Folded waveguide slow wave structure, traveling wave tube and design method

Abstract

The invention provides a folded waveguide slow-wave structure, a traveling wave tube and a design method, the folded waveguide slow-wave structure comprises a multi-periodic structure defined by a plurality of upper grid bodies and a plurality of lower grid bodies which are distributed in a staggered manner, and the folded waveguide slow-wave structure comprises a straight waveguide section, a bent waveguide connection section and an electron beam channel which are communicated with each other; the bent waveguide connecting section comprises an inner arc boundary; an inner arc joint part is arranged between the inner arc boundary and the straight waveguide section; the circle center corresponding to the inner arc boundary and the inner arc joint part are both located in the boundary limited by the electron beam channel, and the arc top end point of the inner arc boundary is located outside the boundary limited by the electron beam channel. The folded waveguide slow wave structure can improve the performance of the terahertz traveling wave tube.

Description

Technical Field

[0001] The present invention relates to the field of microwave vacuum electron technology. More specifically, it relates to a folded waveguide slow-wave structure, a traveling wave tube, and a design method. Background Art

[0002] Terahertz traveling wave tubes are a type of electro-vacuum amplifier that realizes power amplification of terahertz waves and is of great significance to the development of terahertz technology. The slow-wave structure is the place where microwave signals and electron beams exchange energy in a traveling wave tube. Currently, the folded waveguide slow-wave structure is mainly suitable for circular beams in the terahertz frequency band. This is an all-metal structure with strong heat dissipation ability, large bandwidth, simple input and output coupling structures that are easy to process, and low high-frequency losses, showing great development potential.

[0003] The traditional folded waveguide slow-wave structure is a pipe structure formed by bending the E-plane of a rectangular waveguide and arranging it in a certain period along the axial direction. The basic structural unit and the main views of this unit are shown in Figures 1A - 1C as follows. The circular channel in the middle is the electron beam channel 30, and the microwave signal travels along a tortuous path in the waveguide cavity 10 to achieve the purpose of reducing the phase velocity. In this structure, the centers of the inner and outer arcs coincide, the inner side walls of the straight waveguide sections are at the same height as the outer side walls, and the centers of the inner and outer arcs are located at the tops of the inner and outer side walls of the straight waveguide. The respective dimensional parameters of this structure are: the radius r of the electron beam channel; the half-period length p of the slow-wave structure (the full-period length is 2p); the length h of the straight waveguide section; the length a of the wide side of the waveguide; the length b of the narrow side of the waveguide. The diameter of the channel is 2r, and the channel penetrates the inner and outer walls of the straight waveguide section and is closed. In this structure, the island region 20 is a combination of a straight waveguide and an ideal semi-circle. In the traditional structure, since h > 2r, it restricts the movement of the inner circle center towards the center of the channel, thereby restricting the expansion of the bandwidth, the improvement of the coupling impedance, and the reduction of losses. This greatly restricts the performance improvement of terahertz traveling wave tubes. Summary of the Invention

[0004] In view of the above problems, the present invention provides a folded waveguide slow-wave structure to improve the performance of terahertz traveling wave tubes.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a folded waveguide slow-wave structure, including a multi-periodic structure defined by a plurality of upper grids and a plurality of lower grids distributed alternately with each other. The folded waveguide slow-wave structure includes a connected straight waveguide section, a bent waveguide connection section, and an electron beam channel; the bent waveguide connection section includes an inner arc boundary; and there is an inner arc junction between the inner arc boundary and the straight waveguide section.

[0007] The center of the circle corresponding to the inner arc boundary and the intersection of the inner arcs are both located within the boundary defined by the electron beam channel, and the arc apex of the inner arc boundary is located outside the boundary defined by the electron beam channel.

[0008] Preferably, the inner arc boundary is a semi-circle.

