Island-free half-slot folded waveguide slow wave structure, slow wave circuit and traveling wave tube

Abstract

The invention provides an islanding-free half-slot folded waveguide slow-wave structure, a slow-wave circuit and a traveling wave tube, and the folded waveguide slow-wave structure comprises a multi-periodic cavity structure which is defined by a plurality of upper grid bodies and a plurality of lower grid bodies, wherein the upper grid bodies and the lower grid bodies are distributed in a staggered manner. The folded waveguide slow wave structure comprises a straight waveguide section, a waveguide connection section and an electron beam channel which are communicated; the waveguide connection section comprises an inner boundary, and the inner boundary is located in the boundary limited by the electron beam channel; the intersection point of the center line of the inner boundary and the axis of the electron beam channel is located on the inner boundary. According to the folded waveguide slow-wave structure, an island structure in a conventional folded waveguide is removed, the electron bombardment resistance of a slow-wave circuit is improved, the electron beam channel has higher structural toughness, and the problem that the strength of the slow-wave structure is insufficient under the terahertz high-frequency band is solved.

Description

Technical Field

[0001] The present invention relates to the field of microwave vacuum electronic technology, and more specifically to a non-island half-slot folded waveguide slow-wave structure, a slow-wave circuit and a traveling wave tube. Background Art

[0002] A terahertz traveling wave tube is a high-frequency vacuum electronic device that can amplify radio frequency electromagnetic signals. It has the advantages of high relative power (relative to solid-state devices), wide operating frequency band, small size, and light weight. It is currently widely used in satellite communications, deep space exploration, radar and other systems. The traveling wave tube consists of an electron gun, a high-frequency system, a focusing system, an energy transmission system, and a collector. The slow-wave circuit is the core component of the high-frequency system of the traveling wave tube. Its function is to reduce the axial velocity of the electromagnetic wave to synchronize it with the electron beam velocity, and to complete energy exchange to achieve electromagnetic wave signal amplification. Therefore, the performance of the slow-wave circuit is a key factor in determining the output power of the traveling wave tube.

[0003] As the operating frequency of the traveling wave tube increases, the size of its components will decrease. When the operating frequency of the traveling wave tube reaches 1THz, the characteristic size of its slow-wave structure has been reduced to the micron level, which puts very high requirements on the processing level. Therefore, it is very important to design a slow-wave structure suitable for processing.

[0004] Folded waveguide is a common slow wave structure in low-frequency and high-frequency systems. The single-period folded waveguide slow wave structure is obtained by bending a rectangular waveguide along the electric field. Several periods of folded waveguides and electron injection channels eventually form a complete slow wave structure. The circular electron injection channel is located on the central axis of the folded waveguide, and the central axis passes through the center of the circle. The connection positions of two adjacent folded waveguides are aligned to ensure that the electron injection channels between adjacent straight waveguides are in a closed state. Figure 1 As shown in the figure, b is the narrow side length of the straight waveguide section of the folded waveguide slow-wave structure, the geometric half period is p, the height of the straight waveguide section is h, and the radius of the electron injection channel is rc. The electron injection channel and the bent waveguide section above it form a metal island structure.

[0005] Conventional folded waveguide structures have poor resistance to electron bombardment in the terahertz frequency band, mainly because they have a metal island structure. In terahertz high-power traveling wave tubes, the characteristic size of the slow-wave structure reaches the micron level, and it is necessary to select a slow-wave structure with good working performance and easy processing. However, the island size of the conventional folded waveguide structure is too small, with a characteristic size of less than 20μm, which is very easy to deform and bend due to external forces, which may cause the periodicity of the structure to be destroyed, making the electromagnetic wave and electron beam energy conversion ineffective, and reducing the output power of the traveling wave tube. Summary of the invention

