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De¢.1o,19.46. -
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'G_L, USSELMAN
2,412,372
MAGNETRON
Filed Oct. 26, 1943
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ATTORNEY
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Patented Dec. 10, 1946'
2,412,372
UNITED "STATES PATENT orifice =
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_ 2,412,312
MAGNETRON
'y _ George L. Usselxnan, Port Jefferson, N. Y., assign
‘or to Radio Corporation of America, a corpora
tion- of Delaware
Application october 26, 1943, serial No. 507,697
16 Claims. (Cl. 179-1715)
1
2.
This invention relates generally .to ultra high
frequency magnetron oscillation generators, and
particularly to magnetrons of the type having an
`upon which the electrons impinge are designated
anode so constructed that it forms a circuit reso
nant to the frequencyA at which the device is in
tended to operate.
s
L. The cathode is K and extends linearly along
the central axis of the magnetron or central
chamber. Split disc-like rings GI and G2 are
shown around each` end of the cathode K and 1o
cated at each end ofthe magnetron central
chamber. The envelope of the magnetron, which
is evacuated, is not shown in order to simplify
For the purpose of generating ultra high fre
quency oscillations modulated in amplitude, it is
the drawing.
,
'
known to employ a magnetron having an anode
An important feature of the magnetron of the
provided on its inner surface with a plurality of 10
substantially cylindrical grooves or cavities dis
invention lies in the novel construction of the
grooves‘or cavities by reason of which the lip
posed parallel to and symmetrical with the cath
circle or inner walls of the central chamber tapers
ode. The grooves or cavities form tubes having
outwardly in going from lthe top to the bottom,
inductances dependent upon the dimensions
thereof, and the portions of the anode between 15 and the diameters vof the grooves grow larger
-the grooves form capacitances with each other
from end e to end e’, as shown. The order of
the change in dimensions may be reversed with
and with the cathode, the capacitances valso be
out añecting the principles of the invention.
ing dependent upon the dimensions of these por
A ñeld magnet with poles N and S (north and'
tions and the spacing thereof relative to each
other and to the cathode. The anode of this 20 south) produces a magnetic iield parallel to the
type of magnetron can be said to be composed of
cathode to influence the movement of the elec- ‘»
a plurality of inwardlyv projecting anode por
trons emanating from the cathode. If_ desired,
_this magnet may be replaced by a iield coil sur
tions. These anode portions may comprise an
rounding the anode and producing an intense
even number and be substantially or effectively
spaced from one another by one-half wavelength 25 but constant magnetic field which has flux lines
running parallel4 through the envelope in a di- f
at the operating frequency of oscillations. Ref
erence is herein made to Hansell United' States
`rection parallel to the cathode.
The disc-like rings GI and G2 may be referred
Patent #2,217,745, granted October 15, 1940, and
to as grids or control electrodes and are shown
to Samuel United States Patent #2,063,342, De
cember 8, 1936, for this known type of mag 30 connected to opposite ends of the secondary wind
netron.
ing S of an audio frequency transformer T to
whose primary Winding P is applied the audio
The present invention, broadly stated, is a
modulating signal in the form of speech or Aoscil
modification of the foregoing type of magnetron
lations. The ring grids are by-passed to" the"
which makes it possible to obtain frequency
modulated oscillations in a novel and eflicient 35 anode A by condensers B. The midpoint ofthe
manner.
' A more detailed description of the invention
follows in'conjunction with a drawing wherein:
Figure 1 shows substantially a half sectional
view, partly in perspective, of a magnetron in ac
cordance with the present invention, in a circuit
for producing frequency modulated oscillations;
secondary winding S is connected to a source of
negative bias potential. The anode A is grounded
at GRD, while high negative direct current po
tential and 10W voltage heater current are sup
plied to the cathode K through leads J and H,
respectively. It will thus be seen that the anode '
A is at a high direct current positive potential ’
relative to the cathode K. An output or pick-`
I
up loop D is located in one of the grooves or
Figure 2 shows a plan view of the magnetron
of Figure 1 with the pole face removed to show 45 cavities for abstracting ultra high frequency
oscillations. This loop connects to a suitable
the configuration of the anode groves more com
and
pletely.
output circuit such as a transmission line or an
The magnetron of the invention isshown as
having an anode A provided with eight grooves
tenna by means of leads F.
