EP3489987A1 - Internal load for travelling-wave tube using a delay line in a folded waveguide - Google Patents

Abstract

Slow wave line in folded guide provided with an internal load comprising: - a central plate (20) comprising a beam sliding hole (21), rectilinear in the same direction as the longitudinal axis (z) of the central plate ( 20), and a serpentine-shaped slit (22) having its folds in the direction of the width of the guide: - a lower plate (23) and a top plate (24) closing the waveguide respectively disposed on and under the central plate (20) - at least one groove (25) of variable section, made along the longitudinal axis (z) of the guide, on at least one inner face of the guide of the lower plate (23) the upper plate (24) or the central plate (20), at least partially comprising a material having microwave losses, to form a closed slow wave guide in which a hybrid slow wave is propagated whose amplitude is attenuated by at least 20 dB between the beginning and the end of the part of the o u the grooves containing a lossy material.

Description

The present invention relates to a folded slow wave guide or waveguide line for a traveling wave tube of the acronym TOP.

• une première étape : obtenir un groupement des électrons en paquets, c'est-à-dire réaliser une modulation de densité du courant du faisceau au rythme du signal hyperfréquence ; et
• une deuxième étape : placer les paquets d'électrons ainsi obtenus dans une phase où ils sont ralentis par le champ afin de céder leur énergie à l'onde.

In most microwave tubes the interaction between the wave and the beam is broken down into two stages:

• a first step: obtaining a grouping of the electrons in packets, that is to say carrying out a density modulation of the beam current at the rate of the microwave signal; and
• a second step: place the electron packets thus obtained in a phase where they are slowed down by the field in order to give up their energy to the wave.

In the case of the TOPs, the grouping of the electrons in a packet is obtained by placing the beam in the field of a progressive wave whose phase velocity is equal to the speed of the electrons. In a moving frame the electrons see the field of a standing wave. The electrons are slowed on one alternation and accelerated on the next. A bundle of electrons forms around the phase for which we move from an accelerator field to a decelerating field.

A conventional waveguide of rectangular or cylindrical section is not suitable for interaction because the phase velocity of the wave propagating in this guide is greater than the speed of light while the velocity of the electrons is lower. at the speed of light. In addition, an electric field parallel to the displacement of the electrons is required, whereas the fundamental mode of rectilinear guides of rectangular or cylindrical section is perpendicular to the axis of the guide. In order to obtain a phase velocity lower than that of light, a special guide called slow waveguide or delay line is required. Most often the delay line is a periodic line obtained by repetitively translating a basic cell, to obtain a succession of identical cells. This is the case of the propeller, the line with coupled cavities, the interdigital line ...

In the field of the TOPs operating at millimeter wavelengths, a so-called folded-delay line is often used. This line is obtained by periodically positioning rectangular waveguide sections perpendicular to the beam axis, and alternatively connecting the straight guide sections by 180 ° E plane bends. The crooked view of the folded guide has the shape of a coil. The beam slip hole is located in the middle of the straight rectangular guide section. The electric field in the guide is perpendicular to the long side of the guide, and therefore parallel to the movement of electrons, which allows to modulate the beam. The electron then moves in the sliding hole, opens into the right guide section where it undergoes the action of the electric field (interaction space), crosses the slip hole and opens into the next interaction space . The electron thus sees the successive interaction spaces with a period equal to the pitch of the line whereas the geometric period of the line is equal to twice the pitch. The pitch is the distance between two straight guides separated by an elbow.

The length of the folded waveguide (right part and bends) is determined so that the phase shift of the wave in the waveguide corresponds to the phase variation related to the displacement of electrons from one interaction space to the next.

Traveling wave tubes use a delay line with a number of sections greater than or equal to 2. The input section is terminated by a load and the output section begins with a load. Intermediate sections begin and end with a load. A charge is defined as a volume containing an RF wave absorbing material connected to the delay line, such that, in the plane of the connection, the impedance presented by the volume is as close as possible to the characteristic impedance of the line to be delay in order to achieve good adaptation (i.e., minimize the wave reflected by the load).

