line which has three ring terminals 54, 55,
3,084,280
4
3
and 56 and will be described more fully hereinafter.
The
‘48 and the ring terminals 54, 55, and 56 are
separated by ceramic insulators 57, 58, and 59, respec
tively, while an insulator 6% supports the collector 12 to
through the tube thereby decreasing the useful output
of the magnetron. Also by applying the novel three
terminal interdigital circuit in a magnetron obnoxious
RF. radiation is reduced because as mentioned above
this sub-assembly through the metal ring 61. VA ceramic
backing member 62 is bonded to ring 61 Opposite the
the ground planes, rings 54 and 56, shield the remaining
cér'an'iic insulator 60.
taining the R.F. Within the ground planes. A coaxial
An'exhaust tabulation '63 is dis
posed in the collector 12.
~
.
_ Thus, the magnetron is shown preferably made in (two
structure of the magnetron from the R.F. energy by con
line can be readily attached to the novel three terminal
line because the center conductor can be connected to
sections which are welded together at the edges of ?ange 10 ring 55 and the outer cylindrical shield of the coaxial
line can be connected to rings 54 and 56 by applying a
39 andlthe sealing ring 52. The cold electrode 20 on the
suitable transition section which encloses the center con
cathode support 10 ?ts ‘within the interaction space 14
ductor.
and the ceramic rod 43 ?ts snugly into Well 44 of the
I claim:
collector, whereby the cathode elements are aligned with
1. A magnetron comprising a cathode and an inter
in the interaction space. The welded envelope is evacu
digital line, said interdigital line comprising a plurality of
ated through the tubulation 63 and then the end of the
segments disposed in a circular array, and at least three
tubula'tion is “nipped-0d” as shown.
terminal rings disposed around the segments, some of said
I. The magnetron operates in the following manner: An
external magnetic circuit (lnot‘shown) forms a relatively
segments being ‘connected to one of said terminal rings
uniform magnetic ‘?eld within 'the‘interaction space 14 20 which is electrically insulated from the other rings, and
the remaining segments being connected to the other said
which ?eld is oriented parallel‘ to the tube axis. The hot
terminal rings.
cathode 16 emits electrons which are ‘attracted by the
2. A magnetron comprising a cathode and an inter
control electrode 18. The electrons, being thus sub
digital line, said interdigital line comprising a plurality of
jected to a force which is oriented radially outward and
perpendicular to the magnetic ?eld, are caused to spiral 25 an even number of segments disposed in a circular array,
and at least three terminal rings disposed around the seg
around the axis of the magnetron. The segments 15
ments, alternate segments being connected to one of said
around the interaction space 14, being more positive
terminal rings ‘which is electrically insulated from the
than the control electrode, attract the spiraling electrons
other rings, and the remaining segments being connected
within the interaction space v14. When the electrons
to the other said terminal rings.
.are‘s‘piraling within the interaction space, RF. electro
magnetic ‘oscillations are formed in the segments in ac
cordance with known theories. The electrons spiral in
a somewhat helical path along the axis, and when the
3. A magnetron comprising a cathode and an inter
digital line, said interdigital line comprising a plurality
of an even number of segments disposed in a circular
array, and at least three terminal rings disposed around
electrons reach the end oflthe interaction space, they are
collected on the collector 12 and prevented from re-enter 35 the segments, alternate segments being connected to one
of said terminal rings which is electrically insulated from
ing the interaction space 14. This reduces the noise in
the other rings, and the remaining segments being con
the radio-freqnency'circuit because out-of-phase electrons
nected to each of the other said terminal rings.
are removed from the interaction space.
_
7 As mentioned above, the segments 15 of the novel
4. A magnetron comprising a cathode and an interdigi
interdigital line are connected to three ring terminals, 40 tal line, said interdigital line comprising a plurality of an
even number of segments disposed in a circular array, and
54, 55, and '56. Referring to FIGURE 2, a perspective
at least three terminal rings disposed around the segments,
vi'ewof the segments 15 and the ring terminals 54, 55,
alternate segments being connected to one of said terminal
and ‘S6 of the interdigital line is shown. In this embodi
rings which ‘is electrically insulated from the other rings,
ment, the interdigi'tal line has preferably eight segments
a, b, c,_ d, e, f, g, and h but more than or less than eight 45 some of the remaining segments being connected to one
segments may comprise the novel interdigital line with
out departing froin the invention. Every other segment,
segments a, c, e, and g, is connected at a point between
of said other terminal rings, and the remaining segments
being connected to another one of the terminal rings.