[0006] In view of the above problems, the present invention provides an island-free half-slot folded waveguide slow-wave structure suitable for a terahertz traveling wave tube, which removes the island structure in the conventional folded waveguide and improves the ability of the slow-wave circuit to resist electron bombardment, so that the electron injection channel has stronger structural toughness, and solves the problem of insufficient strength of the slow-wave structure in the terahertz high frequency band.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a non-island half-slot folded waveguide slow-wave structure suitable for a terahertz traveling wave tube, comprising a multi-periodic cavity structure defined by a plurality of upper grid bodies and a plurality of lower grid bodies that are staggered and distributed with each other, wherein the folded waveguide slow-wave structure comprises a connected straight waveguide section, a waveguide connecting section and an electron injection channel;

[0009] The waveguide connecting section includes an inner boundary, and the inner boundary is located within the boundary defined by the electron injection channel;

[0010] The intersection point of the center line of the inner boundary and the axis of the electron injection channel is located on the inner boundary.

[0011] A preferred solution is that the inner boundary is an arc-shaped boundary, and the axis of the electron injection channel is tangent to the inner boundary.

[0012] A preferred solution is that the radius of the electron injection channel is r, the radius corresponding to the inner boundary is r1, and r1 is greater than r.

[0013] A preferred solution is that the narrow side length of the straight waveguide section is b, the height of the straight waveguide section is h, the waveguide connecting section further includes an outer arc boundary; a first inner intersection portion is included between the inner boundary and the straight waveguide section, a first outer intersection portion is included between the outer arc boundary and the straight waveguide section, an angle α is formed between a line connecting the first inner intersection portion and the first outer intersection portion and the boundary of the straight waveguide section, and the angle α satisfies the following conditions:

[0014] A preferred solution is that the inner boundary is a straight line boundary, and the axis of the electron injection channel coincides with the inner boundary.

[0015] A preferred solution is that the narrow side length of the straight waveguide section is b, and the height of the straight waveguide section is h; the waveguide connecting section also includes an outer boundary, a second inner junction is included between the inner boundary and the straight waveguide section, a second outer junction is included between the outer boundary and the straight waveguide section, and an angle β is formed between a line connecting the second inner junction and the second outer junction and the boundary of the straight waveguide section, and the angle β satisfies the following conditions:

[0016] A preferred solution is that the outer boundary includes an outer straight boundary and an arc-shaped boundary connected to both ends of the outer straight boundary; the other end of the arc-shaped boundary is connected to the boundary of the straight waveguide section.

[0017] A preferred solution is that the folded waveguide slow-wave structure is applied to a traveling wave tube in the terahertz frequency band.

[0018] The present invention also provides a slow-wave circuit, comprising the island-free half-slot folded waveguide slow-wave structure and the coupler as described above;

[0019] The coupler comprises a gradient waveguide section for connecting to the island-free half-slot folded waveguide slow-wave structure and an external waveguide section for connecting to the energy transmission structure; the gradient waveguide section has a coupling cavity structure with the same cavity structure shape as that of the island-free half-slot folded waveguide slow-wave structure;

[0020] The gradient waveguide section is composed of two rows of grid structures that are staggered and distributed with each other;

[0021] Counting from the port connected to the slow-wave structure, the height and width of the upper and lower rows of grating structures gradually decrease, and the width of the cavity connection section of the coupled cavity structure of the gradient waveguide section gradually increases.

[0022] The present invention also provides a traveling wave tube, comprising the island-free half-slot folded waveguide slow-wave structure as described above. The beneficial effects of the present invention are:

[0023] The island-free half-slot folded waveguide slow-wave structure provided by the present invention removes the island structure in the conventional folded waveguide, improves the ability of the slow-wave circuit to resist electron bombardment, and has stronger structural toughness at the electron injection channel, solving the problem of insufficient strength of the slow-wave structure in the terahertz high-frequency band. In addition, the island-free half-slot folded waveguide slow-wave structure of the present invention has both normal dispersion and abnormal dispersion, which increases the design dimension and improves the diversity of the design. Since the normal and abnormal dispersion junctions of the island-free half-slot folded waveguide of the present invention are located within the working frequency band, the dispersion curve is flatter than that of the conventional folded waveguide, the electronic injection synchronization consistency is good, and it has a wider working bandwidth and less loss. In addition, the coupler suitable for the island-free half-slot folded waveguide slow-wave structure of the present invention can achieve impedance matching between the energy transmission structure and the slow-wave structure, and reduce electromagnetic wave reflection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0025] Figure 1 This is a schematic diagram of the single-period structure of a conventional folded waveguide slow-wave structure.

