Folded waveguide slow wave structure, traveling wave tube and design method

Abstract

This invention provides a folded waveguide slow-wave structure, a traveling wave tube, and a design method. The folded waveguide slow-wave structure includes multiple folded waveguide units of a periodic structure and an electron beam channel. Each folded waveguide unit includes a straight waveguide segment and a waveguide connection segment. In the direction from the electron beam channel towards the waveguide connection segment, adjacent straight waveguide segments are arranged obliquely and symmetrically. The angle formed by the axes of adjacent straight waveguide segments is α; 10°≤α≤60°. This folded waveguide slow-wave structure can reduce dispersion variation while maintaining a certain coupling impedance, effectively improving the device bandwidth.

Description

Technical Field

[0001] This invention relates to the field of microwave vacuum electronics technology. More specifically, it relates to a folded waveguide slow-wave structure, a traveling wave tube, and a design method thereof. Background Technology

[0002] Slow-wave structures are the core component of microwave vacuum electronic devices. Their function is to reduce the phase velocity of electromagnetic waves transmitted within them, ensuring synchronization between a spatial harmonic and the electron beam. An interaction occurs between the electron beam and the electromagnetic field, amplifying the electromagnetic wave through energy exchange. In the short millimeter-wave and terahertz frequency bands, helical slow-wave structures are extremely difficult to fabricate, and their power handling capacity is low at high frequencies, with significant heat dissipation challenges. Therefore, all-metal folded waveguide slow-wave structures are commonly used in short millimeter-wave and terahertz traveling-wave tube devices. Folded waveguide slow-wave structures offer advantages such as high mechanical strength, good heat dissipation, large power capacity, wide bandwidth, ease of fabrication, and compatibility with microfabrication techniques, making them widely studied by vacuum electronic research institutions both domestically and internationally.

[0003] like Figure 1 , Figure 2 and Figure 3 As shown, a conventional folded waveguide slow-wave structure is a periodic structure formed by bending a rectangular waveguide along an electric field. The electron beam channel is a cylindrical structure located on the longitudinal central axis of the folded waveguide slow-wave structure. The electron beam channel (denoted as 10) and the interior of the folded waveguide are vacuum, while the rest is made of metallic material. The radius of the electron beam channel is denoted as rc, the width of the folded waveguide is denoted as a, the geometric period of the slow-wave structure is denoted as p, the height of the straight waveguide (denoted as 30) is denoted as h, the narrow side is denoted as b, and the curved waveguide segment (denoted as 20) is denoted as b.

[0004] However, in the E-band, the dispersion curve of conventional folded waveguides varies considerably, and the phase velocity ratio changes significantly with frequency. This limits the improvement of bandwidth and, to some extent, affects the application of this type of slow-wave structure. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a folded waveguide slow-wave structure that can reduce dispersion variation while maintaining a certain coupling impedance, thereby effectively improving the device bandwidth.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a folded waveguide slow-wave structure, comprising:

[0008] Multiple folded waveguide units and electron beam channels of a periodic structure; the folded waveguide unit includes a straight waveguide section and a waveguide connection section;

[0009] In the direction of the electron beam channel toward the waveguide connection section, two adjacent straight waveguide sections are arranged in an inclined symmetrical manner;

[0010] The included angle between the axes of two adjacent straight waveguide segments is α; 10°≤α≤60°.

[0011] The preferred configuration is that, within one cycle, two adjacent straight waveguide segments are tilted outwards symmetrically.

[0012] The preferred embodiment is that, in the height direction of the slow wave structure, the boundary formed by the vertical cross-section of the waveguide connection section is elliptical, and the major axis of the ellipse is parallel to the axis of the electron beam channel.

[0013] The preferred embodiment is that the included angle formed by the axes of two adjacent straight waveguide segments is α, where 30°≤α≤50°.

[0014] The preferred embodiment is that the major axis length of the waveguide connection segment is denoted as ra, the minor axis length is denoted as rb, and 0.5 < rb / ra < 1.

