JPS6336103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a traveling wave tube having a helical slow wave circuit provided with a velocity taper for suppressing backward wave oscillation.

As is well known, a traveling wave tube consists of an electron gun section for emitting an electron beam, a slow wave circuit section where the electron beam and electromagnetic waves interact, and a collector for collecting electrons that have finished interacting with the electromagnetic waves. an electromagnetic wave input section for guiding the electromagnetic waves to the slow wave circuit section;
It consists of an electromagnetic wave extraction section for extracting electromagnetic waves from the slow wave circuit to the outside. Among these, the slow wave circuit reduces the phase velocity of the electromagnetic wave input from the electromagnetic wave input section to almost the same speed as the electron beam,
By maintaining a synchronized relationship between the two, an amplification effect is caused. Depending on the structure, there are several types, such as helix-type slow-wave circuits and coupled cavity-type slow-wave circuits. The present invention relates to a helical slow wave circuit.

Traditionally, helix-type slow-wave circuits have been used as slow-wave circuits in relatively low-power or medium-power high-frequency amplifier tubes because of their structural simplicity compared to coupled cavity-type slow-wave circuits and other slow-wave circuits. However, because it has a structure in which a helix wound with thin wire is supported by a dielectric material with low thermal conductivity, it is thermally weak, and furthermore, when operated at high frequency and high power, it causes backward wave oscillation. It was not used as a high-frequency, high-power amplifier tube. However, in recent years, due to technical advances in helical traveling wave tubes, thermal problems are being solved, and along with this, it has become necessary to suppress backward wave oscillation.

According to electromagnetic field analysis of helices, helices can propagate many spatial harmonics in addition to the fundamental wave with positive phase velocity and positive group velocity used for actual amplification. Backward wave oscillation, which is a problem in helical traveling wave tubes, occurs when the phase velocity is positive and the group velocity is negative (n = -
1) It is caused by the interaction between the backward wave component of the spatial harmonic and the electron beam. This (n=-1)
The next spatial harmonic component is the phase constant ka (=
ωa/c, ω is the angular frequency of electromagnetic waves, c is the speed of light,
a represents the average radius of the helix). Therefore, in a helical traveling wave tube with high frequency and high power, the propagation constant γa (=
ωa/v _p ; ω is the angular frequency of the electromagnetic wave, v _p is the phase velocity of the electromagnetic wave, and a is the average radius of the helix) must be selected between a certain value (1.0 to 2.0), and the beam transmission Since the operating voltage needs to be increased due to the requirement of

Currently, three types of methods have been proposed as methods for suppressing this backward wave oscillation. The first method is
IEDM (IEDM) published in December 1978
By using the method described above, by baking a meander line-shaped electromagnetic wave absorber onto the dielectric material used to support the helix, it is possible to selectively attenuate the nearby frequencies that cause backward wave oscillation, thereby suppressing backward wave oscillation. do. In this method, in addition to the backward wave oscillation frequency,
Since it provides considerable attenuation to all frequencies other than the fundamental wave band used, good operating characteristics as a tube can be expected. However, the technique of printing a meander line-shaped electromagnetic wave absorber onto a dielectric material is extremely difficult and impractical. The second method is described in US Pat. No. 3,761,760 (registered September 25, 1973), and is a method in which a special speed taper is provided in the output slow wave circuit. This method is based on the idea that when an electromagnetic wave interacts with the fast space charge wave of an electron beam, the energy of the electromagnetic wave is absorbed by the electron beam. By combining the backward wave and the slow wave of the space charge wave of the electron beam on the high-frequency attenuator side, backward wave oscillation can be suppressed. However, this method requires a speed taper of about 20%, which deteriorates the matching characteristics for the fundamental wave.In addition to the length required for fundamental wave amplification, it is necessary to provide a speed taper of about 20%. requires a length of
There are disadvantages such as the length of the tube.

The third method is the method described in Japanese Patent Application No. 101450/1984, and is the same as the second method in that the output side slow wave circuit is provided with a speed taper, but the concept of suppressing backward wave oscillation is different. Therefore, the backward wave oscillation is (n=
-1) This occurs when the backward wave component of the next spatial harmonic and the electron beam combine, so the frequency range in which they interact is very narrow compared to the frequency range in which the fundamental wave and the electron beam interact. We are focusing on this. This method is practical because it allows the use of a velocity taper within a range that does not significantly affect the operation of the fundamental wave.

An object of the present invention is to provide a practical traveling wave tube that suppresses backward wave oscillation with a simple configuration.

