JPS6110938B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention makes the phase velocity of electromagnetic waves near the collector side end, ie, the output end, of a traveling wave tube, particularly a slow wave circuit, smaller than the phase velocity near the electron gun side end, ie, the input end. This invention relates to a traveling wave tube that enhances the interaction between electron beams and electromagnetic waves and improves efficiency. As is well known, in traveling wave tubes,
An electromagnetic wave propagates on a slow-wave circuit having a periodic structure at a phase velocity in the tube axis direction of about 1/10 of the speed of light, and an electromagnetic wave propagates along the tube axis at a synchronous speed slightly larger than the phase velocity of this electromagnetic wave. The electron beam traveling in the direction interacts with the electron beam, and as a result, the kinetic energy of the electron beam is converted into electromagnetic wave energy, resulting in an electromagnetic wave amplification effect.

However, in accordance with the kinetic energy of the electron beam, the electron beam velocity decreases as the energy conversion into electromagnetic waves occurs as a result of the interaction. Therefore, the fixed wave phase velocity determined by the period of the slow wave circuit and the electron beam velocity no longer satisfy a synchronous relationship, and the conversion efficiency finally reaches saturation at a certain value according to the electromagnetic wave output. To eliminate this limitation in conversion efficiency common to types of equipment that convert the kinetic energy of an electron beam to electromagnetic energy, in traveling wave tubes
As a result of the interaction with electromagnetic waves, the electron beam's velocity decreases, and the phase velocity of the electromagnetic waves also decreases.
A method of increasing conversion efficiency by maintaining a synchronized relationship between the two has been well known. In other words, the phase velocity of an electromagnetic wave propagating on a slow-wave circuit with a periodic structure is determined by its period, and by utilizing the fact that the smaller the period, the smaller the phase velocity becomes, the interaction of the electromagnetic wave with the electron beam can be dramatically reduced. This is a method in which the frequency near the output end of the strengthened traveling wave tube is made smaller than the period near the input end. Traveling wave tubes manufactured by such a method were described in IEEE
Transactions on Electron Devices) No. 441~
It is described on page 447.

However, in this type of conventional traveling wave tube in which the slow wave circuit includes a phase speed reduction section, the slow wave circuit is usually An attenuator made of electromagnetic wave absorbing material is installed near the center, but sufficient consideration was not given to its installation location. That is,
In the conventional example, the ratio of the length of the phase velocity reduction section to the length from the collector side end of the attenuator (terminal end of the attenuator) to the electron gun side end of the phase velocity reduction section (starting end of the phase velocity reduction section) is usually chosen to be 1.0 or higher (“Calculation of Coupled Cavity TWT
Performance”in October1975issue of IEEE
Transactions on Electron Devices at
pages 880-890), an example of at most 0.52 (JA
Christensen and Dr.I.Tammaru“Development
of a 200W CW High Efficiency Traveling
−wave Tube at12GHZ”NASA−CR−134734,
Pages22-23) to some extent. Therefore, the interaction between the electron beam and the electromagnetic waves is adversely affected by the attenuator, and a sufficiently high conversion efficiency cannot be obtained. Therefore, an object of the present invention is to appropriately select the ratio of the length of the phase velocity reduction section to the length from the collector side end of the attenuator to the beginning of the phase velocity reduction section, thereby increasing the conversion efficiency of the attenuator. The object of the present invention is to provide a highly stable and highly efficient traveling wave tube that eliminates adverse effects. The traveling wave tube according to the present invention has a constant phase velocity section which is disposed close to the electron gun side and gives a constant phase velocity to electromagnetic waves propagating along the tube axis, and a constant phase velocity section which is disposed close to the collector side. a phase velocity that gives the electromagnetic wave a phase velocity smaller than the constant phase velocity. and a phase velocity reduction section corresponding to the length from the collector side end of the oscillation prevention attenuator installed near the center of the slow wave circuit to the electron gun side end of the phase velocity reduction section. It is characterized by having a length ratio of less than 0.4. This invention appropriately selects two parameters, the length of the phase velocity reduction part of the slow wave circuit and the ratio of the phase velocity at the output end to the phase velocity at the input end, and also the position of the phase velocity reduction part with respect to the oscillation prevention attenuator. The selection of the ratio of the length of the phase velocity reduction section to the length from the collector side end of the attenuator to the electron gun side end of the phase velocity attenuation section is extremely important for improving the conversion efficiency of the traveling wave tube. It is based on the fact that certain things have become clear as a result of calculations and experiments.