[0026] Figure 2 It is a three-dimensional schematic diagram of the structure of one period of the folded waveguide slow-wave structure provided by the present invention.

[0027] Figure 3 yes Figure 2 main view.

[0028] Figure 4It is a cross-sectional metal structure diagram of the island-free half-slot folded waveguide slow-wave structure of the present invention.

[0029] Figure 5 It is a structural schematic diagram of the island-free half-slot folded waveguide slow-wave structure of the present invention.

[0030] Fig. 6A It is a cross-sectional view of the island-free half-slot folded waveguide slow-wave structure of the present invention in the xy plane.

[0031] Figure 6B It is a cross-sectional view of the slow-wave structure with inferior arc groove structure in the xy plane.

[0032] Figure 6C It is a cross-sectional view of the slow-wave structure with the superior arc groove structure in the xy plane.

[0033] Figure 7 It is a phase light velocity ratio curve diagram of a conventional folded waveguide slow-wave structure and an island-free half-slot folded waveguide slow-wave structure of the present invention under similar phase velocity conditions within the same working frequency band.

[0034] Figure 8 It is a comparison diagram of coupling impedance between the island-free half-slot folded waveguide slow-wave structure of the present invention and the conventional folded waveguide slow-wave structure under the condition of similar in-band phase velocity.

[0035] Fig. 9 This is a comparison diagram of the loss characteristics of the island-free half-slot folded waveguide slow-wave structure of the present invention and the conventional folded waveguide slow-wave structure under similar in-band phase velocities.

[0036] Fig.10 It is a three-dimensional schematic diagram of the structure of the coupler of the present invention.

[0037] Fig.11 yes Fig.10 main view.

[0038] Fig.12 It is a schematic diagram of the structure of the slow-wave interaction circuit after the coupler is connected to the present invention.

[0039] Fig.13 It is a reflection parameter curve diagram of the slow-wave interaction circuit of the present invention. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0041] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0042] Techniques and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the techniques and equipment should be considered part of the specification.

[0043] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0044] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0045] When conventional folded waveguide slow-wave structures are applied to traveling wave tubes, the -1 spatial harmonic is usually selected as the operating point, and the corresponding phase shift is 360° to 720°. Among them, the coupling impedance between the phase shift of 360° to 540° is large, but the dispersion is strong; the dispersion between the phase shift of 540° to 720° is weak, but the coupling impedance is small. When conventional folded waveguide slow-wave structures are applied to traveling wave tubes in the terahertz frequency band, in order to obtain sufficient bandwidth, the operating point is usually selected in the dispersion flat region between the phase shift of 540° to 720°, resulting in a small coupling impedance of the electron injection channel axis, which limits the output power, gain and electronic efficiency of the traveling wave tube.