According to the present invention, in the third method, the ratio of the length L ₁ of the slow wave circuit of the speed taper section to the length L ₂ of the slow wave circuit on the entire output side is set according to the operating current I _cpl . As a result, it is possible to obtain a traveling wave tube that suppresses backward wave oscillation and has a velocity taper that is optimal for operation as a traveling wave tube. More specifically, in a traveling wave tube consisting of an electron gun, a collector, an electromagnetic wave input section, an electromagnetic wave extraction section, and a slow wave circuit divided in high frequency by an electromagnetic attenuator in the middle, an electromagnetic wave attenuator and an electromagnetic wave extraction section are used. A slow wave circuit between the electromagnetic wave input part and the electromagnetic wave attenuator has a circuit period P ₁ larger than the circuit period P ₀ , a slow wave circuit with a small circuit period P 2, and a slow wave circuit between the electromagnetic wave input section and the electromagnetic wave attenuator with a circuit period P ₁ larger than 0, and a slow wave circuit with a circuit period P 2 larger than Backward wave oscillation starting current (I stp ) when an output-side slow wave circuit is configured with a speed taper section that changes with the circuit period and the average circuit period ((P ₁ + P ₂ )/2) in the speed taper _section . Between the ratio of the operating current (I _cpl ) and the ratio of the length of the slow wave circuit in the speed taper section (L ₁ ) to the length of the slow wave circuit on the output side (L ₂ ), L ₁ /L ₂ A traveling wave tube characterized in that the following inequality (I _cpl /I _stp )<13.3×(L ₁ /L ₂ )+6.7 holds true is obtained. Furthermore, a slow wave circuit divided in terms of high frequency may be provided by a plurality of electromagnetic wave attenuators.

Embodiments of the present invention will be described using the drawings. 1st
The figure is a schematic diagram of a helical traveling wave tube according to the invention. In the figure, 1 is an electron gun, 2 is an electromagnetic wave input section, 3 is an input slow wave circuit, 4 is an electromagnetic wave attenuator, 5 is the collector side end of the attenuator, and 6 is the attenuator side of the output slow wave circuit. , 7 is a speed taper part, 8 is a collector side part of the output side slow wave circuit, 9 is an output side slow wave circuit, 10 is an electromagnetic wave extraction part, 11 is a collector,
12 represents an electron beam.

In the case of a fundamental wave, as shown in the figure, the electron beam 12 emitted from the electron gun 1 interacts with the high frequency signal that has entered through the electromagnetic wave input section 2, the high frequency signal is amplified, and the electron beam 12 is modulated while passing through the collector. Proceed to the 11th side. On the way, the high-frequency signal is almost attenuated by the electromagnetic wave attenuator 4, but immediately after leaving the high-frequency attenuator 4, a high-frequency signal is induced in the attenuator side 6 of the output slow-wave circuit by the modulated electron beam. The electromagnetic wave is then interacted with the electron beam 12 again, amplified, and taken out from the electromagnetic wave extraction section 10. In addition, in the case of a backward wave oscillation component of the (n=-1)th order spatial harmonic, it has a frequency that is synchronized with the speed of the electron beam 12 generated by thermal disturbance in the slow wave circuit near the electromagnetic wave extraction section. =-1) The backward wave component energy of the spatial harmonic is amplified by interacting with the electron beam 12 while traveling in the opposite direction, and finally, the energy of the backward wave component of the spatial harmonic is amplified.
absorbed by. At this time, if the backward wave gain becomes infinite before reaching the electromagnetic wave extraction section, the tube will cause backward wave oscillation.

Here, in the output side slow wave circuit 9, the circuit period P ₁ of the attenuator side part 6 is larger than the circuit period P ₀ synchronized with the electron beam in the input side slow wave circuit 3, and If a speed taper is provided approximately in the center of the circuit so that the circuit period P ₂ of the collector side portion 8 is smaller than the period of the input side slow wave circuit 3,
Backward wave oscillation can be suppressed, and nonlinear distortion can also be improved. Here, the difference between P ₁ and P ₀ , and the difference between P ₀ and P ₂ are
The larger the value, the lower the degree of coupling to the fundamental wave, and the longer the circuit length L ₂ must be in order to obtain a predetermined gain. On the other hand, for backward wave oscillation, P ₁ and
Even if the difference between P ₀ or the difference between P ₀ and P ₂ is increased beyond a certain level, it will not have much effect. This means (P ₁ -
Taking P ₂ )/P ₀ as the horizontal axis, the ratio of backward wave oscillation starting current I _stp without speed taper to backward wave oscillation starting current I _st when speed taper is provided, (I _st /I _stp )
This is clear from Figure 2, where the vertical axis is . The present invention further advances the above-mentioned method, and the minimum value A after the rise of (I _st /I _stp ) in _FIG . Clarify the relationship of the ratio of length L ₁ (L ₁ /L ₂ ) and calculate I _stp
and collector current I _cpl (I _cpl /I _stp ).

