Electron beam channel opening type folded waveguide slow wave structure, slow wave circuit, and method

Abstract

The application provides an electron beam channel opening type folded waveguide slow wave structure, a slow wave circuit and a method, the electron beam channel opening type folded waveguide slow wave structure comprising a cavity unit and an electron beam channel; the cavity unit comprises two curved waveguide cavities with opposite convex directions and being in communication with each other; the curved waveguide cavity comprises an inner arc boundary and an outer arc boundary, and two straight line boundaries connected with two ends of the outer arc boundary respectively, and the other end of the straight line boundary is connected with the inner arc boundary of the adjacent curved waveguide cavity; the inner arc boundary is located within the boundary defined by the electron beam channel; the two straight line boundaries of the same curved waveguide cavity have the same length; the folded waveguide slow wave structure comprises a uniform section and a gradual change section located at the input / output end of both sides of the uniform section; the end connected with the uniform section of the gradual change section is a first end, and the end away from the uniform section is a second end; from the first end of the gradual change section to the second end of the gradual change section, the length of the straight line boundary of the curved waveguide cavity gradually decreases.

Description

Technical Field

[0001] This invention relates to the field of microwave vacuum electronics technology. More specifically, it relates to a slow-wave structure, slow-wave circuit, and method of an electron beam channel-opening folded waveguide. Background Technology

[0002] A traveling wave tube (TWT) is a vacuum electronic device capable of generating or amplifying microwave signals, and it has broad development prospects in fields such as communications, electronic countermeasures, and radar systems. A TWT mainly consists of an electron gun, a slow-wave structure, a collector, input / output devices, and a magnetic focusing system. The slow-wave structure is the site of beam-wave interaction, a key component for generating or amplifying microwave signals. Currently, folded waveguide-type slow-wave structures are one of the main slow-wave structures used in millimeter-wave / terahertz band TWTs. Conventional folded waveguides are formed by bending a rectangular waveguide along an electric field to create a periodic structure of straight and curved waveguide segments. A new type of folded waveguide is the open-channel electron beam type, which directly connects the electron beam channel to the curved waveguide, offering advantages such as flatter dispersion and higher coupling impedance, thus improving the performance of broadband TWTs. Besides the periodic structure of the folded waveguide, another key factor determining the application of slow-wave structures is the matching structure. Its function is to achieve low-reflection feeding and extraction of microwave signals, maximizing transmission power. The matching structure directly affects the practicality of slow-wave circuits.

[0003] Figure 1 The diagram shows a conventional folded waveguide slow wave structure 10 and a conventional matching structure 20. The conventional matching structure 20 is currently commonly composed of two straight waveguides of different widths with rounded corners. Figure 2 The diagram shows an open-channel folded waveguide slow-wave structure. Compared to a conventional folded waveguide slow-wave structure, the boundary conditions of the electromagnetic field in the open-channel folded waveguide slow-wave structure are altered, resulting in a new field distribution. If... Figure 1 Conventional matching structures (e.g., 20) cannot meet design specifications. A design analysis is conducted using a G-band slow-wave structure as an example. Figure 1 The reflection loss (S) of the conventional matching structure 20-time electron beam channel open-type folded waveguide slow wave structure is as follows: 11 The lowest is only -0.6dB (combined with) Figure 3 As shown, the value is far higher than the design requirement of -15dB, making it impossible to feed / extract microwave signals from slow-wave circuits, which severely limits the practical application of open-channel folded waveguide slow-wave structures. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an electron beam channel open-type folded waveguide slow-wave structure to solve the problem that existing matching structures, when matched with the electron beam channel open-type folded waveguide slow-wave structure, cannot achieve the feeding / extraction of microwave signals in the slow-wave circuit, which severely limits the practical application level of the electron beam channel open-type folded waveguide slow-wave structure.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides an open-type folded waveguide slow-wave structure with an electron beam channel, comprising: a cavity unit and an electron beam channel; the cavity unit includes two interconnected curved waveguide cavities with opposite convex directions; each curved waveguide cavity includes an inner arc boundary and an outer arc boundary, and two straight boundaries respectively connected to both ends of the outer arc boundary, the other end of each straight boundary being connected to the inner arc boundary of an adjacent curved waveguide cavity; the inner arc boundary is located within the boundary defined by the electron beam channel; the two straight boundaries of the same curved waveguide cavity have the same length;

