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Патент USA US2110564

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March 8, 1938.
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27,110,564
ELECTHON DISCHARGE DEVICE
Filed Feb. �, 1936
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Patented Mar. 8, 1938
P�EENT @t'r?i鋒
unirse stares
2,110,564
ELECTRON DISCHARGE DEV虲E
Irving Wold, Merchantville, N. .,l., assignorlto
Radio Corporation of America, a corporation
of Delaware
Application February 28, 1936, Serial No. 66,198
3 Claims.
(C?l. 250-36)
My invention relates to ultra high frequency
oscillators of the magnetron or Barkhausen
Kurz type. More specifically my invention deals
with means for preventing electronic bombard
5 ment of the cathodes of such oscillators.
The term electronic oscillators may� be applied
to vacuum tube devices in which the electron
transit times are of appreciable duration with re
spect to the periods of associated circuits. In
10 particular cases, the period of oscillation is deter
mined by the electron transit time.
Unstable os
cillations have characterized thev operation of
electronic oscillators of the magnetron or Bark
hausen-Kurz type. It was previously believed
15 that the anode became highly heated and radi
ated this heat to the cathode. The increased
heating of the cathode increased the anode cur
rent and thereby varied the operation of the os
cillator. 'An attempt to overcome the di駃culty
20 by water cooling the anode has proven insu�-i
cient. Current limiters in the anode circuit have
been partially successful in stabilizing ultra high
frequency oscillators.
The real primary difficulty is that some of the
25 electrons which leave the cathode, either fail to
reach the anode, or reach the anode and liberate
secondary electrons which oscillate back and
forth between anode and cathode. These free
electrons under the iniiuence of synchronous al
30 ternating electrostatic -forces acquire high veloc
ity. Many of these free electrons bombard the
cathode and liberate substantial amounts of en
ergy. Thus the cathode is. unduly heated.
Control of. anode current will not completely
35 solve this problem because the free electrons may
still bombard the cathode. Likewise, cooling the
anode will not stop the bombardment. The prin
cipal object of my invention is to provide means
.for preventing cathode bombardment. Another
40 object is to form a virtual cathode in an ultra
high frequency oscillator of the character de
scribed. Another object is in the method of
preventing electronic bombardment in an elec
tronic device of the character described.
45 In the accompanying drawing, Figure I is a cir
cuit diagram of a magnetron oscillator embodying
my invention, and
*
Figure II is a circuit diagram of a Barkhausen
Kurz oscillator including my invention.
50
In Figure I is shown an evacuated envelope l
and a cathode 3 mounted on a pair of lead wires
5, l. A grid electrode 9 is arranged to surround
the cathode 3. This grid electrode maybe of
spiral construction, with or without lateral con
55 necting wires, or the grid may befof lattice con
struction, or parallel wires may be used. In any
event the grid should be spaced from the cathode
and preferably non-resonant at the operating
frequencies of the tube.
The grid may be supported by a pair of lead 5
wires l l. The cathode is energized by abattery I3.
A biasing battery i5 is connected between the
grid and cathode to bias the grid negatively with
respect to cathode. A pair of cylindrically shaped
anodes l'i-IQ are mounted on lead wires 2l-I-23. 10
The lead wires 2%-23 extend through the en
velope and form a transmission line. The trans
mission line is terminated in a dipole antenna 25.
A bridging conductor 2l may be connected
across the transmission line to establish a reso- 15
nant circuit including the anodes. The anode
battery 2t is connected through the radio fre
quency choke coil 3i to the said point of the
antenna 25. The negative terminal of the anode
battery is connected to cathode battery I3.
20
The magnetic field for the magnetron is sup- `
plied by an electro-magnet 33.
This magnet con
sists of a suitable core 35 on which is mounted a
coil 3l. The coil is energized by a battery 39.
The pole pieces M, lit of the magnet are posi- 25
tioned so that the magnetic lines of force sur
round and are substantially parallel to the
cathode.
If the grid il were omitted from the magnetron
and the magnetic field reduced to Zero, electrons
would be emitted from the cathode.' Almost all
of these electrons would travel in straight paths
to the anodes. Substantially no electrons would
return to the cathode. Such as did return would
strike the cathode at very low, or Zero, velocity
and would not liberate appreciable energy.