[0015] A preferred embodiment is that the waveguide connection segment includes an inner elliptical arc boundary and an outer elliptical arc boundary;

[0016] The connection point between the outer elliptical arc boundary and the straight waveguide segment is located on the major axis of the waveguide connection segment.

[0017] A preferred embodiment is that the inner elliptical arc boundary of the waveguide connection segment is located within the boundary defined by the electron beam channel.

[0018] The preferred option is to apply this folded waveguide slow wave structure to traveling wave tubes in the short millimeter wave and terahertz frequency bands.

[0019] The present invention also provides a traveling wave tube, comprising the folded waveguide slow wave structure described above.

[0020] This invention also provides a design method for a folded waveguide slow-wave structure, comprising the following steps:

[0021] An initial folded waveguide slow wave structure is designed according to requirements. This initial folded waveguide slow wave structure includes a connected straight waveguide section, a waveguide connection section, and an electron beam channel.

[0022] In the direction of the electron beam channel toward the waveguide connection section, two adjacent straight waveguide sections are set at an angle symmetrically.

[0023] The angle between the axes of two adjacent straight waveguide segments is designed to be α, where 10°≤α≤60°.

[0024] The beneficial effects of this invention are as follows:

[0025] The folded waveguide slow-wave structure provided by this invention is an optimization of the conventional folded waveguide slow-wave structure. The straight waveguide segments are tilted so that the angle between the axes of adjacent straight waveguide segments is α. Compared to the conventional folded waveguide slow-wave structure, by changing the tilt angle of the straight waveguides, the longitudinal undulation of the slow-wave structure is reduced, thereby adjusting the dispersion curve to make it smoother and enhancing broadband performance. Furthermore, by designing the waveguide connection segment as an elliptical cavity structure, the internal cavity of the waveguide connection segment is enlarged, which alters the field strength distribution inside the existing folded waveguide, increasing the field strength near the electron beam channel, thereby improving the coupling impedance of the slow-wave structure. Ultimately, this optimization achieves a reduction of more than 77% in dispersion difference within the 71-96 GHz frequency band. This invention is applicable to short millimeter and terahertz traveling-wave tube slow-wave structures. Attached Figure Description

[0026] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0027] Figure 1 This is one of the structural schematic diagrams of a conventional folded waveguide slow wave structure.

[0028] Figure 2 This is the second schematic diagram of a conventional folded waveguide slow wave structure.

[0029] Figure 3 This is the third schematic diagram of a conventional folded waveguide slow wave structure.

[0030] Figures 4A-4B This is a schematic diagram of the vertical cross-section of the single-period folded waveguide slow wave structure of the present invention.

[0031] Figure 5 This is a schematic diagram of the single-period folded waveguide slow wave structure of the present invention.

[0032] Figure 6 This is a schematic diagram of the multi-period folded waveguide slow wave structure of the present invention.

[0033] Figure 7 This is a comparison curve of the coupling impedance between the folded waveguide slow wave structure of the present invention and the conventional folded waveguide slow wave structure.

[0034] Figure 8 This is a dispersion comparison curve between the folded waveguide slow wave structure of the present invention and the conventional folded waveguide slow wave structure.

[0035] Figure 9 This is a dispersion contrast curve corresponding to the parameter ra of the folded waveguide slow wave structure of the present invention.

[0036] Figure 10 This is a comparison curve of the coupling impedance corresponding to the parameter ra of the folded waveguide slow wave structure of the present invention.

[0037] Figure 11 This is a dispersion contrast curve corresponding to the parameter rb of the folded waveguide slow wave structure of the present invention.

[0038] Figure 12 This is a comparison curve of the coupling impedance corresponding to the parameter rb of the folded waveguide slow wave structure of the present invention.

[0039] Figure 13 This is a normalized phase velocity curve of the folded waveguide slow wave structure of the present invention under different α conditions.