[0009] Preferably, the radius of the electron beam channel is r, the half-period length of the slow-wave structure is p, the narrow-side length of the straight waveguide section is b, and the first spacing height between the center of the circle corresponding to the inner arc boundary and the axis of the electron beam channel in the radial direction of the electron beam channel is h 1 ; 2r - p + b < h 1 < r.

[0010] Preferably, the curved waveguide connection section further includes an outer arc boundary, and the second spacing height between the center of the circle corresponding to the outer arc boundary and the axis of the electron beam channel in the radial direction of the electron beam channel is greater than the radius of the electron beam channel.

[0011] Preferably, the outer arc boundary is a semi-circle or a major arc.

[0012] Preferably, the first spacing height between the center of the circle corresponding to the inner arc boundary and the axis of the electron beam channel in the radial direction of the electron beam channel is h 1 , and the second spacing height between the center of the circle corresponding to the outer arc boundary and the axis of the electron beam channel in the radial direction of the electron beam channel is h 2 ; h 1 <h 2 .

[0013] The present invention also provides a traveling wave tube, including the folded waveguide slow-wave structure as described above.

[0014] The present invention also provides a design method for a folded waveguide slow-wave structure, and the design method includes:

[0015] Designing an initial folded waveguide slow-wave structure as needed, where the initial folded waveguide slow-wave structure includes a connected straight waveguide section, a curved waveguide connection section, and an electron beam channel;

[0016] Using three-dimensional electromagnetic field simulation software, moving down the center of the circle corresponding to the inner arc boundary and the intersection of the inner arc boundary and the straight waveguide section so that the center of the circle corresponding to the inner arc boundary and the intersection of the inner arcs are both located within the boundary defined by the electron beam channel, and the arc apex of the inner arc boundary is located outside the boundary defined by the electron beam channel.

[0017] Preferably, the inner arc boundary is a semi - circle; the radius of the electron beam channel is r, the half - period length of the slow - wave structure is p, the narrow - side length of the straight waveguide section is b, and the first interval height between the center of the circle corresponding to the inner arc boundary and the axis of the electron beam channel in the radial direction of the electron beam channel is h 1 ; 2r - p + b < h 1 < r.

[0018] Preferably, by changing the first interval height between the center of the circle corresponding to the inner arc boundary and the axis of the electron beam channel in the radial direction of the electron beam channel, the coupling impedance and loss of the folded - waveguide slow - wave structure are adjusted to optimize the performance of the folded - waveguide slow - wave structure.

[0019] The beneficial effects of the present invention are as follows:

[0020] In the present invention, by moving down the center of the circle corresponding to the inner arc boundary and the inner - arc junction part, the center of the inner arc boundary and the inner - arc junction part between the inner arc boundary and the straight waveguide section are located within the boundary defined by the electron beam channel, and the arc - top point of the inner arc boundary is located outside the boundary defined by the electron beam channel while maintaining the integrity of the electron beam channel, so as to achieve the effects of improving the coupling impedance, dispersion and loss of the high - frequency slow - wave structure. Compared with the traditional folded - waveguide slow - wave structure, within the working frequency band, the coupling impedance of the slow - wave structure of the present invention can increase by up to 40% at the low - frequency end and up to 11% at the high - frequency end, having a stronger interaction intensity and enabling the traveling - wave tube to have a greater output power. The dispersion flatness of the slow - wave structure of the present invention is significantly improved, the dispersion curve is flatter, thus having a larger bandwidth and the loss can be reduced by up to 30%, resulting in a significant reduction in line loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The following further describes in detail the specific embodiments of the present invention with reference to the drawings.

[0022] Figures 1A - 1C is a schematic structural diagram of a traditional folded - waveguide slow - wave structure.

[0023] Figures 2A - 2C is a schematic structural diagram of the folded - waveguide slow - wave structure of the present invention.

[0024] Figure 3 is a comparison diagram of the coupling impedance curves between the present invention and the traditional folded - waveguide slow - wave structure.