As the magnetic iield is applied, the electrons
flow in curved paths, to the anode electrodes.
Increasing the 馿ld strength will increase the
curvature of the electron paths. An operating
characteristic will be reached in which the elec
trons will follow closed or spiral paths about the
cathode. As is well known, with proper adjust~
ment of the circuit constants and magnetic iield,r
oscillations will be established in these circuits.
Of the electrons traveling closed paths, some
will reach the cathode with all of their energy
expended. These electrons will not bombard the
cathode. I-Iowever, the oscillatory currents and
the electronic new to the ancdes may establish
relative phases such that electrons gain energy
from the alternating circuit both in their trip
to the anode and on the return. A simple case in
which this occurs is where the electron leaves
the cathode while the anode isin the positive
30
35
40
45
50
55
2
2,110,564
phase of the alternating potential and returns to
the cathode when the polarity of the anode re
verses. These electrons may strike the cathode
and give up a very substantial amount of energy.
tronic oscillators which are essentially the same.
In each case electronic bombardment of the
cathodes is Vprevented by establishing a virtual
cathode about a negatively charged grid which
rI?he cathode bombardment by electrons travel
surrounds the` actual cathode. Preventing ca
ing at high velocities may become so intense thatV thode bombardment stabilizes the oscillator and
the cathode will be destroyed. . In any event the
cathode bombardment causes undesired varia
tions of anode current.
I prevent these undesired
10 effects by surrounding the cathode with'a grid. VA
negative potential is applied to the grid with re
spect to cathode which is su耦cient to prevent
most of the in phase or ?re-entrant? electrons
from reaching the cathode. The negative charge
15 on the grid is maintained at a potential which
does not prevent emission of electrons ~from the
cathode. Thus a negatively charged grid pre
vents electrons from damaging the cathode and
forms a virtual cathode intermediate the grid
20 and anode.
In Figure II a Barkhausen-Kurz oscillator has
been shown. lI?he essential difference between a
Barkhausen-Kurz oscillator and a magnetron is
that the former employs a positively polarized
grid and omits the' magnetic field of the magn- Y
tron. Within an evacuated envelope 5| are
mounted a pair of lead wires 53, 55. These lead
wires support a cathode 5l. The outer terminals
of the lead wires are connected to a battery 59.
30 A second pair of wires 6l, S3 support an inner
grid electrode 55.
One of these wires 6| extends
through the envelope 5l and is connected to the
negative terminal of a biasingY battery Bl. The
remaining terminal of the biasing battery is
` joined to the cathode lead wire 55.
'
At the opposite end of the envelope 5I a second
pair of leads Bil-ll and a supporting wire 13
are arranged as follows:V The lead 69 and support
513 carry the outer grid 15, which is preferably
40 concentrically arranged with respect to the inner
grid and cathode. A cylindrical anode 1l is con
centrically positioned with respect to the other
electrodes and is suitably attached to the lead
wire ll. rI?he lead wires 69 and ?H may be used
as a transmission line. Blocking capacitors 19,
8l are included in each lead of the transmission
line. The transmission line is terminated in a
dipole antenna 83.
The anode battery 85 is connected to the
cathode and through a radioV frequency choke 81
to the connecting'lead ll. The second grid l5 is
biased positively by a battery 89 which is con
nected to cathode and'through a radio frequency
choke Si to the grid lead 69.
55
'
?
In an oscillator of the present type, as shown
in Figure II,> the theory of oscillation is that elec
trons emitted from the cathode proceed toward"
the anode. The space between cathode and
anode is such that electrons require one half Vof
60 the oscillatory period to traverse the space.
On
the second half period the electrons reverse their
path. Some of the electrons will reach the
cathode in a phasal relation which permits the
cathode to be bombarded. These bombarding
prevents damage `to the cathode. Y Although I
have specifically described and referred to elec
tronic oscillators, the term is not intended to ex
clude the use of an electronic tube for amplifying 10
ultra high frequencies.
I claim as' my invention:
1. An electron discharge device having cathode
and anode electrodes, means for imparting Vto the
electrons in said device oscillatory movements 15
which free electrons and cause cathode bombard
ment, a tuned circuit connected to said electrodes,
a source of voltage for said electrodes, means po
sitioned between said cathode and anode elec
trodes for limiting the electronic bombardment of
said cathode 'and means for maintaining said
last mentioned means sufliciently negative with
respect to said cathode under all conditions of
operation to limit cathode bombardment.