[0046] Based on the conventional folded waveguide structure, the present invention proposes a non-island half-slot folded waveguide slow-wave structure working in the terahertz frequency band, and provides design ideas for structures in different frequency bands in combination with dispersion curves. Figures 1 to 13As shown, specifically, the island-free half-slot folded waveguide slow-wave structure 1 suitable for a terahertz traveling wave tube includes: a multi-periodic cavity structure defined by a plurality of upper grid bodies and a plurality of lower grid bodies that are staggered and distributed with each other, the folded waveguide slow-wave structure includes a connected straight waveguide section 11, a waveguide connecting section 12, and an electron injection channel 13; the waveguide connecting section 11 includes an inner boundary, and the inner boundary is located within the boundary defined by the electron injection channel; the center line L of the inner boundary intersects with the electron injection channel axis K, and the intersection of the center line L of the inner boundary and the electron injection channel axis K is located on the inner boundary, and the intersection is the midpoint of the inner boundary. That is to say, in the radial direction of the electron injection channel 13, the vertical distance between the midpoint of the inner boundary and the upper and lower boundaries of the electron injection channel 13 (in the y direction) is equal to the electron injection channel radius r. The island-free half-slot folded waveguide slow-wave structure is symmetrical about the center line L. The electron injection channel 13 of the present invention adopts a half-groove metal structure, that is, the supporting metal at the groove of the electron injection channel 13 is just in a semicircular shape. The existing processing level can manufacture this structure, and the structural strength is relatively high; the island-free folded waveguide is a two-dimensional planar metal structure, which is obtained by deforming a conventional folded waveguide. In order to avoid the appearance of a micro-island structure during processing, thereby causing insufficient metal strength at this part, the conventional folded waveguide structure is deformed and half of the metal at the electron injection channel is cut off, making the processing method simpler, and finally leaving a metal groove of half of the electron injection channel, eliminating the metal island structure, and improving the anti-electron bombardment ability of the slow-wave circuit, so that the electron injection channel has stronger structural toughness, such as Figure 2 As shown, the folded waveguide slow-wave structure is applied to a traveling wave tube in the terahertz frequency band.

[0047] like Figure 3 As shown, in a specific embodiment, the inner boundary is an arc boundary C1, and the electron injection channel axis K is set tangent to the arc boundary C1; the electron injection channel radius is r, and the radius corresponding to the arc boundary C1 is r1, r1 is greater than r, and the arc boundary C1 is a minor arc.

[0048] Further, the narrow side length of the straight waveguide section 11 is b, the height of the straight waveguide section 11 is h, and the waveguide connecting section 12 further includes an outer arc boundary C2; a first inner intersection Q1 is included between the arc boundary C1 and the straight waveguide section 11, and a first outer intersection Q2 is included between the outer arc boundary C2 and the straight waveguide section 11. An angle α is formed between a line connecting the first inner intersection Q1 and the first outer intersection Q2 and the boundary of the straight waveguide section 11, and the angle α satisfies the following conditions:

[0049] The island-free half-slot folded waveguide slow-wave structure of the present invention is based on the conventional folded waveguide, and the rectangular cross-section of the H-plane of the folded waveguide straight waveguide section is replaced with a parallelogram cross-section, where a is the length of the wide side of the E-plane of the folded waveguide, and the half-period of the slow-wave structure is p. Since the micro-milling cutter cannot process a smoothly connected waveguide connecting section and a straight waveguide section, the connection between the two can be rounded.

[0050] In order to optimize the new slow-wave structure, Figure 3 The inner and outer arc boundaries are replaced by straight line boundaries, which not only further reduces the processing difficulty, but also makes the dispersion curve of the slow-wave structure flatter, and can obtain a wider synchronization bandwidth. Figure 4 A cross-sectional metal structure diagram of the improved island-free half-slot folded waveguide slow-wave structure is shown.

[0051] In a specific embodiment, in combination Figure 5 As shown, the inner boundary is a straight boundary, and the electron injection channel axis K coincides with the straight boundary. The electron injection channel axis K is set along the z direction, and the center line L of the inner boundary is set along the y direction, and the electron injection channel axis K is perpendicular to the center line L of the inner boundary.

[0052] Furthermore, the narrow side length of the straight waveguide section 11 is b, and the height of the straight waveguide section 11 is h; the waveguide connecting section 12 also includes an outer boundary, a second inner intersection Q3 is included between the inner boundary and the straight waveguide section 11, and a second outer intersection Q4 is included between the outer boundary and the straight waveguide section 11. An angle β is formed between the connecting line of the second inner intersection Q3 and the second outer intersection Q4 and the boundary of the straight waveguide section 11, and the angle β satisfies the following conditions:

[0053] More specifically, the outer boundary includes an outer straight boundary and an arc-shaped boundary connected to both ends of the outer straight boundary; the other end of the arc-shaped boundary is connected to the boundary of the straight waveguide section to achieve a smooth connection between the straight waveguide section and the waveguide connecting section, and the arc-shaped boundary is formed by chamfering.