[0007] The folded waveguide slow wave structure includes a uniform section and a gradient section located at the input / output ends on both sides of the uniform section; the end of the gradient section connected to the uniform section is the first end, and the end away from the uniform section is the second end; from the first end to the second end of the gradient section, the straight boundary length of the curved waveguide cavity gradually decreases.

[0008] A preferred embodiment is that the inner arc boundary and the straight boundary of the adjacent curved waveguide cavity include an inner arc junction, the inner arc junction being located on the electron beam channel axis; within the same curved waveguide cavity, the outer arc boundary and the straight boundary include an outer arc junction, the outer arc junction and the electron beam channel axis forming a gap height in the radial direction of the electron beam channel, the gap height being equal to the length of the straight boundary.

[0009] In a preferred embodiment, the gradient segment comprises multiple cavity units with a periodic structure; the straight boundary length of the curved waveguide cavity in the uniform segment is h0; from the first end to the second end of the gradient segment, the straight boundary length of the first curved waveguide cavity in the gradient segment is h1, and the straight boundary length of the m-th curved waveguide cavity is h... m The number of curved waveguide cavities contained in the gradient section is n, the electron beam channel radius is r, and the straight boundary length of the m-th curved waveguide cavity satisfies the following relationship:

[0010] A preferred embodiment is that the end of the gradient segment away from the uniform segment includes a connecting segment; the connecting segment is a gradient waveguide structure; the connecting segment includes an inclined boundary connected to one end of the outer arc boundary of the curved waveguide cavity and a vertical boundary connected to one end of the inner arc boundary of the curved waveguide cavity; the distance between the inclined boundary and the vertical boundary gradually decreases along the signal input direction.

[0011] A preferred embodiment is that the boundary of the electron injection channel is located between the two ends of the inclined boundary.

[0012] A preferred embodiment is that the height of the inclined boundary in the radial direction of the electron beam channel is equal to twice the length of the straight boundary of the curved waveguide cavity connected to the connecting section.

[0013] In a preferred embodiment, the distance between the apex point of the inner arc boundary and the apex point of the outer arc boundary of the curved waveguide cavity connected to the connecting segment in the radial direction of the electron beam channel is equal to the opening width of the end of the connecting segment away from the transition segment in the axial direction of the electron beam channel.

[0014] The present invention also provides a slow-wave circuit, including the electron beam channel open-type folded waveguide slow-wave structure as described above and a rectangular waveguide connected to the input end and / or output end of the electron beam channel open-type folded waveguide slow-wave structure.

[0015] This invention also provides a design method for an electron beam channel open-type folded waveguide slow-wave structure, comprising the following steps:

[0016] Design a folded waveguide slow wave structure, the folded waveguide slow wave structure includes a cavity unit and an electron beam channel; the cavity unit includes two curved waveguide cavities with opposite protrusion directions that are interconnected; the curved waveguide cavity includes an inner arc boundary and an outer arc boundary, and two straight boundaries that are respectively connected to both ends of the outer arc boundary, and the other end of the straight boundary is connected to the inner arc boundary of the adjacent curved waveguide cavity;

[0017] Using three-dimensional electromagnetic field simulation software, the inner arc boundary of the curved waveguide cavity is moved down to the boundary defined by the electron beam channel; the two straight boundaries of the same curved waveguide cavity are designed to have the same length.

[0018] The folded waveguide slow wave structure includes a uniform section and a gradient section located at the input / output ends on both sides of the uniform section; the end of the gradient section connected to the uniform section is the first end, and the end away from the uniform section is the second end; from the first end to the second end of the gradient section, the straight boundary length of the curved waveguide cavity is designed to gradually decrease.