[0025] Figure 4 is a comparison diagram of the dispersion curves between the present invention and the traditional folded - waveguide slow - wave structure.

[0026] Figure 5 is a comparison diagram of the loss characteristic curves between the present invention and the traditional folded - waveguide slow - wave structure.

[0027] Figure 6It is a schematic structural diagram of a structural semi-body of the present invention.

[0028] Figure 7 It is a schematic diagram showing the change of the in-band coupling impedance of the folded waveguide slow-wave structure of the present invention with the first interval height h 1 of the present invention.

[0029] Figure 8 It is a schematic diagram showing the change of the loss characteristic of the folded waveguide slow-wave structure of the present invention with the first interval height h 1 of the present invention. Detailed implementation manners

[0030] Now, various exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that: Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions and values set forth in these embodiments do not limit the scope of the present invention.

[0031] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way a limitation on the present invention or its application or use.

[0032] Technologies and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies and devices should be regarded as part of the specification.

[0033] In all the examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

[0034] It should be noted that: Similar reference numerals and letters denote similar items in the following drawings, and thus, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0035] In order to improve the performance of a terahertz traveling-wave tube, the present invention provides a folded waveguide slow-wave structure. As shown in combination with Figures 1A to 8 , specifically, the folded waveguide slow-wave structure includes a multi-periodic structure defined by a plurality of upper grids and a plurality of lower grids distributed alternately with each other. The folded waveguide slow-wave structure includes a connected straight waveguide section 1, a bent waveguide connection section 2, and an electron beam channel 3. The electron beam channel 3 is a circular cross-section channel. The bent waveguide connection section 2 includes an inner arc boundary C 1 ; there is an inner arc junction Q 1 between the inner arc boundary C 1 and the straight waveguide section 1; the center O 1 corresponding to the inner arc boundary and the inner arc junction Q 1 are both located within the boundary defined by the electron beam channel 3, and the inner arc boundary C 1The arc top point of lies outside the boundary defined by the electron beam channel 3. The present invention can improve the slow-wave structure without increasing the structural complexity, enabling the slow-wave structure to have the advantages of high coupling impedance, low loss, and flat dispersion, significantly increasing the power capacity, reducing the line loss, and expanding the bandwidth. The straight waveguide section 1 includes an inner straight boundary and an outer straight boundary, and the inner arc boundary C 1 and the inner straight boundary of the straight waveguide section 1 include an inner arc junction Q 1 , and the present invention adjusts the height of only the inner straight boundary of the straight waveguide section 1 to adjust the center O 1 corresponding to the inner arc boundary and the first interval height h 0 between the electron beam channel axis L 1 , realizing the adjustment of the position of the center O 1 of the inner arc boundary and the position of the inner arc junction Q 1 , and further improving the performance of the slow-wave structure. It can be understood that taking the folded waveguide slow-wave structure of a single period as an example, the heights of the inner side boundaries of the two straight waveguide sections 1 are adjusted simultaneously, and the heights of the inner side boundaries of the two straight waveguide sections 1 are always equal.

[0036] In the above embodiment, the inner arc boundary C 1 is a semi-circle. At this time, the center O 1 corresponding to the inner arc boundary is located on the line connecting the two inner arc junctions Q 1 . That is to say, there are two intersection points between the inner arc boundary C 1 and the boundary defined by the electron beam channel 3; in the height direction of the slow-wave structure, the two intersection points are located between the inner arc junction Q 1 and the arc top point of the inner arc boundary C 1 .