[0054] The present invention does not increase the process complexity and precision on the basis of the conventional folded waveguide slow-wave structure. The length of the wide side of the folded waveguide is a, the length of the narrow side of the straight waveguide section 11 is b, the cross-section of the straight waveguide section 11 is designed to be a parallelogram, and a given angle α is given. The side surface of the hexahedron stretched from the parallelogram cross-section is rotated by α similar to the conventional folded waveguide, and the outer boundary of the junction of the waveguide connecting section 12 and the straight waveguide section 11 is chamfered to obtain an island-free half-slot folded waveguide slow-wave structure.

[0055] More specifically, the island-free folded waveguide can be made by two UV-LIGA micromachinings, and the specific operation steps are: using a spin coating or scraping method, a layer of high viscosity photoresist is coated on the surface of the substrate coated with the tackifier; pre-baking and curing the photoresist layer, and using ultraviolet contact exposure to transfer the waveguide structure pattern on the mask plate to the photoresist layer; then post-baking the photoresist, and removing the unnecessary part of the photoresist by development, and obtaining a photoresist mold of the waveguide structure on the substrate; using a precision electroforming method, oxygen-free copper is deposited on the substrate through the photoresist mold, and the electroforming layer completely covers the photoresist structure; the electroforming / photoresist mixed layer is ground, thinned and surface polished to obtain an oxygen-free copper structure layer with thickness and surface roughness that meet the requirements. Repeat the above process for a second UV-LIGA, mainly to process the electron injection channel on the waveguide structure substrate to obtain a slow-wave circuit semi-structure, during which the photolithography requires a strict alignment process. The photoresist in the electroforming / photoresist mixed layer is removed to obtain a complete oxygen-free copper folded waveguide slow-wave semi-structure. The same process is used to process the other half of the structure with mirror symmetry, and the two half structures are strictly aligned and bonded together to obtain a complete all-metal island-free folded waveguide high-frequency circuit.

[0056] In the terahertz band (1 THz and above), the geometric dimensions of the island-free half-slot folded waveguide slow-wave structure are as follows: the length of the folded waveguide wide side a = 210 μm, the length of the narrow side of the straight waveguide section b = 50 μm, the geometric half-period p = 80 μm, the height of the straight waveguide section h = 50 μm, the angle β = 36°, the electron beam channel radius r = 25 μm, and the corresponding radius of the arc-shaped boundary chamfer = 25 μm.

[0057] In the technical solution of conventional folded waveguide, the characteristic size of the island structure of the folded waveguide of the terahertz traveling wave tube is about 20μm. This size not only brings great challenges to the processing technology, but even if an island structure with tolerances that meet the requirements is manufactured, a slight force under the tiny size will cause the structure to deform and damage, making it impossible to achieve the preset electromagnetic performance of the slow-wave structure, and even cause the transducer to fail, reducing the output power of the traveling wave tube. Compared with the existing technical solutions, the technical solution of the present invention removes the island structure of the conventional folded waveguide of the terahertz traveling wave tube, and improves the ability of the slow-wave circuit to resist electron bombardment; the half-slot structure at the electron injection channel has stronger structural toughness, which solves the problem of insufficient strength of the slow-wave structure of the terahertz traveling wave tube, and takes into account the characteristics of strong resistance to electron bombardment and high coupling impedance. Taking the island-free half-slot folded waveguide slow-wave structure with a circular cross-section channel as the electron injection channel and an arc-shaped inner boundary as an example, when the structural size parameters are the same but the values ​​of the angle α are different, the electron injection channel position corresponds to the half-slot, inferior arc slot, and superior arc slot structures respectively. Reference Fig. 6A As shown in Figure 2, when α = 36°, the electron injection channel position corresponds to a half-groove structure, and the inner boundary is tangent to the electron injection channel axis. Figure 6BAs shown in the figure, when α = 32°, the electron injection channel corresponds to the inferior arc groove structure. At this time, in the y direction, the midpoint of the inner boundary must be higher than the axis of the electron injection channel. The electron bombardment range of the section at the inferior arc groove structure is smaller, but the corresponding coupling impedance is low. This structure cannot stimulate effective injection-wave interaction and has poor electrical performance. Figure 6C As shown, when α=45°, the electron injection channel position corresponds to the superior arc slot structure. At this time, in the y direction, the midpoint of the inner boundary must be lower than the axis of the electron injection channel. Compared with the half-slot structure of the present application, the electron injection channel above the midline of the superior arc slot structure will be subjected to additional electron bombardment. Although it does not have the problem of low coupling impedance, the electron bombardment resistance of the superior arc slot structure is not as good as the half-slot structure of the present application, and it is easy to cause damage during operation. Taking all factors into consideration, the present invention adopts a half-slot structure with excellent electrical properties and electron bombardment resistance. In addition, the island-free half-slot folded waveguide slow-wave structure greatly reduces the difficulty of processing, and the processing accuracy can meet the size and tolerance requirements under this scheme. It should be noted that Figure 6A-6C All are cross sections obtained by cutting along the center line L of the inner boundary. Figure 6A-6C The area with bold lines is the area where the metal grid is bombarded by electrons.