The figure 1 schematically represents a delay line or waveguide for traveling wave tube comprising three sections 1, 2, 3. The delay line shown comprises an input 4 and an output 5.

The charges 6 at the exit of the first section 1, at the entry of the second section 2, at the exit of the second section 2, and at the entrance of the third section 3 are called charge at the cutoff or "sever loads" in the English language. Between the end of one line and the beginning of the next, the electron beam passes through a slip hole without an RF field, which helps to ungroup the beam (so it is a loss of modulation).

If the reflection coefficients at both ends of a section and the gain of the section are too high, it is possible to observe an oscillation in the delay line section. This is why the length of the different sections is determined so as to limit the gain, given the reflection coefficient of the loads at the cut.

The most common TOPs, an example of which is illustrated on the figure 2 , use a delay line comprising a propeller 7 held in a sleeve 8 by three dielectric uprights 9.

On a delay line of the figure 2 , the charge is generally made by depositing on the uprights 9 supporting the helix 7 a layer of material having high microwave losses, such as graphite. A material with microwave losses is characterized by a finite electrical conductivity σ (unlike a perfect conductor whose electrical conductivity is infinite), which results in a conduction current σE (E being the electric field) and losses resistive σE ² . In a medium with microwave losses the wave undergoes exponential attenuation as a function of distance. By varying the thickness of the deposit, a load is produced whose attenuation (microwave loss) and the reflection coefficient increase progressively, thus making it possible to obtain good adaptation over a wide frequency band.

In such a helix delay line, the length of the charge leads to a significant loss of modulation, and therefore to a gain loss of the TOP, which must be compensated by an increase in the gain of the other sections, and therefore to an increase in the total length of the TOP.

The figure 3 schematically represents the attenuation on an upright 9, as a function of the thickness z of the deposition of the material having high microwave losses, such as graphite. The higher the attenuation, the darker the gray color that represents it.

In the case of TOP using a folded-line delay line, it is known to interrupt the undulations to pass from a folded guide 10 to a straight guide 11, in which is placed a load absorbing electromagnetic energy. Such a straight guide can be either parallel, as shown on the Figures 4 and 5 , perpendicular, as shown on the figure 6 at the slip hole 12 of the beam.

For such embodiments, although using the same guide section, the periodic line in folded guide and the straight guide containing the load do not have the same impedance and it is necessary to make an adaptation between the two, which is not broadband, and limits the band of the TOP.

Alternatively, as shown on the figure 7 , it is known to interrupt the delay line in folded guide to place a lossy dielectric block 13 of a determined geometry to minimize reflections of the load.

This variant comprises a sudden transition between the periodic folded guide 10 and the microwave loss dielectric block 13 which is equivalent to charging the periodic folded guide 10 by a resonator with microwave losses having numerous resonances, which limits the frequency band in which the charge is well suited.

An object of the invention is to overcome the problems mentioned above.

• une plaque centrale comprenant un trou de glissement de faisceau, rectiligne de même direction que l'axe longitudinal de la plaque centrale, et une fente repliée en forme de serpentin ayant ses replis dans le sens de la largeur du guide ;
• une plaque inférieure et une plaque supérieure fermant le guide d'onde, respectivement disposées sur et sous la plaque centrale ;
• au moins une rainure de section pouvant être variable, réalisée selon l'axe longitudinal du guide, sur au moins une face interne au guide de la plaque inférieure, la plaque supérieure ou la plaque centrale, comprenant au moins partiellement un matériau présentant des pertes hyperfréquences ;

pour former un guide à onde lente fermé dans lequel se propage une onde lente hybride dont l'amplitude est atténuée d'au moins 20 dB entre le début et la fin de la partie de la ou les rainures contenant un matériau à pertes.According to one aspect of the invention, there is provided a folded wave slow wave line provided with an internal charge comprising:

• a central plate comprising a beam sliding hole, rectilinear in the same direction as the longitudinal axis of the central plate, and a folded slot in the form of a coil having its folds in the direction of the width of the guide;
• a bottom plate and an upper plate closing the waveguide respectively disposed on and under the central plate;
• at least one groove of variable section, made along the longitudinal axis of the guide, on at least one inner face of the guide of the lower plate, the upper plate or the central plate, comprising at least partially a material having microwave losses ;

to form a closed slow wave guide in which propagates a hybrid slow wave whose amplitude is attenuated by at least 20 dB between the beginning and the end of the portion or grooves containing a lossy material.