_5. A magnetron comprising a cathode and an interdigi—
tal line, said interdigital line comprising a plurality of seg—
its ends to the ring 55 that is disposed between rings 54
and 56. Every fourth ‘segment, segments‘ b and f, is 50 ments disposed in a circular array, and at least three ter
connected at one end to the ring 54 in the manner as
shown and the remaining segments a? and h are connected
at one end to vthe ring 56 as shown. The other end of
segments b and 7‘ may also be connected to ring 56 and
minal rings disposed around the segments, some of said
segments being connected to one of said terminal rings
which is electrically insulated from the other rings, some
of the remaining segments being connected to one of the
also theother end of segments d and k may be connected 55 other terminal rings, and the remaining segments being
to ring 54. ‘If both ends of segments b, a‘, f, and h are
connected to rings 54 and 56 instead of being connected
at only one end to one ring,‘ the electrical'characteristics
oi the magnetron are improved, but the process for as
sembling the novel interdigital line is more complicated 60
and expensive. One method ‘for. connecting segments
connected to another one of the terminal rings.
‘ 6. A magnetron comprising a cathode and an interdigi
tal line, said interdigital line comprising a plurality of an
even number of segments disposed in a circular array, and
at least three terminal rings disposed around the segments,
alternate segments being connected to one of said terminal
b,'d, f,jand h to both rings 54 and 56 is to braze the free
rings which is electrically insulated from the other rings,
endsfof segments b and f to ring 56 and to braze the free
half of the remaining segments being connected to one of
ends of segments d and h to ring S‘t'after the insulating
the other terminal rings and the remaining segments being
rings 58 ‘and 59 are brazed to rings 54, 55, and 56.
65 connected to another one of the terminal rings;
The magnetron which incorporates the novel interdigi~
7. A magnetron comprising a cathode and an interdigi
tal line is“ able to deliver more power than a magnetron
tal
line, said interdigital line comprising a plurality of seg_
which incorporates an interdigital line of the prior art
ments disposed in a circular‘array, and at least three ter¥
because most of the radiov frequency energy is shielded
from the other tube electrode by the two rings 54 and 56 70 minal rings disposed around the segments with one of said
rings electrically insulated from the other rings, every
which act as ground planes. The rings 54 and 56 acting
fourthrone of said segments being connected to one of the
as ground planes on both sides of ring 55 reduce the
terminal rings which is axially displaced from the other
RF. leakage currents which are induced in the DC.
rings, every ?rst and third one of said segments being con
rents are undesirable because they shunt the RF. energy 75 nected to the terminal ring which is electrically insulated
electrodes in, a’tube of the prior art. These leakage cur
5
3,084,280
6
from the other rings, and the remaining segments being
cylinder attached coaxially to said tubular structure and
passing through the anode, said cathode being attached
connected to another terminal ring.
‘3. A magnetron including an evacuated envelope and
comprising an anode formed by an interdigital line, a
to said tubular structure at a position between said anode
and the end of the magnetron remote from said collector,
a post attached to one end of said tubular structure and
non-emitting electrode disposed through and axially With—
in said interdigital line, an electron emitting cathode
?tting snugly within said well in the collector, and me
chanical means connecting the other end of said tubular
spaced axially from said interdigital line, a control elec
trode surrounding said emitting cathode, and a collector
structure to said second envelope wall portion, said
electrode spaced from and insulated from said non-emit—
interdigital line comprising a plurality of segments dis
ting electrode and said anode and disposed on the opposite 10 posed in a circular array, and at least three annular ter
side of said anode from said electron emitting cathode,
minal rings having their inner peripheries disposed around
said interdigital line comprising a plurality of segments
the segments within the envelope and having their outer
disposed in a circular array, and at least three annular ter
peripheries outside the envelope, some of said segments
minal rings disposed around the segments and having their
being connected within the envelope to one of said ter~
outer peripheries outside the envelope, some of said seg
minal rings, and the remaining segments being connected
ments being connected within the envelope to one of said
to the other said terminal rings.
terminal rings which is electrically insulated within and
13. A magnetron comprising a ?rst tubular envelope
outside the envelope from the other rings, and the remain
wall portion to which is attached a collector, an anode,
ing segments being connected to the other said terminal
and a control electrode, said collector being positioned
rings.
20 closing one end of said ?rst tubular envelope wall portion
9. A magnetron comprising an anode formed by an in
and having a well therein opening toward the other end,
terdigital line, an elongated non-emitting electrode dis
a ?rst sealing ring attached to said other end of said ?rst
posed through and axially Within said interdigital line, and
envelope wall portion, said anode being disposed between
an electron emitting cathode spaced from said non-emit
said collector and said ?rst sealing ring, said anode com
prising a plurality of segments supported in a cylindrical
ting electrode, said interdigital line comprising a plurality
of segments disposed in a circular array, and at least three
array to form an interaction space, at least three terminal
terminal rings disposed around the segments, some of said
segments being connected to one of said terminal rings
which is electrically insulated from the other rings, and
the remaining segments being connected to the other said 30
rings disposed around said segments, some of said segments
being electrically connected together to one of said ter
terminal rings.
