An energy-coupling structure suitable for a symmetrical double-slot coupled cavity slow-wave structure

Abstract

The application provides an energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow wave structure, which comprises a tapered waveguide section used for connecting with the symmetrical double-slot coupled cavity slow wave structure; the tapered waveguide section comprises a plurality of cavity units of a periodic structure and an electron beam channel located at the central axis position of the cavity units; the cavity unit comprises two straight waveguide cavities and two connecting cavities located between the two straight waveguide cavities; the two connecting cavities are symmetrically arranged relative to the electron beam channel and axially communicate the two straight waveguide cavities along the electron beam channel; the straight waveguide cavities of adjacent cavity units are connected in communication; the height of the straight waveguide cavities, the length of the narrow side of the straight waveguide cavities and the period length of the cavity units in communication in sequence from one end of the energy transmission coupling structure used for connecting with the symmetrical double-slot coupled cavity slow wave structure gradually increase. The energy transmission coupling structure can solve the problem that the existing energy transmission coupling structure has a relatively narrow bandwidth and affects the working performance of the symmetrical double-slot coupled cavity slow wave structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of vacuum electron technology, and more particularly to an energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow wave structure. BACKGROUND

[0002] Millimeter wave / terahertz technology has important application value in the fields of future communication, imaging, radar, etc. At present, the main obstacle restricting its development is the lack of compact structure, moderate power level, and wideband coherent radiation source. Traveling wave tube is a kind of vacuum electron device, which can realize the generation or amplification of millimeter wave / terahertz signals. Compared with other types of devices, the traveling wave tube is one of the few devices that can work at millimeter wave and terahertz frequency bands with wide frequency band, high gain, large power capacity, and compact structure. The traditional system of the traveling wave tube device is limited by the size of the effect, that is, as the frequency increases, the output power decreases with the square of the frequency, which greatly limits the ability of the traveling wave tube to work at high frequency. The strip electron beam technology is an effective technical approach to overcome this problem, and is currently one of the research hotspots in the field of terahertz vacuum electron devices.

[0003] The symmetrical double-slot coupled cavity slow wave structure is a full-metal slow wave structure suitable for strip electron beam, which has the advantages of large electron beam channel and high coupling impedance, and its basic structure is shown in Figure 1 Although the electromagnetic wave propagation path and the electron beam transmission path in the symmetrical double-slot coupled cavity slow wave structure are separated from each other, which is beneficial to the feeding and extraction of electromagnetic field, due to the existence of the coupled cavity structure, it is relatively difficult to broaden the bandwidth of the slow wave structure, and a complex design is required. The existing energy transmission coupling structure has a relatively narrow bandwidth, which will affect the working performance of the symmetrical double-slot coupled cavity slow wave structure. SUMMARY

[0004] In view of the above problems, the present application provides an energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow wave structure to solve the problem that the existing energy transmission coupling structure has a relatively narrow bandwidth, which will affect the working performance of the symmetrical double-slot coupled cavity slow wave structure.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] The present application provides an energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow wave structure, comprising: a tapered waveguide section connected with the symmetrical double-slot coupled cavity slow wave structure; the tapered waveguide section comprises a plurality of cavity units of periodic structure and an electron beam channel located at the central axis position of the cavity units;

[0007] The cavity unit comprises two straight waveguide cavities and two connecting cavities located between the two straight waveguide cavities; the two connecting cavities are symmetrically arranged with respect to the electron beam channel and axially communicate the two straight waveguide cavities; the straight waveguide cavities of adjacent cavity units are connected;

[0008] The straight waveguide cavity height, the straight waveguide cavity narrow edge length and the period length of the cavity units successively connected from the end of the energy transmission coupling structure connected with the symmetric double-slot coupled cavity slow wave structure gradually increase.

[0009] Preferably, the straight waveguide cavity height, the straight waveguide cavity narrow edge length and the period length of the cavity units successively connected from the end of the energy transmission coupling structure connected with the symmetric double-slot coupled cavity slow wave structure gradually increase in a linear manner.