[0019] The preferred approach is to adjust the reflection loss of the folded waveguide slow-wave structure by changing the straight boundary length of the curved waveguide cavity, thereby optimizing the matching performance of the folded waveguide slow-wave structure.

[0020] The beneficial effects of this invention are as follows:

[0021] The novel electron beam channel open-type folded waveguide slow-wave structure provided by this invention meets the usage requirements of electron beam channel open-type folded waveguide slow-wave structures, enabling the feeding / extraction of microwave signals within these structures, improving their practicality, and achieving good matching characteristics. The structure of this invention possesses the advantage of wide bandwidth. Taking the G-band as an example, this structure can achieve a bandwidth of 30 GHz, with a relative bandwidth of 13.5%, fully covering the operating bandwidth of broadband traveling wave tubes, demonstrating strong applicability. The structure of this invention offers high design flexibility; the number of cavity units and the ratio of the straight boundary length between adjacent curved waveguide cavities can be flexibly adjusted, better meeting the needs of the slow-wave structure's operating frequency band. Through the combination of cavity units and connecting sections, this invention results in a small overall lateral dimension, offering the advantages of a compact structure and easy fabrication, facilitating the miniaturization requirements of traveling wave tubes. Attached Figure Description

[0022] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0023] Figure 1 This is a schematic diagram of the combination of a conventional folded waveguide slow wave structure and a conventional matching structure.

[0024] Figure 2 This is a schematic diagram of an existing open-type folded waveguide slow wave structure with electron beam channel.

[0025] Figure 3 This is a reflection loss curve of an existing electron beam channel open-type folded waveguide slow wave structure using a conventional matching structure.

[0026] Figure 4A This is one of the structural schematic diagrams of the open-type folded waveguide slow wave structure of the electron beam channel of the present invention.

[0027] Figure 4B This is the second schematic diagram of the open-type folded waveguide slow wave structure of the electron beam channel of the present invention.

[0028] Figure 4C This is the third schematic diagram of the open-type folded waveguide slow wave structure of the electron beam channel of the present invention.

[0029] Figure 5 This is a reflection loss curve of the electron beam channel open-type folded waveguide slow wave structure of the present invention.

[0030] Figure 6 This is a reflection loss curve of the electron beam channel open-type folded waveguide slow wave structure of the present invention after fine-tuning the parameters. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention.

[0032] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0033] Technologies and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such technologies and equipment should be considered part of the specification.

[0034] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0035] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0036] To address the problem that existing matching structures, when matched with existing electron beam channel open-type folded waveguide slow-wave structures, cannot achieve the feeding / extraction of microwave signals in slow-wave circuits, severely limiting the practical application of electron beam channel open-type folded waveguide slow-wave structures, this invention provides an electron beam channel open-type folded waveguide slow-wave structure, combined with... Figures 1 to 6 As shown, the electron beam channel-opening folded waveguide slow-wave structure specifically includes: a cavity unit and an electron beam channel 22. The cavity unit includes two interconnected, oppositely oriented curved waveguide cavities 21; each curved waveguide cavity 21 includes an inner arc boundary C1 and an outer arc boundary C2, and two straight boundaries L1 connected to both ends of the outer arc boundary C2, with the other end of each straight boundary L1 connected to the inner arc boundary C1 of the adjacent curved waveguide cavity 21. The inner arc boundary C1 is located within the boundary defined by the electron beam channel 22; the two straight boundaries L1 of the same curved waveguide cavity 21 have the same length. The folded waveguide slow-wave structure includes a uniform section 11 and gradient sections 12 located at the input / output ends on both sides of the uniform section 11; the gradient sections 12 have the same cavity structure shape as the uniform section 11. Figure 4A and Figure 4COnly the gradient segment 12 located on one side of the uniform segment 11 is shown. The end of the gradient segment 12 connected to the uniform segment 11 is the first end, and the end away from the uniform segment 11 is the second end. From the first end to the second end of the gradient segment 12, the straight boundary length of the curved waveguide cavity 21 gradually decreases. That is, starting from the end of the gradient segment 12 connected to the uniform segment 11, the straight boundary length of the curved waveguide cavity 21 of the gradient segment 12 gradually decreases. The dimensions of each curved waveguide cavity 21 in the uniform segment 11 remain consistent. This invention features low reflection loss, wide bandwidth, and simple and easy-to-manufacture structure, significantly improving the practicality of slow-wave structures, thereby enhancing the performance of millimeter-wave / terahertz broadband traveling-wave tubes.

