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

Abstract

The invention 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 comprises a cavity unit and an electron beam channel, the cavity unit comprises two bent waveguide cavities which are communicated with each other and are opposite in protruding direction. Each bent waveguide cavity comprises an inner arc boundary, an outer arc boundary and two linear boundaries connected with the two ends of the outer arc boundary respectively, and the other end of each linear boundary is connected with the inner arc boundary of the adjacent bent waveguide cavity. The inner arc boundary is located in the boundary limited by the electron beam channel; the two straight line boundaries of the same bent waveguide cavity have the same length; the folded waveguide slow wave structure comprises a uniform section and transition sections located at the input / output ends on the two sides of the uniform section. One end of the transition section connected with the uniform section is a first end, and one end far away from the uniform section is a second end; and the linear boundary length of the bent waveguide cavity is gradually reduced from the first end of the transition section to the second end of the transition section.

Description

Technical Field

[0001] The present invention relates to the field of microwave vacuum electronic technology, and more specifically to an electron injection channel opening type folded waveguide slow-wave structure, a slow-wave circuit and a method. Background Art

[0002] A traveling wave tube is a vacuum electronic device that can generate or amplify microwave signals. It has broad development prospects in the fields of communications, electronic countermeasures, radar systems, etc. A traveling wave tube is mainly composed of an electron gun, a slow wave structure, a collector, an input and output device, and a magnetic focusing system. The slow wave structure is the place for injection-wave interaction, that is, the key component for generating or amplifying microwave signals. At present, the folded waveguide type slow wave structure is one of the main slow wave structures used in traveling wave tubes in the millimeter wave / terahertz frequency band. Conventional folded waveguides are rectangular waveguides that are bent along the electric field to form a periodic structure of a series of straight waveguide segments and arc waveguide segments. A new type of folded waveguide is an electron injection channel opening type, that is, on the basis of conventional folded waveguides, the electron injection channel is directly connected to the arc waveguide. It has the advantages of flatter dispersion and higher coupling impedance, which can improve the performance of broadband traveling wave tubes. In addition to the folded waveguide periodic structure, another key to the application of slow wave structure is the matching structure, which is to achieve low reflection feeding and extraction of microwave signals and maximize transmission power. The matching structure directly affects the practical level of slow wave circuits.

[0003] Figure 1 Shown are a conventional folded waveguide slow-wave structure 10 and a conventional matching structure 20 matched therewith. The conventional matching structure 20 is currently generally composed of two straight waveguides of different widths transitioned through rounded corners. Figure 2 The figure shows an electron injection channel opening type folded waveguide slow-wave structure. Compared with the conventional folded waveguide slow-wave structure, the boundary conditions of the electromagnetic field of the electron injection channel opening type folded waveguide slow-wave structure have changed, forming a new field distribution. Figure 1 The conventional matching structure 20 cannot meet the design index requirements. Taking the G-band slow-wave structure as an example for design analysis, Figure 1 The reflection loss (S 11 ) is only -0.6dB (combined Figure 3 As shown in the figure, it is far higher than the design requirement of -15dB, and it is completely impossible to feed / extract microwave signals into the slow-wave circuit, which seriously limits the practical application of the electron injection channel open-type folded waveguide slow-wave structure. Summary of the invention

[0004] In view of the above problems, the present invention provides an electron beam channel opening type folded waveguide slow wave structure to solve the problem that when the existing matching structure is matched with the electron beam channel opening type folded waveguide slow wave structure, the feeding / extraction of microwave signals in the slow wave circuit cannot be realized, which severely limits the practical level of the electron beam channel opening type folded waveguide slow wave structure.