[0010] Preferably, the two straight waveguide cavities of the same cavity unit have the same structural size, and the two connecting cavities of the same cavity unit have the same structural size.

[0011] Preferably, the straight waveguide cavity height of the first cavity unit connected with the slow wave structure is h1, the straight waveguide cavity narrow edge length is d1, and the period length is p1; the straight waveguide cavity height of the nth cavity unit is h n , the straight waveguide cavity narrow edge length is d n , and the period length is p n ; the straight waveguide cavity height of the last cavity unit is h N , the straight waveguide cavity narrow edge length is d N , and the period length is p N ; and the number of the cavity units is N.

[0012] The straight waveguide cavity height, the straight waveguide cavity narrow edge length and the period length of the nth cavity unit satisfy the following relationships respectively:

[0013] h n =h1+n(h N -h1) / (N+1);

[0014] d n =d1+n(d N -d1) / (N+1);

[0015] p n =p1+n(p N -p1) / (N+1)。

[0016] Preferably, the energy transmission coupling structure further comprises a connecting waveguide section.

[0017] The connecting waveguide section comprises a coupling cavity connected with the straight waveguide cavity of the energy transmission coupling structure away from the slow wave structure and a standard waveguide connected with the coupling cavity; the coupling cavity has the same structural size as the connected straight waveguide cavity; the coupling cavity and the standard waveguide are coaxially arranged and the axis is perpendicular to the electron beam passage axis.

[0018] Preferably, the electron beam passage is a rectangular cross-section passage.

[0019] Preferably, the energy-coupling structure is an input-coupling structure or an output-coupling structure.

[0020] The present application also provides a slow-wave circuit comprising a symmetric double-slot coupled cavity slow-wave structure and an energy-coupling structure as described above; the energy-coupling structure is connected to the input end and / or the output end of the symmetric double-slot coupled cavity slow-wave structure; the cavity unit connected to the input end of the symmetric double-slot coupled cavity slow-wave structure has the same structural dimensions as the single-period symmetric double-slot coupled cavity slow-wave structure and / or the cavity unit connected to the output end of the symmetric double-slot coupled cavity slow-wave structure has the same structural dimensions as the single-period symmetric double-slot coupled cavity slow-wave structure.

[0021] The present application also provides a design method of an energy-coupling structure suitable for a symmetric double-slot coupled cavity slow-wave structure, comprising the following steps: designing a tapered waveguide section to be connected to the symmetric double-slot coupled cavity slow-wave structure; the tapered waveguide section comprises a plurality of cavity units of periodic structure and an electron beam channel located at the central axis of the cavity units; the cavity unit comprises two straight waveguide cavities and two connecting cavities located between the two straight waveguide cavities; the two connecting cavities are symmetrically arranged with respect to the electron beam channel and axially communicate the two straight waveguide cavities along the electron beam channel; the straight waveguide cavities of adjacent cavity units are connected;

[0022] Using a three-dimensional electromagnetic field simulation software, the straight waveguide cavity height, the straight waveguide cavity narrow side length and the period length of the cavity units connected in sequence are all designed to gradually increase from the end of the energy-coupling structure to be connected to the symmetric double-slot coupled cavity slow-wave structure.

[0023] Preferably, by gradually increasing the period length of the energy-coupling structure, the influences of the gradually increasing straight waveguide cavity height and the gradually increasing straight waveguide cavity narrow side length on the structural characteristic impedance are balanced, so that the overall impedance of the energy-coupling structure is smoothly and gradually changed, and the matching performance of the energy-coupling structure is improved.

[0024] The present application has the following beneficial effects:

[0025] The present application can greatly widen the structural bandwidth and optimize the electromagnetic performance of the structure. In the range of 205.5GHz-222.5GHz, the corresponding S 11 The bandwidth of the parameter below -15dB can reach 17GHz, and the relative bandwidth is 8%. The requirement of the symmetric double-slot coupled cavity slow-wave structure for matching the working bandwidth of the structure can be fully met.

