JPH04218241A - Microwave tube - Google Patents

Abstract

PURPOSE: To provide a microwave tube having a frequency-tunable cavity which suppresses the increase of not only the tube action but also tube volume and capacity. CONSTITUTION: A microwave tube, which is structured, such that an XX' axis places the center of this structure, including at least one longitudinal electron beam which moves across at least one cavity containing a frequency tuner, is disclosed. The tuner has at least one rod which protrudes into the cavity, being almost parallel with the XX' axis. The rod is movable along the XX' axis and operable from the outside of the tube. In addition, the device is applicable for a single-beam klystron or a multi-beam klystron.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to microwave tubes in which a longitudinal electron beam passes through at least one frequency-tunable cavity. The invention is applicable to klystrons such as single beam klystrons or multi-beam klystrons.

Single beam klystrons are assembled around an axis. The klystron primarily has an electron gun that produces a longitudinal electron beam. The electron beam passes through a subsequent cavity and drift tube. A drift tube connects two successive cavities. The cavity is used to modulate the velocity of the electrons. The electron beam is focused on a collector pole located within the extension of the last cavity. A concentrator surrounds the cavity. The concentrator prevents the electron beam from spreading.

Frequency tuning of the klystron cavity is necessary to optimize the performance characteristics of the klystron during testing. In fact, a certain number of parameters of the klystron depend on the frequency transition between frequencies and on the operating frequency of the klystron.

These parameters are, for example, the gain of the klystron, its efficiency or its instantaneous passband.

[0005] Many mechanical operations and many thermal operations are performed between the time the klystron is assembled and the time the klystron is tested, during which time the frequency tuning may change. These mechanical and thermal operations are, for example, updated mechanical operations, baking operations, spraying operations, etc.

Furthermore, the electronic means, microwave power output devices, etc. are not exactly the same as originally planned, and some kind of readjustment can be carried out by changing the resonant frequency of the cavity. .

[0007] In certain applications, it is possible to vary the operating frequency of the klystron. This is especially
This is the case in television transmitters, air traffic control radar, and telecommunications equipment. Therefore, it is desirable to provide the klystron with a device for setting the resonant frequency of its cavity in the field.

[0008]

[Prior Art] Multi-beam klystrons are well known;
French Patent No. 992853 and French Patent No. 2596
It is described in the specification No. 198, the specification No. 2596199, etc.

A multi-beam klystron can be constructed by centering on a certain axis. These electron guns produce an elementary electron beam parallel to their axis. The elementary electron beams pass through successive cavities separated by drift tubes. All elementary electron beams traverse each cavity. The electron beam can be collected by a common collector pole. The focusing device can be common to all electron beams.

Single-beam klystrons are being developed more and more because multi-beam klystrons are smaller, more efficient, and at the same time use lower accelerating voltages.

[0011] In a single beam klystron, these three requirements are mutually exclusive. This is because, in order to increase efficiency, it is necessary to use an electron beam with low perveance, that is, with high acceleration voltage. Furthermore, the length of the tube increases in proportion to the square root of the accelerating voltage.

[0012] The cavity of a klystron, whether a single beam klystron or a multi-beam klystron, generally has a simple shape. Their shape is often cylindrical or rectangular. The klystron has two holes in two opposing walls. The holes also face each other and allow the electron beam to pass through. The ends of the drift tubes joining two successive cavities pass through those holes and into the cavities. The drift tube thus forms a protrusion inside the cavity. The space between two protrusions facing each other forms an interaction space.

The resonant frequency of the cavity is the product (L・C)−1/2
is proportional to.

L and C represent the equivalent inductance and equivalent capacitance of the cavity, respectively. Those parameters depend on the shape of the cavity.

To change the resonant frequency of the cavity, it is possible to change L to make it an inductive tuner, or change C to make it a capacitive tuner, or a combination of both.

The inductive tuner changes the position of one or more walls of the cavity. Generally, a device with a piston and a membrane is used. This device deforms the side walls of the cavity approximately parallel to the axis of the microwave tube. This device is activated from outside the tube by a fairly large control mechanism. A focusing device surrounds the cavity. The focusing device is formed by a set of coils. The focusing device is placed very close to the side walls of the cavity so as not to increase the volume and weight of the tube. This reduces the space for inserting the tuner control mechanism with the piston and membrane between the cavity and the control mechanism.

