EP1145268B1 - Multiband travelling wave tube of reduced length capable of high power functioning - Google Patents

Description

The present invention relates to a traveling wave tube multiband capable of operating at high power. This tube intended particularly to be used in airborne or space applications, must be relatively short.

The development of techniques and the growing mastery of materials have made it possible to develop traveling wave tubes intended to operate in a very wide frequency band and which are relatively short. These tubes are known under the name of mini-TOP. These are traveling wave tubes monobloc helical line tight. From the frequency point of view, we got a report from minus three between the high frequency and the low frequency of the band.

In terms of dimensions, these tubes do not exceed about thirty centimeters but from the point of view of power they do not reach little more than a few tens of watts.

We could have thought about extrapolating these tubes to increase their power. But for a given gain, getting more power high causes an increase in the propeller voltage and a increase in length. But there is no question of reducing the gain, in order to obtain the required power without increasing the length of the propeller. This path does not lead a multiband wave tube, of reduced length, able to operate at high power.

The object of the present invention is a traveling wave tube multiband whose length is of the order of that of the mini-TOP but which is able to operate at higher powers while retaining a gain of the same order.

The multiband traveling wave tube according to the invention is defined by claim 1.

For this purpose the multiband wave tube according to the invention comprises a microwave line traversed by electrons and wherein a signal is amplified. This microwave line comprises successively a section of microwave input line separated from a succession of disjoint output microwave line sections, each output section working in one of the operating bands of the tube.

The inlet section is connected at one end to means input signal to amplify and works in a frequency band encompassing the operating frequency bands of the tube. It is for preamplifying the signal to be amplified.

The succession of output sections receives the pre-amplified signal, each of its output sections being intended to amplify it, if it is at a frequency in his working frequency band and to leave it pass virtually without intervention, if it is at an external frequency to its working frequency band, each of the output sections being connected at one end to output means of the preamplified signal that it has amplified.

Preferably, the center frequencies of the working bands exit sections decrease with their distance from the section input.

Regarding the signal power amplified by a stretch of output, it increases the more the output section is far from the stretch input.

The microwave line sections are in a helix, each propeller is held in a sheath by dielectric supports, the different sleeves being secured to each other.

To be able to work in a very broad band, the section input includes dispersion correction means such as valves

The propeller of the first output section will preferably be substantially the same length and / or the same inside diameter as the propeller of the entrance section.

The propeller wire of the first exit section will also have preferably the same section as that of the helix wire of the input section.

To keep in the first output section, the synchronism acquired in the input section, between the speed of the beam of electrons and the speed of the signal, the pitch of the helix of the first stretch of output will preferably be smaller than that of the impeller of the inlet section.

Preferably, the length and / or the pitch and / or the inside diameter propellers of the output sections will increase with their distance from the entrance section. It is the same for the section of the helix wire.

To avoid the appearance of self-oscillation phenomena, the inlet section has an attenuation zone at the opposite end to that connected to the input means of the signal to be amplified.

For this purpose, each exit section has a zone attenuation at the opposite end to that connected to the output means of the signal that he amplified.

• la figure 1 une coupe longitudinale schématisée d'un tube à ondes progressives selon l'invention ;
• la figure 2 une vue schématique éclatée d'un tube à ondes progressives à hélice serrée conforme à l'invention ;
• les figures 3a, 3b des coupes transversales de deux variantes du tronçon d'entrée ;
• les figures 3c, 3d respectivement la vitesse de phase normalisée et le gain en fonction de la fréquence du tronçon d'entrée de la figure 3a ;
• la figure 4a une coupe transversale du premier tronçon de sortie;
• les figures 4b, 4c respectivement la vitesse de phase normalisée et le gain en fonction de la fréquence du premier tronçon de sortie de la figure 4a ;
• la figure 5a une coupe transversale du dernier tronçon de sortie;
• les figures 5b, 5c respectivement la vitesse de phase normalisée et le gain en fonction de la fréquence du dernier tronçon de sortie de la figure 5a ;
• la figure 6 l'allure de la puissance d'un signal injecté dans le tube de la figure 2 et parcourant la ligne hyperfréquence en fonction de sa fréquence.

