JPS6226137B2 - - 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. and an electromagnetic wave extraction section for guiding the electromagnetic waves to the slow wave circuit section. Among these, the slow wave circuit causes an amplification effect by reducing the phase velocity of the electromagnetic wave input from the electromagnetic wave input section to almost the same speed as the electron beam and maintaining a synchronized relationship between the two. , helix type slow wave circuit,
There are several types, including coupled cavity 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, it is thermally weak because it has a structure in which a helix wound with thin wire is supported by a dielectric material with low thermal conductivity, and furthermore, when operated at high frequency and high power, it causes backward wave oscillation. However, 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) This 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 in free space
It increases with an increase in ka (=ωa/c, where ω is the angular frequency of the electromagnetic wave, c is the speed of light, and a is the average radius of the helix). The phase constant βa (=
(ωa/vpiω is the angular frequency of the electromagnetic wave, vp is the phase velocity of the electromagnetic wave, and a is the average radius of the helix) must be selected within a certain range (1 to 2), and the operation is determined by the requirements of output power and beam focusing. Since it is necessary to increase the voltage, the value of ka increases, and therefore backward wave oscillation is more likely to occur.

Conventionally, two types of methods have been proposed as methods for suppressing this backward wave oscillation. The first method is
This is a method announced at IEDM in December 1978, which produces backward wave oscillation by baking meander line-shaped electromagnetic wave absorbers onto the dielectric material used to support the helix. Provides selective attenuation to nearby frequencies to suppress backward wave oscillation. This method provides considerable attenuation not only to the backward wave oscillation frequency but also to all frequencies other than the used band of the fundamental wave, so 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 the method described in US Pat. No. 3,761,760 (registered September 25, 1973), 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 oscillation frequency and the fast wave of the space charge wave of the electron beam on the electromagnetic wave attenuator side, backward wave oscillation can be suppressed. However, with this method, it is necessary to provide a velocity taper with a phase velocity ratio of about 20%, which deteriorates the matching characteristics for the fundamental wave. It requires a length to suppress oscillation, and has drawbacks such as a longer tube.

An object of the present invention is to provide a helical traveling wave tube that can effectively suppress backward wave oscillation.

The method of suppressing backward wave oscillation according to the present invention is the same as the second method described above in providing a speed taper in the output side slow wave circuit, but the concept of suppressing backward wave oscillation is different, and the backward wave oscillation is n=-1) Since the backward wave component of the next spatial harmonic and the electron beam are combined, the frequency range in which they interact is smaller than the frequency range in which the fundamental wave and the electron beam interact. We are focusing on something very narrow. 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.

According to the present invention, in a traveling wave tube comprising 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 in the middle, the electromagnetic wave attenuator and the electromagnetic wave extraction section are provided. The slow-wave circuit between the electromagnetic wave input section and the electromagnetic wave attenuator is divided into 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 ). , consists of three parts: 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) at the collector side end of the electromagnetic wave attenuator and the speed taper section. The length of the slow wave circuit (L ₁ ) between the position in the tube axis direction that gives the average circuit period, and the length (L ₂ ) of the slow wave circuit between the position in the tube axis direction and the electromagnetic wave extraction part that gives the average circuit period. Ratio (L ₁ /L ₂ )
is between 0.6 and 2, and the ratio of the difference between the large circuit period and the small circuit period to the average circuit period (2・(P ₁ − P ₂ )/(P ₁ + P ₂ )) is between 0.04 and 0.14. A helical traveling wave tube is obtained which is characterized by the following.

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, 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 flowing toward the collector 11. proceed. 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. and interacts with the electron beam 12 again,
It is amplified and taken out from the electromagnetic wave extraction section 10. At this time, the circuit period (P ₁ ) of the attenuator side part 6 of the output side slow wave circuit is set larger than the circuit period (P ₀ ) synchronized with the electron beam in the input side slow wave circuit 3, and Collector side part 8 of the wave circuit
The circuit period (P ₂ ) is set to be smaller than the input side slow wave circuit period. With this setting, nonlinear distortion can be improved without deteriorating the electron beam efficiency with respect to the fundamental wave, compared to a traveling wave tube having a slow wave circuit with a constant circuit period without a velocity taper. In addition, in the circuit period set in this way, the collector side 8 of the output slow wave circuit and the attenuator side 6 of the output slow wave circuit both contribute to the amplification of the fundamental wave. From theoretical analysis, the synchronization range of the traveling wave tube is approximately on the order of the coupling parameter, C, so the average circuit period in the speed taper section 7 ((P ₁ + P ₂ )/
The ratio of the difference between _{the circuit period (P 2 )} of the collector side 8 of the output side slow wave circuit and the circuit period (P ₁ ) of the attenuator side 6 of the output side slow wave circuit to・(P ₁ −
P ₂ )/(P ₁ +P ₂ ))) is usually given as 0.14 or less.

In the case of a backward wave component of the (n=-1) 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 unit 10 (n=-1). 1) The backward wave component energy of the spatial harmonic interacts with the electron beam 12 while traveling in the opposite direction, is amplified, and is finally absorbed by the electromagnetic wave attenuator 4. At this time,
If the backward wave gain becomes infinite before reaching the electromagnetic wave extraction section, the tube will cause backward oscillation. According to the inventor's detailed analysis, in the case of a normal traveling wave tube, the collector side 8 of the output slow wave circuit
The conditions required for each circuit period for both sides of the attenuator side part 6 to contribute to the amplification of the backward wave is that the value of 2・(P ₁ − P ₂ )/(P ₁ +P ₂ ) is 0.04. It is given below. This means that 2(P ₁ − P ₂ )/(P ₁ +
P ₂ ), the second graph shows the backward wave oscillation starting current.
It is also clear by referring to the figure.