'
~
The principles of operation of the magnetro
or cavities, although it should be understood that 50 and its circuit will now be described. In gen
any other desired number of grooves can be em
ployed. The upper end of these cavities are des
ignated e, while the lower ends are designated e'.
The lips of the cavities which define the bound- ‘
eral, when free electrons are liberated from the
cathode K by the action ofy heat, they are pulled
toward the anode by its positive potential. Now it
is known that when an electron moves perpendic
aries of the inwardly protruding anode portions 55 ularly across a magnetic field it will describe a
2,418,878
l
v
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3
~ concentric or curved path in the magnetic field.
The curvature. of the path depends upon the
vof the magnetron of Figures 1 and 2 are entirely
illustrative and not definitive.' It should be
strength óf the- magnetic ñeld and the velocity
The velocity depends on the
potential difference between the cathode and
anode. _When certain adjustments of the i‘leld
- understood that the theoretical explanation given
above is for the purpose of exposition in order
r vof the electron.
that the inventionmay be better appreciated.
While this explanation is believed to be correct,
it is notl of necessity complete. nor does the
operation of the invention depend upon its ac
strength and .anode voltage are made, the elec- .
trons will curve into the magnetron inner walls
and start feeble oscillations in the cavities. Once
oscillations have started, alternate positive and
negative potentials appear on the lips L of the
cavities. The electrons, in passing these alter
curacy or otherwise.
w
-
ì l. An electron discharge device comprising
cathode electrode and an anode electrode cooper
nately charged cavity lips in their curved orbits,
become hunched in groups.
.
What is claimed is:
atively disposed with respect to said cathode, said
By proper adjust
anode having an electron receiving portion in
ments of Áfield strength and anode potential,
proximity to said cathode and a grooved portion
these bunches of electrons are caused to fall at
spaced from said first portion forming an induct
reduced velocity on the negatively charged lips ‘ ance which together with the capacitances be
of the cavities. 'I'his increases the efllciency of
tween said electrodes constitutes an electrical cir
the magnetron and causes the oscillations in the
cuit, said grooved portion tapering from. one end
cavities to grow stronger so thatv comparatively 20 to the other.
large amounts of ultra high frequency power may
2. An electron discharge device comprising a
be obtained from this type of magnetron.
, cathode. and an anode having electron receiving
The electrons from the cathode ,K are caused ` surfaces disposed about said cathode. said anode
to move toward the anode in either the larger or
having also a plurality of longitudinal groovœ
the smaller end of the magnetron by the differ 26 in its inner walls disposed remote from, and sym
ences of negative bias potentials on ring grids
metrical with said cathode, said grooves being
-Gi and G2 produced by the applied signals. In `
smaller at one end than at the other.
A
’
other words, if ring grid Gi is more' negative than
3. An electron discharge device comprising an
grid G2. the electrons will be forced to occupy, or '
anode having arms bounding a cavity and form
be repelled to. the smaller dimensioned portions ao ing an inductance, said arms and said cavity
of the magnetron, as a result of which the fre
tapering from one end to the other.
quency of the magnetron oscillations will be in
4. An electron discharge device comprising a
creased. Again,'if in the audio signal cycle the
cathode and a continuous anode surrounding said
grid G2 is biased more negative than grid- GI,
cathode, said anode having an even number of
then the electrons, willbe forced to occupy the
portion of the magnetron chamber having larger
regularly spaced portions bent inwardly toward
said cathode and terminating in juxtaposed sur
dimensions as a consequence of which the fre
faces, thereby substantially enclosing a plurality
quency of themagnetron will be decreased. This
of cavities, said cavities each having an opening
followsbecause with proper design, changes in
which tapers from one end to a larger opening
dimensions of a magnetron changes its operat 40 at the other end, and means for producing a
ing frequency. due to changes in the orbital paths
magnetic i‘leld with flux lines running parallel to
taken by the electrons. Of course, this ordinarily
said cathode. '
'
'f
requires changes 4in magnetic field density and
5. A magnetron oscillator comprising an elec
cathode-to-anode potential. Howevena certain
tron discharge device having an enclosing vessel
amount of frequency variation can be obtained 45 containing an electrode having arms bounding a
by causing the electrons to oscillate in various
cavity and forming an inductance, said arms
regions of the magnetron having different . terminating. in juxtaposed substantially parallel
dimensions but with fixed magnetic field and
lines, said cavity having an opening which tapers \
fixed electric potentials. Because of the fact that
from one end to an opening of different dimen
the Q of a circuit becomes lower as the operat 60 sions at the other end.