[0037] In one specific embodiment, the inner arc boundary C1 and the straight boundary L1 of the adjacent curved waveguide cavity 21 include an inner arc junction Q1, which is located on the electron beam channel axis L0. Within the same curved waveguide cavity 21, the outer arc boundary C2 and the straight boundary L1 include an outer arc junction Q2. The outer arc junction Q2 and the electron beam channel axis L0 form a gap height in the radial direction of the electron beam channel, which is equal to the length of the straight boundary. Through this configuration, the thin-walled arc structure at the opening of the electron beam channel can be eliminated while ensuring the coupling impedance of the slow-wave structure. This design is characterized by easy processing and high structural strength, making it more suitable for engineering applications.

[0038] In one specific embodiment, the gradient segment 12 includes multiple cavity units with a periodic structure, and the specific number of cavity units can be selected according to the specific design requirements of the slow-wave structure. The straight boundary length of the curved waveguide cavity 21 of the uniform segment 11 is h0. From the first end to the second end of the gradient segment 12, the straight boundary length of the first curved waveguide cavity of the gradient segment 12 connected to the uniform segment 11 is h1, and the straight boundary length of the m-th curved waveguide cavity is h. m The number of curved waveguide cavities 21 contained in the gradient segment 12 is n, the radius of the electron beam channel 22 is r, and the straight boundary length of the m-th curved waveguide cavity satisfies the following relationship: The electron beam channel radius *r* mentioned above is generally selected when designing the electrical performance of slow-wave structures. Combined with... Figure 4CTaking a gradient section 12 with four curved waveguide cavities 21 on one side as an example, when the electron beam channel radius is selected as 0.12 mm, and the straight boundary length h0 of the curved waveguide cavity 21 in the uniform section 11 is 0.3 mm, the straight boundary length h1 of the first curved waveguide cavity in the gradient section 12 is 0.26 mm, the straight boundary length h2 of the second curved waveguide cavity in the gradient section is 0.22 mm, the straight boundary length h3 of the third curved waveguide cavity in the gradient section is 0.18 mm, and the straight boundary length h4 of the fourth curved waveguide cavity in the gradient section is 0.14 mm. In this case, the electron beam channel open-type folded waveguide slow-wave structure of the present invention can achieve both broadband and low reflection loss in the operating frequency band, meeting the design requirements.

[0039] In one specific embodiment, to further reduce the reflection loss of the folded waveguide slow-wave structure and reduce the number of cavity units required in the gradient section, the end of the gradient section 12 away from the uniform section 11 includes a connecting section 13; the connecting section 13 is a gradient waveguide structure; the connecting section 13 includes an inclined boundary L2 connected to one end of the outer arc boundary C2 of the curved waveguide cavity 21 and a vertical boundary L3 connected to one end of the inner arc boundary C1 of the curved waveguide cavity 21. When the gradient section 12 is connected to the connecting section 13, the straight boundary of the adjacent side of the curved waveguide cavity 21 that is connected to the connecting section 13 is replaced by the inclined boundary L2 of the connecting section 13. It can be understood that the inclined boundary L2 of the connecting section 13 corresponds to an inclined plane, and the vertical boundary L3 corresponds to a vertical plane. At the input end of the folded waveguide slow-wave structure, the distance between the inclined boundary L2 and the vertical boundary L3 gradually decreases along the signal input direction. Furthermore, the boundary of the electron injection channel 22 is located between the two ends of the inclined boundary L2.

