High Frequency Electronic Devices

Abstract

An electronic device wherein an interaction of an electron beam and a high frequency wave propagating through a delay line is achieved. The electron beam is made to strike substantially the whole length of said delay line simultaneously, which line upon this strike emits secondary electrons which are collected either by a grid parallel to the delay line or by the surface itself of said line. Such devices constituting either electronic amplifier or storage tubes.

Description

The present invention relates to microwave electron tubes.

In this art the interaction between the electron beam and the electric fields generated by the wave in a structure parallel to the beam along which the wave propagates is utilized when it is desired to amplify or delay a microwave, for example in a traveling wave tube.

To provide for the interaction the wave velocity is reduced to a value comparable to that of the electrons of the beam by suitable selection of the delaying characteristics of the structure.

However, the microwave amplification of this type of mechanism is subject to limitations including the difficulties entailed in the efficient transfer of energy from the beam to the wave since the said beam and wave are geometrically separate in parallel planes.

The object of the present invention is to elimimate these difficulties. For this purpose the relative shifts of the beam and the wave are controlled in two perpendicular directions so that all the electromagnetic fields traveling along the delay line interact simultaneously with the beam. In addition, an increase in the beam amplification results from the utilization of the secondary electron emission at the point of impingement of the beam on the delay line.

More specifically the invention relates to a microwave electron tube comprising a wave delaying structure, an electron emission source directing electrons onto the longitudinal surface of the said structure, means controlling the said emission, and coupling means injecting and ejecting the waves propagating in the said structure, the secondary emission ratio of the structure being greater than one when the structure is exposed to the said electron emission.

The invention will be better understood from a consideration of the ensuing description and by reference to the attached figures in which :

FIG. 1 illustrates the assembly for one embodiment of an electronic tube in accordance with the invention ;

FIG. 2 illustrates a detail of this tube ;

FIG. 3 illustrates another embodiment of the tube of FIG. 1 ;

FIG. 4 illustrates another electronic tube in accordance with the invention ; and

FIG. 5 illustrates an electronic tube in accordance with the invention provided with several inputs and outputs.

Every kind of electronic tube in accordance with the invention and described hereinafter comprises, as shown on FIG. 1 for example, within an evacuated envelope schematically represented in E, an electron gun (1, 2, 3, 4) providing a wide electron beam (not shown) and a delay line 5, of the interleaved kind for example, located opposite the electron gun in such a way that said line is bombarded by said electron beam simultaneously onto the almost entirety of its length. A grid 10 the potential of which is positive relative to the cathode 1 accelerates the electron beam towards the delay line 5. Said delay line 5 is connected at one of its extremities to a coupling device 6 applying thereto the microwave to be processed while a second device 7 connected to the other extremity of said line picks up the processed wave.

The electron gun comprises for example in a classical way an electron-emisive cathode 1 heated by a winding 2, bunching and deflection electrodes 3 and a beam current control electrode constituted by the grid 4. Classical biasing means not represented are also provided.

Thus, the processing of a microwave injected to the delay line 5 by the coupling device 6 is provided in accordance with the invention by an electron beam striking said line simultaneously onto its whole effective length (except of course onto the coupling devices 6 and 7).

A convenient processing of said microwave, as concerning an amplification as well as concerning a delay as described hereinafter, is obtained in devices according to the invention with delay lines exhibiting the phenomenon of secondary electrons emission when bombarded by the electron beam emitted by the cathode 1. For this purpose, the delay line 5 is either covered with a layer 8 of a material which will emit secondary electrons, or constituted by a material exhibiting itself this phenomenon, this depending on the embodiment considered.

In the embodiment illustrated by FIGS. 1 and 2, the delay line 5 is constituted by an electric conductive material covered by a layer 8 of an electric insulating material which is able of emitting secondary electrons when striked by the electron beam of the electron gun.

Furthermore, in the tube here represented where the processing of the microwave injected by the coupling device 6 is an amplification, said layer 8 is covered with a thin film 9 of an electric conductive material.

This film 9 is provided to permit electrical charges to circulate through the delay line in such a way that the distribution of said charges being continuously leveled out onto the surface of the layer 8, the microwave to be processed may travel through the delay line. The grid 10 has very high positive potential in relation to the line 5 and collects secondary electrons produced by layer 8 when said layer is striked by the electron beam emitted by the electron gun of the device. The thickness of the film 9 is choosen to not disturb the passage of secondary electrons such produced.

The high frequency energy to be amplified is introduced at the input 6 of the delay line and is propagated along same, creating between the elements thereof a system of moving electric and magnetic fields which induce in the conductive elements of said line an electric current whose value at any point is determined by that of the said fields at said same point.