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

[0006] The present invention provides an electron beam channel opening type folded waveguide slow wave structure, including: a cavity unit and an electron beam channel; the cavity unit includes two bent waveguide cavities with opposite protruding directions that are interconnected; the bent 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, and the other ends of the straight boundaries are connected to the inner arc boundary of the adjacent bent waveguide cavity; the inner arc boundary is located within the boundary defined by the electron beam channel; the two straight boundaries of the same bent waveguide cavity have the same length;

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

[0008] Preferably, an inner arc junction part is included between the inner arc boundary and the straight boundary of the adjacent bent waveguide cavity, and the inner arc junction part is located on the axis of the electron beam channel; within the same bent waveguide cavity, an outer arc junction part is included between the outer arc boundary and the straight boundary, and a spacing height is formed between the outer arc junction part and the axis of the electron beam channel in the radial direction of the electron beam channel, and the spacing height is equal to the length of the straight boundary.

[0009] Preferably, the tapered section includes a plurality of cavity units with a periodic structure; the length of the straight boundary of the bent waveguide cavity in the uniform section is h 0 ; from the first end of the tapered section to the second end of the tapered section, the length of the straight boundary of the first bent waveguide cavity in the tapered section is h 1 , the length of the straight boundary of the mth bent waveguide cavity is h m , the number of bent waveguide cavities included in the tapered section is n, the radius of the electron beam channel is r, and the length of the straight boundary of the mth bent waveguide cavity satisfies the following relationship:

[0010] Preferably, one end of the tapered section away from the uniform section includes a connection section; the connection section is a tapered waveguide structure; the connection section 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.

[0011] Preferably, the boundary of the electron beam channel is located between the two ends of the inclined boundary.

[0012] Preferably, 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 connection section.

[0013] Preferably, the distance between the arc top points of the inner arc boundary and the outer arc boundary of the curved waveguide cavity connected to the connection section in the radial direction of the electron beam channel is equal to the opening width of the end of the connection section away from the tapered section in the axial direction of the electron beam channel.

[0014] The present invention also provides a slow-wave circuit, including the electron beam channel opening 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 opening type folded waveguide slow-wave structure.

[0015] The present invention also provides a design method for an electron beam channel opening type folded waveguide slow-wave structure, including the following steps:

[0016] Design a folded waveguide slow-wave structure, the folded waveguide slow-wave structure including cavity units and an electron beam channel; the cavity units include two curved waveguide cavities with opposite protruding directions communicating with each other; the 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, and the other ends of the straight boundaries are connected to the inner arc boundary of the adjacent curved waveguide cavity;

[0017] Using a three-dimensional electromagnetic field simulation software, move down the inner arc boundary of the curved waveguide cavity to within 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 tapered sections at both sides of the uniform section for the input / output ends; one end of the tapered 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 of the tapered section to the second end of the tapered section, the length of the straight boundary of the curved waveguide cavity is designed to gradually decrease.

[0019] Preferably, the reflection loss of the folded waveguide slow-wave structure is adjusted by changing the length of the straight boundary of the curved waveguide cavity, and the matching performance of the folded waveguide slow-wave structure is optimized.

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

[0021] The novel electron beam channel opening type folded waveguide slow-wave structure provided by the present invention can meet the usage requirements of the electron beam channel opening type folded waveguide slow-wave structure, can realize the feeding / extraction of microwave signals in the electron beam channel opening type folded waveguide slow-wave structure, improve its practical level and realize good matching characteristics of the electron beam channel opening type folded waveguide slow-wave structure. The structure of the present invention has the advantage of wide bandwidth. Taking the G band as an example, this structure can achieve a bandwidth of 30 GHz, and the relative bandwidth reaches 13.5%, which can fully cover the usage bandwidth of broadband traveling wave tubes and has strong applicability. The structure of the present invention has a high degree of design flexibility. The number of cavity units and the ratio of the straight boundary length between adjacent bent waveguide cavities can be flexibly adjusted, which can better meet the needs of the working frequency band of the slow-wave structure. The present invention makes the overall transverse size of the structure small through the cooperation of cavity units and connection segments, and has the advantages of compact structure and easy processing, which facilitates the miniaturization requirements of traveling wave tubes. Description of the Drawings

[0022] The following further elaborates in detail on the specific embodiments of the present invention with reference to the drawings.