[0037] Furthermore, the inner arc boundary C 1 satisfies the following relationship: 2r - p + b < h 1 < r, where r is the radius of the electron beam channel; p is the half-period length of the slow-wave structure; b is the narrow side length of the straight waveguide section, and h 1 is the first interval height h 1 between the center O 0 corresponding to the inner arc boundary and the electron beam channel axis L 1 in the radial direction of the electron beam channel. It should be noted that as the center O 1 of the inner arc boundary continuously moves downward, the isolated island area 4 formed by the enclosure of the inner arc boundary C 1 of the folded waveguide and the electron beam channel boundary gradually becomes smaller. When the height h 1 where the center O 1When it drops to a certain level, the isolated island region 4 will disappear. At this time, the electron beam channel will penetrate the waveguide slot, which will cause the field distribution to change and no longer have the performance of the folded waveguide slow-wave structure. In the present invention, the boundary of the electron beam channel and the inner arc boundary C 1 still form the isolated island region 4, and a complete electron beam channel is still formed at the center position of the entire structure. Therefore, it is necessary to make the height h 1 where the center O 1 of the inner arc boundary is located satisfy 2r - p + b < h 1 < r.

[0038] In a specific embodiment, the curved waveguide connection section further includes an outer arc boundary C 2 , and the center O 2 corresponding to the outer arc boundary and the electron beam channel axis L 0 have a second spacing height h 2 in the radial direction of the electron beam channel that is greater than the radius of the electron beam channel. The center O 2 corresponding to the outer arc boundary and the electron beam channel axis L 0 form a second spacing height h 2 in the radial direction of the electron beam channel; the center O 1 corresponding to the inner arc boundary and the electron beam channel axis L 0 have a first spacing height h 1 in the radial direction of the electron beam channel, and the center O 2 corresponding to the outer arc boundary and the electron beam channel axis L 0 have a second spacing height h 2 in the radial direction of the electron beam channel, and they satisfy the following relationship: h 1 < h 2 .

[0039] Furthermore, in order to ensure the electrical performance of the slow-wave structure, the outer arc boundary C 2 is a semi-circular arc or a major arc. This is because when the outer arc boundary is designed as a minor arc, the electrical performance of the slow-wave structure will deteriorate.

[0040] The center corresponding to the above-mentioned inner arc boundary is O 1 , and the position of the center O 1 of the inner arc boundary is determined by the first spacing height h 1 between the center corresponding to the inner arc boundary and the electron beam channel axis. The center corresponding to the outer arc boundary is O 2 , and the position of the center O 2 of the outer arc boundary is determined by the second spacing height h 2 . By adjusting h 1 and h 2 , the center O 1and the center O of the outer arc boundary 2 whose position directly affects the performance of the slow-wave structure.

[0041] The present invention also provides a traveling wave tube, including the folded waveguide slow-wave structure as described above.

[0042] The present invention also provides a design method for a folded waveguide slow-wave structure. The design method includes: designing an initial folded waveguide slow-wave structure according to requirements, where the initial folded waveguide slow-wave structure includes a connected straight waveguide section 1, a curved waveguide connection section 2, and an electron beam channel 3; using three-dimensional electromagnetic field simulation software, moving down the center O 1 corresponding to the inner arc boundary and the inner arc boundary C 1 and the inner arc junction Q 1 between the inner arc boundary and the straight waveguide section 1 1 so that the center O 1 corresponding to the inner arc boundary and the inner arc junction Q 1 are both located within the boundary defined by the electron beam channel 3 and the arc apex of the inner arc boundary C

[0043] Further, the inner arc boundary C 1 is a semi-circle; the radius of the electron beam channel is r, the half-period length of the slow-wave structure is p, the narrow-side length of the straight waveguide section is b, and the first spacing height h 1 between the center O 0 corresponding to the inner arc boundary and the axis L 1 of the electron beam channel in the radial direction of the electron beam channel is; 2r - p + b < h 1 < r. The present invention optimizes the performance of the folded waveguide slow-wave structure by keeping the center O 1 corresponding to the inner arc boundary at the first spacing height h 1 and shortening the first spacing height h 1 at the same time.

