RU2479882C2 - Wideband lamp of travelling wave with drift channel reducing towards energy output - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: wideband travelling wave lamp (TWL) comprises a moderating system (MS) of a spiral type, which has an area in an output section, where the diameter of the drift channel (internal diameter of the spiral-type MS) is smoothly or unevenly reduced at least with one jump in direction towards energy output. The minimum diameter of the drift channel of the area with the reducing diameter may amount to not more than 0.95 of the initial diameter value, and the minimum pitch on the section of this area shall not exceed the ratio of diameters before and after reduction multiplied by the pitch of the MS area, which precedes the diameter reduction.

EFFECT: increasing of resistance to self-excitation at a backward wave and increasing of electronic coefficient of efficiency of interaction between wideband lamp of travelling wave with a helical moderating system.

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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 eliminating self-excitation on the backward wave and increasing the electronic efficiency of broadband spiral TWTs is still relevant.

Known technical solutions in which the TWT contains a retardation system (ZS) of the spiral type with a variable diameter of the passage channel.

In FR 2365218 (publ. 09/21/1976) the spiral is made in the form of a truncated cone with a continuous increase in internal diameter. The diameter increases due to the transformation of the circular cross section of the spiral into a trihedral in the direction of energy output. Since the fixing dielectric rods have a constant height, the inner diameter of the spiral in the sections between them grows.

In FR 2543734 (published March 31, 1983), fixing rods of constant height are proposed to be inserted into the grooves of the housing, the depth of which increases with increasing diameter of the CS.

The disadvantage of such technical solutions is a significant decrease in the coupling resistance of zero spatial harmonic with an increase in the internal diameter of the CS, which leads to a decrease in electronic efficiency.

In [1] it is said that the problem of suppressing spurious generation on the back wave of high voltage TWTs (with an operating voltage of 11 ... 12 kV) can be solved by simultaneously changing the pitch and diameter of the spiral. However, nothing is said about how they should change in the direction of energy output - increase or decrease.

In DE 3540998 (publ. 21.05.1987) it is proposed to have at least two sections with different inner diameter of the ES and a smooth transition between them. At the same time, it is not indicated which section is located at the exit of the LC, at the collector end, with a larger diameter or with a smaller one. There is no mention of a change in the pitch of the AP.

In WO 2004 / 114350A2 (published on December 29, 2004), in order to increase the efficiency, it is proposed to reduce the diameter of the CS at the output end of the traveling wave lamp, but there are no recommendations for changing the pitch of the spiral.

In US 6356022 B1 (publ. 12.03.2002) it is proposed to change the diameter and, in proportion to it, the pitch of the spiral spiral type according to the linear law, and the change can be made both in the direction of increasing or decreasing these parameters. In this case, the phase velocity of the fundamental harmonic remains unchanged, and only the phase velocities of the remaining, undesirable spatial harmonics change, which leads to their suppression. This relates, first of all, to the minus of the first spatial harmonic, which leads to parasitic self-excitation of the TWT on the backward wave. To increase the efficiency at the exit section of the TWT, it is proposed to introduce a change in the pitch of the CS according to the exponential law, leaving the diameter of the CS constant. The disadvantage of this technical solution is that the ZS diameter is changed only in the input part of the TWT, while the greatest increase in efficiency can be obtained by changing it in the output part of the TWT, while simultaneously suppressing oscillations in the backward wave.

In US 6356023 B1 (publ. 12.03.2002), which is a continuation of the previous source, in addition to it, it is also proposed (to increase the efficiency) to reduce the attenuation of the absorber, since the excitation on the backward wave will be suppressed by changing the diameter of the CS. However, the possibility of this is far from obvious, since the TWT sectioning by introducing absorbers is introduced, first of all, to suppress self-excitation on the reflected direct wave.

The claimed technical solution is aimed at increasing the resistance to self-excitation on the backward wave and increasing the electronic efficiency of the interaction of broadband TWTs with a spiral moderating system.