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

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

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

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

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

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

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

[0030] Figure 6 is a reflection loss curve diagram of the electron beam channel opening type folded waveguide slow-wave structure of the present invention after fine-tuning the parameters. Specific Embodiments

[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 arrangements of components and steps, numerical expressions and values set forth in these embodiments do not limit the scope of the present invention.

[0032] 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.

[0033] 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.

[0034] In all the examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Accordingly, other examples of the exemplary embodiments may have different values.

[0035] It should be noted that: like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, further discussion thereof is not required in subsequent drawings.

[0036] In order to solve the problem that when the existing matching structure is matched with the existing electron beam channel opening type folded waveguide slow wave structure, the feeding / extraction of microwave signals in the slow wave circuit cannot be achieved, which severely limits the practical level of the electron beam channel opening type folded waveguide slow wave structure. The present invention provides an electron beam channel opening type folded waveguide slow wave structure, combined with Figures 1 to 6 As shown, specifically, the electron beam channel opening type folded waveguide slow wave structure includes: a cavity unit and an electron beam channel 22. The cavity unit includes two curved waveguide cavities 21 with opposite protruding directions that are interconnected; the curved waveguide cavity 21 includes an inner circular arc boundary C 1 and an outer circular arc boundary C 2 , and two straight boundaries L 2 respectively connected to both ends of the outer circular arc boundary C 1 , and the other end of the straight boundary L 1 is connected to the inner circular arc boundary C 1 of the adjacent curved waveguide cavity 21. The inner circular arc boundary C 1 is located within the boundary defined by the electron beam channel 22; the two straight boundaries L 1 of the same curved waveguide cavity 21 have the same length. The folded waveguide slow wave structure includes a uniform section 11 and tapered sections 12 at the input / output ends on both sides of the uniform section 11; the tapered sections 12 have the same cavity structure shape as the uniform section 11, in Figure 4A and Figure 4COnly the tapered section 12 located on one side of the uniform section 11 is shown. One end of the tapered section 12 connected to the uniform section 11 is the first end, and the end far from the uniform section 11 is the second end; from the first end of the tapered section 12 to the second end of the tapered section 12, the linear boundary length of the curved waveguide cavity 21 gradually decreases. That is, starting from the end of the tapered section 12 connected to the uniform section 11, the linear boundary length of the curved waveguide cavity 21 of the tapered section 12 gradually decreases. The sizes of the curved waveguide cavities 21 in the uniform section 11 always remain the same. The present invention has the characteristics of low reflection loss, wideband, and simple and easy-to-process structure, significantly improving the practical level of the slow-wave structure, thereby improving the performance of millimeter-wave / terahertz broadband traveling wave tubes.

[0037] In a specific embodiment, the inner arc boundary C 1 and the linear boundary L of the adjacent curved waveguide cavity 21 1 include an inner arc junction Q 1 , and the inner arc junction Q 1 is located on the axis L of the electron beam channel 0 ; within the same curved waveguide cavity 21, the outer arc boundary C 2 and the linear boundary L 1 include an outer arc junction Q 2 , and the outer arc junction Q 2 and the axis L of the electron beam channel 0 form a spacing height in the radial direction of the electron beam channel, and the spacing height is equal to the linear boundary length. Through the above settings, while ensuring the coupling impedance of the slow-wave structure, the thin-walled arc structure at the opening position of the electron beam channel can be eliminated, which has the characteristics of easy processing and high structural strength, and better meets the requirements of engineering applications.

