U.S. patent number 3,742,292 [Application Number 05/203,360] was granted by the patent office on 1973-06-26 for electronic tubes such as tetrodes for very high-frequency operation.
This patent grant is currently assigned to Thomson-CSF. Invention is credited to Pierre Gerlach, Gerard Sire.
United States Patent |
3,742,292 |
Gerlach , et al. |
June 26, 1973 |
ELECTRONIC TUBES SUCH AS TETRODES FOR VERY HIGH-FREQUENCY
OPERATION
Abstract
Tetrode operating at very high frequencies according to a
"grounded cathode" mode. All the coaxial cylindrical electrodes are
extended outside the exhausted enclosure, with cylindrical
conductive walls forming coaxial cavities which are tunable by
means of ring pistons. Furthermore, the screen-grid is connected to
a central conductive cylinder passing through the cathode and
extending, as the electrodes do, with a cylindrical conductive wall
constituting with that one extending from the cathode a cavity
which is tuned for ensuring a high frequency short-circuit between
the cathode and the screen-grid.
Inventors: |
Gerlach; Pierre (Paris,
FR), Sire; Gerard (Paris, FR) |
Assignee: |
Thomson-CSF (Paris,
FR)
|
Family
ID: |
9065262 |
Appl.
No.: |
05/203,360 |
Filed: |
November 30, 1971 |
Foreign Application Priority Data
Current U.S.
Class: |
315/39;
331/101 |
Current CPC
Class: |
H01P
7/04 (20130101); H01J 19/80 (20130101) |
Current International
Class: |
H01P
7/04 (20060101); H01J 19/80 (20060101); H01J
19/00 (20060101); H01j 007/46 (); H01j
019/80 () |
Field of
Search: |
;315/39 ;331/101 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rolinec; Rudolph V.
Assistant Examiner: Chatmon, Jr.; Saxfield
Claims
What is claimed is:
1. A high frequency operating tetrode comprising:
cylindrical electrodes arranged coaxially within a tight exhausted
enclosure about the tube axis, including successively from said
axis, an electron-emissive cathode, a control-grid, a screen-grid
and an anode,
input coupling means applying a high frequency input wave between
said control-grid and said cathode,
output coupling means extracting an output high-frequency wave
between said anode and said screen-grid,
tunable coaxial cavities including conductive cylindrical walls
arranged coaxially about said axis and respectively connected to
one extremity of the of the electrodes,
a central conductive cylinder coaxially arranged about said axis
and passing through said cathode, said central cylinder having a
first extremity extending from said cathode towards said
cylindrical walls and a second extremity extending from the cathode
opposite the first extremity,
a further conductive clyindrical wall establishing a coaxial cavity
being coupled to said first mentioned extremity of the central
cylinder and the second mentioned extremity of the central cylinder
being coupled to the screen grid at one end and the opposite end of
the screen grid being coupled to one of the cylindrical walls,
and ring pistons movable along said coaxial cavities for providing
their respective tuning, the ring piston movable along one of said
coaxial cavities between the cylindrical wall coupled to the
cathode and the cylindrical wall coupled to the first extremity of
the said central cylinder being adjusted for ensuring a
high-frequency short-circuit between said cathode and said
screen-grid.
2. A high frequency operating tetrode according to claim 1 wherein
the coaxial cavity between the walls extending from said
control-grid and said screen-grid is tuned for providing a
quasi-infinite high frequency impedance between said control-grid
and said screen-grid.
3. A high frequency operating tetrode according to claim 1 wherein
said input coupling means is coupled between the cylindrical walls
extending from said control-grid and said cathode forming the
associated coaxial cavity.
4. A high frequency operating tetrode according to claim 1 wherein
said output coupling means is coupled between the cylindrical walls
extending from said screen-grid and said anode forming the
associated coaxial cavity.
Description
The present invention relates to electronic tubes for operation at
very high frequencies, and in particular to tetrode tubes of
high-gain and high-power type.
These very high-frequency tubes predominantly utilize coaxial
cavities, the electrodes there more often than not being
constituted by coaxial cylinders which respectively play the part
of cathode, control grid, screen-grid and anode. They are prolonged
with coaxial lines which are chiefly made by means of coaxial
cylinders between which the cavities are located, said cavities
being for example an input and an output one.
However, it is well known that the attainment of a high power gain
is facilitated by arranging the tube in a "grounded cathode"
circuit, in this case the input power simply having to control the
grid courant.
However, in the case of the tetrode tubes most generally used,
unless special modifications to the internal connections of the
electrodes, of the kind described hereinafter, are made, the only
kind of operation possible is the "grounded grid" system, in which
the input power has to control the whole of the cathode current.
The simplest explanation of this is provided by an analysis of the
voltages at work in the conventional kind of circuit, that is to
say the "grounded grid" one.
It is well known that a circuit diagram equivalent to a tetrode
tube operating on microwave signals, according to a grounded grid
mode, comprises a resistor in series with the cathode circuit.