[0058] Figure 7 The phase velocity ratio curves of the conventional folded waveguide slow-wave structure and the island-free half-slot folded waveguide slow-wave structure in the same working frequency band are shown. By comparison, it is found that the island-free half-slot folded waveguide has both normal dispersion region and abnormal dispersion region. Not only can the design ideas of different frequency bands be adopted according to different needs, but also the flat part of the dispersion curve at the junction of normal and abnormal dispersion can be reasonably selected as the working area of ​​the traveling wave tube, which greatly improves the bandwidth. Both slow-wave structures work in the 1.2THz-1.3THz frequency band, and the maximum phase velocity ratio difference between the two is less than 0.001. Since the junction of normal and abnormal dispersion of the island-free half-slot folded waveguide is located in the frequency band, its dispersion curve is flatter in this area than that of the conventional folded waveguide, the electron beam synchronization consistency is good, and it has a wider working bandwidth.

[0059] Figure 8 The figure shows the coupling impedance comparison of the half-slot folded waveguide slow-wave structure without island and the conventional folded waveguide slow-wave structure under the condition of similar phase velocity in the band. The simulation results show that below the working frequency of 1.2T, the coupling impedance of the half-slot folded waveguide without island is always lower than that of the conventional folded waveguide. In the working frequency band of 1.2T-1.25T, the coupling impedance of the conventional folded waveguide is higher; in 1.25T-1.3T, the coupling impedance of the half-slot folded waveguide without island is higher, achieving a higher performance, but the absolute difference in the coupling impedance of the two in the working frequency band is not large.

[0060] Fig. 9The figure shows the loss characteristics comparison of the half-slot folded waveguide slow-wave structure without islands and the conventional folded waveguide slow-wave structure under the condition of similar phase velocity in the band. In the design of the slow-wave structure size parameters, the loss value is the first consideration. In the high-frequency terahertz band, if a structure with large loss is used for design, it will inevitably lead to limited gain of the traveling wave tube. The simulation results show that the attenuation constant of the half-slot folded waveguide without islands in the working frequency band is lower than that of the conventional folded waveguide, and the loss value per unit distance in the working frequency band is relatively small, with an average of less than 1500dB / m.

[0061] The island-free half-slot folded waveguide slow-wave structure provided by the present invention cannot be directly connected to the input and output structures of the traveling wave tube, otherwise the two will cause the characteristic impedance of the microwave transmission line to be mismatched due to the difference in shape and size, and a strong electromagnetic wave reflection phenomenon will occur at the connection to form a standing wave. In order to solve this problem and achieve a matching connection, the present invention designs a coupler suitable for connecting the island-free half-slot folded waveguide slow-wave structure with the energy transmission structure, that is, an impedance transformer, and its structure is as follows Fig.10 and Fig.11 shown.

