A slow wave structure, a slow wave circuit and a traveling wave tube with a half-slot folded waveguide without island

Abstract

This invention provides an islandless half-slot folded waveguide slow-wave structure, a slow-wave circuit, and a traveling wave tube. The folded waveguide slow-wave structure includes a multi-periodic cavity structure defined by multiple staggered upper and lower gratings. The folded waveguide slow-wave structure includes a connected straight waveguide section, a waveguide connecting section, and an electron beam channel. The waveguide connecting section includes an inner boundary located within the boundary defined by the electron beam channel. The intersection of the centerline of the inner boundary and the axis of the electron beam channel is located on the inner boundary. This folded waveguide slow-wave structure eliminates the island structure found in conventional folded waveguides, improves the slow-wave circuit's resistance to electron bombardment, and provides stronger structural toughness at the electron beam channel, thus solving the problem of insufficient strength in slow-wave structures at terahertz high frequencies.

Description

Technical Field

[0001] This invention relates to the field of microwave vacuum electronics technology. More specifically, it relates to an islandless half-slot folded waveguide slow-wave structure, a slow-wave circuit, and a traveling-wave tube. Background Technology

[0002] A terahertz traveling wave tube (TWT) is a high-frequency vacuum electronic device capable of amplifying radio frequency electromagnetic signals. It boasts advantages such as relatively high power (compared to solid-state devices), wide operating bandwidth, small size, and light weight, and is currently widely used in satellite communications, deep space exploration, and radar systems. A TWT consists of an electron gun, a high-frequency system, a focusing system, a power delivery system, and a collector. The slow-wave circuit is the core component of the TWT's high-frequency system. 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 amplify the electromagnetic wave signal. Therefore, the performance of the slow-wave circuit is a key factor determining the output power of the TWT.

[0003] As the operating frequency of a traveling wave tube (TWT) increases, the size of its components decreases. When the operating frequency of a TWT reaches 1 THz, the feature size of its slow-wave structure has been reduced to the micrometer level, which places very high demands on the manufacturing process. Therefore, designing a slow-wave structure suitable for manufacturing is crucial.

[0004] Folded waveguides are commonly used slow-wave structures in low-frequency high-frequency systems. A single-period folded waveguide slow-wave structure is obtained by bending a rectangular waveguide along an electric field. Several periods of folded waveguides and electron beam channels ultimately form a complete slow-wave structure. The circular electron beam channel is located on the central axis of the folded waveguide, and the central axis passes through the center of the circle. The connection points of adjacent folded waveguides are aligned pairwise to ensure that the electron beam channels between adjacent straight waveguides are all in a closed state. (Refer to...) Figure 1 As shown in the figure, b represents the narrow side length of the straight waveguide segment of the folded waveguide slow wave structure, with a geometric half-period of p, a height of h, and an electron beam channel radius of rc. The electron beam channel and the bent waveguide segment above it form a metallic island structure.

[0005] Conventional folded waveguide structures exhibit poor resistance to electron bombardment in the terahertz band, primarily due to their metallic island structure. In high-power terahertz traveling wave tubes (TWTs), the characteristic dimensions of slow-wave structures reach the micrometer scale, necessitating the selection of slow-wave structures with good performance and ease of fabrication. However, the island size of conventional folded waveguide structures is too small, with a characteristic dimension less than 20 μm, making them highly susceptible to deformation and bending under external forces. This can lead to periodic damage to the structure, causing transduction failure of electromagnetic waves and electron beams, and reducing the output power of the TWT. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides an islandless half-slot folded waveguide slow-wave structure suitable for terahertz traveling wave tubes. This structure eliminates the island structure in conventional folded waveguides and improves the resistance of slow-wave circuits to electron bombardment, resulting in stronger structural toughness at the electron beam channel. This solves the problem of insufficient strength of slow-wave structures in the terahertz high-frequency band.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides an islandless half-slot folded waveguide slow wave structure suitable for terahertz traveling wave tubes, comprising a multi-periodic cavity structure defined by multiple upper gratings and multiple lower gratings that are staggered together. The folded waveguide slow wave structure includes a connected straight waveguide section, a waveguide connection section, and an electron beam channel.