[0040] Figure 14 This is a diagram showing the coupling impedance curves of the folded waveguide slow wave structure of the present invention under different α conditions. Detailed Implementation

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] To improve the broadband performance of folded waveguide slow-wave structures, this invention provides a folded waveguide slow-wave structure applicable to traveling-wave tubes in the short millimeter-wave and terahertz frequency bands. Combined with... Figures 1 to 14 As shown, the folded waveguide slow-wave structure specifically includes: multiple folded waveguide units with a periodic structure and an electron beam channel. Each folded waveguide unit includes a straight waveguide segment 3 and a waveguide connecting segment 2. In the direction from the electron beam channel 1 towards the waveguide connecting segment 2, adjacent straight waveguide segments 3 are arranged at an inclined symmetrical configuration; combined with... Figure 4A As shown, the angle formed by the axes L1 and L2 of two adjacent straight waveguide segments 3 is α; 10°≤α≤60°.

[0047] This slow-wave structure features a large bandwidth and high design flexibility. Based on a conventional folded waveguide, this invention tilts the straight waveguide segment 3 so that the axes of adjacent straight waveguide segments 3 form an angle α, where 10°≤α≤60°. Within this angle range, excessive higher-order modes are not generated, and dispersion tuning is beneficial, thereby increasing the bandwidth of the folded waveguide slow-wave structure and improving device power and efficiency. The values ​​of parameters a, b, p, and h provided by this invention are determined by adjusting the structural dimensions of a conventional folded waveguide slow-wave structure at a center frequency of 78GHz.

[0048] In the above embodiment, within one period (2p), two adjacent straight waveguide segments 3 are tilted outward symmetrically. That is, along the radial direction from the electron beam channel 1 toward the waveguide connection segment 2, the distance between two adjacent straight waveguide segments 3 gradually decreases. The folded waveguide slow-wave structure of the present invention is an optimization based on the conventional folded waveguide. By designing the waveguide connection segment 2 as an elliptical cavity structure and tilting the original straight waveguide segments outward, the folded waveguide slow-wave structure of the present invention can be formed. Compared with the conventional folded waveguide slow-wave structure, the present invention tilts the straight waveguide segments 3, making the dispersion curve of the waveguide smoother. The design of the elliptical cavity structure increases the inner cavity of the waveguide connection segment 2, which can change the field strength distribution inside the existing folded waveguide, increase the field strength near the electron beam channel, and thus further improve the coupling impedance of the slow-wave structure. Finally, after optimization, a dispersion difference reduction of more than 77% can be achieved in the 71-96GHz frequency band.

[0049] Furthermore, in one specific embodiment, the boundary formed by the vertical cross-section of the waveguide connection segment 2 in the height direction of the slow-wave structure is elliptical, forming an elliptical cavity structure. The major axis of this elliptical cavity is parallel to the axis of the electron beam channel. The axial direction of the electron beam channel is the X-direction, the height direction of the slow-wave structure is the Y-direction, and the width direction of the slow-wave structure is the Z-direction. Here, the vertical cross-section of the waveguide connection segment 2 refers to the cross-section of the waveguide connection segment 2 in the XY plane. In this embodiment, by designing the waveguide connection segment 2 as an elliptical cavity structure, the internal cavity of the waveguide connection segment 2 is enlarged, changing the field strength distribution inside the existing folded waveguide, and increasing the field strength of the electron beam channel. This further enhances the coupling impedance amplitude of the slow-wave structure, achieving a small decrease in coupling impedance while increasing the bandwidth.

[0050] To match the elliptical cross-section of waveguide connection segment 2, the included angle between the axes of two adjacent straight waveguide segments 3 is α, where 30° ≤ α ≤ 50°. Within this angle range, it is possible to reduce the dispersion variation while maintaining a certain coupling impedance, thereby effectively improving the device bandwidth.

[0051] Figure 13The normalized phase velocity plots are for the folded waveguide slow-wave structure corresponding to different α values. As α increases from 30° to 50°, the normalized phase velocity increases by 66.6%. At 71 GHz, the normalized phase velocity increases from 0.242 to 0.273, an increase of 12.88%. At 86 GHz, the normalized phase velocity increases from 0.243 to 0.27, an increase of 11.1%. The normalized phase velocity curves show an almost horizontal shift, but the upper cutoff frequency also decreases accordingly, weakening the anomalous dispersion phenomenon. Overall, it has little impact on the dispersion smoothness within the operating frequency band.

