RU2472245C2 - Wideband travelling-wave tube - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: wideband travelling-wave tube (TWT) has a spiral slow-wave structure whose output section has a screen with longitudinally conducting metal fins, the gap between which and the spiral (not less than twice) increases gradually or in steps towards the end of the slow-wave structure. The length of the section of the slow-wave structure with the increasing gap can range from 20 to 100% of the clean (free from absorbent) section of the output section of the slow-wave structure. The maximum size of the gap between fins of the screen and the spiral can be not less than twice the minimum size of the gap which corresponds to the beginning of the section and can reach a size which corresponds to absence of fins. Increasing the gap increases phase velocity and coupling impedance. Varying these values according to a given law along the length of the spiral slow-wave structure enables to obtain improved characteristics of the travelling-wave tube. Simultaneous variation of the spacing of the slow-wave structure with the varying gap enables to further improve parameters of the travelling-wave tube.

EFFECT: low level of the second harmonic, high resistance to self-excitation on the return wave and high electronic efficiency of interaction of wideband travelling-wave tubes with a spiral slow-wave structure.

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Description

The invention relates to the field of microwave electronic devices, in particular to traveling-wave spiral tubes (TWTs) of the O-type.

The problem of increasing electronic efficiency, lowering the second harmonic level and suppressing self-excitation on the backward wave of broadband spiral TWTs is still relevant. To ensure the maximum instantaneous operating frequency band, the main efforts have to be concentrated on obtaining high efficiency in the upper part of the operating range, which is why it is necessary to choose the lowest possible internal diameter of a retarding system (ZS) like a spiral. As a result, at the lower frequency of the operating range, the level of the second harmonic increases sharply, while decreasing the electronic efficiency of the main signal. To expand the working frequency band and reduce the second harmonic level in spiral TWTs, screens are used with longitudinally conducting ribs parallel to the axis of the lamp, realizing anomalous dispersion [1]. However, this reduces the electronic efficiency (by reducing the coupling resistance) and increases the tendency to self-excitation on the backward wave.

Known technical solutions to increase electronic efficiency, reduce the second harmonic level and suppress self-excitation on the backward wave by creating a spiral type inhomogeneous along the length of the CS, realized by changing the pitch of the spiral.

Technical solutions are known when, by applying a CS section with an increased helix pitch, back-wave generation is suppressed.

In US 3761760 (publ. September 25, 1973), it is proposed to suppress backward generation by the interaction of an electron beam with a fast space-charge wave in a region with an increased phase velocity of the wave realized by increasing the pitch of a spiral spiral type. A backward wave, excited in a subsequent section with a smaller step, on which a slow wave of space charge is realized, enters the section with a fast wave and is suppressed in it due to the Komfner effect [2]. The implementation of such a technical solution entails an increase in the length of the output section, which can be avoided by the recommended choice of section steps in US 4378512 (published on March 29, 1983).

The disadvantage of these two technical solutions, as shown in [3], is the lack of complete suppression of generation on the backward wave of the region with a slow wave of space charge, the region ahead of it with the fast wave and the length of the region with the slow wave is larger than the start wave.

A technical solution is known in which a dispersion jump in the output section is applied due to a single jump-like increase in the gap between the ribs and the spiral [4]; at the same time, with an increase in resistance to self-excitation, the efficiency increases due to an increase in coupling resistance.

A technical solution is known that leads to an increase in efficiency [5] and a decrease in the level of the second harmonic due to a smooth increase in phase velocity by increasing the pitch of a spiral spiral type in a finite section of the interaction space [6, 7].

A drawback of such a technical solution may be that the frequency of self-excitation on the backward wave approaches the working frequency band, since with an increase in the pitch of a spiral type spiral, the frequency of self-excitation on the backward wave decreases and, therefore, the resistance of the spiral TWT to this self-excitation can decrease, all other things being equal.

The claimed technical solution is aimed at increasing the electronic efficiency, decreasing the second harmonic level and increasing the resistance to self-excitation on the backward wave of broadband TWTs with a retarding spiral system.

The technical result in the claimed technical solution is achieved by the fact that a broadband traveling wave lamp (TWT) contains a retardation system (ZS) of the spiral type with a certain pitch h, an output section with an absorber and a screen having longitudinally conducting ribs parallel to the axis of the lamp, while the output section along the axis of the lamp has a section of length L _uv , on which the gap g between the edges of the screen and the spiral increases from g _min to g _max in the direction from the beginning to the end of the output section, which allows increasing the phase velocity of the wave gradually in the direction toward the output of energy with a simultaneous increase in the bond resistance.