Next, the reason why the conversion efficiency is improved in the traveling wave tube of the present invention will be described. In order for this type of traveling wave tube to operate most efficiently, the starting end position of the phase velocity reduction section should be set at a position where a saturated output can be obtained even if there is no phase velocity reduction section. It has been discovered by other researchers (O.
Sauseng, “Efficiency Enhancement of
Traveling Wave Tubes By Velocity
Resynchronization” MOGA68, Pages 16−20,
VDE-Verlag-GMBH) It was further confirmed by various numerical calculations by the inventor. Although the optimal length of the phase velocity reduction section will vary for each individual traveling wave tube and must be determined by specific numerical calculations, its optimal length will vary within the normal operating parameter range of traveling wave tubes. As a result of various numerical calculations conducted by the inventors, it has become clear that ? exists in the following range.

1≦βeCZ ₂ ≦3 (1) Here, βe is the phase constant of a wave with the same velocity as the initial velocity of the electron beam, C is the gain parameter of the traveling wave tube, and Z ₂ is the length of the phase velocity reduction section. In other words, the central term in equation (1) represents the normalized length of Z ₂ . In addition, in order to prevent the interaction between the electron beam and electromagnetic waves from being adversely affected by the oscillation prevention attenuator, the length must correspond to the length from the collector side end of the attenuator to the position where saturated output is obtained. It is also a well-known fact that a gain of 26 dB or more is required. Further, in order to prevent oscillation caused by discontinuity of the circuit at the beginning of the phase velocity reduction section, it has been found through experiments that the gain of this section must be 50 dB or less. Therefore, the gain corresponding to the distance Z from the collector side end of the attenuator to the position where the saturated output is obtained (from the above, this position should be the starting position of the phase velocity reduction section) BC(βe/2π)Z ₁
is subject to the following restrictions:

50≧BC(βe/2π)Z ₁ ≧26 (2) Here, B is an increased wave parameter and is usually about 32 dB.

From equations (1) and (2), Z ₂ /Z ₁ ≦3・B/163=96/163<
0.6(3) Equation (3) shows that in a traveling wave tube in which the slow wave circuit includes a phase velocity reduction section, the magnitude of the saturated output is not reduced by the oscillation prevention attenuator and high conversion efficiency is achieved. According to this, the ratio of the length of the phase velocity reduction part to the length from the end of the collector side of the attenuator to the beginning of the phase velocity reduction part is less than 0.6. Indicates that it must be small. Furthermore, in order to investigate how the conversion efficiency changes in the range of Z ₂ /Z ₁ shown by equation (3), a computer simulation was performed using a variable diameter disk model of the electron beam and based on the large signal theory of traveling wave tubes. I went there. In this simulation, parameters other than Z ₂ /Z ₁ were adjusted to maximize conversion efficiency. The ratio of the output Po with a phase speed reduction section to the output Pu when there is no phase speed reduction section Po/Pu
Figure 1 shows how Z ₂ /Z ₁ changes. From this figure, it can be seen that as Z ₂ /Z ₁ decreases from around 0.6, the conversion efficiency begins to improve and when it becomes 0.4 or less, the degree of improvement becomes extremely significant. In addition, as conditions for stable operation without oscillation, (1) and (2)
Since the lower limit of Z ₂ /Z ₁ is determined from the formula, the optimal condition for Z ₂ /Z ₁ is expressed by the following formula.