Considering the cathode high frequency potential as being the high
frequency reference potential the other electrodes have a high
frequency potential which cannot be zero.
A known solution to the increase of the power gain of a tetrode is,
as has been mentioned hereinbefore, the modification of the
arrangement of the electrode connections, in order to enable the
grounded cathode system to be used, in which system the resistor of
the equivalent circuit diagram is connected in the control-grid
circuit and consequently wherein a high-frequency short circuit is
provided between the cathode and the screen-grid. This modification
can be effected inside the tube by crossing the connections of
cathode and control-grid but has the drawback that it introduces a
top limit on the operating frequency, which is due to parasitic
coupling and increase in the inductances produced by these
connections. It can equally well be achieved externally of the tube
by using a special tube design of the double-ended kind, which,
although it enables the aforesaid drawbacks to be overcome,
necessitates a dismantleable cavity for the installation and
replacement of the tube. Finally, it can be achieved by yet a third
method, which consists in suspending the control grid from a
support passing through the cylindrical cathode, this method not
exhibiting the aforesaid drawbacks. However, the excessive length
of the line in the input circuit, inside the tube, which results
from this technique, brings about a considerable reduction in the
effective passband, this as a consequence of a physical mechanism
which is detailled hereinafter.
The present invention relates to a tetrode for microwave operation
which can be operated in a grounded cathode system, in order to
achieve a substantial power gain whilst avoiding the aforestated
drawbacks by suitable assembly of the screengrid, the latter being
arranged upon a support passing through the cathode and connected
to the high frequency circuits of the tube through the medium of
two connections. One of these connections contributes to the output
for the amplified microwave power and is an element of the output
line, at the same time producing an effective screen between the
input and output circuits; the other connection satisfies the
condition which must be met by the desired mode of operation,
ensuring the production of a zero high-frequency potential in
relation to the cathode.
The ensuing description will provide a better understanding of the
invention and is based upon the attached figures in which:
FIG. 1 illustrates a schematic view of a known type of tetrode, for
operation at very high frequencies;
FIG. 2 illustrates a microwave tetrode in accordance with the
invention.
FIG. 1 provides a schematic view of a known kind of tetrode
operating at very high frequency and arranged in a grounded cathode
system, the illustration not being a scale one and having been
given in fact purely by way of an example of the prior art.
The tetrode tube itself comprises four cylindrical electrodes, a
cathode 1, a control grid 2, suspended at one of its ends from a
central support 5 used as the grid connection, a screen-grid 3, and
an anode 4.
The resonant cavities of the tube are constituted by cylindrical
rings 6, 7 and 8, composed of the intervals between conductive
walls (103 for example) extending the electrodes 2, 1, 3 and 4, and
constituting coaxial cylinders; these conductive walls are fixed to
the electrodes by means of conductive collars (101 for example)
making possible the transition between the small distances between
the electrodes and the distances necessary between the cylindrical
wall for a convenient operation of the cavities.
The means for assuming the tightness of the exhausted enclosure for
the electrodes are schematically represented on the figure between
the cylindrical walls; they are for example constituted by ceramic
rings tightly closing the cavities near the collars.
Pistons 16, 17 and 18, of ring-form, are movable in the cavities 6,
7 and 8.
Classical biasing means, not shown, are used for applying
continuous convenient voltages onto the electrodes. The conductive
walls are isolated from the continuous biasing voltages by
electrically insulating means constituted for example by mica rings
(102 for example).
The high frequency power input and output are respectively assumed
by microwave couplers 10 and 11.
The operation of this kind of device is as follows:
The microwave input to the tube is effected through the coupler 10
into the cavity 6 between the cathode 1 and the control grid 2; the
output is through the coupler 11, via the cavity 8 between the
screen-grid 3 and the anode 4. The pistons 16 and 18 assume the
tuning of the input and output cavities.
The grounded cathode arrangement is rendered possible by the
special disposition of the connections of the control grid 2,
inside the tube. In other words, with the help of the piston 17 it
is possible to achieve a microwave short-circuit between the
cathode 1 and the screen-grid 3. In this fashion, the production of
the grounded cathode arrangement is not accompanied by the
aforestated drawbacks such as parasitic coupling or obligatory
dismantling of the cavities on installation of the tube.
Nevertheless, the substantial length of the input circuit
constituted by the cavity 6 and its extension between the
electrodes up to the space 100 where is provided the interaction
between the high frequency waves and the electron beam emitted by
the cathode 1, introduces a limitation upon the pass bandwidth,
because of the following mechanism:
The tuning of the input circuit which is effected by the piston 16,
to the .lambda. /4 mode for example can only be achieved for long
wavelengths .lambda., that is to say relatively low frequencies,
since the piston 16 cannot penetrate into the inside of the tetrode
tube itself, and thus reach the position 19, for example shown in
dotted fashion. The higher order mode can then be used, this
enabling the piston 16 to reach a viable position, albeit at the
expense of the passband which, considering for example the (3
.lambda.)/4 mode, is reduced in the ratio of around 4.