[0009] The waveguide connection segment includes an inner boundary, which is located within the boundary defined by the electron beam channel;

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

[0011] The preferred embodiment 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] The preferred embodiment is that the radius of the electron beam channel is r, and the radius corresponding to the inner boundary is r1, where r1 is greater than r.

[0013] The preferred embodiment is that the narrow side length of the straight waveguide segment is b, the height of the straight waveguide segment is h, and the waveguide connecting segment further includes an outer circular arc boundary; the inner boundary and the straight waveguide segment include a first inner junction, and the outer circular arc boundary and the straight waveguide segment include a first outer junction. The line connecting the first inner junction and the first outer junction forms an angle α with the boundary of the straight waveguide segment, and the angle α satisfies the following condition:

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

[0015] The preferred embodiment is that the narrow side length of the straight waveguide segment is b, and the height of the straight waveguide segment is h; the waveguide connecting segment further includes an outer boundary, a second inner junction between the inner boundary and the straight waveguide segment, and a second outer junction between the outer boundary and the straight waveguide segment. The line connecting the second inner junction and the second outer junction forms an angle β with the boundary of the straight waveguide segment, and the angle β satisfies the following condition:

[0016] A preferred embodiment is that the outer boundary includes an outer straight boundary and an arc-shaped boundary connecting the two ends of the outer straight boundary; the other end of the arc-shaped boundary is connected to the boundary of the straight waveguide segment.

[0017] The preferred approach is to apply this folded waveguide slow wave structure to a traveling wave tube in the terahertz band.

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

[0019] The coupler includes a tapered waveguide section for connection to the islandless half-groove folded waveguide slow wave structure and an external waveguide section for connection to the power transmission structure; the tapered waveguide section has a coupling cavity structure with the same cavity structure shape as the islandless half-groove folded waveguide slow wave structure.

[0020] The gradient waveguide segment is composed of two rows of staggered grating structures.

[0021] Starting from the port connected to the slow wave structure, the height and width of the gratings in the upper and lower rows of grating structures gradually decrease, while the width of the cavity connection section of the coupling cavity structure of the gradient waveguide section gradually increases.

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

[0023] The islandless half-slot folded waveguide slow-wave structure provided by this invention eliminates the island structure in conventional folded waveguides, improving the slow-wave circuit's resistance to electron bombardment and exhibiting stronger structural toughness at the electron beam channel, thus solving the problem of insufficient slow-wave structure strength in the terahertz high-frequency band. Furthermore, the islandless half-slot folded waveguide slow-wave structure of this invention possesses both normal and anomalous dispersion, increasing design dimensionality and diversity. Since the boundary between normal and anomalous dispersion in the islandless half-slot folded waveguide of this invention is located within the operating frequency band, the dispersion curve is flatter than that of conventional folded waveguides, resulting in better electron beam synchronization consistency, a wider operating bandwidth, and lower losses. Additionally, the coupler of this invention, applicable to the islandless half-slot folded waveguide slow-wave structure, can achieve impedance matching between the power transmission structure and the slow-wave structure, reducing electromagnetic wave reflection. Attached Figure Description

[0024] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

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

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

[0027] Figure 3 yes Figure 2 The main view.

[0028] Figure 4This is a cross-sectional metal structure diagram of the islandless half-groove folded waveguide slow wave structure of the present invention.

[0029] Figure 5 This is a schematic diagram of the islandless half-groove folded waveguide slow wave structure of the present invention.

[0030] Figure 6A This is a cross-sectional view of the islandless half-groove folded waveguide slow wave structure of the present invention in the xy plane.

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

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

[0033] Figure 7 The graph shows the phase velocity ratio of a conventional folded waveguide slow wave structure and the islandless half-groove folded waveguide slow wave structure of this invention within the same operating frequency band, under similar phase velocity conditions.