[0038] In a specific embodiment, the tapered section 12 includes a plurality of 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 linear boundary length of the curved waveguide cavity 21 in the uniform section 11 is h 0 . From the first end of the tapered section 12 to the second end of the tapered section 12, the linear boundary length of the first curved waveguide cavity connected to the uniform section 11 in the tapered section 12 is h 1 , the linear boundary length of the mth curved waveguide cavity is h m , the number of curved waveguide cavities 21 included in the tapered section 12 is n, the radius of the electron beam channel 22 is r, and the linear boundary length of the mth curved waveguide cavity satisfies the following relationship: The above electron beam channel radius r is generally selected when designing the electrical performance of the slow-wave structure. Combining Figure 4C, taking the example that one side of the gradual change section 12 includes four bent waveguide cavities 21, when the radius of the electron beam channel is selected to be 0.12 mm and the straight boundary length h of the bent waveguide cavity 21 in the uniform section 11 0 = 0.3 mm, the straight boundary length h of the first bent waveguide cavity in the gradual change section 12 1 = 0.26 mm, the straight boundary length h of the second bent waveguide cavity in the gradual change section 2 = 0.22 mm, the straight boundary length h of the third bent waveguide cavity in the gradual change section 3 = 0.18 mm, the straight boundary length h of the fourth bent waveguide cavity in the gradual change section 4 = 0.14 mm. At this time, the open-type folded waveguide slow-wave structure of the electron beam channel of the present invention can take into account the advantages of broadband and low reflection loss in the working frequency band and meet the design requirements.

[0039] In a specific embodiment, in order to further reduce the reflection loss of the folded waveguide slow-wave structure and reduce the number of cavity units required for the gradual change section, one end of the gradual change section 12 far from the uniform section 11 includes a connection section 13; the connection section 13 is a gradually changing waveguide structure; the connection section 13 includes an inclined boundary L 2 connected to one end of the outer arc boundary C of the bent waveguide cavity 21 2 and a vertical boundary L 1 connected to one end of the inner arc boundary C of the bent waveguide cavity 21 3 . When the gradual change section 12 is connected and matched with the connection section 13, the straight boundary on the adjacent side of the bent waveguide cavity 21 of the gradual change section 12 that cooperates with the connection section 13 is replaced by the inclined boundary L of the connection section 13 2 . It can be understood that the inclined boundary L of the connection section 13 2 corresponds to an inclined plane, and the vertical boundary L 3 corresponds to a vertical plane. At the input end of the folded waveguide slow-wave structure, along the signal input direction, the distance between the inclined boundary L 2 and the vertical boundary L 3 gradually becomes smaller. Further, the boundary of the electron beam channel 22 is located between the two ends of the inclined boundary L 2 .

[0040] In a specific embodiment, the height of the inclined boundary L 2 in the radial direction of the electron beam channel is equal to twice the straight boundary length of the bent waveguide cavity 21 connected to the connection section 13. When the inclined boundary L 2When the height of the electron beam channel in the radial direction is equal to twice the length of the straight boundary of the curved waveguide cavity 21 connected to the connection section 13, the reflection loss of the open-folded waveguide slow-wave structure of the electron beam channel 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 connection section, the reflection loss of the open-folded waveguide slow-wave structure of the electron beam channel increases in the operating frequency band.

[0041] In a specific embodiment, the inner arc boundary C of the curved waveguide cavity 21 connected to the connection section 13 1 The arc top point of and the outer arc boundary C 2 The distance between the arc top points in the radial direction of the electron beam channel is equal to the opening width of the end of the connection section 13 away from the tapered section 12 in the axial direction of the electron beam channel. When the two are equal, the bandwidth of the open-folded waveguide slow-wave structure of the electron beam channel is the widest in the operating frequency band. When the two are not equal, the bandwidth of the open-folded waveguide slow-wave structure of the electron beam channel becomes narrower in the operating frequency band.