[0040] In one specific embodiment, the height of the inclined boundary L2 in the radial direction of the electron beam channel is equal to twice the length of the straight boundary of the curved waveguide cavity 21 connected to the connecting section 13. When the height of the inclined boundary L2 in the radial direction of the electron beam channel is equal to twice the length of the straight boundary of the curved waveguide cavity 21 connected to the connecting section 13, the reflection loss of the electron beam channel open-type folded waveguide slow-wave structure is the lowest in the operating frequency band. When the height of the inclined boundary in the radial direction of the electron beam channel is not equal to twice the length of the straight boundary of the curved waveguide cavity connected to the connecting section, the reflection loss of the electron beam channel open-type folded waveguide slow-wave structure increases in the operating frequency band.

[0041] In one specific embodiment, the distance between the apex of the inner arc boundary C1 and the apex of the outer arc boundary C2 of the curved waveguide cavity 21 connected to the connecting segment 13 in the radial direction of the electron beam channel is equal to the opening width of the end of the connecting segment 13 away from the transition segment 12 in the axial direction of the electron beam channel. When the two are equal, the electron beam channel opening-type folded waveguide slow-wave structure has the widest bandwidth in the operating frequency band. When the two are not equal, the bandwidth of the electron beam channel opening-type folded waveguide slow-wave structure in the operating frequency band becomes narrower.

[0042] The following are embodiments of the present invention, including specific dimensions. Figures 4A-4B As shown, the structural dimensions of the electron beam channel-opening folded waveguide slow-wave structure are set as follows (unit: mm): the wide side length of uniform segment 11 is a = 0.84, the narrow side length of uniform segment 11 is b = 0.1, the geometric period length of uniform segment 11 is p = 0.55, the electron beam channel radius is r = 0.12, and the straight boundary length of uniform segment 11 is h0 = 0.28. The structure of this invention was simulated and optimized using the three-dimensional electromagnetic software CST Microwave Studio. The final parameter design values ​​for the transition segment 12 are: the straight boundary length of the first curved waveguide cavity of the transition segment 12 is h1 = 0.21, the straight boundary length of the second curved waveguide cavity of the transition segment 12 is h2 = 0.14, and the distance w between the apex point of the inner arc boundary C1 and the apex point of the outer arc boundary C2 of the second curved waveguide cavity in the radial direction of the electron beam channel is 0.24. The remaining structural dimensions are the same as those of the uniform segment. The structural parameters of connecting segment 13 are designed as follows: the height H of the inclined boundary L2 in the radial direction of the electron beam channel is 0.28, and the opening width d of the end of connecting segment 13 away from the gradient segment 12 in the axial direction of the electron beam channel is 0.24. The simulation results of the corresponding reflection loss of this folded waveguide slow-wave structure are as follows: Figure 5 As shown, its S frequency is between 206 GHz and 236 GHz. 11 With parameters below -15dB and a bandwidth up to 30GHz (relative bandwidth 13.5%), it fully meets the operating bandwidth requirements of open-channel slow-wave structures. Furthermore, the gradient section of this structure only gradients a single structural parameter within a single cavity unit, resulting in a simple, compact, and easily manufactured overall structure. It is fully compatible with existing folded waveguide fabrication processes, and high-speed milling can achieve integrated precision machining.

[0043] Figure 6The diagram shows the reflection loss after only minor adjustments to h1 and h2 based on the specific structural parameters described above in this invention. The corresponding specific structural parameters are (unit: mm): Wide side length a = 0.84 for uniform segment 11, narrow side length b = 0.1 for uniform segment 11, geometric period length p = 0.55 for uniform segment 11, electron beam channel radius r = 0.12, and straight boundary length h0 = 0.28 for uniform segment 11. Straight boundary length h1 = 0.23 for the first curved waveguide cavity of the transition segment 12, straight boundary length h2 = 0.13 for the second curved waveguide cavity of the transition segment 12, and the distance w = 0.24 between the apex points of the inner and outer circular arc boundaries C1 and C2 of the second curved waveguide cavity in the radial direction of the electron beam channel. Opening width d = 0.24 in the axial direction of the electron beam channel at the end of the connecting segment 13 away from the transition segment 12, and height H = 0.28 in the radial direction of the electron beam channel for the inclined boundary L2. Figure 6 and Figure 5 The comparison shows that after fine-tuning the dimensions of h1 and h2, the requirements for traveling wave tubes operating at frequencies close to 230GHz can be better met.