Another drawback appears in the case of multibeam klystrons. The multibeam klystron cavity is generally cylindrical, and its diameter is greater than its height. In order to create a strong electric field in the central region of the cavity, the electron beam is positioned on a circle with a diameter smaller than the diameter of the cavity. Given that the tuner must not occupy too much space, the device used acts only on a small portion of the side wall. This device then has little effect on the volume of the cavity.

In a capacitive tuner, the interaction space between two drift tubes facing each other is changed, or the capacitance is changed by a tuning arm that is moved closer to or away from the drift tube. The tuning arm is actuated from outside the tube and moved across the axis of the tube. This capacitive tuner also suffers from the same disadvantages mentioned at the beginning, due to the narrow space between the outside of the cavity and the focusing device.

[0019] In a multi-beam klystron, the electric field in the interaction space is asymmetric due to the device with the tuning arm. This asymmetry causes defocusing, oscillations, and the appearance of parasitic modes.

[0020]

SUMMARY OF THE INVENTION The present invention overcomes the aforementioned disadvantages by providing a microwave tube having at least one frequency tunable cavity. The frequency tuner does not increase tube operation, nor does it increase tube volume or capacity.

[0021]

[Means for Solving the Problems] The present invention provides at least one
XX
a frequency tuner including at least one rod substantially parallel to the XX' axis, the rod being movable along the XX'axis; It is. A rod projects into the cavity in an area contained between the electron beam and the sidewall.

The tuner rod is a microwave tube operated by a control mechanism, the control mechanism being XX'
an axis external to the microwave tube substantially parallel to the axis and driving a first gear element rotationally actuated and fixed during movement to a transmission projecting into the microwave tube; , at least one second gear element in the microwave tube, driven in rotation by a transmission;
fixed to the gear element of and substantially parallel to the XX' axis,
a threaded rod that is screwed into the interior of the tuner rod, and the threaded rod is screwed so that the tuner rod can be moved while substantially sliding inside the guide section. A mechanism may actuate the tuner rod.

[0023] The tuner can include one or more rods.

Preferably, the number of rods is equal to the number of electron beams, or equal to a submultiple or multiple of the electron beams. Preferably, the rod has a rounded end within the cavity. In a tuner with several rods, the rods are uniformly distributed in a circle centered on the XX' axis,
Preferably, the circle surrounds the electron beam.

According to one modification, when there are several rods, the ends of those rods inside the cavity are fixed in one ring. The rods are then actuated simultaneously. At least one of the rod and ring is metal;
For example, it can be made of copper.

[0026] The rod and/or ring can be made of dielectric material, for example alumina or beryllium oxide.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cavity in which an inductive tuner is provided. This cavity belongs to a single beam klystron assembled around the XX' axis. It is assumed that this cavity has the shape of a parallelepiped with two walls 1 facing perpendicularly to the XX' axis and four walls 2 facing in pairs and parallel to the XX' axis. electron beam 5
crosses the cavity from one side to the other. Each wall 1 is provided with a drift tube 3. The drift tubes 3 face each other and form a projection into the interior of the cavity.

Focusing device 8 formed by a set of coils
surrounds the klystron cavity. The coils are placed as close as possible to the wall 2 of the cavity.

The tuner 4 is a tuner having a piston 6 and a membrane 7. The membrane 7 has at least one wall 2 parallel to the XX′ axis.
can be partially or completely replaced by The piston 6 is actuated from outside the tube, approximately transversely to the XX' axis, by a suitable control mechanism. This control mechanism is large;
It is placed between the cavity and the focusing device 8 on the outside of the tube. When the control mechanism is actuated, the piston moves the membrane 7. Movement of the membrane 7 can increase or decrease the volume of the cavity. As a result, the frequency of the cavity changes. A bellows device (not shown) is provided to maintain the vacuum of the cavity to the outside of the tube.