[0026] And the application realizes H-plane matching output, can prevent electromagnetic wave from leaking through the electron beam channel without using a reflector, which improves the longitudinal compactness of the structure. In the transverse direction, the matching output is realized only through a tapered waveguide segment, and the transverse compactness is high. The S 31 The value of the parameter is below -150dB, which indicates that the leakage is below the order of 10 -15 magnitude, further improving the isolation performance. The straight waveguide cavity height, straight waveguide cavity narrow edge length and period length of the energy transmission coupling structure cavity unit are linearly tapered, so that the design flexibility is high. For different size parameters of the symmetric double-slot coupled cavity slow wave structure and its bandwidth requirements, the tapered parameters can be flexibly adjusted to achieve the requirements. BRIEF DESCRIPTION OF DRAWINGS

[0027] The specific embodiments of the application will be further described in detail below with reference to the accompanying drawings.

[0028] Figure 1 is a structural schematic diagram of a single-period symmetric double-slot coupled cavity slow wave structure.

[0029] Figure 2A is a whole structural schematic diagram of the energy transmission coupling structure of the application.

[0030] Figure 2B is a structural schematic diagram of the tapered waveguide segment of the application.

[0031] Figure 3 is the corresponding S 11 performance parameter curve of the application.

[0032] Figure 4 is the corresponding S 31 performance parameter curve of the application.

[0033] Figure 5 is a period length size tapering effect on impedance curve of the application.

[0034] Reference signs: 1, tapered waveguide segment, 2, coupled cavity, 3, standard waveguide, 11, electron beam channel, 12, straight waveguide cavity, 13, connecting cavity, 101, first cavity unit, 102, second cavity unit, 103, third cavity unit. DETAILED DESCRIPTION

[0035] Various exemplary embodiments of the application will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement, numerical expressions and values of the components and steps set forth in these embodiments do not limit the scope of the application unless otherwise specifically stated.

[0036] The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the application or its application or uses.

[0037] Techniques and devices known to those of ordinary skill in the relevant art can not be discussed in detail herein, but should be considered as part of the specification.

[0038] In all of the compositions and methods shown and discussed herein, any particular value is to be construed merely as an example, and not a limitation. Other examples of the exemplary embodiments can have different values.

[0039] It should be noted that like reference numerals and letters refer to like items throughout the several views of the drawings, and that discussion of one item in a drawing does not require further discussion of that item in subsequent drawings.

[0040] Due to the limitation of machining means in the terahertz band, the input and output structure should be a full-metal waveguide structure with machinability. The structure must have sufficient bandwidth to meet the performance requirements of the symmetrical double-slot coupled cavity slow wave structure. In order to not increase the complexity of the magnetic field design, it should be introduced from the H plane, and the length should be shortened as much as possible.

[0041] In order to solve the problem that the existing coupling structure is difficult to realize bandwidth widening, which affects the working performance of the symmetrical double-slot coupled cavity slow wave structure. The application provides an energy input and output coupling structure suitable for the symmetrical double-slot coupled cavity slow wave structure, which combines Figures 1 to 5As shown, in particular, the power-coupling structure suitable for the symmetrical double-slot coupled cavity slow-wave structure comprises: a tapered waveguide section 1 for connecting with the symmetrical double-slot coupled cavity slow-wave structure; the tapered waveguide section 1 comprises a plurality of cavity units of periodic structure and an electron beam channel 11 located at the central axis position of the cavity units; the cavity unit comprises two straight waveguide cavities 12 and two connecting cavities 13 located between the two straight waveguide cavities 12; the two connecting cavities 13 are symmetrically arranged relative to the electron beam channel 11 and axially communicate the two straight waveguide cavities 12 along the electron beam channel 11; the straight waveguide cavities 12 of adjacent cavity units are communicated; from the end of the power-coupling structure for connecting with the symmetrical double-slot coupled cavity slow-wave structure, the height h of the straight waveguide cavities of the cavity units, the narrow side length d of the straight waveguide cavities and the period length p of the cavity units communicated in sequence gradually increase. The cavity unit of the power-coupling structure of the present application has the same structural appearance as the single-period symmetrical double-slot coupled cavity slow-wave structure. It should be noted that the cavity units of the present application are consistent in shape and arranged according to certain rules, and even if their sizes are different, they can be considered to constitute a periodic structure. Further, the two straight waveguide cavities of the same cavity unit have the same structural size, and the two connecting cavities of the same cavity unit have the same structural size. The present application has compact structure, wide bandwidth and can meet the practical requirements, and at the same time, good characteristics of matching, reflection and isolation can be realized.