ing frequency becomes higher, it is possible to
6. An oscillation generator comprising an elec
obtain more frequency deviation at these high
tron discharge device having a cathode and a
frequencies than that usually obtained at the
lower frequencies. In other words, a high fre
anode consisting of an even number of regularly
quency circuit can be frequency modulated over
a wider band when compared to that obtained
spaced portions bent inwardly toward said cath
ode and terminating in juxtaposed surfaces to
in low frequency oscillators, although the per
lcentage of frequency variation might be the same
in both cases. The ileld strength and electric
potentials serve as limiting factors controlling
`the amount of frequency deviation obtainable
from the magnetron of this invention.
‘l The ring grids GI and G2 -are shown split in
one place in order to eliminate the possibility of
magnetic effect on them. Grids GI and G2 are
by-passed with condensers B to prevent the radio
frequency from aifecting the modulating circuits.
Insulation and mounting means are not shown
since they do not- ail'ect the principle of opera
continuous anode surrounding said cathode, said
` thereby form an even number of similarly ar
ranged cavities, said cavities each having an
opening which is smaller at one end 4than at
its other end, means for subjecting the electrons
emanating from said cathode to a magnetic ñeld
in a direction running substantially parallel to
said cathod'e, and means for modulating the
oscillations produced.
7. An electron discharge device comprising a
cathode and a continuous anode surrounding said
cathode, said anode having arms bounding a
cavity and forming an inductance, said arms and
said cavity tapering from one end to the other.
tion which the invention describes. 'I'he cooling 70 and a pair of control electrodes at >opposite ends
fins usually fastened to the anode are omitted ` of said cathode and located between said cathode
here for simplicity. Only such parts of the mag
and the adjacent surfaces of said anode.
netron considered necessary for the description
8. An electron discharge device comprising a ‘ '
of the invention are shown.
cathode and a continuous anode surrounding said
It should be understood that the dimensions 75 cathode, said anode having an even number of
2,412,372
5
regularly spaced portions bent inwardly toward
and located at opposite- ends of >said, chamber,
said cathode and terminating in juxtaposed sur
said control electrodes substantially surround- ,
faces to thereby substantially -enclosing a plural
ing said cathode in said planes, means for pro
ducing a magnetic ñeld having flux lines running
parallel to said cathode, and means coupled vto
both of said control electrodes for modulating the
oscillations produced by said electron discharge
ity of cavities, said anode spaced portions sur
rounding a central chamber along whose axis the
cathode is located, said chamber tapering from
one end to the other, and a pair of disc-like con
trol electrodes at opposite ends of said chamber
device, said last means including an audio fre
quency transformer having a primary winding
9. An electron discharge device comprising-a l0 coupled to a source of modulating potentials'and
substantially surrounding said cathode.
cathode and a continuous anodesurrounding said
cathode, said anode having an even number of
a secondary winding each of whose terminals is y
connected to a different control electrode.
regularly spaced portions bent inwardly toward
13. A frequency modulation system comprising
said cathode thereby enclosing a central cham
ber along whose axis the cathode is> located, ad
an electron discharge device oscillator having
jacent anode spaced portions also formingv
grooves with one another winch form induct
ances, said central chamber and saidl grooves
tapering in the same direction from one end to
15 within an evacuated envelopeal cathodeand a
continuous lanode surrounding said cathode, said
anode havinga number of regularly spaced por
tions bent inwardly toward'said cathode thereby
enclosing Aa central chamber along whose axis
the other, a pair of disc-like control electrodes 20 the cathode is located, adjacent anode spaced
arranged in different planes and located at oppo
site ends of said chamber, said control electrodes
` portions also forming grooves with one another
substantiallyv surrounding said cathode in said
and said grooves tapering in the same' direction
from one end to the other, a pair of control elec
planes.