[0030] To house the control mechanism it is necessary to use a focusing device 8. The focusing device 8 is larger and heavier than the focusing device used without a tuner.

This tuner is not well suited to the frequencies of multibeam klystrons. The reason is that the cavity of a multibeam klystron is large and the electron beams are concentrated in the center. Deformation of a portion of the cavity wall has a small effect on the frequency. For the deformation to be effective, larger mechanisms should be used.

FIG. 2 shows the tuner 2 of a multi-beam klystron.
FIG. This cavity is cylindrical. This klystron has six electron beams 21. These electron beams are distributed on a circle centered on the central axis of the cylinder. electron beam 21
exits the drift tube 22 and enters the cavity 20, exits the cavity 20 and enters another drift tube 22. Inside the cavity, two drift tubes 22 for each electron beam 21 face each other. The drift tubes are separated by an interaction space. The diameter of the circle on which the electron beam is distributed is considerably smaller than the diameter of the cylinder. The tuner 25 is the tuning arm 23
It is a capacitive tuner with

The tuning arm 23 is actuated from outside the tube. By moving generally in a radial direction, the tuning arm 23 can be moved closer to or away from the drift tube. A bellows device 24 is used to maintain a vacuum inside the cavity. A focusing device is not shown. This tuner is efficient in changing the resonant frequency of the cavity. In contrast, it disturbs the electric field within the interaction volume that is close to the tuner and has little or no disturbance to the electric field within the interaction volume that is far from the tuner. Due to disturbances in the electric field, the focus is loosened, oscillations are induced, and parasitic modes appear.

FIG. 3 shows a cavity 30 in which the frequency tuner of the invention is provided. This cavity contains six electron beams 31
It forms part of a klystron with a Only two electron beams 31 are shown in the figure. Another cavity 40 is similar to cavity 30 without a tuner. The two cavities 30 and 40 are separated by a free space 39. Cavity 40 is only partially shown.

The electron beam 31 is uniformly distributed on a circle centered on the XX' axis and traverses the cavities 30 and 40 from one side to the other. A drift tube 32 connects two successive cavities 30 and 40. Each drift tube contains an electron beam 31. The drift tube enters the cavity from one side and into the next cavity on the other side. This forms a protrusion 36 inside the cavity. FIG. 3 shows two facing projections 36 for each electron beam inside the cavity 30 in which the tuner is provided. An interaction space exists between the two facing protrusions.

Cavities 30 and 40 are preferably cylindrical and identical. The cavity 30 has side walls 34 and XX'
two walls 33 facing each other, approximately perpendicular to the axis;
and has. Two walls 33 define the drift tube 32. They are traversed by the electron beam 31. A focusing device 42 surrounds cavities 30 and 40. The focusing device has a set of coils 41 that generate a magnetic flux that is used to prevent divergence of the electron beam.

The frequency tuner is capacitive. The frequency tuner has at least one rod 35 substantially parallel to the XX' axis. This rod 35 projects across one of the walls 33 and into the cavity 30. Rod 35 can move along the XX' axis.

The end of each rod 35 inside the cavity is preferably rounded to reduce the risk of arcing.

The rod 35 is actuated from outside the tube by a suitable control mechanism. This control mechanism can, for example, convert a rotational movement into a translational movement. A shaft 43 provided outside the tube is driven to rotate. This axis is parallel to the XX' axis. The shaft 43 is fixed to a first gear element 44 which rotationally drives a transmission element such as a link chain. The transmission element 45 passes between the two coils 41 and enters the tube.

Inside the tube, the transmission element 45 drives at least one other gear element 46 in rotation. The gear element 46 has a threaded rod substantially parallel to the XX' axis associated with the tuner rod 35. Threaded rod 4
7 is screwed into the other end 48 of the tuner rod 35. The other end 48 is provided outside the cavity 30. The end portion 48 has, for example, a disk-shaped foot 52 having a diameter longer than the diameter of the rod 35 . The legs 52 are hollow guide parts 49
Slide inside. This guide 49 can be cylindrical. One side of the guide 49 is fixed to the wall 33 of the cavity 30.