[0044] More specifically, by changing the first spacing height h 1 between the center O 0 corresponding to the inner arc boundary and the axis L 1 of the electron beam channel in the radial direction of the electron beam channel, the coupling impedance and loss of the folded waveguide slow-wave structure are adjusted to optimize the performance of the folded waveguide slow-wave structure. The decrease in the first spacing height h 1 where the center O 1 of the inner arc boundary is located increases the width of the curved waveguide and enhances the electromagnetic field in the direction of the electron beam in the straight waveguide gap, thereby increasing the coupling impedance; at the same time, the first spacing height h 1The reduction shortens the equivalent transmission path of electromagnetic waves, thereby reducing the transmission loss. The slow-wave structure is the place where the electron beam exchanges energy with the microwave signal. The shape and size of the slow-wave structure determine the field distribution and transmission situation. When studying the performance of the slow-wave structure, mainly focus on three major characteristics of the slow-wave structure, including coupling impedance characteristics, loss characteristics, and dispersion characteristics. Using three-dimensional electromagnetic field simulation software, the influence of the continuous downward movement of the center O of the inner circular arc boundary on the coupling impedance and loss characteristics was simulated. 1 The influence of the continuous downward movement of the position on the coupling impedance and loss characteristics was studied. Refer to Figure 7 As shown, ensure that the distance height h between the center O corresponding to the outer circular arc boundary of the slow-wave structure and the axis L of the electron beam channel in the radial direction of the electron beam channel remains unchanged. As the first interval height h gradually decreases, the position of the center O of the inner circular arc boundary continuously moves downward. The coupling impedance of the slow-wave structure of the present invention increases significantly, indicating a stronger interaction strength, predicting that the traveling wave tube has a greater output power. Refer to 2 the axis L of the electron beam channel 0 is h in the radial direction of the electron beam channel. 2 remains unchanged. As the first interval height h 1 gradually decreases, the position of the center O of the inner circular arc boundary 1 continuously moves downward. The coupling impedance of the slow-wave structure of the present invention increases significantly, indicating a stronger interaction strength, predicting that the traveling wave tube has a greater output power. Refer to Figure 8 As shown, ensure that the distance height h between the center O corresponding to the outer circular arc boundary of the slow-wave structure and the axis L of the electron beam channel in the radial direction of the electron beam channel remains unchanged. As the first interval height h 2 the axis L of the electron beam channel 0 is h in the radial direction of the electron beam channel. 2 remains unchanged. As the first interval height h 1 gradually decreases, the position of the center O of the inner circular arc boundary 1 continuously moves downward. The line loss of the present invention gradually decreases, predicting that it has a greater output power.

[0045] Next, an implementation scheme with specific structural parameters of the present invention is given. First, design a conventional folded waveguide slow-wave structure to obtain the size parameters of the conventional folded waveguide: a = 0.74 mm, b = 0.12 mm, r = 0.12 mm, p = 0.275 mm, h = 0.3 mm. Based on the above conventional folded waveguide slow-wave structure, first adjust the first interval height h and the second interval height h between the center O corresponding to the inner circular arc boundary and the axis of the electron beam channel, that is, adjust the positions of the center O of the inner circular arc boundary and the center O of the outer circular arc boundary. According to the design of the present invention, the downward movement of the center O of the inner circular arc boundary will greatly improve the three major characteristics of the slow-wave structure. Continuously move the center O of the inner circular arc boundary downward. When h 1 the first interval height h between the center O corresponding to the inner circular arc boundary and the axis of the electron beam channel 1 and the second interval height h 2 That is, for the center O of the inner circular arc boundary 1 and the center O of the outer circular arc boundary 2 the positions are adjusted. According to the design of the present invention, the downward movement of the center O of the inner circular arc boundary will greatly improve the three major characteristics of the slow-wave structure. Move the center O of the inner circular arc boundary 1 downward continuously. When h 1 continuously moves downward. When h 1=(2r - p + b)=(2 * 0.12 - 0.275 + 0.12)=0.085 mm, the island region 4 will be in a critical state. To ensure the three major characteristics, h is required. 1 > (2r - p + b), the slow-wave structure of the present invention takes h 1 = 0.15. h 2 remains unchanged, h 2 = 0.3. p remains unchanged, p = 0.275 mm. The value of a is optimized according to the synchronous voltage equivalent to the conventional structure, that is, the normalized phase velocity, and finally a = 0.755 mm is determined. Therefore, the main parameters of the slow-wave structure of the present invention are selected as a = 0.755 mm, h 1 = 0.15 mm, h 2 = 0.3 mm, b = 0.12 mm, p = 0.27 mm, r = 0.12 mm. The calculation results of the three major performances (coupling impedance characteristics, dispersion characteristics, loss characteristics) of the slow-wave structure of the present invention based on the above structural parameters are as Figures 3 - 5 shown.