[0052] Figure 14 This is a coupling impedance diagram of a folded waveguide slow-wave structure corresponding to different α values. As α increases from 30° to 50°, the coupling impedance remains essentially unchanged at 71 GHz, but increases from 1.08 Ω to 1.22 Ω at 86 GHz, an increase of 24.39%. With increasing α, the coupling impedance increases at the end of the operating frequency band.

[0053] Adjusting the value of α can affect the vertical shift of the phase velocity ratio curve and adjust the coupling impedance at the high-frequency end. Based on this, the slow-wave structure parameters can be better adjusted according to the requirements.

[0054] In one specific embodiment, the major axis length of the waveguide connection segment 2 is denoted as ra, and the minor axis length is denoted as rb, where 0.5 < rb / ra < 1. The value of rb / ra within this range makes the parameter adjustment significantly different from the conventional structural changes.

[0055] In one specific embodiment, the waveguide connecting segment 2 includes an inner elliptical arc boundary and an outer elliptical arc boundary; the connection point between the outer elliptical arc boundary and the straight waveguide segment 3 is located on the major axis of the waveguide connecting segment. The portion of the straight waveguide segment 3 that contacts the elliptical cavity is chosen to be the endpoint of the major axis of the elliptical cavity. Adjusting the value of α does not create a new structure. Unlike conventional folded waveguides, the folded waveguide slow-wave structure of this invention changes the tilt angle of the straight waveguide segment 3, reducing the undulation in the longitudinal dimension of the slow-wave structure, which can adjust the dispersion curve and enhance broadband performance. It is understood that the location of the connection point between the outer elliptical arc boundary and the straight waveguide segment is higher in the radial direction of the electron beam channel than the location of the connection point between the inner elliptical arc boundary and the straight waveguide segment.

[0056] In one specific embodiment, the inner elliptical arc boundary of the waveguide connection segment 2 is located within the boundary defined by the electron beam channel 1. This configuration solves the problems of uneven electromagnetic field distribution and unstable signal transmission that may exist in conventional slow-wave structures.

[0057] Specifically, the dimensions of the folded waveguide slow-wave structure of this invention are set as follows (unit: mm): a = 2.46, b = 0.24, p = 0.7, h = 0.6, rc = 0.2, ra = 0.58, rb = 0.32, α = 30°. A folded waveguide model was established using the three-dimensional electromagnetic software CST. Simulations were performed on both conventional and this invention's folded waveguide, and their performance was compared and analyzed. To calculate the dispersion curve of the folded waveguide slow-wave structure, the structural parameters were adjusted so that the center frequency coupling impedance (Kc) of this invention's folded waveguide slow-wave structure was similar to that of a conventional folded waveguide. Figure 7 and Figure 8 The figures show a comparison of coupling impedance and dispersion curves between the folded waveguide slow-wave structure of this invention and a conventional folded waveguide slow-wave structure. Compared to the conventional folded waveguide slow-wave structure, the phase velocity ratio difference of the folded waveguide slow-wave structure of this invention is reduced by more than 70% in the 71-96 GHz frequency band. Therefore, under otherwise unchanged conditions, using the folded waveguide slow-wave structure of this invention as the interaction circuit, microwave vacuum electronic devices can achieve a larger bandwidth due to the flatter dispersion.

[0058] Figure 9 and Figure 10 This is a comparison curve showing the different parameters ra in this invention. Figure 11 and Figure 12 The comparison curves show different values ​​for parameter rb in this invention. Ra has a relatively small impact, while rb adjusts the upper cutoff frequency when the coupling impedance changes little. Aside from the structural parameters (a, b, p, h) similar to conventional folded waveguides, adjusting ra can regulate the anomalous dispersion characteristics of the dispersion curve, adjusting rb allows for adjustment of the upper cutoff frequency when the coupling impedance changes little, and adjusting α affects the vertical shift of the phase velocity ratio curve and adjusts the coupling impedance at the high-frequency end. Based on this, the slow-wave structure parameters can be better adjusted according to requirements.