Other advantages and characteristics of the invention will appear on reading the following description of embodiments of tubes according to the invention, a description illustrated by the figures which represent:

• Figure 1 a schematic longitudinal section of a traveling wave tube according to the invention;
• FIG. 2 is an exploded schematic view of a traveling propeller tube with a tight propeller according to the invention;
• Figures 3a, 3b cross sections of two variants of the inlet section;
• FIGS. 3c, 3d respectively the normalized phase velocity and the gain as a function of the frequency of the input section of FIG. 3a;
• Figure 4a cross-section of the first output section;
• FIGS. 4b, 4c respectively the normalized phase velocity and the gain as a function of the frequency of the first output section of FIG. 4a;
• Figure 5a cross-section of the last output section;
• FIGS. 5b and 5c respectively the normalized phase velocity and the gain as a function of the frequency of the last output section of FIG. 5a;
• Figure 6 shows the power of a signal injected into the tube of Figure 2 and traversing the microwave line according to its frequency.

In these figures, the scales are not necessarily respected for the sake of clarity.

Figure 1 shows a multi-band traveling wave tube according to the invention.

In a conventional way, it comprises successively in an envelope 5, a barrel 1 for producing a beam 2 of electrons, a body 3 in which an interaction occurs between the beam 2 of electrons and a signal to be amplified, a collector 4 for collecting the electrons of the beam 2 at their exit from the body 3.

According to the invention, the beam 2 of electrons crosses between the entrance 6 and the output 7 of the body 3, a microwave line 8 formed of several sections h, h1 ..., hi, ... hn of disjoint microwave lines arranged one after another. Among these sections, the first section crossed by the beam 2 is a h entrance section, other h1, hi, hn form a succession of so-called output sections and their number n is equal to number of frequency bands B1, Bi, Bn in which the tube is intended to function, n being an integer greater than or equal to two. Each output sections h1, ... hi, ... hn is intended to work in one of operating bands of the tube respectively B1 ..., Bi, ... Bn. Each frequency band B1 ..., Bi, ... Bn is centered on a central frequency respectively F1, Fi, Fn. Each frequency band is associated with a exit section.

The electron beam 2 enters each of the sections h, h1, ... hi, .... hn by an input end ee and leaves by an end of exit es.

The input section h is intended to function as a preamplifier in a very broadband B encompassing all the bands B1, Bi, Bn of tube operation. The entrance end ee of section h input is connected to input means E of a signal to be amplified in the tube. Its exit end is near the entrance end ee of the first exit section h1.

The central frequencies F1, Fi, Fn of the bands B1, Bi, Bn of work output sections h1, hi, hn decrease with their distance of the entrance section h. We then have F1> Fi> Fn.

Each output section h1, hi, hn of the succession is intended for amplify the preamplified signal in the input section h, if the signal preamplifier is at a frequency within its frequency band work B1, Bi, Bn. The output sections h1, hi, hn are practically without action on the preamplified signal that runs through them and is not at a frequency in their working frequency band.

Each of the output ends are output sections h1, hi, hn is connected to output means S1, Si, Sn of the preamplified signal on browsing, if the latter has been amplified in the said output section h1, hi, hn.

The signal to be amplified, injected at the input end ee of the section input, goes through it, is preamplified and enters the first h1 section output. The pre-amplified signal that runs through the first section of output h1 is amplified, if its frequency is included in the band B1, it is then extracted by the output means S1. If the signal frequency preamplifier is not in band B1, the pre-amplified signal travels first output section h1 practically, without coupling with the beam of electrons 2, and at the exit end es of the first section h1, it enters in the second h2 output section where it is amplified, if its frequency is in the B2 band, then it is extracted. If its frequency is not in the band B2 it gets into the third h3 exit section and so on section in section until amplified in the appropriate section, then extracted.

It is assumed that a signal of frequency F propagates in the output section hi (i integer between 1 and n - 2), if it is not amplified this means that the frequency F is not included in the band Bi. The signal of frequency F is not extracted at the output end of the hi output section and it then enters the next output section hi + 1. If its frequency F is in the frequency band Bi + 1 associated with the output section hi + 1, it is amplified then extracted at the end es of said hi + section 1. If its frequency F is out of the band Bi + 1, it enters the next segment hi + 2 and and so on.