0.1<Z ₂ /Z ₁ ≦0.4 (4) In other words, the ratio of the length of the phase velocity reduction section to the length from the collector side end of the attenuator to the start end of the phase velocity reduction section should be greater than 0.1 and less than or equal to 0.4. is extremely important for improving the conversion efficiency of the tube.

Next, an embodiment of the present invention will be described using a spiral traveling wave tube with reference to the drawings.

As shown in FIG. 2, the electron beam 16 is connected to the electron gun 1
The electromagnetic wave is formed by injection at a collector 3, travels close to the slow wave circuit 2, interacts with the electromagnetic waves propagating on the slow wave circuit 2, and is finally collected by the collector 3. The electromagnetic wave is input from the input end 5 of the slow wave circuit 2, absorbs energy from the electron beam while propagating on the slow wave circuit 2, is amplified, and is output from the output end 8. The slow wave circuit 2 is divided into two parts: a part 17 having a constant phase velocity from the input end 5 to the position 9, and a phase velocity reduction part 11 having a smaller phase velocity from the position 9 to the output end 8. Phase speed reduction section 11
The period of the slow wave circuit at is smaller than the period at section 17. Near the starting end 9 of the phase velocity reduction section 11, the period changes in a tapered manner to avoid sudden changes. The attenuator 4 is introduced to prevent oscillation caused by impedance mismatch at the input and output terminals 5 and 8 of the slow wave circuit 2, and provides sufficient attenuation for electromagnetic waves propagating on the slow wave circuit 2. of the electron beam, but does not affect the modulation current of the electron beam. Therefore, after passing through the attenuator 4, electromagnetic wave energy is induced in the circuit, and interaction between the two begins again. The normalized length βeCZ ₂ of the phase velocity reduction section 11 is 2.0, and the gain corresponding to the length Z ₁ of the portion 10 from the collector side end 7 of the attenuator 4 to the starting end 9 of the phase velocity reduction section 11 is 30 dB. Z ₂ /Z ₁ is
It is 0.34. And the starting end 9 of the phase velocity reduction section 11
is located at a position where a saturated output can be obtained if the phase velocity reduction section 11 is not provided.

In Figure 3, the horizontal axis represents the length L along the tube axis of the slow wave circuit 2, and the vertical axis represents the phase velocity V of each part of the slow wave circuit at the input end 5.
The values are normalized by the phase velocity V0 at .

Curve 12 shows the change in phase velocity of the traveling wave tube according to the present invention, and curve 13 shows an example of the same kind of traveling wave tube that could only obtain a conventional low conversion efficiency. The numbers on the horizontal axis correspond to the numbers in FIG. V/V0 from the input end 5 to the starting end 9 of the phase velocity reduction section 11 is 1, and the phase velocity reduction section 1
1, the period is getting smaller, so V/V0 is 1
smaller, V/V0 at output 8 is 0.8. Further, since the period changes in a tapered manner near position 9, the phase velocity also changes in a tapered manner. In the case of curve 12, the ratio of the length Z ₂ of part 11 to the length Z ₁ of part 10 is 0.34;
3, this ratio is greater than 1.0.