[0059] The folded waveguide slow wave structure of the present invention is an improvement on the conventional folded waveguide. Compared with the conventional slow wave structure, the broadband performance is significantly improved. With the axial coupling impedance reduced by 3.8%, the phase velocity ratio difference is reduced by more than 77%, which is suitable for improving the broadband performance of E-band devices.

[0060] The present invention also provides a traveling wave tube comprising the folded waveguide slow wave structure described above.

[0061] This invention also provides a design method for a folded waveguide slow wave structure, which includes the following steps: designing an initial folded waveguide slow wave structure as needed, the initial folded waveguide slow wave structure including a connected straight waveguide segment, a waveguide connecting segment, and an electron beam channel; in the direction of the electron beam channel toward the waveguide connecting segment, two adjacent straight waveguide segments are arranged obliquely and symmetrically; the included angle formed by the axes of two adjacent straight waveguide segments is designed to be α, where 10°≤α≤60°.

[0062] In summary, the folded waveguide slow-wave structure provided by this invention is an optimization based on the conventional folded waveguide slow-wave structure. The straight waveguide segments are tilted so that the angle between the axes of two adjacent straight waveguide segments is α. Compared with the conventional folded waveguide slow-wave structure, by changing the tilt angle of the straight waveguides, the undulation of the slow-wave structure in the longitudinal dimension is reduced, thereby adjusting the dispersion curve to make it smoother and enhancing broadband performance. Furthermore, by designing the waveguide connection segment as an elliptical cavity structure, the internal cavity of the waveguide connection segment can be enlarged, changing the field strength distribution inside the existing folded waveguide and increasing the field strength near the electron beam channel, thereby improving the coupling impedance of the slow-wave structure. Ultimately, this optimization achieves a reduction of more than 77% in the dispersion difference within the 71-96 GHz frequency band. This invention is applicable to short millimeter and terahertz traveling wave tube slow-wave structures.

[0063] 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 folded waveguide slow wave structure, characterized by, include: Multiple folded waveguide units and electron beam channels in a periodic structure; The folded waveguide unit includes a straight waveguide segment and a waveguide connection segment; In the direction of the electron beam channel toward the waveguide connection section, two adjacent straight waveguide sections are arranged in an inclined symmetrical manner; The angle formed by the axes of two adjacent straight waveguide segments is α; 10°≤α≤60°; In the height direction of the slow wave structure, the boundary formed by the vertical cross-section of the waveguide connection section is elliptical, and the major axis of the ellipse is parallel to the axis of the electron beam channel.

2. The folded waveguide slow wave structure of claim 1, wherein, Within one cycle, two adjacent straight waveguide segments are tilted outward symmetrically.

3. The folded waveguide slow-wave structure according to claim 1, characterized in that, The angle formed by the axes of two adjacent straight waveguide segments is α, where 30°≤α≤50°.

4. The folded waveguide slow-wave structure according to claim 1, characterized in that, The major axis length of the waveguide connection segment is denoted as ra, and the minor axis length is denoted as rb, where 0.5 < rb / ra < 1.

5. The folded waveguide slow-wave structure according to claim 1, characterized in that, The waveguide connection segment includes an inner elliptical arc boundary and an outer elliptical arc boundary; The connection point between the outer elliptical arc boundary and the straight waveguide segment is located on the major axis of the waveguide connection segment.

6. The folded waveguide slow-wave structure according to claim 5, characterized in that, The inner elliptical arc boundary of the waveguide connection segment is located within the boundary defined by the electron beam channel.

7. The 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 short millimeter wave and terahertz frequency bands.

8. A traveling wave tube, characterized in that, Including the folded waveguide slow wave structure as described in any one of claims 1-7.

9. A design method for a folded waveguide slow-wave structure, characterized in that, Includes the following steps: An initial folded waveguide slow wave structure is designed according to requirements. This initial folded waveguide slow wave structure includes a connected straight waveguide section, a waveguide connection section, and an electron beam channel. In the direction of the electron beam channel toward the waveguide connection section, two adjacent straight waveguide sections are set at an angle symmetrically. The angle between the axes of two adjacent straight waveguide segments is designed to be α, where 10°≤α≤60°.

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