[0062] Furthermore, the present invention also provides a slow-wave circuit, comprising the island-free half-slot folded waveguide slow-wave structure 1 and the coupler 2 as described above; the coupler comprises a gradual waveguide section 21 for connecting to the island-free half-slot folded waveguide slow-wave structure and an external waveguide section 22 for connecting to the energy transmission structure; the gradual waveguide section 21 has a coupling cavity structure with the same cavity structure shape as the island-free half-slot folded waveguide slow-wave structure 1; the gradual waveguide section 21 is composed of two rows of grid structures that are staggered with each other; starting from the port connected to the island-free half-slot folded waveguide slow-wave structure 1, the grid height and grid width of the upper and lower rows of grid structures are gradually reduced and the cavity connection section width w1 of the coupling cavity structure of the gradual waveguide section is gradually increased. That is to say, combined with Figure 7 As shown, along the z direction toward the left, the interval height h1, the interval width w2 and the cavity connecting section width w1 all gradually increase.

[0063] The reflection coefficient of the coupler 2 applicable to the island-free half-slot folded waveguide slow-wave structure 1 is determined according to binomial distribution or Chebyshev distribution.

[0064] Specifically, the most basic way of impedance converter is to match two sections of transmission lines with different characteristic impedances based on the input impedance characteristics of a quarter-wavelength transmission line. The impedance converter composed of a quarter-wavelength transmission line has a simple structure, but because the converter length is exactly equal to a quarter of the waveguide wavelength only at a certain frequency, deviation from this frequency will lead to an impedance that cannot be ideally matched and increased reflection, so the converter's operating frequency band is narrow. The waveguide wavelength is not only related to the operating frequency, but also to the waveform, structural shape, and structural size. In order to widen the operating frequency band, a multi-section quarter-wavelength impedance converter can be used. Generally speaking, the more sections there are, the more frequency points of full matching will appear, and the wider the bandwidth.

[0065] The coupler 2 of the present invention, which is suitable for the island-free half-slot folded waveguide slow-wave structure 1, is based on the principle of a multi-section impedance converter. By reasonably selecting the values ​​of the spacing height h1, the spacing width w2 and the cavity connection section width w1, it will not cause a change in the guided wave wavelength, and at the same time determine the reflection coefficient, so that the impedance converter is fully matched at several frequencies. The values ​​of the spacing height h1, the spacing width w2 and the cavity connection section width w1 of the coupler 2 of the present invention are slightly proportionally increased based on the corresponding size parameters of the normal periodic slow-wave structure. As for the selection of the reflection coefficient, it can be determined according to the binomial distribution or the Chebyshev distribution, and the latter can obtain a better and wider bandwidth than the former. In the present invention, the coupler has a coupling cavity structure with the same appearance as the island-free half-slot folded waveguide slow-wave structure 1, and the cavity structure not only has good transmission characteristics, but also is easy to process in engineering. From the slow-wave structure to the energy transmission structure, the spacing height h1, spacing width w2 and cavity connection section width w1 of the coupler 2 are proportionally enlarged. The coupler 2 is connected to the signal input / output structure after passing through four quasi-periodic structures with gradually varying sizes.

[0066] Fig.12 The schematic diagram of the slow-wave interaction circuit after connecting to the coupler 2 is given. One side of the coupler 2 is connected to the signal energy transmission structure, and the other side is connected to the periodic island-free half-slot folded waveguide slow-wave structure 1. Fig.13 The reflection parameter curve of the slow wave interaction circuit is shown. The above coupler 2 effectively reduces the reflection of electromagnetic waves in the structure, so that the reflection parameter S11 of the slow wave interaction circuit within 974.4GHz-1060GHz is less than -20dB, meeting the working bandwidth and transmission characteristic indicators required by the traveling wave tube.

[0067] The present invention also provides a traveling wave tube, which comprises the island-free half-slot folded waveguide slow-wave structure as described above.