Under these conditions, permanent electron bombardment of the delay line is carried out. For this purpose, from its cathode 1 the electron-gun emits a beam of electrons which are focussed and guided by the electrode 3, the intensity of the beam being regulated by the grid 4 and its velocity by the grid 10 ; the electrons strike the surface of the delay line after passing the grid 10. Under the impact of the incident electrons, the layer of material 8 emits secondary electrons which are immediately attracted to and absorbed by the said grid. Potentials of the various electrodes of the tube and layers 8 and 9 (thickness and kind of material) are chosen so that the secondary emission operates with a coefficient advantageoussly higher than unity and that secondary electrons thus emitted by layer 8 have energy enough to cross over the film 9, being afterwards catched by grid 10.

The distribution of the incident electrons is not uniform at the surface of the delay line ; in other words, because of the presence of the electric fields propagating through the line, the incident electrons are attracted by zones corresponding to positive peaks in the travelling wave. Under the impact of said incident electrons said zones of layer 8 emit secondary electrons absorbed by grid 10. Departure of said secondary electrons raises the corresponding zones of the delay line (it has already been explained that these zones coincide with the positive peaks in the travelling wave), to a still higher positive potential.

The amplitude of the positive peaks due to the microwave alone, is considerably increased by this mechanism of local augmenting of the positive charges ; thus, the travelling microwave is amplified.

FIG. 3 illustrates another embodiment of an electronic tube in accordance with the invention, differing from that of FIG. 1 solely in terms of the type of delay line used.

Whereas the delay line 5 of FIG. 1 is of the electrical delay type, that of FIG. 3 is of the mechanical type. In accordance with a known embodiment, it is constituted by a plate 11 of a piezoelectric material provided at its ends with two high frequency coupling devices.

On this figure is only represented the beginning of the device enclosed in an envelope (not shown) for constituting a tube . So, one can see only the input coupling device (an equivalent output coupling device being disposed identically at the end of said device). Said input coupling device comprises for example an input line 20 connected to the high frequency source (not shown) and passing through the plate 11 by a hole 21 and connected to a piece of an interleaved metallic line 12 laid on the surface of the plate 11 facing the electron gun (1, 2, 3, 4) in such a way that said coupling device (20, 12) causes excitation of said plate 11. In the embodiment here described said piece of line 11 is set on the plate 11 itself (it's the reason why it is represented by dashed lines) ; this piece of line 11 might be set on layer 9 (not shown) providing that an electric isolation is realised between said piece 11 and said layer 9.

In this embodiment, the delay is of mechanical origin and corresponds to the reduced velocity at which an acoustic wave propagates through the piezoelectric material, said wave being associated with the mechanical stresses produced by the propagation of the electromagnetic wave ejected through the input coupler (20, 12).

In accordance with the invention, said delay line is covered, as in the case of FIGS. 1 and 2, with a layer 8 of a material which exhibits the secondary emission phenomenon, and a thin film 9 of a conductive material. In some cases, the material of the plate 11 itself may exhibit the secondary emission phenomenon ; the layer 8 is then superfluous and the device is devoid of such a layer.

The operation of the device thus constituted is the same as that of the one already described in relation to FIGS. 1 and 2.

FIG. 4 illustrates a variant embodiment of the electronic tube in accordance with the invention, in which the processing operated onto the high frequency signal injected to the delay line consists in stocking for an arbitrary period of time an information which is a very short portion of said high frequency signal.

This variant embodiment of a tube in accordance with the invention is here described with a mechanical delay line constituted by a plate 11 of a piezoelectric material as in FIG. 3. It is quite clear that such a variant which consists in a storage tube for stocking informations may also be realised with an electrical delay line as that one of FIG. 1 for example.

Such storage tubes according to the invention are equivalent with regard to their general conception to the amplifier tubes described with reference to FIGS. 1 to 3. They only differ from said amplifier tubes by the suppression of the conductive film 9 which was laid on layer 8 in said tubes (FIGS. 2, 3) and by a different setting of the potential of the grid 10.

This absence of film 9 enables static charges to accumulate thus allowing the high frequency signal to be blocked in the manner described hereinafter in the context of a piezoelectric delay line.

A very short high frequency signal is ejected in the form of a pulse through the input coupler of the delay line, electron emission from the gun being inhibited by the grid 4. When the pulse, in the form of a wave train of both electrical and mechanical nature is fully contained on the surface of the line, the grid 4 is used to unblock the electron-gun 1 for a very short time, for example in the order of magnitude of, or less than, one quarter of the periodicity of the high frequency signal.