[0044] The present invention also provides a slow-wave circuit, which includes the electron beam channel open-type folded waveguide slow-wave structure as described above and a rectangular waveguide 14 connected to the input end and / or output end of the electron beam channel open-type folded waveguide slow-wave structure. The rectangular waveguide 14 is used to realize the input of microwave signals into the electron beam channel open-type folded waveguide slow-wave structure or the output of microwave signals from the electron beam channel open-type folded waveguide slow-wave structure.

[0045] This invention also provides a design method for an electron beam channel-opening folded waveguide slow-wave structure. The method includes the following steps: designing a folded waveguide slow-wave structure, wherein the folded waveguide slow-wave structure includes a cavity unit and an electron beam channel 22; the cavity unit includes two interconnected curved waveguide cavities 21 with opposite protrusion directions; each curved waveguide cavity 21 includes an inner arc boundary C1 and an outer arc boundary C2, and two straight boundaries L1 respectively connected to both ends of the outer arc boundary C2, the other end of each straight boundary L1 being connected to the inner arc boundary C1 of an adjacent curved waveguide cavity 21; utilizing three... The electromagnetic field simulation software was used to move the inner arc boundary C1 of the curved waveguide cavity 21 downwards to the boundary defined by the electron beam channel 22; the two straight boundaries L1 of the same curved waveguide cavity 21 were designed to have the same length; the folded waveguide slow-wave structure includes a uniform section 11 and a gradient section 12 located on both sides of the uniform section 11 at the input / output ends; the end of the gradient section 12 connected to the uniform section 11 is the first end, and the end away from the uniform section 11 is the second end; from the first end to the second end of the gradient section 12, the length of the straight boundary of the curved waveguide cavity 21 is designed to gradually decrease. Furthermore, by changing the length of the straight boundary of the curved waveguide cavity 21, the reflection loss of the folded waveguide slow-wave structure is adjusted, and the matching performance of the folded waveguide slow-wave structure is optimized. More specifically, by fine-tuning the dimensions of h1 and h2, the requirements for traveling wave tubes operating at frequencies close to 230 GHz can be better met.

[0046] In summary, the novel electron beam channel open-type folded waveguide slow-wave structure provided by this invention can meet the usage requirements of electron beam channel open-type folded waveguide slow-wave structures, enabling the feeding / extraction of microwave signals in these structures, improving their practicality, and achieving good matching characteristics. The structure of this invention has the advantage of wide bandwidth. Taking the G-band as an example, this structure can achieve a bandwidth of 30 GHz, with a relative bandwidth of 13.5%, which can completely cover the operating bandwidth of broadband traveling wave tubes, demonstrating strong applicability. The structure of this invention has high design flexibility; the number of cavity units and the ratio of the straight boundary length between adjacent curved waveguide cavities can be flexibly adjusted, better meeting the needs of the operating frequency band of the slow-wave structure. Through the cavity units and connecting sections, this invention results in a small overall lateral dimension, offering the advantages of a compact structure and easy fabrication, facilitating the miniaturization requirements of traveling wave tubes.

[0047] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A slow-wave structure of an electron beam channel-opening folded waveguide, characterized in that, include: Cavity unit and electron beam channel; the cavity unit includes two interconnected curved waveguide cavities with opposite protrusion directions; The curved waveguide cavity includes an inner circular arc boundary and an outer circular arc boundary, and two straight boundaries that are respectively connected to both ends of the outer circular arc boundary. The other end of the straight boundary is connected to the inner circular arc boundary of the adjacent curved waveguide cavity. The inner circular arc boundary is located within the boundary defined by the electron beam channel. The two straight boundaries of the same curved waveguide cavity have the same length. The folded waveguide slow wave structure includes a uniform section and a gradient section located at the input / output ends on both sides of the uniform section; the end of the gradient section connected to the uniform section is the first end, and the end away from the uniform section is the second end; from the first end to the second end of the gradient section, the straight boundary length of the curved waveguide cavity gradually decreases.