We will now see in more detail an example of a mode of realization of a tube according to the invention. It is assumed that this is a tube two-band progressive waves.

FIG. 2 shows such a tube seen from the outside but of which the envelope 5 is partially open so as to reveal the different sections of microwave line h, h1, h2 which are helical. The other elements inside the envelope such as the barrel, the focuser, the collector are not represented for the sake of clarity.

The propellers 20, 21, 22 each inserted in a sleeve 11, 11.1, 11.2 conductor are held in the sleeve 11, 11.1, 11.2 to using supports 12, 12.1, 12.2 insulators. In the example we have three supports 12, 12.1, 12.2 propeller insulators (but only one is visible on the 2) and these are substantially the length of the helix 20, 21, 22 that they maintain. The supports can be so conventional, boron nitride, alumina or beryllium oxide by example. The propellers 20, 21, 22 are without contact with each other. The different sleeves 11, 11.1, 11.2 are integral with each other. This fastening is waterproof.

The input end ee of the input section h is connected to input means E of a signal to be amplified represented in the form of a coaxial line.

The two output sections h1, h2 work respectively in the band B1, B2, of respective central frequency F1, F2. The frequency F1 is greater than frequency F2. The output end of the section h1 is connected to output means S1 of the preamplified signal if it has amplified by said section h1. The output means S1 are represented by a waveguide which is conventional at high frequency. The end of output of section h2 is connected to output means S2 of the signal which has has been amplified by section h2. In the example it is a coaxial line. he is of course that each of the means of entry and exit could be of different nature. Section h is intended to work in a very wide band B encompassing the two bands B1 and B2.

We will see more precisely the characteristics of each sections of line h, h1, h2.

So that the input section h can work in the very wide band B, while imposing only the normalized phase speed of the signal to be preamplified remains substantially constant regardless of the frequency, the input section h comprises means for correcting dispersion 13 such as valves for example. In Figure 3a, the valves 13 are distinct from the supports 12, they are conductors extending longitudinally along the helix 20 and projecting from the sheath 11 to the propeller 20. These valves 13 are separated from the propeller 20 by a space 14. They are placed between the supports 12.

Another type of valves can be used as illustrated in Figure 3b. These valves integrated in the dielectric supports are described in the European patent EP-B-0 401 065. The propeller is maintained by the dielectric supports 120 which are in turn supported by elements conductors 130 projecting from the inner wall of the sheath 11 towards the propeller 20. This configuration has the advantage of less obstructing the inside of the sheath, which reduces the time required for pumping and qualitatively improve the vacuum.

We can hope to obtain a ratio between 2 and 4 between the lowest center frequency F2 and highest center frequency F1.

Figures 3a and 3b show cross sections of entrance section h. The inside diameter d of the propeller 20 is relatively small so that section h can work in preamplifier in the band B encompassing all the operating bands of the tube. This diameter depends on the frequency band to be amplified.

Figure 3c is a diagram of the normalized phase velocity c / vφ of the signal propagating in the input section h according to the frequency F. It is assumed in the example described that the tube is intended for operate in two bands B1, B2 centered respectively around the frequency F0 and frequency 3F0. The standard c / vφ phase velocity is the ratio of the phase velocity vφ to the speed of light c. The curve in solid line is obtained in the inlet section h with valves 13 different from the supports 12 and the dashed curve is the one that is would get in the absence of valves 13.

FIG. 3d is the gain G of the input section h as a function of the frequency F. The maximum gain Gmax is obtained in the middle part of the curve, that is to say for a median frequency, the frequencies F0 and 3F0 are located on both sides of the median frequency. In the bands B1, B2 of operation, the gain is about 4 to 5 dB lower compared to the maximum gain.

The first output section h1 is the one that works in amplification at the highest frequency, here 3F0. His band B1 operation is narrower than the B band and the h1 section does not require no means of dispersion correction.