[0046] Specifically, using three-dimensional electromagnetic field simulation software, the performance comparison of two circuits of the slow-wave structure of the present application and the conventional folded waveguide slow-wave structure is simulated. Figure 3 is the comparison chart of the coupling impedance curves of the slow-wave structure of the present application and the conventional folded waveguide slow-wave structure. Compared with the conventional folded waveguide slow-wave structure, the coupling impedance in the frequency band of the present invention is increased from 2 - 5.2 Ω to 2.8 - 5.8 Ω. The increase at the low-frequency end is as high as 40%, and the increase at the high-frequency end is 11%, indicating a stronger interaction intensity and predicting that the traveling wave tube has a greater output power. Figure 4 is the comparison chart of the dispersion curves of the slow-wave structure of the present application and the conventional folded waveguide slow-wave structure, which characterizes the operating voltage and bandwidth of the traveling wave tube. At 217 GHz, the two have the same normalized phase velocity, predicting that the traveling wave tube has the same voltage; within the bandwidth, the phase velocity change rate of the slow-wave structure of the present invention is 0.0012C / GHz, and that of the conventional slow-wave structure is 0.0018C / GHz. The dispersion flatness of the slow-wave structure of the present invention is significantly improved, predicting that the slow-wave structure of the present invention has a greater bandwidth. Figure 5 is the comparison chart of the loss characteristic curves of the slow-wave structure of the present application and the conventional folded waveguide slow-wave structure. Compared with the conventional folded waveguide slow-wave structure, the loss in the frequency band of the present invention is reduced from 310 - 440 dB / m to 230 - 310 dB / m, with a reduction of up to 30%, predicting a significant reduction in line loss. In summary, the slow-wave structure of the present invention has obvious advantages in three aspects: coupling impedance, dispersion characteristics, and loss characteristics, and is also compatible with the existing precision machining process.

[0047] In the actual processing of the slow-wave structure of the present invention, the whole circular copper column can be cut along the yz plane into two semi-circular copper columns. A row of folded waveguide slots and half of the electron beam channel are processed on each semi-circular copper column. The actual processing model of the semi-circular copper column is as shown in Figure 6 shown. After processing, the two semi-circular copper columns are buckled together and diffusion welded into one body by pressure, and the slow-wave structure of the present application can be obtained. The region formed by the folded waveguide slots on the two semi-circular copper columns encloses the waveguide cavity of the folded waveguide slow-wave structure; the region formed by the electron beam channels on the two semi-circular copper columns encloses the electron beam channel of the folded waveguide slow-wave structure.

[0048] In summary, the present invention moves down the center of the circle corresponding to the inner arc boundary and the inner arc intersection part, so that the center of the inner arc boundary and the inner arc intersection part between the inner arc boundary and the straight waveguide section are located within the boundary defined by the electron beam channel, and the arc top point of the inner arc boundary is located outside the boundary defined by the electron beam channel, while retaining the integrity of the electron beam channel, achieving the effects of improving the coupling impedance, dispersion and loss of the high-frequency slow-wave structure. Compared with the traditional folded waveguide slow-wave structure, within the working frequency band, the coupling impedance of the slow-wave structure of the present invention can increase by up to 40% at the low-frequency end and up to 11% at the high-frequency end, with a stronger interaction intensity, enabling the traveling-wave tube to have a greater output power. The dispersion flatness of the slow-wave structure of the present invention is significantly improved, the dispersion curve is flatter, so it has a larger bandwidth and the loss reduction can reach 30%, greatly reducing the line loss.