The technical result in the claimed technical solution is achieved by the fact that a wide-band traveling wave lamp (TWT) containing a retardation system (ZS) of the spiral type has a section at the output whose diameter of the passage channel d (inner diameter of the ZS) on which gradually or abruptly decreases towards energy output. Moreover, the minimum diameter of the passage channel d ₂ can be no more than 0.95 from the diameter of the passage channel to the beginning of the section d ₁ , that is, d ₂ ≤0.95d ₁ . And on the segment of this section, the spiral pitch h ₂ should not exceed the ratio of the diameters before and after reduction, multiplied by the spiral pitch h ₁ before the start of the section with a decreasing diameter, i.e.

On figa presents a diagram of the CS spiral TWT.

ZS spiral TWT (figa) with the initial values of the diameter of the passage channel and the step of the ZS (1) contains a plot (2) with varying values of these parameters.

On figb presents a schematic representation of changes in the diameter of the passage channel (inner diameter of the AP) along the length of the spiral TWT.

The diameter of the passage channel has a constant value (3) and decreases gradually (4) or stepwise (5).

Figure 1c shows a schematic representation of the ST of a spiral TWT with a spiral pitch varying along the length.

ZS spiral type (figv) has a constant step (6) and decreasing smoothly (4) or stepwise (5) step along the length of the spiral TWT.

The maximum allowable ratio of reduced and initial diameters is determined from the condition that the starting current in static mode due to a decrease in diameter increased by at least 1.15 times. As calculations performed in [2] showed, such an increase in the starting current at the jump in the diameter of the passage channel occurs when the frequency ratio of the π-type of the second and first sections is 1.05. At the frequency of the π-type, the phase shift by the ST step is π [3]. Based on the definition of the phase shift [4], we can write:

Here f is the frequency, c is the speed of light in vacuum, v _f is the phase velocity of the microwave signal, h is the helix pitch.

Replacing c / v _Φ in formula (2) with geometric deceleration (πd _cp / h) [4], where d _cp is the average spiral diameter, which is approximately replaced by the internal one, we find the π-type frequency close to the TWT self-excitation frequency by minus the first spatial harmonics f _-1

Since the self-excitation frequency is inversely proportional to the diameter of the passage channel, the maximum ratio of the diameters of the second and first sections (d ₂ / d ₁ ) with a π-type frequency ratio equal to 1.05 will be 0.95. Then the condition, which must meet the minimum diameter of the passage channel d ₂ , is written in the form

Here d ₁ is the diameter of the passage channel to the beginning of the section with decreasing diameter.

It can be seen from formula (3) that the smaller the diameter of the passage channel d, the higher the frequency of self-excitation of TWTs in the backward wave. Thus, with a decrease in the diameter of the passage channel, the frequency of self-excitation on the backward wave increases. And if, say, earlier it could be in the working frequency band, then by reducing the diameter of the span channel it can be taken outside the working frequencies and thereby increase the resistance to self-excitation on the backward wave.

In addition, only a decrease in the diameter of the passage channel in the direction of energy output, in addition to increasing the coupling resistance and providing the maximum difference in phase velocities minus the first spatial harmonic (backward wave) in areas with different channels, makes it possible to realize optimal values of the phase velocities of the zero harmonic of the microwave signal for maximum efficiency. Show it.

Suppose that there are two sections of ZS, 1 and 2, with identical ZS steps h and two different dependences of deceleration (c / v _f ) ₁ and (c / v _f ) ₂ on wavelength λ (in particular, due to different values of the diameter of the span channel). Denote the deceleration with / v _f by n:

Here, indices 0 and -1 refer to zero and minus the first spatial harmonics, and indices 1 and 2 to sections 1 and 2.

The deceleration of the m-th spatial harmonic n _m is determined by deceleration of the zero spatial harmonic n ₀ according to the Rayleigh formula [5]

where m is the number of spatial harmonics.

Then, for minus the first spatial harmonic in sections 1 and 2, we can write

Denoting the difference in deceleration in a direct wave in sections 1 and 2 with the same step h as

from (7) and (7 ') we find

That is, the difference in deceleration by minus the first spatial harmonic in sections 1 and 2 is equal to the difference in decelerations in a direct wave at the same ES step h in both sections.