[0034] Figure 8 This is a comparison diagram of the coupling impedance of the islandless half-groove 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] Figure 9 This is a comparison diagram of the loss characteristics of the islandless half-groove folded waveguide slow wave structure of the present invention and the conventional folded waveguide slow wave structure under similar in-band phase velocities.

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

[0037] Figure 11 yes Figure 10 The main view.

[0038] Figure 12 This is a schematic diagram of the slow-wave interaction circuit after the connection coupler of the present invention.

[0039] Figure 13 This is a graph showing the reflection parameters of the slow-wave interaction circuit of the present invention. Detailed Implementation

[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, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention.

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

[0042] Technologies and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such technologies and equipment should be considered part of the specification.

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

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

[0045] When conventional folded waveguide slow-wave structures are applied to traveling-wave tubes (TWTs), the -1st spatial harmonic is typically chosen as the operating point, corresponding to a phase shift of 360°–720°. The coupling impedance is relatively high between 360° and 540°, but dispersion is strong; the dispersion is weaker between 540° and 720°, but the coupling impedance is lower. When conventional folded waveguide slow-wave structures are applied to terahertz TWTs, to obtain sufficient bandwidth, the operating point is usually chosen in the dispersion-flat region between 540° and 720°, resulting in a low coupling impedance along the electron beam channel axis, which limits the TWT's output power, gain, and electronic efficiency.

[0046] This invention proposes a non-islandable half-slot folded waveguide slow-wave structure operating in the terahertz band, based on conventional folded waveguide structures, and provides design ideas for structures in different frequency bands by combining dispersion curves. Figures 1 to 13As shown, the islandless half-slot folded waveguide slow-wave structure 1 suitable for terahertz traveling wave tubes specifically includes: a multi-periodic cavity structure defined by multiple upper and lower grids distributed in an alternating manner; the folded waveguide slow-wave structure includes a connected straight waveguide section 11, a waveguide connecting section 12, and an electron beam channel 13; the waveguide connecting section 11 includes an inner boundary, which is located within the boundary defined by the electron beam channel; the centerline L of the inner boundary intersects the axis K of the electron beam channel, and the intersection point of the centerline L of the inner boundary and the axis K of the electron beam channel is located on the inner boundary, which is the midpoint of the inner boundary. That is, in the radial direction of the electron beam channel 13, the vertical distance between the midpoint of the inner boundary and the upper and lower boundaries (in the y-direction) of the electron beam channel 13 is equal to the radius r of the electron beam channel. The islandless half-slot folded waveguide slow-wave structure is symmetrical about the centerline L. The electron beam channel 13 of this invention employs a semi-groove metal structure, meaning the supporting metal at the slot of the electron beam channel 13 is precisely semi-circular. Current manufacturing capabilities can produce this structure, which exhibits high structural strength. The island-free folded waveguide is a two-dimensional planar metal structure obtained by deforming a conventional folded waveguide. To avoid the formation of micro-island structures during processing, which would lead to insufficient metal strength in this area, the conventional folded waveguide structure is deformed, removing half of the metal at the electron beam channel. This simplifies the manufacturing process, leaving only a half-groove for the electron beam channel. This eliminates metal island structures and improves the slow-wave circuit's resistance to electron bombardment, resulting in greater structural toughness at the electron beam channel. Figure 2 As shown, this folded waveguide slow wave structure is applied to a traveling wave tube in the terahertz band.