Thus the reflections of the charge are minimized, and the attenuation of the electromagnetic energy is not brutal.

Losses are progressively introduced into the folded guide line, which is analogous to the gradual increase in graphite deposition on the propeller supports.

In one embodiment, the material having microwave losses is a microwave loss dielectric.

Thus, the wave undergoes an exponential attenuation with a maximum of power dissipated at the beginning of the attenuated zone if the distribution of the lossy material is uniform.

According to one embodiment, at least one groove has a constant section and comprises an increasing amount of the same microwave loss dielectric when the abscissa increases along the axis of the guide oriented in the direction of wave propagation.

Thus, a small proportion of the power can be absorbed at the beginning of the load and a higher proportion thereafter, with the advantage of better distributing the power dissipated over the length of the load.

In one embodiment, at least one groove has a constant or increasing section when said abscissa increases and is full of microwave loss dielectric whose level of microwave losses increases as said abscissa increases.

Thus, a small proportion of the power can be absorbed at the beginning of the load and a higher proportion thereafter, with the advantage of better distributing the power dissipated over the length of the load.

Alternatively, the microwave loss material is a layer of a mixture of metals selected from iron, nickel, molybdenum, and titanium, at least partially covering the inner surface of a groove.

Thus, it is not necessary to machine a dielectric block, then solder this block or crimp it in the lower or upper plates to ensure the flow of heat between the dielectric block where the power is dissipated and the cold source placed around the delay line.

For example, at least one groove has a section whose stop length is constant and comprises an increasing amount of a layer of the same said mixture of metals when said abscissa increases.

Alternatively, at least one groove has a section whose stopping length is constant or increasing as said abscissa increases and comprises a layer of the same said mixture of metals.

• percer dans une plaque centrale un trou de glissement de faisceau, rectiligne de même direction que l'axe longitudinal d'une plaque centrale, et une fente repliée en forme de serpentin ayant ses replis dans le sens de la largeur du guide ;
• réaliser au moins une rainure de section pouvant être variable, selon l'axe longitudinal du guide, sur au moins une face interne au guide d'une plaque inférieure, une plaque supérieure ou la plaque centrale, comprenant au moins partiellement un matériau présentant des pertes hyperfréquences ;
• disposer la plaque inférieure et la plaque supérieure fermant le guide d'onde, respectivement sous et sur la plaque centrale ;

de manière à former un guide à onde lente fermé dans lequel se propage une onde lente hybride dont l'amplitude est atténuée d'au moins 20 dB entre le début et la fin de la partie de la ou les rainures contenant un matériau à pertes.It is also proposed, according to another aspect of the invention, a method of manufacturing a folded wave slow wave line provided with an internal charge comprising the steps of:

• piercing in a central plate a beam sliding hole, rectilinear in the same direction as the longitudinal axis of a central plate, and a folded slot in the form of a coil having its folds in the direction of the width of the guide;
• performing at least one groove of variable section, along the longitudinal axis of the guide, on at least one internal face to the guide of a lower plate, an upper plate or the central plate, comprising at least partially a material having losses microwave;
• arranging the lower plate and the upper plate closing the waveguide, respectively under and on the central plate;

to form a closed slow wave guide in which propagates a hybrid slow wave whose amplitude is attenuated by at least 20 dB between the beginning and the end of the portion or grooves containing a lossy material.

In one embodiment, the method further comprises a step of closing the guide by the lower plate and the upper plate, respectively fixed on the lower face and on the upper face of the central plate.