If now in one of the sections (for example, in section 2) the pitch of the spacer h is changed to h ', then, considering that, within certain limits, the pitch of the spacer is proportional to the deceleration, we can write

Here, all the hatched values are recorded for the plot with a modified pitch.

Then the difference in deceleration is

Given that at the frequency of the π-type n ₀ = -n _-1 , for it we get

That is, the difference in deceleration in the backward wave is not equal to the difference in deceleration in the forward wave.

For the simple case when (n ₀ ) ₁ = (n ₀ ) ₂ (there is no difference in deceleration in a direct wave), we find

When changing the step so that

That is, there is a difference in deceleration in the forward wave, but not in the backward wave.

We turn to the formula (16). If two sections have different spiral diameters, d ₁ and d ₂ , then, ceteris paribus (in particular, with equal steps), if d ₂ > d ₁ , then (n ₀ ) ₂ > (n ₀ ) ₁ and Δn> 0.

With decreasing step (h / h '> 1) so that

and with decreasing step (h / h '> 1) so that

From formulas (16), (22) and (22 ') it follows that, regardless of the degree of step reduction, the inequality

that is, with an increase in the diameter of the passage channel (d ₂ > d ₁ ) and a decrease in the step toward the end of the GL, the difference in deceleration in the forward wave is always greater than in the reverse wave.

With increasing step (h / h '<1) so that

and with increasing step (h / h '<1) so that

From formulas (16), (22``) and (22 ''') it follows that, regardless of the degree of step increase, for d ₂ > d ₁ the inequality

that is, the difference in deceleration in the forward wave is always smaller than in the backward wave.

Consider the case of reducing the diameter of the passage channel to the end of the GL (d ₂ <d ₁ ). With a constant step of the GL (h = h '), the inequality (n ₀ ) ₂ <(n ₀ ) ₁ holds, i.e., Δn <0.

When the step is reduced in section 2, (h / h ')> 1, having performed calculations similar to formulas (21) - (23), we obtain

that is, the difference in deceleration in the forward wave is always smaller than in the backward wave.

With increasing step in section 2, (h / h ') <1, we arrive at the expression

that is, the difference in deceleration in the forward wave is always greater than in the reverse wave.

The most favorable design options for the TWT output section from the point of view of suppressing self-excitation on the backward wave are those in which the difference in deceleration on the backward wave is greater than on the direct wave:

1) d ₂ > d ₁ , (h / h ') <1, i.e. h ₂ > h ₁ ,

2) d ₂ <d ₁ , (h / h ')> 1, i.e. h ₂ <h ₁ .

However, option 1 with an increase in the diameter of the passage channel to the end of the AP is disadvantageous, firstly, due to a decrease in the coupling resistance in the section of increasing diameter, and secondly, because in this section, to increase the efficiency, it is desirable to have an increase in the deceleration of the straight line waves, which is not realized with increasing step h _{2 in} excess of (d ₂ / d ₁ ) h ₁ . Therefore, option 2 is optimal with decreasing the diameter of the passage channel to the end of the AP, where the step h _{2 of the} section with decreasing diameter satisfies the condition h ₂ ≤ (d ₂ / d ₁ ) · h ₁ .

If, with a decrease in the diameter of the passage channel, d ₂ <d ₁ , the condition is satisfied that (h / h ')> [(n ₀ ) ₁ / (n ₀ ) ₂ ], then the difference in decelerations by minus the first spatial harmonic, according to the formula ( 16) will amount to more than 2Δn:

Thus, the option of decreasing the diameter to the end of the SW and decreasing the step is the most resistant to back-wave excitation and the most optimal from the point of view of increasing efficiency.

All of the above is illustrated by the graphs presented in figure 2.