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

[0048] Furthermore, the narrow side length of the straight waveguide segment 11 is b, and the height of the straight waveguide segment 11 is h. The waveguide connecting segment 12 also includes an outer arc boundary C2. The arc boundary C1 and the straight waveguide segment 11 include a first inner junction Q1, and the outer arc boundary C2 and the straight waveguide segment 11 include a first outer junction Q2. The line connecting the first inner junction Q1 and the first outer junction Q2 forms an angle α with the boundary of the straight waveguide segment 11. The angle α satisfies the following condition:

[0049] The islandless half-groove folded waveguide slow-wave structure of this invention is based on a conventional folded waveguide, replacing the rectangular cross-section of the straight waveguide section H with a parallelogram cross-section, where 'a' is the length of the wide side of the folded waveguide E, and the half-period of the slow-wave structure is 'p'. Since micro-milling cutters cannot machine a smoothly connected waveguide connection section and a straight waveguide section, the connection point can be rounded.

[0050] To optimize the novel slow-wave structure, Figure 3 Replacing the inner and outer circular arc boundaries with straight line boundaries not only further reduces the processing difficulty, but also makes the dispersion curve of the slow wave structure flatter, enabling a wider synchronization bandwidth. Figure 4 The diagram shows a cross-sectional metal structure of the improved islandless half-groove folded waveguide slow wave structure.

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

[0052] Furthermore, the narrow side length of the straight waveguide segment 11 is b, and the height of the straight waveguide segment 11 is h; the waveguide connecting segment 12 also includes an outer boundary, and the inner boundary includes a second inner junction Q3 with the straight waveguide segment 11, and the outer boundary includes a second outer junction Q4 with the straight waveguide segment 11. The line connecting the second inner junction Q3 and the second outer junction Q4 forms an angle β with the boundary of the straight waveguide segment 11, and the angle β satisfies the following condition:

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

[0054] This invention, without increasing the complexity and precision of the conventional folded waveguide slow wave structure, uses a folded waveguide with a wide side length of 'a' and a straight waveguide segment 11 with a narrow side length of 'b'. The cross-section of the straight waveguide segment 11 is designed as a parallelogram, with an included angle α. The sides of the hexahedron formed by stretching the parallelogram cross-section are rotated in a manner similar to that of a conventional folded waveguide, rotating by α. The outer boundary at the junction of the waveguide connecting segment 12 and the straight waveguide segment 11 is then chamfered to obtain an islandless half-groove folded waveguide slow wave structure.

[0055] More specifically, this island-free folded waveguide can be fabricated using two UV-LIGA micromachining processes. The specific steps are as follows: A layer of high-viscosity photoresist is applied to the surface of a substrate coated with an adhesive using spin coating or scraping. The photoresist layer is pre-baked and cured, and UV contact exposure is used to transfer the waveguide structure pattern from the mask to the photoresist layer. Subsequently, the photoresist is post-baked, and unwanted portions are removed by development, resulting in a photoresist mold of the waveguide structure on the substrate. Oxygen-free copper is deposited onto the substrate through the photoresist mold using precision electroforming, with the electroformed layer completely covering the photoresist structure. The electroformed / photoresist hybrid layer is then thinned and polished to obtain an oxygen-free copper structure layer with the required thickness and surface roughness. The above process is repeated for a second UV-LIGA process, primarily to fabricate electron beam channels on the waveguide structure substrate, obtaining a slow-wave circuit half-structure. During this process, strict alignment of the photolithography process is required. Finally, the photoresist in the electroformed / photoresist hybrid layer is removed, yielding a complete oxygen-free copper folded waveguide slow-wave half-structure. The other half of the structure is fabricated using the same process, and the two halves are strictly aligned and bonded together to obtain a complete all-metal, island-free folded waveguide high-frequency circuit.