2. The electron beam channel open-type folded waveguide slow-wave structure according to claim 1, characterized in that, The inner arc boundary and the straight boundary of the adjacent curved waveguide cavity include an inner arc junction, which is located on the electron beam channel axis; within the same curved waveguide cavity, the outer arc boundary and the straight boundary include an outer arc junction, which forms a gap height with the electron beam channel axis in the radial direction of the electron beam channel, and the gap height is equal to the length of the straight boundary.

3. The electron beam channel open-type folded waveguide slow wave structure according to claim 1, characterized in that, The gradient segment comprises multiple cavity units with a periodic structure; the straight boundary length of the curved waveguide cavity in the uniform segment is h0; from the first end to the second end of the gradient segment, the straight boundary length of the first curved waveguide cavity in the gradient segment is h1, and the straight boundary length of the m-th curved waveguide cavity is h... m The number of curved waveguide cavities contained in the gradient section is n, the electron beam channel radius is r, and the straight boundary length of the m-th curved waveguide cavity satisfies the following relationship:

4. The electron beam channel open-type folded waveguide slow-wave structure according to claim 1, characterized in that, The end of the gradient segment away from the uniform segment includes a connecting segment; the connecting segment is a gradient waveguide structure; the connecting segment includes an inclined boundary connected to one end of the outer arc boundary of the curved waveguide cavity and a vertical boundary connected to one end of the inner arc boundary of the curved waveguide cavity; along the signal input direction, the distance between the inclined boundary and the vertical boundary gradually decreases.

5. The electron beam channel open-type folded waveguide slow wave structure according to claim 4, characterized in that, The boundary of the electron injection channel is located between the two ends of the inclined boundary.

6. The electron beam channel open-type folded waveguide slow wave structure according to claim 4, characterized in that, The height of the inclined boundary in the radial direction of the electron beam channel is equal to twice the length of the straight boundary of the curved waveguide cavity connected to the connecting section.

7. The electron beam channel open-type folded waveguide slow wave structure according to claim 4, characterized in that, The distance between the apex of the inner arc boundary and the apex of the outer arc boundary of the curved waveguide cavity connected to the connecting section in the radial direction of the electron beam channel is equal to the opening width of the end of the connecting section away from the transition section in the axial direction of the electron beam channel.

8. A slow-wave circuit, characterized in that, It includes the electron beam channel open-type folded waveguide slow wave structure as described in any one of claims 1-7, and a rectangular waveguide connected to the input and / or output ends of the electron beam channel open-type folded waveguide slow wave structure.

9. A design method for an electron beam channel open-type folded waveguide slow-wave structure, characterized in that, Includes the following steps: Design a folded waveguide slow wave structure, the folded waveguide slow wave structure includes a cavity unit and an electron beam channel; the cavity unit includes two curved waveguide cavities with opposite protrusion directions that are interconnected; the curved waveguide cavity includes an inner arc boundary and an outer arc boundary, and two straight boundaries that are respectively connected to both ends of the outer arc boundary, and the other end of the straight boundary is connected to the inner arc boundary of the adjacent curved waveguide cavity; Using three-dimensional electromagnetic field simulation software, the inner arc boundary of the curved waveguide cavity is moved down to the boundary defined by the electron beam channel; the two straight boundaries of the same curved waveguide cavity are designed to have the same length. The folded waveguide slow wave structure includes a uniform section and a gradient section located at the input / output ends on both sides of the uniform section; the end of the gradient section connected to the uniform section is the first end, and the end away from the uniform section is the second end; from the first end to the second end of the gradient section, the straight boundary length of the curved waveguide cavity is designed to gradually decrease.

10. The design method according to claim 9, characterized in that, The reflection loss of the folded waveguide slow wave structure is adjusted by changing the straight boundary length of the curved waveguide cavity, thereby optimizing the matching performance of the folded waveguide slow wave structure.

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