10. A magnetron comprising a cathode disposed on the
tube axis and an interdigital line disposed coaxially, said
interdigital line comprising a plurality of segments dis
posed in a circular array, and at least three terminal rings
disposed around the segments, some of said segments
being connected to one of said terminal rings which is
electrically insulated from the other rings, and the remain
ing segments being connected to the other said terminal
minal rings and the remaining segments being connected
to the other said terminal rings, said control electrode
being positioned adjacent the end of the anode remote
from the collector and having a bore therein axially
aligned with said interaction space, a second tubular en
velope wall portion to which is attached a hot tubular
cathode and an axially aligned non-emitting tubular elec
trode, an end plate closing one end of said second envelope
wall portion, a tubular structure ?xed coaxially on said
end plate, said cathode and non-emitting electrode being
mounted on said tubular structure, a second sealing ring
40 disposed on the other end of said second envelope wall
rings.
portion, a post attached to the free end of said tubular
111. A magnetron comprising an anode formed by an
interdigital line disposed about an axis, an axially disposed
thin-wall metallic sleeve, a tubular non-emitting electrode
coaxially mounted on said thin-wall sleeve and disposed
within said interdigital line, an indirectly heated electron
emitting cathode mounted coaxially on said thin-Wall
sleeve and spaced from said non-emitting electrode and
from one end of said interaction space, a filament for
heating said cathode disposed between said thin-wall
sleeve and said cathode, a tubular control electrode dis
posed coaxially around said cathode, a collector disposed
and spaced from the other end of said interaction space,
and an insulating rod disposed between said collector and
said thin-wall axial sleeve for supporting said sleeve, said
interdigital line comprising a plurality of segments dis
posed in a circular array, and at least three axially spaced
terminal rings disposed around the segments, some of said
segments being connected to one of said terminal rings
structure, said ?rst and second envelope wall portions
being disposed in axially aligned relationship with said
?rst and second sealing rings bonded together, said post
?tting snugly within said well, said cathode being spaced
axially from said interaction space, and said non-emitting
electrode disposed within said interaction space.
14. A magnetron comprising a tubular envelope, a
collector, an anode, a control electrode, an indirectly
50 heated tubular cathode, and a non-emitting electrode, said
collector being positioned adjacent one end of said en
velope and having an axially aligned well therein opening
toward the other end of said magnetron, said anode being
formed by an interdigital line and positioned adjacent said
collector, said control electrode being positioned adjacent
the end of‘ the anode remote from the collector and having
a bore therein axially aligned, a tubular structure disposed
coaxially, said non-emitting electrode being a cylinder at
tached to said tubular structure and passing through the
and the remaining segments being connected to the other
said terminal rings.
tit) anode, said cathode being attached to said tubular struc
ture at a position between said anode and the other end
12. A magnetron comprising a tubular envelope wall
of said envelope remote from said collector, a post having
portion to which is attached a collector, an anode, and a
one end portion attached to one end of said tubular struc
control electrode, a sealing ring attached to said- envelope
ture and its other end supported against lateral displace
portion, a second envelope wall portion to which is at
tached a cathode, and a non-emitting electrode, a second 65 ment by the collector, and mechanical means connecting
the other end of said tubular structure to said other end
sealing ring attached to said second envelope portion and
of the envelope, said interdigital line comprising a plu
a vacuum tight bond joining said sealing rings, said col
rality of segments disposed in a circular array, and at
lector being positioned adjacent one end of said magnetron
least three terminal rings disposed around the segments,
and having a well therein opening toward the other end
of said magnetron, said anode being formed by an inter 70 some of said segments being connected to one of said
terminal rings and the remaining segments ‘being con
digital line and positioned adjacent said collector, said
nected to the other said terminal rings.
control electrode being positioned adjacent the end of
15. In a voltage tunable magnetron having an evacuated
envelope elongated about a central axis, an interdigital
disposed coaxially, said non-emitting electrode being a 75 anode structure comprising a plurality of circularly ar
the anode remote from the collector and having a bore
therein axially aligned with said Well, a tubular structure
3,084,280
7
8
ranged metallic anode segments extending axially within
velope portions with the outer peripheries of the annular
said envelope and circurnferentially spaced to provide a
plurality of interaction gaps therehetweenyand at least
three annular axiallyrspaced terminal rings circumscribing
said metallic anode segments, the inner ‘peripheries of
said annular terminal rings beingrintegrally connected to
selected ones of said anodesegments Within the envelope
while being electrically insulated from an adjacent ter
minal ring and the outer peripheries of‘said annular ter
minal rings being electrically insulated from each other. 10
16. The combination according to claim 15 in which
said envelope includes a plurality of axially stacked alter
nate metallic and dielectric portions, and said annular
terminal members outsidethe envelope and the inner pe
terminal rings constitute selected ones of said metallic en
ripheries thereof inside therenvelope.
:17. The conibination;according toclairn .15, in which
selected ones of said metallic anode segments have oppo
site ends integrally connected toalternate ones of said
axially spaced terminal rings.
References Cited in the ?le of‘this patent
UNITED STATES PATENTS
2,607,905
2,930,933
2,941,109
Ludi ________________ __ Aug. 19, 1952
‘Grif?n et a1 ___________ __ Mar. 29', 1960
Senior et a1 ___________ __ June 14, 1960
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