[0042] In the present application, the height h of the straight waveguide cavities, the narrow side length d of the straight waveguide cavities and the period length p of the cavity units of the periodic structure are tapered. The height h of the straight waveguide cavities and the narrow side length d of the straight waveguide cavities are tapered to make the size of the coupled cavity close to that of the standard waveguide in size, so as to reduce the return loss caused by the sudden change in transverse size between the coupled cavity and the standard waveguide.

[0043] The period length p is tapered to balance the influence of the tapering of the height h of the straight waveguide cavities and the narrow side length d of the straight waveguide cavities on the structural characteristic impedance, so that the overall impedance is smoothly tapered to achieve the best matching effect. Figure 5 As shown, it describes the influence relationship of the size tapering of the period length p on the impedance, and it can be seen that the impedance is smoothly changed.

[0044] In a specific embodiment, from the end of the symmetrical double-slot coupled cavity slow-wave structure for connecting, the height h of the straight waveguide cavities of the cavity units, the narrow side length d of the straight waveguide cavities and the period length p of the cavity units communicated in sequence gradually increase in a linear rule. The power-coupling structure is an input coupling structure or an output coupling structure. When the power-coupling structure is an input coupling structure, it is connected with the input end of the symmetrical double-slot coupled cavity slow-wave structure to realize the input of the microwave signal into the symmetrical double-slot coupled cavity slow-wave structure. When the power-coupling structure is an output coupling structure, it is connected with the output end of the symmetrical double-slot coupled cavity slow-wave structure to realize the output of the microwave signal from the symmetrical double-slot coupled cavity slow-wave structure.

[0045] More specifically, the straight waveguide cavity height of the first cavity unit connected to the symmetrical double-slot coupled cavity slow-wave structure is h1, the narrow side length of the straight waveguide cavity is d1, and the period length is p1; the straight waveguide cavity height of the nth cavity unit is h n , the narrow side length of the straight waveguide cavity is d n , the period length is p n ; The height of the straight waveguide cavity of the last cavity unit is h N , the narrow side length of the straight waveguide cavity is d N , the period length is p N The number of cavity units is N, which can be selected according to the required bandwidth size and can be selected in the range of 2-4. The height of the straight waveguide cavity, the narrow side length of the straight waveguide cavity and the period length of the nth cavity unit respectively satisfy the following relationship: h n =h1+n(h N -h1) / (N+1);d n =d1+n(d N -d1) / (N+1);p n =p1+n(p N -p1) / (N+1).

[0046] Combine Figure 2B As shown, there are three cavity units, namely, from left to right, the first cavity unit 101, the second cavity unit 102, and the third cavity unit 103. The three cavity units have the same structural appearance, and the straight waveguide cavity height h, the straight waveguide cavity narrow side length d, and the period length p gradually increase from the first cavity unit 101 to the third cavity unit 103. The first cavity unit 101 is connected to the symmetrical double-slot coupled cavity slow-wave structure, and the third cavity unit 103 is connected to the coupled cavity. The two straight waveguide cavities of the first cavity unit 101 have the same structural dimensions, and the two connected cavities of the first cavity unit 101 have the same structural dimensions. The two straight waveguide cavities of the second cavity unit 102 have the same structural dimensions, and the two connected cavities of the second cavity unit 102 have the same structural dimensions. The two straight waveguide cavities of the third cavity unit 103 have the same structural dimensions, and the two connected cavities of the third cavity unit 103 have the same structural dimensions.