Therefore, in a normal traveling wave tube, the attenuator side part 6 of the output side slow wave circuit and the slow wave circuit of the collector side part 8 amplify the fundamental wave, and (n
=-1) For the next spatial harmonic component, the conditions for the circuit period of each slow-wave circuit such that it is not amplified are given by the following equation.

0.04<2( _P1 - _P2 )/ _P1 + _P2 <0.14 (1) On the other hand, according to detailed analysis by the inventor, the average circuit period ((( The length of the slow wave circuit (L ₁ ) between the position in the tube axis direction, which is P ₁ + P ₂ )/2), and the average circuit period ((P ₁ + P ₂ )/
2) The position in the tube axis direction and the electromagnetic wave extraction part 10
Ratio (L ₁ /L ₂ ) of the length (L ₂ ) of the slow wave circuit between
If the parameter is 2(P ₁ − P ₂ )/(P ₁ +
P ₂ ) with respect to a constant average circuit period ((P ₁
+P ₂ )/2) Ratio of the backward wave oscillation start current (Isto) in the output side slow wave circuit and the backward wave oscillation start current (Ist) when there is a speed taper in the present invention (Ist/Isto) is shown in FIG. As can be seen from the figure, when L ₁ /L ₂ = 1.16, 2 (P ₁ −
While the value of P ₂ )/(P ₁ + P ₂ ) is small, the value of Ist/Isto increases gradually, but the value of 2(P ₁ − P ₂ )/
The value of (P ₁ + P ₂ ) starts to rise rapidly around 0.04, and the value of Ist/Isto reaches 20 or more around 0.047. After that, the value of Ist/Isto is 2(P ₁ − P ₂ )/
It decreases as (P ₁ + P ₂ ) increases, and 2 (P − P ₂ )/
Ist/Isto becomes minimum when the value of (P ₁ +P ₂ ) is around 0.075. Also, with respect to the value of L ₁ /L ₂ , even if L ₁ /L ₂ is increased or decreased from 1.16, both the peak value and the minimum value decrease, and L ₁ /L ₂ peaks at 0.6 and 2. The value is 12,
The minimum value is 6. In the case of a normal traveling wave tube, the minimum value of Ist/Isto must be six times or more, although it also depends on the operating current, as a condition for suppressing backward wave oscillation. Therefore, the position of the velocity taper that is effective for suppressing backward wave oscillation is preferably selected within the range given by the following equation.

0.6<L ₁ /L ₂ <2 (2) As stated above, the circuit period of the attenuator side 6 and collector side 8 of the output slow wave circuit is set within the range shown by equation (1), and the speed is If the position of the tapered portion 7 is set within the range shown by equation (2), the electron beam efficiency will not deteriorate, the length of the tube will not become so long, and high-frequency output with suppressed backward wave oscillation can be achieved. A helical traveling wave tube can be provided.

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 to the case where the slow wave circuit is divided by a plurality of electromagnetic wave attenuators. It can also be applied to a slow wave circuit between an electromagnetic wave extractor and an electromagnetic wave attenuator, or a slow wave circuit between the electromagnetic attenuators.

[Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of a traveling wave tube according to the invention. Figure 2 shows the length (L ₁ ) of the slow wave circuit between the collector side end 5 of the electromagnetic wave attenuator and the position in the tube axis direction that is the average circuit period in the velocity taper part 7, and the average length in the velocity taper part 7. In the case where the ratio (L ₁ /L ₂ ) of the length (L ₂ ) of the slow wave circuit between the position in the tube axis direction, which is the circuit period, and the electromagnetic wave extraction section 10 is used as a parameter, 2 (P ₁ − P ₂ )/(P ₁ + P ₂ ) shows the change in oscillation start current. In the figure, the curves , , , have L ₁ /L ₂ values of 0.6, 1,
Corresponds to 1.16, 1.66, 2. 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)

[Claims] 1. In a traveling wave tube consisting of an electron gun, a collector, an electromagnetic wave input section, an electromagnetic wave extraction section, and a helical slow wave circuit divided in high frequency by an electromagnetic wave attenuator in the middle, the electromagnetic wave attenuator and the electromagnetic wave extraction section The slow wave circuit between the electromagnetic wave input section and the electromagnetic wave attenuator has a circuit period (P ₁ ) larger than the circuit period (P ₀ ) of the slow wave circuit between the electromagnetic wave attenuator and a slow wave circuit with a smaller circuit period (P ₂ ). and a speed taper portion that changes from a large circuit period to a small circuit period, and the collector side end portion of the electromagnetic wave attenuator, and the average circuit period ((P ₁ + P ₂ )/ 2) The length of the slow wave circuit (L ₁ ) between the position in the tube axis direction that gives the average circuit period, and the length (L _{2 )} of the slow wave circuit between the position in the tube axis direction that gives the average circuit period and the electromagnetic wave extraction section. ) is between _0.6 and ₂ , and the ratio of the difference between the large circuit period and the small circuit period with respect to the average circuit period (2・(P ₁ − P ₂ )/
(P ₁ +P ₂ )) is between 0.04 and 0.14.