The horizontal axis in FIG. 4 represents the length L along the tube axis as in FIG. 3, and the numbers correspond to the numbers in FIGS. 2 and 3. The vertical axis represents the magnitude of electromagnetic wave output. Curve 14 shows the change in output along the tube axis of the traveling wave tube according to the invention, and is similar to curve 12 in FIG.
It corresponds to the case of Curve 15 corresponds to the case of curve 13 in FIG. After the output is once attenuated by the attenuator 4, it begins to amplify again and once reaches saturation at the starting end 9 of the phase velocity reduction section 11. However, since the phase velocity of the electromagnetic wave also decreases from there, the electron beam and the electromagnetic wave regain synchronization again, and the electromagnetic wave output increases and reaches saturation again at the output end 8. In the case of curve 15, the length Z 1 between the starting end 9 of the phase velocity reduction section 11 and the end 7 on the collector side of the attenuator ₄ is too small, and the length Z ₂ of the phase velocity reduction section 11 is too large. As a result, the ratio (Z ₂ /Z ₁ ) becomes larger than 1.0, resulting in only a low conversion efficiency. In the case of curve 14, the output, that is, the conversion efficiency, increased by 1.6 times compared to a traveling wave tube having a slow wave circuit with a uniform period. Although this improvement in conversion efficiency is somewhat lower than the calculated value shown in FIG. 1, the effect of the improvement is significant. On the other hand, in the case of curve 15, it was almost the same as that of the uniform period. In this case, when the velocity distribution of the electron beam incident on the collector 3 is investigated by changing the potential of the collector 3, it is found that although the output is almost the same as in the case of uniform synchronization, the electron beam has a lower speed. Electrons are present and the velocity distribution is expanding. This clearly shows that the conversion efficiency was adversely affected by the attenuator 4. As can be seen from the above, according to the present invention, the conversion efficiency can be significantly improved by the oscillation prevention attenuator without being adversely affected.

The present invention is not only applicable to the traveling wave tube shown in the figure, but also can be applied to the electromagnetic wave near the output end of the slow wave circuit without changing the slow wave circuit period or by using other methods and changing the period. It is clear that the present invention is applicable to all traveling wave tubes having phase velocity reduction means whose phase velocity is smaller than the phase velocity near the input end. Further, although the slow-wave circuit of the traveling-wave tube in this embodiment is made of a spiral wire, it is obvious that the present invention can also be applied to a traveling-wave tube using a slow-wave circuit constructed of a coupled cavity array, for example. be.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the improvement in conversion efficiency of the present invention;
FIG. 2 is a schematic diagram of a traveling wave tube according to the present invention, and FIG.
The figure is a diagram showing the change in phase velocity of each part of the slow wave circuit along the tube axis, and FIG. 4 is a diagram showing how the output increases along the tube axis. DESCRIPTION OF SYMBOLS 1... Electron gun, 2... Slow wave circuit, 3... Collector, 4... Attenuator for preventing oscillation, 5... Slow wave circuit input end, 6... End of attenuator on the electron gun side, 7 ……
Collector side end of the attenuator, 8... Slow wave circuit output end, 9... Start end of the phase speed reduction section, 10... Portion from the collector side end of the attenuator to the phase speed reduction section start end, 11 ...Reduced phase velocity section, 16...
...electron beam.

Claims (1)

[Scope of Claims] 1. An electron gun that emits an electron beam, a collector that collects the electron beam, and an electron beam disposed between the electron gun and the collector for causing interaction between the electron beam and electromagnetic waves. In a traveling wave tube comprising a slow wave circuit and an oscillation prevention attenuator disposed along the slow wave circuit, the slow wave circuit is disposed close to the electron gun side and transmits waves along the tube axis. a constant phase velocity part that gives a constant phase velocity to the electromagnetic wave;
a phase velocity reducing section disposed close to the collector side and giving the electromagnetic wave a phase velocity smaller than the constant phase velocity; A traveling wave tube characterized in that the ratio of the length of the phase velocity reduction part to the length to the gun side end is selected to be 0.4 or less. 2. Claim 1, wherein the ratio of the length of the decreasing phase velocity reducing section to the length from the collector side end of the oscillation prevention attenuator to the electron gun side end of the decreasing phase velocity reducing section is greater than 0.1. The traveling wave tube described. 3. Claim 2, characterized in that the electron gun side end of the phase velocity reduction section is disposed at a position of the slow wave circuit where a saturated output can be obtained in a traveling wave tube that does not have a phase velocity reduction section. The traveling wave tube described. 4. The traveling wave tube according to claim 3, wherein the slow wave circuit of the traveling wave tube is constituted by a helix. 5. The traveling wave tube according to claim 3, wherein the slow wave circuit of the traveling wave tube is constituted by a coupled cavity.