[0047] In one specific embodiment, the energy transmission coupling structure further includes a connecting waveguide segment; the connecting waveguide segment comprises a coupling cavity 2 connected to a straight waveguide cavity 12 of the symmetrical double-slot coupled cavity slow-wave structure, which is located away from the cavity unit of the energy transmission coupling structure and is separated from the symmetrical double-slot coupled cavity slow-wave structure, and a standard waveguide 3 connected to the coupling cavity 2. The coupling cavity 2 and the connected straight waveguide cavity 12 have the same structural dimensions. The coupling cavity 2 and the standard waveguide 3 are coaxially arranged, with their axes perpendicular to the axis of the electron beam channel. The present invention utilizes a linearly tapered waveguide segment 1 coupled to the connecting waveguide segment to achieve input and output matching of the electromagnetic field of the symmetrical double-slot coupled cavity slow-wave structure. From the end connected to the slow-wave structure, the straight waveguide cavity height h and the narrow side length d of the energy transmission coupling structure gradually increase from the same dimensions as those of the single-period symmetrical double-slot coupled cavity slow-wave structure to the same dimensions as those of the coupling cavity 2, achieving a matching connection between the symmetrical double-slot coupled cavity slow-wave structure and the coupling cavity 2, while the period length p gradually increases. The coupling cavity 2 connects the tapered waveguide segment 1 with the standard waveguide 3, enabling the transmission of electromagnetic energy from the symmetrical double-slot coupled cavity slow-wave structure to the standard waveguide 3 and providing impedance matching. Because the electric field in the coupling cavity 2 is aligned with the direction of electron beam transmission, electromagnetic transmission cannot be stimulated within the electron beam channel. The electromagnetic field is cut off along the direction of the electron beam channel, preventing leakage from the electron beam channel. The electron beam channel 11 has a rectangular cross-section, and the structural dimensions of the electron beam channel 11 remain unchanged throughout the energy transmission coupling structure of the present invention.

[0048] In a specific embodiment, the straight waveguide cavity height of the first cavity unit of the tapered waveguide section 1 connected to the symmetrical double-slot coupled cavity slow-wave structure is h1, the straight waveguide cavity narrow side length is d1, and the period length is p1. The straight waveguide cavity height of the last cavity unit of the tapered waveguide section 1 connected to the coupled cavity 2 is h N , the narrow side length of the straight waveguide cavity is d N , the period length is p N ; The number of cavity units is N. The following is a set of specific values ​​of the above parameters (unit: mm): h1 = 0.72, d1 = 0.34, p1 = 0.46, h N =0.78,d N =0.3, p N = 0.3, N = 3. A set of dimensional parameters (unit: mm) of the coupling cavity 2 and the standard waveguide 3 are also given: coupling cavity wide side length = 0.6, coupling cavity narrow side length = 0.33, coupling cavity height = 0.78, standard waveguide height = 1.092, standard waveguide width = 0.546.

[0049] Due to the electromagnetic characteristics of the coupling cavity structure in the symmetric double-slot coupled cavity slow wave structure, the bandwidth of the structure is relatively narrow, and it is difficult to increase the bandwidth.

[0050] With reference to Figure 3 It can be seen that, between 205.5GHz and 222.5GHz, S 11 The parameter is below -15dB, and the bandwidth can reach 17GHz, and the relative bandwidth is 8%. This can fully meet the requirement of the symmetric double-slot coupled cavity slow wave structure for matching the working bandwidth of the structure. Compared with the relative matching bandwidth of 8% of the present application, the relative matching bandwidth of the existing non-gradual input / output coupling structure does not exceed 2%.

[0051] The present application can prevent electromagnetic wave leakage through the electron beam channel without using a reflector due to the realization of H-plane matching. For details, refer to Figure 5 It can be seen that, between 205.5GHz and 222.5GHz, S 31 The parameter is below -150dB, which indicates that the leakage is below the order of 10 -15 .

[0052] The present application also provides a slow wave circuit, which comprises a symmetric double-slot coupled cavity slow wave structure and an energy-coupling structure as described above; the energy-coupling structure is connected with the input end and / or the output end of the symmetric double-slot coupled cavity slow wave structure; the cavity unit connected with the input end of the symmetric double-slot coupled cavity slow wave structure has the same structural size as the single-period symmetric double-slot coupled cavity slow wave structure, and / or the cavity unit connected with the output end of the symmetric double-slot coupled cavity slow wave structure has the same structural size as the single-period symmetric double-slot coupled cavity slow wave structure.