[0068] In summary, the island-free half-slot folded waveguide slow-wave structure provided by the present invention removes the island structure in the conventional folded waveguide, improves the ability of the slow-wave circuit to resist electron bombardment, and has stronger structural toughness at the electron injection channel, solving the problem of insufficient strength of the slow-wave structure in the terahertz high frequency band. In addition, the island-free half-slot folded waveguide slow-wave structure of the present invention has both normal dispersion and abnormal dispersion, which increases the design dimension and improves the diversity of the design. Since the junction of normal and abnormal dispersion of the island-free half-slot folded waveguide of the present invention is located within the working frequency band, the dispersion curve is flatter than that of the conventional folded waveguide, the electronic beam synchronization consistency is good, and it has a wider working bandwidth and less loss. In addition, the coupler suitable for the island-free half-slot folded waveguide slow-wave structure of the present invention can achieve impedance matching between the energy transmission structure and the slow-wave structure, and reduce electromagnetic wave reflection.

[0069] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A half-slot folded waveguide slow-wave structure without islands, characterized in that: It comprises a multi-periodic cavity structure defined by a plurality of upper grid bodies and a plurality of lower grid bodies which are staggered and distributed with each other, and the folded waveguide slow-wave structure comprises a connected straight waveguide section, a waveguide connecting section and an electron injection channel; The waveguide connecting section includes an inner boundary, and the inner boundary is located within the boundary defined by the electron injection channel; The intersection point of the center line of the inner boundary and the axis of the electron injection channel is located on the inner boundary.

2. The island-free half-slot folded waveguide slow-wave structure according to claim 1, characterized in that: The inner boundary is an arc-shaped boundary, and the axis of the electron injection channel is tangent to the inner boundary.

3. The island-free half-slot folded waveguide slow-wave structure according to claim 2, characterized in that: The radius of the electron injection channel is r, and the radius corresponding to the inner boundary is r1, which is greater than r.

4. The island-free half-slot folded waveguide slow-wave structure according to claim 3, characterized in that: The narrow side length of the straight waveguide section is b, the height of the straight waveguide section is h, the waveguide connecting section also includes an outer arc boundary; the inner boundary and the straight waveguide section include a first inner intersection, the outer arc boundary and the straight waveguide section include a first outer intersection, and a line connecting the first inner intersection and the first outer intersection forms an angle α with the boundary of the straight waveguide section, and the angle α satisfies the following conditions:

5. The island-free half-slot folded waveguide slow-wave structure according to claim 1, characterized in that: The inner boundary is a straight line boundary, and the axis of the electron injection channel coincides with the inner boundary.

6. The island-free half-slot folded waveguide slow-wave structure according to claim 5, characterized in that: The narrow side length of the straight waveguide section is b, and the height of the straight waveguide section is h; the waveguide connecting section also includes an outer boundary, a second inner junction is included between the inner boundary and the straight waveguide section, a second outer junction is included between the outer boundary and the straight waveguide section, and an angle β is formed between a line connecting the second inner junction and the second outer junction and the boundary of the straight waveguide section, and the angle β satisfies the following conditions:

7. The island-free half-slot folded waveguide slow-wave structure according to claim 6, characterized in that: The outer boundary includes an outer straight boundary and an arc-shaped boundary connected to two ends of the outer straight boundary; the other end of the arc-shaped boundary is connected to the boundary of the straight waveguide section.

8. The island-free half-slot folded waveguide slow-wave structure according to claim 1, characterized in that: The folded waveguide slow-wave structure is applied to traveling wave tubes in the terahertz frequency band.

9. A slow wave circuit, characterized in that: It comprises the island-free half-slot folded waveguide slow-wave structure and coupler as described in any one of claims 1 to 8; The coupler comprises a gradient waveguide section for connecting to the island-free half-slot folded waveguide slow-wave structure and an external waveguide section for connecting to the energy transmission structure; the gradient waveguide section has a coupling cavity structure with the same cavity structure shape as that of the island-free half-slot folded waveguide slow-wave structure; The gradient waveguide section is composed of two rows of grid structures that are staggered and distributed with each other; Counting from the port connected to the slow-wave structure, the height and width of the upper and lower rows of grating structures gradually decrease, and the width of the cavity connection section of the coupled cavity structure of the gradient waveguide section gradually increases.

10. A traveling wave tube, characterized in that: It comprises the island-free half-slot folded waveguide slow-wave structure as described in any one of claims 1 to 8.

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