2. In an electronic device of the character de 25
scribed a vacuum tube having cathode, and anode
electrodes, means for imparting to the electrons
in said device oscillatory movements which free
electrons and cause cathode bombardment, a
tuned circuit connected to said electrodes, a 30.
source of voltage for said electrodes, a grid posi
tioned between said cathode and anode electrodes',
and Vmeans for biasing said grid continuously
negative with respect to said cathode electrode
for limiting the bombardment of said cathode by
electrons under all conditions of operation.
3. An electron discharge device of the magne
tron type having a thermionic cathode, and anode
electrodes, means for imparting to said electrons
oscillatory movements, which free electrons and
cause cathode bombardment, an oscillating cir
cuit connected to said electrodes, a source of
voltage for said electrodes, a grid arranged be
tween said cathode and anode electrodes for limit
ing the bombardment of said cathode by electrons 45
and establishing a virtual cathode between said
negative grid and anode electrodes and means
for Vmaintaining said grid sufficiently negative
under all conditions of operation to thereby limit
cathode bombardment.
' v
501
4. An electron discharge device having cathode
and aV pair of anode electrodes, an oscillating cir
cuit connected between said pair of electrodes, a
source of voltage for said electrodes, a magnetic
iield whose lines of force are substantially parallel 55
to said cathode, and means positioned between
said cathode and anode electrodes for limiting
the electronic bombardment of said cathode. ?
Y 5. An electron discharge device of the Bark-
hausen-Kurz type having a thermionic cathode,
a grid positively polarized with respect to said
60
cathode, and anode electrodes, an oscillating cir
cuit _connected >between said positive grid and
anode electrodes, a source of voltage Vfor said
electrodes', means positioned between said cathode 65
to the cathode. In this respect the present os
`and positively charged grid for limiting the elec
cillator and the magnetron are similar.
tronic bombardment of said cathode and means
The linner grid is charged negatively. The Y for maintaining said lastV mentioned means nega
charge is sut頸cient to repel most electrons which tive with respect to said cathode under all Voper
70 tend to bombard the cathode, but is not so great ating conditions Vto thereby limit cathode bom
70
that electron emission is prevented. The inner
grid not only prevents electron bombardment of
6. An ultra. high frequency electronic oscillator
the cathode but also establishes a virtual cathode having a thermionic cathode and a pair of anode
between the inner and outer grids.
electrodes, a `magnetic 馿ld Vwhose lines of force
75
I have described the operation of the two elec
are substantially parallel with said cathode, aV
65 electrons convey substantial amounts of energy
bardment.
Y
Y
'
2,110,564,l
source of electric power for said electrodes, an
oscillatory circuit connected between said anode
electrodes, and means?for establishinga virtual
cathode between said thermionic cathode and.l
anode electrodes wherebyv electronic bombard
ment of said thermionic cathode is substantially
` prevented.
7. An ultra high frequency electronic oscillator
of the Barkhausen-Kurz type having a thermionic
10
cathode, a grid positively charged with respect
to said thermionic cathode, and an anode elec
trode, a source of electric power for said elec
trodes, an oscillatory circuit connected between
said positive grid and anode electrodes, means for
15 establishing a virtual cathode between said ther
mionic cathode and said positive grid whereby
electronic bombardment of said thermionic
cathode is substantially prevented and means for
maintaining said last mentioned means su�l
ciently negative with respect to said cathode un
3
`
der all operating conditions to substantially elim
inate cathode bombardment.
8. The method of preventing bombardment of
a therrnion韈 cathode by electrons in an ultra
high frequency electronic oscillator having ther
mionic cathode, and anode electrodes, an oscil
latory circuit connected thereto, and a grid elec
trode surrounding and adjacent said thermionic
cathode,v which comprises emitting electrons
from said thermionic cathode, forcing said elec 10
tron to traverse paths through said grid electrode
and toward said cathode, imparting an oscillatory
movement to said electrons, preventing the return
of electrons to said cathode by negatively polar
izing said grid with respect to said cathode and 15
maintaining said grid sufficiently negative with
respect to said cathode under all conditions of
operation to substantially eliminate cathode bom
bardment.
?
IRV'ING WOLFF.
20
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