Figure 2a shows the case of a constant helix pitch h = h ₁ = h ₂ with increasing diameter of the passage channel, d ₂ > d ₁ , described by formula (9). It shows the dispersion characteristics (the dependence of deceleration n on frequency) minus the first [d ₁ (-1), d ₂ (-1)] and zero [d ₁ (0), d ₂ (0)] spatial harmonics, the intersection points of which correspond to π-type frequencies. It can be seen that the deceleration in section 2 is larger than the deceleration in section 1. The decelerations at minus the first spatial harmonic differ by the same amount at the same frequency. The π-type frequencies of sections 1 and 2 are also different. All this provides an increase in the resistance of TWT to self-excitation on the backward wave.

Figure 2b shows the dispersion curves for the increasing diameter of the passage channel, d ₂ > d ₁ , and the pitch of the spacer, h ₂ '> h ₁ , when the dispersion curves of zero spatial harmonics for both channels merge with each other. This case is described by formula (18). The difference between the decelerations at minus the first harmonic between sections 1 and 2 is large and, therefore, the resistance to self-excitation in the backward wave is high. But at the same time, the dispersion curve minus the first harmonic in section 2 is shifted toward lower frequencies and may be in the working band, which may impede the increase in resistance to self-excitation. In addition, by reducing the coupling resistance, the efficiency will decrease. If we change the indices 1 and 2 in fig.2b in places, then it will describe the case of decreasing diameter and step to the end of the AP. In this case, due to an increase in the coupling resistance, the efficiency will increase and the resistance to self-excitation on the backward wave will be high.

Figure 2c shows the dispersion curves for the increasing diameter of the passage channel, d ₂ > d ₁ , and the decreasing pitch of the spacer, h ₂ '<h ₁ , when the dispersion curves minus the first spatial harmonic for both channels merge with each other. This case is described by formulas (19), (20). For him, no increase in resistance to self-excitation will occur, although the jump in deceleration in a direct wave is very large.

Figure 2g shows the dispersion curves of zero and minus the first spatial harmonics (forward and backward waves) for the diameter of the passage channel decreasing towards the end of the ZS, d ₂ <d ₁ , and the decreasing step of the ZS, h ₂ '<h ₁ , when the deceleration of zero harmonic is growing. This case is described by relation (24). Here, the difference in phase velocities minus the first harmonic is quite large, and its dispersion curve for section 2 is shifted toward higher frequencies. All this provides high resistance to self-excitation on the backward wave. By reducing the diameter, the coupling resistance increases, and, consequently, the efficiency, which also increases due to an increase in the deceleration of the direct wave towards the end of the GL.

Thus, it is precisely the reduction in the diameter of the passage channel (the internal diameter of a spiral coil type ES) in a certain TWT section before the energy output, in combination with a smaller pitch of the CS that provides the strongest increase in the resistance to self-excitation in the backward wave while increasing the electronic efficiency.

Information sources

1. Fleury G., Devillé C, and Kuntzmann J.-C. Average power limits of brazed-helix TWT's // Intern. Electron Devices Meet. Washington, D.C. - New York, 1980. P.806-809.

2. Ilyina E.M., Mitezhnikov S.A., Polyakov I.V. Powerful broadband traveling wave lamp with jumps in diameter of the passage channel. // Radio engineering and electronics. 2007. V. 52, No. 8. S.1018-1023.

3. Kudryashov V.P. Side fluctuations in broadband LBVO (according to the paternal and foreign press for 1952-1972): Reviews on electronic technology. - M.: Central Research Institute "Electronics", 1977. Ser. 1, Microwave Electronics. Issue 3 (442). 85 sec

4. Silin R.A., Sazonov V.P. Slow down systems. - M .: Owls. Radio, 1966.632 s.

Claims (1)

A traveling-wave broadband lamp (TWT) containing a spiral system (ZS) of the spiral type, characterized in that it has a section at the exit whose span channel diameter d (inner diameter of the ZS) decreases smoothly or stepwise towards energy output, with the minimum diameter the span channel d ₂ in the section satisfies the condition d ₂ ≤0.95d ₁ , and the spiral pitch in the segment of this section h ₂ satisfies the condition h ₂ ≤ (d ₂ / d ₁ ) · h ₁ , where d ₁ and h ₁ is the diameter of the span channel and spiral pitch to the area with decreasing diameter, respectively.

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