FIG. 2 illustrates a tetrode in accordance with the invention.
The continuous biasing voltages are applied onto the electrodes as
earlier said in connection with FIG. 1; the biasing means are not
represented on FIG. 2 because they are similar to the classical
ones.
The four electrodes themselves are arranged as electrodes of every
microwave operating tetrode and for example tetrode of FIG. 1.
An anode 24 having a cylindrical shape contains the tight exhausted
enclosure 20 wherein are arranged the three other electrodes:
cathode 21, control-grid 22, screen-grid 23.
On the other hand, the connections of said electrodes and the
cavities of the tube are realized in a new arrangement
characteristic of the invention.
The electrodes are extended with conductive walls having an
approximately cylindrical shape and constituting the beginning of
the tube cavities. The electrical insulation of said walls and the
tightness of the enclosure 20 are assumed by rings 44 made of a
material being mechanically strong and electrically insulating,
ceramic for example.
The resonant cavities are extended outside the exhausted enclosure
20 with conductive cylindrical walls, looking like those of FIG. 1
and being also electrically insulated from the continuous voltages
appearing between the electrodes. by insulating rings 104 made of
mica for example.
On FIG. 2, two cylindrical walls 105 and 106 are extending from the
cathode 21. They are equivalent with regard to the high frequency
signal and are only used for applying a small continuous heating
voltage between the two ends of a cylindrical mesh 110 which is
mounted onto the cathode 21 for heating it.
In accordance with the invention, the control-grid 22 is
prolongated with a cylindrical wall 108 while the screen-grid 23 is
carried by a cylindrical support 25 passing through the cathode 21,
whose walls are electrically conductive, constituting one of the
two connections by means of which the screen-grid 23 is connected
with the exterior, and on which is mounted a conductive cylinder
109, the other connection of said screen-grid being prolongated
with the cylindrical wall 107. The anode 24 is prolongated with the
cylindrical wall 103.
This new arrangement of the electrodes connections and consequently
of the associated cavities, makes possible using the tetrode in a
grounded cathode mode while avoiding the aforementioned drawbacks
by tuning the cavities by means of ring pistons schematically shown
by 111, 112, 113 and 114; said pistons being able to be moved in
the cavities thus ensuring the adjustment of the electrical length
of said cavities.
The high frequency wave is applied to the control-grid 22 by means
of a coupling device entering for example into the input cavity
delimitated by the walls 105 and 108 and their extensions towards
the cathode and the control-grid. This coupling device is not shown
on FIG. 2 which is a sectional view; it is indeed disposed in a
zone of the pheriphery of the tube not encumbered with the pistons
rods which rods are shown on the figure. Said input cavity is tuned
by means of the piston 113.
The extraction of the high frequency amplified wave is realized for
example by means of a coupling device 120 entering into the output
cavity of the tube which cavity is delimitated by the walls 107 and
103 extending towards the screen-grid 23 and the anode 24. Said
output cavity is tuned by means of the piston 111.
The grounded cathode arrangement is easily obtained by adjusting
the piston 114 which is movable in the cavity delimitated by the
walls 106 and 109 and their extensions, is such a way that a
high-frequency short circuit is established between the cathode 21
and the screen-grid 23, that is to say between the cathode and the
walls of the cylindrical support 25.
At last, a piston 112 is movable in the cavity delimitated by the
walls 107 and 108 and their extensions towards the screen-grid 23
and the control-grid 22, and is adjusted in such a way that it
brings about a quasi-infinite high frequency impedance between said
two electrodes for avoiding production of disturbances in the tube
operating due to said cavity.
As in the case of the preceding figure, there are none of the
drawbacks referred to above, namely parasitic coupling, increase in
inductance due to internal connections, or requirement for
dismantling of cavities.
Moreover, the microwave input line between the cathode 21 and the
control grid 22, is of small length, contrary to the case of FIG.
1, so that there is less limitation on frequency. Thus, the first
connection of the screen-grid 23, which connection is constituted
by the wall of the support 25, forms one of the elements of the
cavity enabling a grounded cathode system to be produced; the
second connection wall 107, of the screen-grid 23 on the one hand
achieved good screening between input and output microwaves, and on
the other hand serves as an element of the output cavity.
The advantages introduced by the present invention are
two-fold:
On the one hand, it is possible to use a grounded cathode
arrangement and this yields a very substantial improvement in power
gain; with this kind of circuit, said gain is in the order of 20 dB
whereas with a grounded grid system it is not possible to achieve
much in excess of 12 dB. On the other hand, it is possible to
operate at frequencies in excess of 500 Mc/s, this with a passband
of sufficient width for it to be applicable with advantage to
television transmitters where it is then possible, thanks in
particular to the improvement in power gain, to reduce the number
of intermediate amplifier stages.
* * * * *