FIG. 4a shows in cross section the first section h1 output with dielectric supports 12.1. Its propeller 21 can be made to simplify with the same wire as the propeller 20 of the input section h if the desired output power of the first output section is not too high. It will have substantially the same internal diameter d1 as that d of the helix 20 of the input section h since this first section h1 of output is associated with the band B1 whose central frequency 3F0 is the most high.

On the other hand its pitch p1 may be smaller than that p of the propeller 20 of the entrance section h to maintain the synchronism between the speed of the electron beam and the speed of the signal that runs through it, synchronism acquired in section h of entry.

The length I1 of the propeller 21 is related to the gain necessary for obtain the desired power at frequency 3F0. It is desirable that the gain of the first section h1 of exit is greater than that of section h input. However, the length I1 of the propeller of the first output section h1 can be of the same order as that of the propeller 20 of the input section h, because the gain per unit length of a helical line without means of dispersion correction is larger than that of a helical line with dispersion correction means.

We can hope to reach for a frequency of several dozens of gigahertz an output power of the order of the hundred or so watt.

Figure 4b shows the trend of the normalized phase velocity in function of the frequency for this first section h1 output while the Figure 4c shows the rate of gain as a function of frequency. The gain is maximum for center frequency 3F0.

FIG. 5a shows a cross section of section h2 of FIG. next exit which here is the last. It is associated with the frequency band B2 F0 central lowest.

This second output section h2 does not require either means of dispersion correction since the band B2 is narrower than band B. It would be the same for all other sections of output.

The inner diameter d2 of its propeller 22 is larger than that of the propeller 21 of the output section h1 which precedes it. The inside diameter of the helix varies in material substantially inversely proportional to the operating frequency so that the amplification parameter remains constant. The ratio of the two diameters d1, d2 is about the same as that of the frequencies 3F0, F0 corresponding central. More generally the inner diameter of the propellers of the output sections h1, h2 increases with their distance from the entrance section h. With such a configuration, the electron beam diameter increases the closer we get to the manifold. The focus of the beam is therefore as a consequence of a classic way for a person skilled in the art.

The supports 12.2 which hold the propeller 22 are adapted to the diameter of the helix and that of section 11.2 of sheath. The different sections 11, 11.1, 11.2 of sheath may not have the same diameter.

The pitch p2 of the propeller 22 of the second output section h2 is greater than that p1 of the output section h1 which precedes it, still in optics to keep the synchronism between the speed of the beam of electrons and the speed of the signal flowing through the propeller 22. More generally the pitch of the propellers of the output sections increases with their distance of the entrance section.

It is assumed that the signal produced by the output section h2 has a higher power than the signal produced by section h1 of exit which precedes it, which leads to giving the wire of the propeller 22 a section larger than that of the propeller wire 21. One can reach the output of h2 output section of the powers three to four times higher than those obtained at the output of the output section h1. By generalizing, the section of the wire propellers of the outlet sections will increase with their distance from the entrance section.

The length I2 of the propeller 22 is related to the gain necessary for obtain the desired power at the frequency F0. We will give to section h2 a length 12 greater than that I1 of the output section h1 which precedes it because the frequency with which he works is lower. More generally in the succession, the length of the propellers of the output sections increases with their distance from the entrance section.

With a length I2 greater than a few centimeters per compared to length I, we can hope to achieve, for a frequency of the order of ten gigahertz, an output power of several hundreds of watts.

FIG. 5b shows the appearance of the normalized phase velocity in frequency function for this second output section h2 while the Figure 5c shows the pace of its gain as a function of frequency. The gain is maximum for the center frequency F0.

Conventionally, to avoid self-oscillation phenomena in the tube, it is expected at the sections h, h1, h2 line microwave an attenuation zone 30, 31, 32. More specifically, these attenuation zones cover the supports 12, 12.1, 12.2 of the propellers 20, 21, 22. These attenuation zones can be realized by a deposit of carbon for example. These attenuation zones are located respectively the first 30 near the exit end es of the input section h and the others 31, 32 near the input end ee of the sections of respective outputs h1, h2. The attenuation zone 31 of the first section h1 of output is approximately the same length as the input section h. In contrast the attenuation zone 32 of another output section h2 is no longer longer than that 31 of the output section h1 which precedes it.