The inventor calculates (P ₁ − P ₂ )/(I _st /I _stp ) for P ₀
Regarding the relationship, a number of calculations were performed using the ratio (L ₁ /L ₂ ) of the length L ₁ of the velocity tapered portion to the total length L ₂ of the output side slow wave circuit 9 as a parameter, and (L ₁ /
If L ₂ ) is small, I _st /I _stp in Figure 2
The value B of rising (P ₁ - P ₂ )/P ₀ is small,
In addition, the minimum value A after rising also becomes smaller,
When (L ₁ /L ₂ ) is large, the value B of (P ₁ - P ₂ )/P ₀ when (I _st /I _stp ) rises is also large, and the minimum value of (I _st /I _stp ) after rising is also large. It turns out that the value A is also large. Therefore, if the ratio of collector current I _cpl to I _stp (I _cpl / I _stp ) is small, (L ₁ /L ₂ ) should be small and the length of the output side slow wave circuit can be adjusted by speed tapering. A predetermined gain can be obtained without increasing the length. Furthermore, when (I _cpl /I _stp ) is large, (L ₁ /L ₂ ) is increased to suppress backward wave oscillation. At this time, the length of the output side slow wave circuit is (L ₁ /
L ₂ ) is somewhat longer than when L 2 ) is small.

FIG. 3 shows the relationship between (L ₁ /L ₂ ) and the minimum value A after (I _st /I _stp ) in FIG. 2 rises. In the figure, a straight line that approximately represents a point is given by the following equation.

I _st /I _stp = 13.3・(L ₁ /L ₂ ) + 6.7 ...(1) Therefore, when the collector current I _cpl in an actual helical traveling wave tube is provided with a speed taper, backward wave oscillation occurs. Since backward wave oscillation is suppressed if I _st is smaller than the collector current that starts , the speed taper can be set to satisfy the inequality given by the following equation.

I _cpl /I _stp <13.3・(L ₁ /L ₂ )+6.7……(2) If the values of L ₁ /L ₂ are set to satisfy formula (2),
It is possible to obtain an optimum speed taper for suppressing backward wave oscillation according to the value of (L _cpl /I _stp ).

Furthermore, the speed taper according to the present invention is applicable not only to the output side slow wave circuit when the slow wave circuit is divided by one electromagnetic wave attenuator, but also when the slow wave circuit is divided by a plurality of electromagnetic wave attenuators. slow wave circuit between the electromagnetic wave extraction part and the electromagnetic wave attenuator when
It is also applicable to slow wave circuits between electromagnetic wave attenuators.

[Brief explanation of drawings]

FIG. 1 shows a schematic diagram of a traveling wave tube according to the invention. Figure 2 shows the change in I _st /I _stp with respect to (P ₁ - P ₂ )/P ₀ . Figure 3 shows I _st /I _stp in Figure 2.
It shows the change in the minimum value A with respect to L ₁ /L ₂ after the rise. 1... Electron gun, 2... Electromagnetic wave input section, 3... Input side slow wave circuit, 4... Electromagnetic wave attenuator, 5... Collector side end of attenuator, 6... Attenuation of output side slow wave circuit 7... Speed taper part, 8... Collector side part of the output side slow wave circuit, 9... Output side slow wave circuit,
10... Electromagnetic wave extraction section, 11... Collector,
12...Electron beam.

Claims (1)

[Scope of Claims] 1. A traveling wave tube having an electron gun, a collector, an electromagnetic wave input section, an electromagnetic wave extraction section, and a slow wave circuit divided in high frequency by an electromagnetic wave attenuator midway, wherein the electromagnetic wave attenuator and the electromagnetic wave attenuator a slow wave circuit between the electromagnetic wave extraction section, a slow wave circuit with a circuit period P ₁ larger than the circuit period P ₀ of the slow wave circuit between the electromagnetic wave input section and the electromagnetic wave attenuator, and a slow wave circuit with a smaller circuit period P ₂ ;
Start of backward wave oscillation when the output side slow wave circuit is configured with a speed taper section that changes from a large circuit period to a small circuit period, and the average circuit period ((P ₁ + P ₂ )/2) in the speed taper section Current (I _stp )
, the ratio between the operating current (I _cpl ) and the ratio L ₁ /L ₂ between the length of the slow wave circuit of the speed taper section (L ₁ ) and the length of the slow wave circuit on the output side (L ₂ ). A traveling wave tube characterized in that the following inequality I _cpl /I _stp <13.3×(L ₁ /L ₂ )+6.7 holds true. 2. The traveling wave tube according to claim 1, characterized in that it has a slow wave circuit divided in terms of high frequency by a plurality of electromagnetic wave attenuators.