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

[0057] In conventional folded waveguide technologies, the characteristic size of the island structure in a terahertz traveling wave tube (TWT) is approximately 20 μm. This size not only poses a significant challenge to the manufacturing process, but even if an island structure with acceptable tolerances is produced, slight stress due to its tiny size can cause structural deformation and damage, preventing the achievement of the intended slow-wave electromagnetic performance and even leading to transducer failure and reduced TWT output power. Compared to existing technologies, this invention removes the island structure of conventional folded waveguides in terahertz TWTs, improving the slow-wave circuit's resistance to electron bombardment. The semi-groove structure at the electron beam channel exhibits greater structural toughness, solving the problem of insufficient strength in the slow-wave structure of terahertz TWTs, while also balancing strong resistance to electron bombardment with high coupling impedance. Taking a non-islanded semi-groove folded waveguide slow-wave structure with a circular cross-section electron beam channel and an arc-shaped inner boundary as an example, when the structural dimensional parameters are the same but the angle α is different, the electron beam channel location corresponds to a semi-groove, a minor arc groove, and a major arc groove structure, respectively. (Refer to...) Figure 6A As shown, when α = 36°, the electron beam channel position corresponds to a semi-groove structure, at which point the inner boundary is tangent to the electron beam channel axis; (Refer to...) Figure 6BAs shown, when α = 32°, the electron beam channel corresponds to a short-circuit groove structure. In this case, in the y-direction, the midpoint of the inner boundary needs to be higher than the electron beam channel axis. The section at the short-circuit groove structure experiences less electron bombardment, but the corresponding coupling impedance is lower. This structure cannot excite effective beam-wave interaction, resulting in poor electrical performance. (Refer to...) Figure 6C As shown, when α = 45°, the electron beam channel position corresponds to a superior arc groove structure. At this time, in the y-direction, the midpoint of the inner boundary needs to be lower than the electron beam channel axis. Compared to the half-groove structure of this application, the electron beam channel above the midline of the superior arc groove structure will be subjected to additional electron bombardment. Although it does not have the problem of low coupling impedance, the superior arc groove structure's resistance to electron bombardment is inferior to that of the half-groove structure of this application, making it prone to damage during operation. Considering all factors, this invention adopts a half-groove structure with superior electrical performance and resistance to electron bombardment. Furthermore, the islandless half-groove folded waveguide slow-wave structure significantly reduces the processing difficulty, and the processing accuracy can meet the dimensional and tolerance requirements of this solution. It should be noted that... Figures 6A-6C Both are cross-sections obtained by cutting along the centerline L of the inner boundary. Figures 6A-6C The area marked with a thicker line represents the region where the metal grid is bombarded by electrons.

[0058] Figure 7 The diagram shows the phase velocity ratio curves of a conventional folded waveguide slow-wave structure and a non-islanded half-slot folded waveguide slow-wave structure within the same operating frequency band, under similar phase velocity conditions. The comparison reveals that the non-islanded half-slot folded waveguide possesses both normal and anomalous dispersion regions. This allows for different frequency band design approaches based on varying needs, and the flat area of ​​the dispersion curve at the boundary between normal and anomalous dispersion can be strategically selected as the operating region of the traveling wave tube, significantly increasing bandwidth. Both slow-wave structures operate within the 1.2THz-1.3THz frequency band, with a maximum phase velocity ratio difference of less than 0.001. Because the boundary between normal and anomalous dispersion in the non-islanded half-slot folded waveguide lies within the frequency band, its dispersion curve is flatter in this region compared to the conventional folded waveguide, resulting in better electron beam synchronization and a wider operating bandwidth.

[0059] Figure 8 The diagram shows a comparison of coupling impedance between the islandless half-slot folded waveguide slow-wave structure and the conventional folded waveguide slow-wave structure under similar in-band phase velocities. Simulation results show that below the operating frequency of 1.2T, the coupling impedance of the islandless half-slot folded waveguide is consistently lower than that of the conventional folded waveguide. Within the operating frequency band of 1.2T-1.25T, the conventional folded waveguide has a higher coupling impedance; within the 1.25T-1.3T band, the islandless half-slot folded waveguide exhibits an even higher coupling impedance, surpassing the conventional folded waveguide, but the absolute difference in coupling impedance between the two within the operating frequency band is not significant.