The legs 52 and the guide 49 each have a device that prevents rotational movement of the rod 35. This device is formed, for example, by a dog point 50 on the foot 52 and a groove 50 formed in the inner wall of the guide 49. Dog point 50 slides in groove 51. The tuner rod 35 only undergoes a translational movement when the threaded rod 47 moves in rotation.

A bellows device 37 maintains a vacuum condition inside the cavity 30. The bellows device 37 is, for example, a guide part 4
9 and surrounds the rod 35. The bellows device 37 can be fixed in an air-tight manner, for example, by first soldering to the inner wall of the cavity 30 and then to the legs 52 of the rod 35, respectively.

FIG. 4 is a cross-sectional view along the XX' axis of the cavity 30 in which the frequency tuner is provided. 3 and 4 are not drawn to the same scale. Three rods 35 are shown. A transmission element 45 transmits motion to three rods 35 simultaneously.

Three gear elements 46 and three threaded rods 47 are used in this case.

Even if the control mechanism is large, it can be accommodated in the space 39 between the two cavities 30 and 40.

Focusing device 42 remains closed to sidewall 34 at frequency 30. The volume and weight of this microwave tube do not increase.

The number of rods is preferably equal to the number of electron beams, but if not, it is preferably a multiple or divisor of the number of electron beams. The cross section of the rod 35 can be circular, but other shapes are also possible.

If several rods are used, they are preferably distributed uniformly on a circle centered on the XX' axis. This condition is configured to allow only the minimum possible disturbance of the symmetry of the electric field inside the interaction space.

In the case of a multi-beam klystron, it is preferred to locate the rod in the space between the projection 36 and the side wall 34 to facilitate assembly.

[0050] The rods can be operated sequentially, or they can be moved together, or sequential and simultaneous operation can be combined.

[0051] Rod 35 can be made of metal or dielectric material. If the rod is made of metal, copper can be used; if it is made of dielectric material, for example low-loss alumina or beryllium oxide can be used.

It is possible to use one or more rods passing through the wall 33 and one or more rods passing through the other opposing wall 33. It is sufficient that the rods do not collide.

Next, varying the resonant frequency of the cavity as a function of the position of one or more rods 35 will be described. The frequency decreases as more rods are pulled inside. The rod 35 acts on the frequency before it reaches the interaction space.

The rod 35 is gradually introduced into the cavity. The operation of inserting the rod 35 is stopped before the end 38 of the rod contacts the wall 33 opposite the wall traversed by the rod 35.

The change in resonance frequency is shown by curve I in FIG.

Curve II shows the change in the resonant frequency of the same cavity when a second rod is inserted while the first rod remains fully inserted.

Curve III shows the change in the resonant frequency of the same frequency when a third rod is inserted while the first two rods remain fully inserted.

The dashed curve shows the change in the resonant frequency of the same cavity of the tuner with three rods moved simultaneously. Changes in frequency are rapid. If the rods are moved simultaneously, when the rods are fully inserted, a frequency approximately equal to that obtained when the rods are moved sequentially is obtained.

The curves were obtained by measurements on a cylindrical cavity with the following dimensions:

[0060] Height: 57mm diameter
… 175mm rod diameter …
3 mm The results of this measurement show that it is possible to make frequency changes on the order of 10-15% before parasitic modes appear.

The results of this measurement show that in the present invention, the radius of the cavity is
/ indicates that it has almost no effect on the Q factor. The R/Q factor of the cavity characterizes the coupling of the cavity to the electron beam and thus affects the gain and efficiency of the tube.

In the case of a multi-beam klystron, the R/Q coefficients in all interaction spaces have approximately constant values. For this reason, it has been found that the tuner does not practically disturb the symmetry of the electric field distribution inside the interaction space.

FIGS. 6 and 7 show longitudinal and cross-sectional views, respectively, of the cavity of a multibeam klystron in which a modified version of the tuner is provided. For clarity of illustration, neither the tuner control mechanism nor the focusing device is shown in the figures.