In the general case, each spiral TWT containing a screen with longitudinally conducting ribs can have its own design features. Ribs can vary in shape and size, their number can also be different; dielectric support rods supporting the spiral (rectangular, round, trapezoidal, etc.) may also differ in shape and size. Dielectric support rods can be attached to the lamp shell both independently of the ribs and forming a cermet structure with them (RU 2067335, publ. 09/27/96), and the ribs can be made in the form of metal spraying on the side surfaces of dielectric rods [8].

The gap between the ribs and the spiral can increase smoothly or stepwise, with at least two jumps (steps), which allows to increase the communication resistance, increase the electronic efficiency, the frequency of self-excitation of the spiral TWT on the backward wave and the resistance of the TWT to such self-excitation.

At the same time, in the area of increasing the gap between the edges of the screen and the spiral of the output section, the pitch of the spiral h can be changed to a greater or lesser side or its constancy can be maintained.

By changing the pitch of the helix h, it is possible to obtain the optimal change in the phase velocity simultaneously with the maximum increase in the coupling resistance and thereby achieve the maximum efficiency.

The length of portion L _uv at which the gap between the screen edges and the coil increases, satisfies L 0.2 _{h uv} ≤L ≤L _h

where L _SW - the length of the section of the output section, which is an increase in the gap between the edges of the screen and the spiral;

L _h is the length of the clean (absorber-free) section of the output section, and the maximum gap between the edges of the screen and the spiral satisfies the condition g _max ≥2g _min .

To check the operability of the claimed design, the TWT design was calculated on the basis of a commercially available device operating in the frequency range of 8-18 GHz, a section with a linearly increasing gap was introduced into the output section of it. This area, as in [6, 7], was preceded by a small spasmodic decrease in the pitch of the GL. Next, the step remained constant.

On figa presents a schematic representation of the output section of the spiral TWT.

The output section of the TWT (Fig. 1a) contains an absorber (1), a clean (absorber-free) section (2), on which there is a small stepwise decrease in the pitch of the CS (3), and then a smooth or stepwise increase in the gap between the edges of the screen and the spiral, starting from section A-A (4) and ending with section BB (5).

On figb presents a schematic representation of the TWT spiral with a constant or changing in a smaller or larger step in a section with an increasing gap.

ZS spiral type (figb) contains a section with an initial step (6), with a reduced step (7) and with a constant (8) or changing towards the end (8a) and (8b) step. Section (7) with a smaller step is intended to increase electronic efficiency and further increase the resistance to self-excitation.

On figv presents a schematic cross-sectional view of the screen with longitudinal ribs at the beginning of the section with a variable gap between the ribs and the spiral (section aa) and at the end of it (section bb), where the gap between the ribs and the spiral can be increased all the way to the transition to a smooth screen without edges.

Helix TWT output section comprises a screen with longitudinal conductive ribs (1c), the gap between them and the helix increases continuously or stepwise over a length L from the initial _uv values g _m (9) at the beginning of it (the cross section A-A) to the increased ( 10) or the maximum maximum, in the complete absence of ribs (10a) g _max at the end of it (section BB). This leads to an increase in the phase velocity of the wave in this area (Fig. 1d) with a constant pitch of the spiral. Thus, the phase velocity initially remains constant (11), then decreases stepwise (12) due to a decrease in the helix pitch, and then gradually (13) or stepwise (13a) increases toward the end of the GL segment due to an increase in the gap between the ribs and the helix. As calculations have shown, increasing the gap between the edges of the screen and the spiral in the final section of the output section, which leads to an increase in the phase velocity, is an effective means of reducing the second harmonic level, increasing the electronic efficiency and starting self-excitation currents in the backward wave.

The length of the section with an increasing gap between the edges of the screen and the spiral satisfies the condition

0,2 L _{h uv} ≤L ≤L _h

where L _SW - the length of the plot on which there is an increase in the gap between the edges of the screen and the spiral;

L _h - the total length of the clean (free from the absorber) section of the output section.

The maximum gap between the edges of the screen and the spiral satisfies the condition

g _max ≥2g _min .

Figure 1g shows the change in the phase velocity of the wave, referred to the speed of light, along the length of the output section of the spiral TWT at the lower frequency of the operating range (f _n = 8 GHz).

On figa presents the calculated dependence of the frequency of self-excitation of the output section of the spiral TWT at minus the first spatial harmonic (backward wave) f _-1 from the step of the ES type spiral.