[0042] The following gives an embodiment of the present invention with specific dimensions. As Figures 4A - 4B shown, the structural dimensions of the open-folded waveguide slow-wave structure of the electron beam channel are set as (unit: mm): the wide side length a of the uniform section 11 = 0.84, the narrow side length b of the uniform section 11 = 0.1, the geometric period length p of the uniform section 11 = 0.55, the electron beam channel radius r = 0.12, and the straight boundary length h of the uniform section 11 0 = 0.28. Using the three-dimensional electromagnetic software CST Microwave Studio to optimize and simulate the structure of the present invention, the final parameter design values of the tapered section 12 are: the straight boundary length h of the first curved waveguide cavity of the tapered section 12 1 = 0.21, the straight boundary length of the second curved waveguide cavity of the tapered section 12 is h 2 = 0.14, the distance w between the arc top points of the inner arc boundary C of the second curved waveguide cavity 1 and the outer arc boundary C 2 in the radial direction of the electron beam channel is 0.24, and the other structural dimensions are the same as those of the uniform section. The structural parameters of the connection section 13 are designed as: the height H of the inclined boundary L 2 in the radial direction of the electron beam channel is 0.28, and the opening width d of the end of the connection section 13 away from the tapered section 12 in the axial direction of the electron beam channel is 0.24. The simulation results of the reflection loss of the corresponding folded waveguide slow-wave structure are as Figure 5 shown, and its S between 206 GHz - 236 GHz 11The parameter is below -15 dB, the bandwidth can reach 30 GHz, and the relative bandwidth is 13.5%. It can fully meet the requirements of the operating bandwidth of the open-type slow-wave structure of the electron beam channel. Moreover, the tapered section of this structure only tapers a single structural parameter within a single cavity unit, featuring a simple and compact overall structure and being easy to process. It can fully be compatible with the existing folded waveguide processing technology, and integrated precision machining can be achieved by using high-speed milling technology.

[0043] Figure 6 Shows the reflection loss schematic diagram after only slightly adjusting h based on the above specific structural parameters of the present invention 1 and h 2 The corresponding specific structural parameters (unit: mm) are as follows: the wide side length a of the uniform section 11 is 0.84, the narrow side length b of the uniform section 11 is 0.1, the geometric period length p of the uniform section 11 is 0.55, the electron beam channel radius r is 0.12, and the straight boundary length h 0 of the uniform section 11 1 = 0.28. The straight boundary length h 2 of the first bent waveguide cavity of the tapered section 12 1 = 0.23, the straight boundary length h 2 of the second bent waveguide cavity of the tapered section 12 2 = 0.13. The distance w between the arc top points of the inner arc boundary C 2 of the second bent waveguide cavity and the arc top points of the outer arc boundary C 2 in the radial direction of the electron beam channel is 0.24. The opening width d of the end of the connection section 13 far from the tapered section 12 in the axial direction of the electron beam channel is 0.24, and the height H of the inclined boundary L 2 1 and h 2 in the radial direction of the electron beam channel is 0.28. By Figure 6 and Figure 5 comparison, it can be seen that after slightly adjusting the dimensions of h 1 and h 2 , the usage requirements of a traveling-wave tube with the operating frequency band close to 230 GHz can be better met.

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

[0045] The present invention also provides a design method for an electron beam channel opening type folded waveguide slow wave structure, and the method includes the following steps: designing a folded waveguide slow wave structure, where the folded waveguide slow wave structure includes cavity units and an electron beam channel 22; the cavity units include two bent waveguide cavities 21 with opposite protruding directions that are interconnected; the bent waveguide cavity 21 includes an inner arc boundary C 1 and an outer arc boundary C 2 , and two straight boundaries L 2 respectively connected to both ends of the outer arc boundary C 1 , and the other end of the straight boundary L 1 is connected to the inner arc boundary C 1 of the adjacent bent waveguide cavity 21; using a three-dimensional electromagnetic field simulation software, moving down the inner arc boundary C 1 of the bent waveguide cavity 21 to within the boundary defined by the electron beam channel 22; the two straight boundaries L 1 of the same bent waveguide cavity 21 are designed to have the same length; the folded waveguide slow wave structure includes a uniform section 11 and tapered sections 12 at the input / output ends on both sides of the uniform section 11; one end of the tapered section 12 connected to the uniform section 11 is the first end, and the end far from the uniform section 11 is the second end; from the first end of the tapered section 12 to the second end of the tapered section 12, the straight boundary length of the bent waveguide cavity 21 is designed to gradually decrease. Further, the reflection loss of the folded waveguide slow wave structure is adjusted by changing the straight boundary length of the bent waveguide cavity 21 to optimize the matching performance of the folded waveguide slow wave structure. More specifically, by finely tuning the dimensions of h 1 and h 2 , the usage requirements of a traveling wave tube with a working frequency band close to 230 GHz can be better met.