[0053] The present application also provides a design method of an energy-coupling structure suitable for a symmetric double-slot coupled cavity slow wave structure, which comprises the following steps: designing a gradual waveguide section 1 to be connected with the symmetric double-slot coupled cavity slow wave structure; the gradual waveguide section 1 comprises a plurality of cavity units of periodic structure and an electron beam channel 11 located at the central axis position of the cavity units; the cavity unit comprises two straight waveguide cavities 12 and two connecting cavities 13 located between the two straight waveguide cavities 12; the two connecting cavities 13 are symmetrically arranged relative to the electron beam channel and axially communicate the two straight waveguide cavities 12; the straight waveguide cavities 12 of adjacent cavity units are communicated; using a three-dimensional electromagnetic field simulation software, the straight waveguide cavity height h, the straight waveguide cavity narrow side length d and the period length p of the cavity units which are sequentially communicated are all designed to gradually increase from the end of the energy-coupling structure to be connected with the symmetric double-slot coupled cavity slow wave structure.

[0054] Further, by gradually increasing the period length p of the energy transmission coupling structure, the influences of gradually increasing the balanced straight waveguide cavity height h and the straight waveguide cavity narrow length d on the structural characteristic impedance are balanced, so that the overall impedance of the energy transmission coupling structure is smoothly changed, and the matching performance of the energy transmission coupling structure is improved.

[0055] In summary, the application can greatly widen the structural bandwidth and optimize the electromagnetic performance of the structure. In the range of 205.5GHz-222.5GHz, the corresponding S 11 The bandwidth of the parameter below-15dB can reach 17GHz, and the relative bandwidth is 8%. The requirement of the symmetric double-slot coupled cavity slow wave structure for matching the structural working bandwidth can be fully met. The application realizes the H-plane matching output, and the effect of preventing electromagnetic wave leakage through the electron beam channel can be achieved without using a reflector, which improves the longitudinal compactness of the structure. In the lateral direction, the matching output is realized only through a tapered waveguide section, and the lateral compactness is high. The S 31 The value of the parameter is below-150dB, which indicates that the leakage is below the order of 10 -15 magnitude, and the isolation performance is further improved. The straight waveguide cavity height, the straight waveguide cavity narrow length and the period length of the energy transmission coupling structure cavity unit of the application are linearly and gradually changed, so that the design flexibility is high. For different size parameters of the symmetric double-slot coupled cavity slow wave structure and the bandwidth requirement, the gradual change parameters can be flexibly adjusted to achieve the requirements.

[0056] Obviously, the above embodiments of the application are only examples for clearly illustrating the application, and are not intended to limit the embodiments of the application. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can be made, and it is impossible to enumerate all the embodiments here. Any changes or variations derived from the technical solutions of the application still fall within the protection scope of the application.

Claims

1. An energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow-wave structure, characterized in that: include: A gradient waveguide section for connecting to a symmetrical double-slot coupled cavity slow-wave structure; the gradient waveguide section comprises a plurality of cavity units of a periodic structure and an electron injection channel located at the central axis of the cavity unit; The cavity unit includes two straight waveguide cavities and two connecting cavities located between the two straight waveguide cavities; the two connecting cavities are symmetrically arranged relative to the electron injection channel and connect the two straight waveguide cavities along the axial direction of the electron injection channel; the straight waveguide cavities of adjacent cavity units are connected; Starting from the end of the energy transmission coupling structure connected to the symmetrical double-slot coupled cavity slow-wave structure, the height, narrow side length and period length of the straight waveguide cavity of the cavity units connected in sequence gradually increase; Starting from the end connected to the symmetrical double-slot coupled cavity slow-wave structure, the straight waveguide cavity height, straight waveguide cavity narrow side length and period length of the cavity units connected in sequence gradually increase in a linear pattern. The two straight waveguide cavities of the same cavity unit have the same structural dimensions, and the two connecting cavities of the same cavity unit have the same structural dimensions.