The potential of the second grid 10 is so adjusted relative to that one of the delay line that the impact of the electrons emitted by said electron gun onto the surface of layer 8 liberates secondary electrons the energy of which is such that they fall back onto the insulating surface of the piezoelectric material, concentrating at the regions of positive potential, that is to say where the wave peaks occur , and remaining "trapped" there to thus form a permanent electrostatic image of the wave at the instant of bombardment ; these charge deposits create associated permanent mechanical stresses inside the crystal.

An unblocking of the signal thus blocked onto the line may be achieved by unblocking the electron-gun under the control of the grid 4. The electron beam thus emitted gives rise to secondary electrons which redistribute themselves onto the delay line at the locations which have been precedently depopulated of electrons, this having the effect of erasing the electrostatic and mechanical record obtained during the afore-described blocking period. This erasing cancels the electric charges thus releasing the internal mechanical stresses and triggering two surface waves which propagate in opposite directions. The one which propagates in the same direction as the initially injected wave in a faithful reconstitution of that wave and is picked up at the output coupler (not shown).

The tube in accordance with this embodiment of the invention thus makes it possible to arbitrarily delay a high frequency signal.

By way of example, the blocking or stocking time depends essentially upon the insulation of the structures utilised to conserve the electrostatic charges and can range from some few microseconds to several months. The high frequency signal ranges between some few megacycles per second and some few gigacycles per second ; the duration of the pulse can be as much as 50 microseconds and the input power is less than some watts.

FIG. 5 illustrates a variant embodiment of the invention, where the provision of several input couplers 12, 13 and 14, and several output couplers (not shown), makes it possible to process several different signals onto several parts of the delay line.

FIG. 5 illustrates a tube where the processing realised is an amplification (see the presence of conductive film 9).

Such a variant embodiment may also concern storage tubes without film 9.

The electron beam 15 can then be selectively applied to one of the corresponding parts of the delay line, this by the application of suitable potentials to the deflecting electrode 3 of the electron-gun, when a separate processing of said parts is wanted, or applied to the whole delay line for a simultaneous processing of said parts.

This variant embodiment is described here with a mechanical delay line ; it may also be realised with an electrical one.

Claims

What is claimed is :

1. Electronic device providing an interaction between a high frequency wave and an electron beam comprising within an evacuated envelope, an electron source delivering an adjustable electron beam, a high frequency source delivering said high frequency wave, a delay line for propagating said wave, first coupling means for coupling said delay line to said high frequency source and constituting the input of said device, second coupling means for extracting said wave from said delay line and constituting the output of said device, means for accelerating said electron beam towards said delay line so that the electrons of said beam strike simultaneously the whole effective length of said delay line, said delay line emitting secondary electrons upon said strike of said electron beam onto its surface, and means for collecting said secondary electrons.

2. Electronic device according to claim 1 wherein said delay line is made of an electric conductive material covered on its side striked by said electron beam with a material emitting secondary electrons upon said strike.

3. Electronic device according to claim 1 wherein said delay line is made of a piezoelectric material.

4. Electronic device according to claim 3 wherein said piezoelectric material emits secondary electrons upon said strike of said electron beam.

5. Electronic device according to claim 3 wherein said piezoelectric material is covered on its side striked by said electron beam with a material emitting secondary electrons upon said strike.

6. Electronic device according to claim 1 wherein said delay line comprises several parts each one having its own said first and second coupling means.

7. Electronic device according to claim 6 wherein means are provided to deflect said electron beam onto one or the other of said parts of said delay line.

8. Electronic device according to claim 1 wherein said means for accelerating said electron beam towards said delay line comprise a grid located in the vicinity of said surface of said delay line striked by said electron beam and means for defining the potential of said grid in a positive way relative to said electron source.

9. Electronic device according to claim 8 wherein said potential of said grid is furthermore defined so as said grid constitute said means for collecting said secondary electrons and wherein said surface of said delay line is covered with a thin film of an electric conductive material connected to means for defining its potential.

10. Electronic device according to claim 8 wherein said means for collecting said secondary electrons is said surface of said delay line striked by said electron beam.

11. Electronic tube for amplification of a high frequency signal comprising an electronic device as claimed in claim 9, said tube providing amplification of said wave applied to said delay line.

12. Electronic tube for the storage of high frequency signals comprising an electronic device as claimed in claim 10, said tube providing storage of high frequency signals the duration of which is less than, or equal to, the propagation time of said high frequency wave to proceed over said delay line.