On figb shows the calculated dependence of the frequency of self-excitation f _-1 from the gap between the edges of the screen and the spiral, presented in the form of the difference between the current g and the minimum g _min values of the gap normalized to g _min

The frequency variation interval (marked by dots at the end of the curves) corresponds to the complete absence of edges at the screen at the end of the spiral segment of the spiral type (Fig.2b) and the equivalent change in the pitch of the ES, leading to the same change in phase velocity (Fig.2a). It is seen that with an increase in the ST pitch of a spiral type, the self-excitation frequency decreases by 0.4 GHz, approaching the working frequency band and the frequency of the previous section, and with an increase in the gap between the screen edges and the spiral, the self-excitation frequency, on the contrary, increases by 1.1 GHz, moving away from the working frequency band and from the frequency of the previous section.

The calculations showed that the level of the second harmonic at the lower frequency of the operating range (f _n = 8 GHz) decreased by 6 dB and amounted to -15 dB instead of -9 dB. In this case, the electronic efficiency at the upper frequency (f _in = 18 GHz) increased 1.17 times and amounted to 11.2% instead of 9.6%. The starting self-excitation current in the backward wave due to the spacing of the self-excitation frequencies of sections with a constant and variable gap between the ribs and the helix increased 1.15 times.

Thus, a smooth or stepwise increase in the gap between the ribs and the helix at the end of the output section of the spiral TWT is an effective means of reducing the second harmonic level, increasing the electronic efficiency, and suppressing self-excitation of the broadband spiral TWTs in the backward wave. In this case, the possibility arises (due to an increase in the starting self-excitation current) of increasing the TWT operating current, which allows increasing the TWT output power.

Information sources

1. Demina G.R., Izyumova T.I., Pchelnikov Yu.N. The effect of a screen with anisotropic conductivity on the dispersion properties and the coupling coefficient of a spiral moderator // Electronic Technology. Ser. 1. Microwave Electronics. 1967. Issue 9. S.41-49.

2. Kompfner R. On the operation of the traveling-wave tube at low level // J. Brit. IRE. 1950. Vol. 10. No.7. P.283-289.

3. Ilyina EM, Kudryashov VP, Filatov V.A. Suppression of generation on the backward wave by the section of the fast wave of the space charge // Electronic Technology. Ser. 1, Microwave Electronics. 1993. Issue 3 (457). S.17-22.

4. Ilyina EM, Kuzmin F.P., Morev S.P. Dynamic defocusing of electron flows in high-power spiral traveling-wave tubes with a dispersion type varying in length // Radio Engineering and Electronics. 2006. V. 51, No. 7. S.870-878.

5. Gerchberg R.W., NIclas K.V. The positively tapered traveling-wave tube // IEEE Trans. Electron Devices. 1969. Vol.16. No. 9. P.827-828.

6. Jung S.S., Soukhov A.V., Jia B., Park G.S., and Vasu B.N. Efficiency enhancement and harmonic reduction of wideband helix traveling-wave tubes with positive phase velocity tapering // Jpn. J. Appl. Phys. Jun. 2002. Vol.41. Pt. 1. No.6A. P.4007-4013.

7. Ghosh, T.K., Jakob A., Tokeley A. et al. Optimization of helix pitch profile for broadband mini-TWTs // Dig. 9 ^th IEEE Intern. Vacuum Electron. Conf. (IVEC 2008). Monterey, California, USA. April 22-24, 2008. P.306-307.

8. Sinha A.K., and Basu B.N. Dispersion-Shaping in Helix Slow-Wave Structure Using Metal Fins // J. Institution Electronics and Telecommunication Engineers. India July 1980. Vol. 26. No.7. P.318-320.

Claims (4)

1. A broadband traveling wave lamp (TWT) containing a retardation system (ZS) of the spiral type with a certain step h, an output section with an absorber and a screen having longitudinally conducting ribs parallel to the lamp axis, characterized in that the output section along the lamp axis has a section length L _SW , on which the gap g between the edges of the screen and the spiral increases smoothly or stepwise with at least two jumps (steps) from g _min to g _max in the direction from the beginning to the end of the output section. 2. The broadband traveling wave lamp according to claim 1, characterized in that in the area of increasing the gap between the edges of the screen and the spiral of the output section, the pitch of the spiral h changes. 3. A broadband traveling wave lamp according to claim 1, characterized in that the length of the section on which the gap between the edges of the screen and the spiral is increased satisfies the condition
0,2 L _{h uv} ≤L ≤L _h
where L _SW - the length of the section of the output section, which is the increase in the gap between the edges of the screen and the spiral,
L _h - the length of the clean (free from the absorber) section of the output section. 4. The broadband traveling wave lamp according to claim 1, characterized in that the maximum gap between the edges of the screen and the spiral satisfies the condition g _max ≥2g _min .

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