• la figure 1 illustre schématiquement une ligne à retard ou guide à onde lente pour tube à ondes progressives comprenant trois sections, selon l'état de la technique ;
• la figure 2 illustre schématiquement une ligne à retard comprenant une hélice maintenue dans un fourreau par trois montants diélectriques, selon l'état de la technique ;
• la figure 3 illustre schématiquement l'atténuation sur un montant d'une ligne à retard de la figure 2, en fonction de l'épaisseur du dépôt du matériau ayant des pertes hyperfréquences élevée, selon l'état de la technique ;
• la figure 4 illustre schématiquement une ligne à retard en guide replié, comprenant une charge absorbant de l'énergie électromagnétique dans un guide droit parallèle au trou de glissement du faisceau, selon l'état de la technique ;
• la figure 5 illustre schématiquement une ligne à retard en guide replié, comprenant une charge absorbant de l'énergie électromagnétique dans un guide droit parallèle au trou de glissement du faisceau et replié vers les cellules de la ligne , selon l'état de la technique ;
• la figure 6 illustre schématiquement une ligne à retard en guide replié, comprenant une charge absorbant de l'énergie électromagnétique dans un guide droit perpendiculaire au trou de glissement du faisceau, selon l'état de la technique ;
• la figure 7 illustre schématiquement une ligne à retard en guide replié interrompue par un bloc de diélectrique à pertes d'une géométrie déterminée pour minimiser les réflexions de la charge, selon l'état de la technique ; et
• les figures 8, 9 et 10 illustrent schématiquement une vue d'ensemble et des vues en coupe d'un guide à onde lente replié pour tube à ondes progressives, selon un aspect de l'invention.

The invention will be better understood by studying a few embodiments described by way of non-limiting examples and illustrated by the appended drawings in which:

• the figure 1 schematically illustrates a delay line or waveguide for traveling wave tube comprising three sections, according to the state of the art;
• the figure 2 schematically illustrates a delay line comprising a propeller held in a sleeve by three dielectric uprights, according to the state of the art;
• the figure 3 schematically illustrates the attenuation on an amount of a delay line of the figure 2 as a function of the thickness of the deposition of the material having high microwave losses, according to the state of the art;
• the figure 4 schematically illustrates a folded guide delay line, comprising a charge absorbing electromagnetic energy in a straight guide parallel to the beam slip hole, according to the state of the art;
• the figure 5 schematically illustrates a folded guide delay line, comprising a load absorbing electromagnetic energy in a straight guide parallel to the beam slip hole and folded towards the cells of the line, according to the state of the art;
• the figure 6 schematically illustrates a folded guide delay line comprising a load absorbing electromagnetic energy in a straight guide perpendicular to the beam slip hole, according to the state of the art;
• the figure 7 schematically illustrates a folded-line delay line interrupted by a lossy dielectric block of a determined geometry to minimize reflections of the load, according to the state of the art; and
• the figures 8 , 9 and 10 schematically illustrate an overview and sectional views of a folded waveguide for traveling wave tube, according to one aspect of the invention.

In all the figures, the elements having identical references are similar.

In the present description, the embodiments described are in no way limiting, and the characteristics and functions well known to those skilled in the art are not described in detail.

• une plaque centrale 20 comprenant un trou 21 de glissement de faisceau, rectiligne de même direction que l'axe longitudinal z de la plaque centrale 20, et une fente 22 repliée en forme de serpentin ayant ses replis dans le sens de la largeur du guide ;
• une plaque inférieure 23 et une plaque supérieure 24 fermant le guide d'onde, respectivement disposées sur et sous la plaque centrale 20 ;
• au moins une rainure 25 de section pouvant être variable, réalisée selon l'axe longitudinal z du guide, sur au moins une face interne au guide de la plaque inférieure 23, la plaque supérieure 24 ou la plaque centrale 20, comprenant au moins partiellement un matériau présentant des pertes hyperfréquences ;

pour former un guide à onde lente hybride tel que l'amplitude d'une onde soit atténuée d'au moins 20 dB entre le début et la fin de la partie de la ou les rainures contenant un matériau à pertes.On the figure 8 is schematically shown a slow wave line in a folded waveguide tube with an internal charge comprising:

• a central plate 20 comprising a beam sliding hole 21, rectilinear in the same direction as the longitudinal axis z of the central plate 20, and a slot 22 folded serpentine having its folds in the direction of the width of the guide;
• a lower plate 23 and an upper plate 24 closing the waveguide respectively disposed on and below the central plate 20;
• at least one groove 25 of variable section, made along the longitudinal axis z of the guide, on at least one inner face of the guide of the lower plate 23, the upper plate 24 or the central plate 20, comprising at least partially a material with microwave losses;

to form a hybrid slow wave guide such that the amplitude of a wave is attenuated by at least 20 dB between the beginning and the end of the portion or grooves containing a lossy material.