[0049] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made on the basis of the above description. It is impossible to list all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A folded waveguide slow-wave structure, characterized in that: The invention comprises a multi-periodic structure defined by a plurality of upper grid bodies and a plurality of lower grid bodies which are staggered and distributed with each other, wherein the folded waveguide slow-wave structure comprises a connected straight waveguide section, a curved waveguide connecting section and an electron injection channel; the curved waveguide connecting section comprises an inner arc boundary; an inner arc intersection portion is comprised between the inner arc boundary and the straight waveguide section; The center of the inner arc boundary and the inner arc intersection are both located within the boundary defined by the electron injection channel, and the arc top point of the inner arc boundary is located outside the boundary defined by the electron injection channel.

2. The folded waveguide slow-wave structure according to claim 1, characterized in that: The inner arc boundary is a semicircular arc.

3. The folded waveguide slow-wave structure according to claim 1, characterized in that: The radius of the electron injection channel is r, the half-period length of the slow wave structure is p, the narrow side length of the straight waveguide section is b, and the first spacing height between the center of the circle corresponding to the inner arc boundary and the axis of the electron injection channel in the radial direction of the electron injection channel is h1; 2r-p+b <h1<r。 4. The folded waveguide slow-wave structure according to claim 1, characterized in that: The curved waveguide connecting section also includes an outer arc boundary, and a second spacing height between the center of a circle corresponding to the outer arc boundary and the axis of the electron injection channel in the radial direction of the electron injection channel is greater than the radius of the electron injection channel.

5. The folded waveguide slow-wave structure according to claim 4, characterized in that: The outer arc boundary is a semicircular arc or a major arc.

6. The folded waveguide slow-wave structure according to claim 4, characterized in that: The first spacing height between the center of the inner arc boundary and the axis of the electron injection channel in the radial direction of the electron injection channel is h1, and the second spacing height between the center of the outer arc boundary and the axis of the electron injection channel in the radial direction of the electron injection channel is h2; h1<h2.

7. A traveling wave tube, characterized in that: It comprises a folded waveguide slow-wave structure as described in any one of claims 1 to 6.

8. A design method for a folded waveguide slow-wave structure, characterized in that: The design approach includes: Designing an initial folded waveguide slow-wave structure according to needs, the initial folded waveguide slow-wave structure comprises a connected straight waveguide section, a curved waveguide connecting section and an electron injection channel; Using three-dimensional electromagnetic field simulation software, the center of the inner arc boundary and the inner arc intersection between the inner arc boundary and the straight waveguide section are moved downward so that the center of the inner arc boundary and the inner arc intersection are both located within the boundary defined by the electron injection channel and the arc top point of the inner arc boundary is located outside the boundary defined by the electron injection channel.

9. The design method according to claim 8, characterized in that: The inner arc boundary is a semicircular arc; the radius of the electron injection channel is r, the half-period length of the slow wave structure is p, the narrow side length of the straight waveguide section is b, and the first spacing height between the center of the circle corresponding to the inner arc boundary and the axis of the electron injection channel in the radial direction of the electron injection channel is h1; 2r-p+b <h1<r。 10. The design method according to claim 9, characterized in that: By changing the first spacing height between the center of the circle corresponding to the inner arc boundary and the axis of the electron injection channel in the radial direction of the electron injection channel, the coupling impedance and loss of the folded waveguide slow-wave structure are adjusted to optimize the performance of the folded waveguide slow-wave structure.

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