The main difference between the device of FIGS. 3 and 4 and the device of FIGS. 6 and 7 is with respect to the end 68 of the rod 65 within the cavity 30. The end 68 of the rod 65 is now fixed to the ring 61. This ring 61 is moved simultaneously with the rods 65, and the rods 65 are actuated simultaneously. The measurement results for this multi-beam klystron are:
It shows that the change in the frequency of the cavity is almost the same regardless of the presence or absence of the ring. It can be seen that the Q-factor Q0 of the cavity is lower. Its Q-factor is on the order of 100, but without the ring it can increase to 600 or even 1000.

However, the main advantage of this modification is that it increases the limits for arcing at the ends of the rods. In effect, the electric field is not superimposed on the ends 68 of the rods, but is distributed over the entire ring.

The value of this device is that it allows the microwave tube to operate at higher peak values.

[0067] The ring can be made of metal or dielectric material. For example, it is possible to use metal, alumina or beryllium oxide.

[0068] The rod and ring may be made of the same material or different materials.

[0069]

According to the present invention, it is possible to provide a microwave tube having a frequency-tunable cavity that does not increase the operation of the tube or increase the volume or capacity of the tube.

[Brief explanation of the drawing]

FIG. 1 shows a longitudinal section through a single beam cavity provided with an inductive tuner.

FIG. 2 shows a cross-sectional view of a multi-beam klystron cavity provided with a capacitive tuner.

FIG. 3 shows a longitudinal section through a cavity in which a device for tuning a multibeam klystron according to the invention is provided.

FIG. 4 is a cross-sectional view along line AA' of the cavity in FIG. 3;

FIG. 5 is a graph showing the change in frequency as a function of rod insertion depth.

FIG. 6 shows a longitudinal sectional view of a variant of a cavity in which a device for tuning a multi-beam klystron according to the invention is provided.

FIG. 7 is a cross-sectional view of the cavity in FIG. 6 along line BB'.

[Explanation of symbols]

1, 2, 33, 34 Wall 3, 22, 32 Drift tube 4, 25 Tuner 6 Piston 7 Membrane 8, 42 Focusing device 20, 30, 40 hollow 23 Synchronized arm 24, 37 Bellows device 35, 65 rod 36 Protruding part 41 Coil 43 axis 44, 46 Gear element 45 Transmission element 47 Threaded rod 61 ring

Claims (11)

[Claims] 1. A frequency tuner comprising at least one cavity surrounded by sidewalls and intersected by at least one electron beam, the cavity comprising at least one rod substantially parallel to the XX' axis. provided, the rod being movable along the XX' axis, in a microwave tube assembled around XX', the rod protruding into the cavity in an area comprised between the electron beam and the side wall; A microwave tube characterized by: 2. A microwave tube in which the rod of the tuner is actuated by a control mechanism, the control mechanism being
external to the microwave tube, approximately parallel to the a shaft and rotationally driven by the transmission device;
at least one second gear element within the microwave tube;
a threaded rod fixed to the second gear element, substantially parallel to the XX' axis, and threaded into the interior of the tuner rod; 2. The microwave tube of claim 1, wherein the tuner rod is moved substantially slidingly inside the guide. 3. The number of rods is equal to the number of electron beams, or
Microwave tube according to claim 1 or 2, or equal to a submultiple or multiple of the number of electron beams. 4. The microwave tube of claim 1, wherein the rod has a rounded end within the cavity. 5. In the case where there are several rods, the rods are uniformly distributed on a circle centered on the XX' axis, the circle surrounding the electron beam. microwave tube. 6. Microwave tube according to claim 1, comprising several rods, the ends of all the rods in the cavity are fixed in one ring, and each rod is actuated simultaneously. 7. The microwave tube according to claim 1, wherein at least one of the rod and the ring is made of metal. 8. The microwave tube of claim 1, wherein at least one of the rod and the ring is made of copper. 9. The microwave tube of claim 1, wherein at least one of the rod and the ring is made of dielectric material. 10. Claim 9, wherein at least one of the rod and the ring is made of alumina or beryllium oxide.
The microwave tube described in. 11. The microwave tube of claim 1, wherein the microwave tube is a single beam klystron or a multibeam klystron.