In other words, the present invention consists in progressively introducing electromagnetic losses into the folded guide delay line to avoid a sudden transition between the periodic line and a rectangular guide, or between the periodic line and a dielectric block. , equivalent to increasing the graphite deposition on the amounts of a propeller delay line known from the state of the art.

To do this, the folded guide delay line is coupled to another transmission line which has significant losses, and the coupling between the two lines increases in the direction of propagation of the wave. If we define a cell as the volume delimited by two planes perpendicular to the axis of the beam distant by one step (that is to say the distance between two straight guides separated by an elbow), the amplitude of the wave decreases from one cell to the next.

On the example of the figure 8 two grooves 25 of variable section, increasing with the abscissa of the z-axis of the guide, in this case symmetrical with respect to the mean plane of the central plate 20, are formed on the inner face of the guide of the lower plate 23 and on the inner face of the guide of the upper plate 24, and are filled with lossy dielectric material microwaves, such as a ceramic material (alumina, beryllium oxide, aluminum nitride) sintered with elements adding microwave losses (carbon, iron, titanium, ...).

The transmission line with high electromagnetic losses can be machined in the lower plates 23 and / or 24 which are brazed with the central plate 20 in which the coil 22 is machined to form the folded guide delay line. It is therefore a hollow waveguide machined in the lower plates 23 and / or higher 24. It can also be machined in part or completely in the central plate 20.

On the example of the figure 8 , the groove of variable section made on the inner face of the guide of the upper plate 24 is not visible.

The figure 9 is a sectional view of a folded waveguide for traveling wave tube according to one aspect of the invention.

The figure 10 represents different section sections of the example of the figure 9 .

Alternatively, any embodiment comprising at least one groove 25 of variable section (variable or constant), made along the longitudinal axis z of the guide, on at least one inner face to the guide of the lower plate, the upper plate or the central plate, comprising at least partially a material having microwave losses, is possible.

To achieve these electromagnetic losses, it is possible to fill all or part of the grooves 25 with one or more microwave loss dielectrics, or deposit on the walls one or more microwave loss materials, so that along said longitudinal axis oriented in the direction of propagation of the wave, when the abscissa increases, the amplitude of the wave is attenuated by 20 dB between the beginning and the end of the load.

The most explicit cases are as follows.

At least one groove 25 may have a constant section and include an increasing amount of the same microwave loss dielectric as said abscissa increases.

Alternatively, at least one groove 25 may have a constant or increasing section as said abscissa increases and be full of microwave loss dielectric whose level of microwave losses increases as the abscissa increases.

In a variant, at least one groove 25 may have a section whose stop length is constant and comprise an increasing quantity of a layer of the same mixture of metals chosen from: iron, nickel, molybdenum, titanium, at least partially covering the inner surface of a groove as the abscissa increases.

In a variant, at least one groove 25 may have a section whose stop length is constant or increasing when said abscissa increases and comprise a layer of the same mixture of metals chosen from: iron, nickel, molybdenum, titanium.

The large side of the guide machined in the lower and upper plates determines the opening in the line folded guide, and thus the coupling between the two transmission lines. A low height of the loss guide may correspond to a guide operating below the cutoff frequency and therefore to energy that does not propagate in the loss guide. In this case the guide behaves rather like a damped resonant cavity coupled to the folded guide.