l
10. An'electron discharge device comprising
a cathode and a continuous anode surrounding
said cathode, said anode having an even num
ber,of regularly spaced portions bent inwardly
toward said cathode thereby enclosing a cen
Which- form inductances, said ycentral chamber
25 trodes arranged in different planes and located
at opposite ends of said chamber, said control
electrodes substantiallysurrounding said cathode
in said planes, means for producing a magnetic
field having flux lines running parallel to said
tral chamber` along whose axis the -cathode is 30 cathode, means for supplying a bias to said con
located, adjacent 'anode spaced portions also
trol electrodes which is negative relative to said
forming grooves with one another which form
cathode, and means for changing the relative
inductances, said central chamber and said
bias of said two control electrodes in accordance
grooves tapering in the same direction from one
with changesl in modulation potential to thereby
end to the other, a pair of control electrodes 35 changethe frequency of the oscillations produced
arranged in different planes and located at op
by said oscillator, and a load circuit coupled to
posite ends of said chamber, said control elec
one of said grooves for deriving frequency modu
trodes substantially surrounding said cathode
in said planes, and means for producing a mag
lated oscillations.
y
14. »An electron discharge device comprising an
netic field with flux lines running parallel to
anode having arms bounding a cavity and form
said cathode.
ingan inductance, said arms and said cavity ta
- i
11. An oscillation generator system compris-
pering from one end to the other, a cathode for
ingk an electron‘discharge device having a cath
said device, and a pair of control electrodes at
ode and a continuous anode surrounding said
opposite ends of said cathode and located be
cathode, said anode having a number of. regu 45 tween said cathode and .the adjacent surfaces of
larly spaced portions bent inwardly toward said
said anode.
cathode thereby enclosing a central chamber
15. An electron discharge device comprising an
along whose axis the cathode is located, adja
anode having arms bounding a cavity and form
cent anode spaced portions also forming grooves
ing an inductance, said arms and said cavity
with one another which form inductances, said 50 tapering from vone end to the other, a cathode
central chamber and said grooves tapering in the
for said device, and a.y pair of `control electrodes
same direction from one end to the other, a
at opposite ends of said cathode an-d located be
pair of control electrodes arranged in different
tween said cathode and the adjacent surfaces
, planes and located at opposite ends of said cham-_
of said anode, means for supplying a bias to said
ber, said control electrodes `substantially sur 55 control electrodes which is negative relative~to
rounding said cathode in said planes, means for
said cathode, and a. circuit for changing the bias
producing a magnetic field having flux lines run
of said pair of control electrodes relative to each
ning parallel to said cathode,-and means coupled
other in accordance with changes in modula-v
to both of said control electrodes for modulating
the oscillations produced by said electron dis
tion potential.
ode thereby enclosing a, central chamber along
whose axis the cathode is located, adjacent anode
spaced portions also forming grooves with one
another which form inductances, said central
stituting capacitances with each other and with
said cathode, said grooved and other portions
forming a tuned circuit, said grooved portions
having diñ'erent dimensions at different points
_
16. A magnetron comprising a cathode, an
60
charge device.
~
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anode encompassing said cathode, means for pro
12. An oscillation generator system comprising
ducing a magnetic field in the vicinity of and
an electron discharge device having 1a cathode
parallel to said cathode, said anode having
and a continuous anode surrounding said cath
grooved portions substantially symmetricallydis
ode,rsaid anode having a number of regularly 65 posed with respect to said cathode and constitut
spaced portions bent inwardly toward said cath
» lng inductances and having other portions- con
chamber and said grooves tapering' in the same 70 in their lengths.
direction from one end to the other, apair of
`
control electrodes arranged in different planes
GEORGE L. USSELMAN.
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