Figure 6 shows the pace of the power P (expressed in dBm) of an injected signal with an amplitude Pe in the tube of FIG. crosses the microwave line until its extraction, or at the level of output means S1, ie at the level of the output means S2.

The signal extracted at the output means S1 has a amplitude power P1 and is at frequency 3F0. The signal extracted level of the output means S2 has a power P2 and is at a frequency F0. The amplitude P2 is about three times larger than the amplitude P1.

We note that the powers are falling sharply at the level of attenuation zones 30, 31, 32 which are symbolized by triangles. In each output section, the signal amplified therein has its amplitude which strongly believes as soon as it spreads beyond the attenuation zone 31, 32 corresponding.

Claims (14)

1. Travelling wave tube capable of operating as an amplifier in several frequency bands (B₁...B_i...B_n), comprising a microwave line (8) along which electrons travel and in which a signal is amplified, characterized in that microwave line (8) comprises, in succession, a microwave line input section (h) separated from a succession of gapped microwave line output sections (h₁...h_i...h_n), each output section (h₁...h_i...h_n) having a respective working band (B₁...B_i...B_n) corresponding to one of the operating bands of the tube, in which band it behaves as an amplifier,

   the input section (h) being connected at one end (e_in) to input means (I) for injecting the signal to be amplified and having a working frequency band (B) encompassing the operating frequency bands (B₁...B_i...B_n) of the tube, in order to preamplify the signal to be amplified,

   the succession of output sections (h₁...h_i...h_n) receiving the preamplified signal and being capable of letting the frequencies lying outside its respective working band pass, virtually without any action, to a following section, each of the output sections (h₁...h_i...h_n) being connected by an output end (e_out) to output means (O₁...O_i...O_n) for extracting the amplified signal.
2. Travelling wave tube according to Claim 1, characterized in that the output sections are placed in the order corresponding to the working frequency bands, the sections furthest from the input section having a central frequency of their operating band which is lower than the closest sections.
3. Travelling wave tube according to either of Claims 1 and 2, characterized in that the output sections are placed in the order corresponding to their power gain, the sections having the highest gain being the furthest from the input section.
4. Travelling wave tube according to one of Claims 1 to 3, characterized in that the input section (h) and output sections (h₁...h₂) are in the form of helices, each helix (20, 21, 22) being held in place in a conducting sheath (11, 11.1, 11.2) by dielectric supports (12, 12.1, 12.2), the sections (11, 11.1, 11.2) being joined together.
5. Travelling wave tube according to Claim 4, characterized in that the input section (h) includes dispersion-correcting means (13).
6. Travelling wave tube according to Claim 5, characterized in that the dispersion-correcting means (13) are gates.
7. Travelling wave tube according to either of Claims 4 and 5, characterized in that the length (l₁) and/or the internal diameter (d₁) of the helix (21) of the first output section (h₁) are substantially the same as those of the helix (20) of the input section.
8. Travelling wave tube according to one of Claims 4 to 7, characterized in that the pitch (p₁) of the helix of the first output section (h₁) is smaller than the pitch (p) of the helix of the input section (h).
9. Travelling wave tube according to one of Claims 4 to 8, characterized in that the cross section of the helical wire of the first output section (h₁) is substantially the same as that of the helical wire of the input section (h).
10. Travelling wave tube according to one of Claims 4 to 9, characterized in that the length and/or the pitch of the helices (22) of the output sections (h₁, h₂) increase with their distance from the input section (h).
11. Travelling wave tube according to one of Claims 4 to 10, characterized in that the internal diameter of the helices of the output sections (h₁, h₂) increases with their distance from the input section (h).
12. Travelling wave tube according to one of Claims 4 to 11, characterized in that the cross section of the helical wire of the output sections (h₁, h₂) increases with their distance from the input section (h).
13. Travelling wave tube according to one of Claims 1 to 12, characterized in that the input section (h) is provided with an attenuation region (30) at the opposite end to that connected to the input means (I) for injecting the signal to be amplified.
14. Travelling wave tube according to one of Claims 1 to 13, characterized in that each output section (h₁, h₂) is provided with an attenuation region (31, 32) at the opposite end to that connected to the output means (O₁, O₂) for extracting the signal that it has amplified.

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