• percer dans une plaque centrale (20) un trou (21) de glissement de faisceau, rectiligne de même direction que l'axe longitudinal (z) d'une plaque centrale (20), et une fente (22) repliée en forme de serpentin ayant ses replis dans le sens de la largeur du guide ;
• réaliser au moins une rainure (25) de section pouvant être variable, selon l'axe longitudinal (z) du guide, sur au moins une face interne au guide d'une plaque inférieure (23), d'une plaque supérieure (24) ou de la plaque centrale (20), comprenant au moins partiellement un matériau présentant des pertes hyperfréquences ;
• disposer la plaque inférieure (23) et la plaque supérieure (24) fermant le guide d'onde, respectivement sous et sur la plaque centrale (20) ;

de manière à former un guide à onde lente fermé dans lequel se propage une onde lente hybride dont l'amplitude est atténuée d'au moins 20 dB entre le début et la fin de la partie de la ou les rainures contenant un matériau à pertes.The method of manufacturing such a folded wave slow wave line provided with an internal charge comprises steps of:

• piercing in a central plate (20) a beam sliding hole (21) rectilinear in the same direction as the longitudinal axis (z) of a central plate (20), and a slit (22) folded into a coil shape having its folds in the direction of the width of the guide;
• producing at least one groove (25) of variable section, along the longitudinal axis (z) of the guide, on at least one inner face of the guide of a lower plate (23), an upper plate (24) or the central plate (20), at least partially comprising a material having microwave losses;
• arranging the lower plate (23) and the upper plate (24) closing the waveguide, respectively under and on the central plate (20);

to form a closed slow wave guide in which propagates a hybrid slow wave whose amplitude is attenuated by at least 20 dB between the beginning and the end of the portion or grooves containing a lossy material.

Plates, generally parallelepipedic can be made by conventional methods of rolling or milling.

The beam slip hole 21 can be made by electroerosion, and the slot 22 in the central plate can be made by wire EDM.

The grooves 25 can be made by micro-milling or electroerosion.

Claims (8)

A slow wave line in a folded guide with an internal charge comprising: a central plate (20) comprising a beam sliding hole (21), rectilinear in the same direction as the longitudinal axis (z) of the central plate (20), and a serpentine-shaped slit (22) having its folds in the direction of the width of the guide; - a lower plate (23) and an upper plate (24) closing the waveguide respectively disposed on and below the central plate (20); - at least one groove (25) of variable section, made along the longitudinal axis (z) of the guide, on at least one inner face to the guide of the lower plate (23), the upper plate (24) or the central plate (20), comprising at least partially a material having microwave losses; to form a closed slow wave guide in which propagates a hybrid slow wave whose amplitude is attenuated by at least 20 dB between the beginning and the end of the portion or grooves containing a lossy material. A folded wave slow wave line according to claim 1, wherein the microwave loss material is a microwave loss dielectric. A folded wave slow wave line according to claim 2, wherein at least one groove (25) has a constant section and comprises an increasing amount of the same microwave loss dielectric as the abscissa increases along the oriented guide axis. in the direction of wave propagation. A folded wave slow wave line according to claim 2, wherein at least one groove (25) has a section constant or increasing when said abscissa increases and is full of microwave loss dielectric whose level of microwave losses increases as said abscissa increases. A folded wave slow wave line according to claim 1, wherein the microwave loss material is a layer of a mixture of metals selected from iron, nickel, molybdenum, and titanium, at least partially covering the inner surface of a groove (25). A folded wave slow wave line according to claim 5, wherein at least one groove (25) has a constant stop length section and comprises an increasing amount of a layer of the same metal mixture when said abscissa increases. A folded wave slow wave line according to claim 5, wherein at least one groove (25) has a section whose stopping length is constant or increasing as said abscissa increases and comprises a layer of the same metal mixture. A method of manufacturing a slow wave line in a folded guide provided with an internal load comprising the steps of: - Drilling in a central plate (20) a hole (21) of beam sliding, rectilinear in the same direction as the longitudinal axis (z) of a central plate (20), and a slot (22) folded in the form of serpentine having its folds in the direction of the width of the guide; performing at least one groove (25) of variable section, along the longitudinal axis (z) of the guide, on at least one internal face to the guide of a lower plate (23), a top plate (24), ) or the central plate (20), comprising at least partially a material having microwave losses; arranging the lower plate (23) and the upper plate (24) closing the waveguide, respectively under and on the central plate (20); to form a closed slow wave guide in which a hybrid slow wave propagates whose amplitude is attenuated by at least 20 dB between the beginning and the end of the portion or the grooves containing a lossy material.

Images