2. The energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow-wave structure according to claim 1, characterized in that: The height of the straight waveguide cavity of the first cavity unit connected to the slow-wave structure is h1, the narrow side length of the straight waveguide cavity is d1, and the period length is p1; the height of the straight waveguide cavity of the nth cavity unit is h n , the narrow side length of the straight waveguide cavity is d n , the period length is p n ; The height of the straight waveguide cavity of the last cavity unit is h N , the narrow side length of the straight waveguide cavity is d N , the period length is p N ;The number of cavity units is N; The height of the straight waveguide cavity, the narrow side length and the period length of the nth cavity unit satisfy the following relationships: h n =h1+n(h N -h1) / (N+1); d n =d1+n(d N -d1) / (N+1); p n =p1+n(p N -p1) / (N+1).

3. The energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow-wave structure according to claim 1, characterized in that: The energy transmission coupling structure further includes a connecting waveguide section; The connecting waveguide section includes a coupling cavity connected to a straight waveguide cavity of an energy transmission coupling structure away from a slow-wave structure, and a standard waveguide connected to the coupling cavity; the coupling cavity and the connected straight waveguide cavity have the same structural dimensions; the coupling cavity and the standard waveguide are coaxially arranged, and the axis is perpendicular to the axis of the electron injection channel.

4. The energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow-wave structure according to claim 1, characterized in that: The electron injection channel is a rectangular cross-section channel.

5. The energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow-wave structure according to claim 1, characterized in that: The energy transmission coupling structure is an input coupling structure or an output coupling structure.

6. A slow-wave circuit, characterized in that: It comprises a symmetrical double-slot coupled cavity slow-wave structure and an energy transmission coupling structure as described in any one of claims 1 to 5; the energy transmission coupling structure is connected to the input end and / or output end of the symmetrical double-slot coupled cavity slow-wave structure; the cavity unit connected to the input end of the symmetrical double-slot coupled cavity slow-wave structure has the same structural dimensions as a single-period symmetrical double-slot coupled cavity slow-wave structure and / or the cavity unit connected to the output end of the symmetrical double-slot coupled cavity slow-wave structure has the same structural dimensions as a single-period symmetrical double-slot coupled cavity slow-wave structure.

7. A design method for an energy transmission coupling structure suitable for a symmetrical double-slot coupled cavity slow-wave structure, characterized in that: The following steps are involved: A tapered waveguide section is designed to connect to a symmetrical double-slot coupled cavity slow-wave structure; the tapered waveguide section comprises a plurality of cavity units of a periodic structure and an electron injection channel located at the central axis of the cavity unit; the cavity unit comprises two straight waveguide cavities and two connecting cavities located between the two straight waveguide cavities; the two connecting cavities are symmetrically arranged relative to the electron injection channel and connect the two straight waveguide cavities along the axis of the electron injection channel; the straight waveguide cavities of adjacent cavity units are connected; Using three-dimensional electromagnetic field simulation software, starting from the end of the energy transmission coupling structure that is connected to the symmetrical double-slot coupled cavity slow-wave structure, the straight waveguide cavity height, straight waveguide cavity narrow side length, and period length of the cavity units connected in sequence are designed to gradually increase. Starting from the end connected to the symmetrical double-slot coupled cavity slow-wave structure, the straight waveguide cavity height, straight waveguide cavity narrow side length and period length of the cavity units connected in sequence gradually increase in a linear pattern. The two straight waveguide cavities of the same cavity unit have the same structural dimensions, and the two connecting cavities of the same cavity unit have the same structural dimensions.

8. The design method according to claim 7, characterized in that: By gradually increasing the period length of the energy transmission coupling structure, the influence of the gradual increase in the straight waveguide cavity height and the narrow side length of the straight waveguide cavity on the structural characteristic impedance is balanced, so that the overall impedance of the energy transmission coupling structure changes smoothly and gradually, and the matching performance of the energy transmission coupling structure is improved.

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