[0060] Figure 9The diagram shows a comparison of the loss characteristics of a slow-wave structure with and without an islanded half-slot folded waveguide, and a conventional folded waveguide, under similar in-band phase velocities. In the design of slow-wave structure dimensions, loss is the primary consideration. In the high-frequency terahertz band, using a structure with high loss will inevitably limit the gain of the traveling wave tube. Simulation results show that the attenuation constant of the islanded half-slot folded waveguide is lower than that of the conventional folded waveguide within the operating frequency band, and the loss per unit distance within the operating frequency band is relatively smaller, averaging below 1500 dB / m.

[0061] The islandless half-slot folded waveguide slow-wave structure provided by this invention cannot be directly connected to the input and output structures of a traveling wave tube. Otherwise, due to differences in shape and size, the characteristic impedance of the microwave transmission line will be mismatched, resulting in strong electromagnetic wave reflection at the connection point and the formation of standing waves. To solve this problem and achieve a matched connection, this invention designs a coupler, i.e., an impedance transformer, suitable for connecting the islandless half-slot folded waveguide slow-wave structure to the power transmission structure. Its structure is as follows: Figure 10 and Figure 11 As shown.

[0062] Furthermore, the present invention also provides a slow-wave circuit, including the islandless half-slot folded waveguide slow-wave structure 1 and coupler 2 as described above; the coupler includes a tapered waveguide section 21 for connecting to the islandless half-slot folded waveguide slow-wave structure and an external waveguide section 22 for connecting to the power transmission structure; the tapered waveguide section 21 has a coupling cavity structure with the same cavity structure shape as the islandless half-slot folded waveguide slow-wave structure 1; the tapered waveguide section 21 is composed of two rows of staggered grid structures; starting from the port connected to the islandless half-slot folded waveguide slow-wave structure 1, the grid height and grid width of the upper and lower rows of grid structures gradually decrease, and the cavity connection section width w1 of the coupling cavity structure of the tapered waveguide section gradually increases. That is, combined with Figure 7 As shown, along the z-direction to the left, the interval height h1, the interval width w2, and the cavity connection segment width w1 all gradually increase.

[0063] The reflection coefficient of the coupler 2, which is applicable to the islandless half-groove folded waveguide slow wave structure 1, is determined according to a binomial distribution or a Chebyshev distribution.

[0064] Specifically, the most basic approach to impedance transformers is to match two transmission lines with different characteristic impedances based on the input impedance characteristics of a quarter-wavelength transmission line. While impedance transformers composed of quarter-wavelength transmission lines are simple in structure, their length is only exactly one-quarter of the guided wave wavelength at a specific frequency. Deviations from this frequency lead to imperfect impedance matching, increased reflection, and thus a narrow operating bandwidth. The guided wave wavelength is not only related to the operating frequency but also to the waveform, structural shape, and structural dimensions. To broaden the operating bandwidth, multiple quarter-wavelength impedance transformers can be used. Generally, the more sections, the more frequency points where perfect matching occurs, and the wider the bandwidth.

[0065] The coupler 2 of this invention, applicable to the islandless half-slot folded waveguide slow-wave structure 1, is based on the principle of a multi-section impedance transformer. By rationally selecting the values ​​of the spacing height h1, spacing width w2, and cavity connection section width w1, it avoids changes in the guided wave wavelength while simultaneously determining the reflection coefficient, enabling the impedance transformer to achieve full matching at several frequencies. The values ​​of the spacing height h1, spacing width w2, and cavity connection section width w1 of the coupler 2 of this invention are increased proportionally by a small amount based on the corresponding dimensional parameters of a normal periodic slow-wave structure. The reflection coefficient can be determined according to a binomial distribution or a Chebyshev distribution; the latter provides a better and wider bandwidth than the former. In this invention, the coupler has a coupling cavity structure with the same shape as the islandless half-slot folded waveguide slow-wave structure 1. This cavity structure not only possesses good transmission characteristics but is also easy to engineer. From a slow-wave structure to a power transmission structure, the spacing height h1, spacing width w2, and cavity connection section width w1 of coupler 2 are all proportionally enlarged. After passing through four quasi-periodic structures with gradually changing dimensions, coupler 2 is connected to the signal input / output structure.