[0046] In summary, the novel electron beam channel opening type folded waveguide slow wave structure provided by the present invention can meet the usage requirements of the electron beam channel opening type folded waveguide slow wave structure, can realize the feeding / extraction of microwave signals in the electron beam channel opening type folded waveguide slow wave structure, improve its practical level and achieve good matching characteristics of the electron beam channel opening type folded waveguide slow wave structure. The structure of the present invention has the advantage of wide bandwidth. Taking the G band as an example, this structure can achieve a bandwidth of 30 GHz, and the relative bandwidth reaches 13.5%, which can fully cover the usage bandwidth of broadband traveling wave tubes and has strong applicability. The structure of the present invention has a high degree of design flexibility, and the number of cavity units and the ratio of the straight boundary lengths between adjacent bent waveguide cavities can be flexibly adjusted to better meet the needs of the working frequency band of the slow wave structure. The present invention enables the overall transverse dimension of the structure to be small through the cooperation of cavity units and connection segments, has the advantages of being structurally compact and easy to process, and provides convenience for 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, rather than limitations on 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 based on the above description. It is impossible to enumerate 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. An electron injection channel opening type folded waveguide slow-wave structure, characterized in that: include: A cavity unit and an electron injection channel; the cavity unit comprises two mutually connected curved waveguide cavities with protrusions in opposite directions; The curved waveguide cavity comprises an inner arc boundary and an outer arc boundary, and two straight line boundaries respectively connected to two ends of the outer arc boundary, and the other end of the straight line boundary is connected to the inner arc boundary of the adjacent curved waveguide cavity; the inner arc boundary is located within the boundary defined by the electron injection 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 gradient section 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 of the gradient section to the second end of the gradient section, the straight boundary length of the curved waveguide cavity gradually decreases.

2. The electron injection channel opening 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 intersection portion, and the inner arc intersection portion is located on the axis of the electron injection channel; in the same curved waveguide cavity, the outer arc boundary and the straight boundary include an outer arc intersection portion, and a spacing height is formed between the outer arc intersection portion and the axis of the electron injection channel in the radial direction of the electron injection channel, and the spacing height is equal to the length of the straight boundary.

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

4. The electron injection channel opening type folded waveguide slow-wave structure according to claim 1, characterized in that: The end of the gradient section away from the uniform section includes a connecting section; the connecting section is a gradient waveguide structure; the connecting section 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 injection channel opening type folded waveguide slow-wave structure according to claim 4, characterized in that: The boundary of the electron injection channel is located between two ends of the inclined boundary.

6. The electron injection channel opening 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 injection channel is equal to twice the length of the straight boundary of the curved waveguide cavity connected to the connecting section.

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

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

9. A design method for an electron injection channel opening type folded waveguide slow-wave structure, characterized in that: The following steps are involved: A folded waveguide slow-wave structure is designed, wherein the folded waveguide slow-wave structure comprises a cavity unit and an electron injection channel; the cavity unit comprises two mutually connected curved waveguide cavities with opposite convex directions; the curved waveguide cavity comprises an inner arc boundary and an outer arc boundary, and two straight line boundaries respectively connected to two ends of the outer arc boundary, and the other end of the straight line 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 injection channel; the two straight line boundaries of the same curved waveguide cavity are designed to have the same length; The folded waveguide slow-wave structure comprises a uniform section and a gradient section 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 of the gradient section 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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