[0066] Figure 12 A schematic diagram of the slow-wave interaction circuit after the connection of coupler 2 is given. One side of coupler 2 is connected to the signal transmission structure, and the other side is connected to the periodic islandless half-slot folded waveguide slow-wave structure 1. Figure 13 The reflection parameter curve of the slow-wave interaction circuit is shown. The aforementioned coupler 2 effectively reduces electromagnetic wave reflection within the structure, ensuring that the reflection parameter S11 of the slow-wave interaction circuit is less than -20dB within the 974.4GHz-1060GHz range, achieving the required operating bandwidth and transmission characteristics of a traveling wave tube.

[0067] The present invention also provides a traveling wave tube comprising the islandless half-slot folded waveguide slow wave structure described above.

[0068] In summary, the islandless half-slot folded waveguide slow-wave structure provided by this invention eliminates the island structure found in conventional folded waveguides, improving the slow-wave circuit's resistance to electron bombardment and exhibiting stronger structural toughness at the electron beam channel, thus solving the problem of insufficient slow-wave structure strength in the terahertz high-frequency band. Furthermore, the islandless half-slot folded waveguide slow-wave structure of this invention possesses both normal and anomalous dispersion, increasing design dimensionality and diversity. Since the boundary between normal and anomalous dispersion in the islandless half-slot folded waveguide of this invention is located within the operating frequency band, its dispersion curve is flatter than that of conventional folded waveguides, resulting in better electron beam synchronization consistency, a wider operating bandwidth, and lower losses. Additionally, the coupler of this invention, applicable to the islandless half-slot folded waveguide slow-wave structure, can achieve impedance matching between the power transmission structure and the slow-wave structure, reducing electromagnetic wave reflection.

[0069] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A slow-wave structure of a non-islanded half-groove folded waveguide, characterized in that, The folded waveguide slow wave structure includes a multi-periodic cavity structure defined by multiple upper gratings and multiple lower gratings that are staggered with each other, and includes a connected straight waveguide section, a waveguide connection section, and an electron beam channel. The waveguide connection segment includes an inner boundary, which is located within the boundary defined by the electron beam channel; The intersection of the centerline of the inner boundary and the axis of the electron injection channel is located on the inner boundary; The electron beam channel employs a semi-groove metal structure, meaning the supporting metal at the slot of the electron beam channel is semi-circular. The inner boundary is an arc-shaped boundary, and the axis of the electron beam channel is tangent to the inner boundary. The radius of the electron beam channel is r, and the radius corresponding to the inner boundary is r1, where r1 is greater than r. The narrow side length of the straight waveguide section is b, and the height of the straight waveguide section is h. The waveguide connection section also includes an outer arc boundary. A first inner junction is included between the inner boundary and the straight waveguide section, and a first outer junction is included between the outer arc boundary and the straight waveguide section. The line connecting the first inner junction and the first outer junction forms an angle α with the boundary of the straight waveguide section. The angle α satisfies the following condition: .

2. The islandless half-groove folded waveguide slow-wave structure according to claim 1, characterized in that, This folded waveguide slow wave structure is applied to traveling wave tubes in the terahertz band.

3. A slow-wave circuit, characterized in that, Including the islandless half-groove folded waveguide slow wave structure and coupler as described in any one of claims 1-2; The coupler includes a tapered waveguide section for connection to the islandless half-groove folded waveguide slow wave structure and an external waveguide section for connection to the power transmission structure; the tapered waveguide section has a coupling cavity structure with the same cavity structure shape as the islandless half-groove folded waveguide slow wave structure. The gradient waveguide segment is composed of two rows of staggered grating structures. Starting from the port connected to the slow wave structure, the height and width of the gratings in the upper and lower rows of grating structures gradually decrease, while the width of the cavity connection section of the coupling cavity structure of the gradient waveguide section gradually increases.

4. A traveling wave tube, characterized in that, Including the islandless half-groove folded waveguide slow wave structure as described in any one of claims 1-2.

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