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

Abstract

The invention provides a folded waveguide slow wave structure, a traveling wave tube and a design method. The folded waveguide slow wave structure comprises a plurality of folded waveguide units of a periodic structure and an electron beam channel. The folded waveguide unit comprises a straight waveguide section and a waveguide connecting section; the two adjacent straight waveguide sections are obliquely and symmetrically arranged in the direction of the electron beam channel towards the waveguide connection section; the included angle formed by the axes of the two adjacent straight waveguide sections is alpha; 10 DEG < = alpha < = 60 DEG. The folded waveguide slow-wave structure can maintain certain coupling impedance while reducing dispersion variation, and realizes effective improvement of device bandwidth.

Description

Technical Field

[0001] The present invention relates to the field of microwave vacuum electronic technology, and more specifically to a folded waveguide slow-wave structure, a traveling wave tube and a design method thereof. Background Art

[0002] The slow-wave structure is the core part of microwave vacuum electronic devices. Its function is to reduce the phase velocity of electromagnetic waves transmitted therein, so that a certain spatial harmonic and the electron beam meet the synchronization conditions. The electron beam and the electromagnetic field will interact with each other, and the electromagnetic wave will be amplified through energy exchange. In the short millimeter wave and terahertz frequency bands, spiral processing will be very difficult, and the power handling capacity of the spiral slow-wave structure is low under high-frequency operation, and there are also huge difficulties in heat dissipation. Therefore, in short millimeter wave and terahertz traveling wave tube devices, all-metal folded waveguide slow-wave structures are mostly used. The folded waveguide slow-wave structure has the advantages of high mechanical strength, good heat dissipation, large power capacity, wide frequency band, easy processing and compatibility with micro-processing technology. It has been widely studied by domestic and foreign electric vacuum research units.

[0003] like Figure 1 , Figure 2 and Figure 3 As shown, the conventional folded waveguide slow-wave structure is a periodic structure formed by bending a rectangular waveguide along an electric field. The electron injection channel is a cylindrical structure located on the longitudinal center axis of the folded waveguide slow-wave structure. The electron injection channel (denoted as 10) and the inside of the folded waveguide are vacuum, and the rest are metal materials. The radius of the electron injection channel is marked as rc, the wide side size of the folded waveguide is represented by 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 section (denoted as 20) is marked as.

[0004] However, within the E-band, the dispersion curve of conventional folded waveguides varies greatly, and the phase velocity ratio changes significantly with frequency, which will limit the improvement of bandwidth and affect the application of this type of slow-wave structure to a certain extent. Summary of the invention

[0005] In view of the above problems, the present invention provides a folded waveguide slow-wave structure that can reduce the dispersion variation while maintaining a certain coupling impedance, thereby effectively improving the bandwidth of the device.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

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

[0008] A plurality of folded waveguide units and electron injection channels of a periodic structure; the folded waveguide unit comprises a straight waveguide section and a waveguide connecting section;

[0009] In the direction from the electron injection channel to the waveguide connecting section, two adjacent straight waveguide sections are arranged in an oblique symmetric manner;

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

[0011] A preferred solution is that within one period, two adjacent straight waveguide sections are symmetrically tilted outward.

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

[0013] A preferred solution is that the angle formed by the axes of two adjacent straight waveguide sections is α, 30°≤α≤50°.

[0014] A preferred solution is that the major axis length of the waveguide connecting section is denoted as ra, the minor axis length is denoted as rb, and 0.5<rb / ra<1.

[0015] Preferably, the waveguide connecting section 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 section is located on the major axis of the waveguide connection section.

[0017] A preferred solution is that the inner elliptical arc boundary of the waveguide connecting section is located within the boundary defined by the electron injection channel.

[0018] The preferred solution is that the folded waveguide slow-wave structure is applied 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 as described above.

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

[0021] Designing an initial folded waveguide slow-wave structure according to needs, the initial folded waveguide slow-wave structure comprises a connected straight waveguide section, a waveguide connecting section and an electron injection channel;

[0022] In the direction from the electron injection channel to the waveguide connecting section, two adjacent straight waveguide sections are arranged obliquely and symmetrically;

[0023] The angle formed by the axes of two adjacent straight waveguide sections is designed to be α, 10°≤α≤60°.

[0024] The beneficial effects of the present invention are:

[0025] The folded waveguide slow-wave structure provided by the present invention is optimized on the basis of the conventional folded waveguide slow-wave structure. The straight waveguide section is tilted so that the angle formed between the axes of two adjacent straight waveguide sections is α. Compared with the conventional folded waveguide slow-wave structure, by changing the tilt angle of the straight waveguide, the fluctuation degree of the slow-wave structure in the longitudinal dimension is reduced, so that the dispersion curve can be adjusted to make the dispersion curve of the slow-wave structure smooth, thereby enhancing the broadband performance. By designing the waveguide connecting section as an elliptical cavity structure so that the inner cavity of the waveguide connecting section is enlarged, the field intensity distribution inside the existing folded waveguide can be changed, and the field intensity near the electron injection channel can be increased, so that the coupling impedance of the slow-wave structure can be improved. The final optimization can achieve a dispersion difference reduction of more than 77% in the 71-96GHz frequency band. The present invention is suitable for short millimeter and terahertz traveling wave tube slow-wave structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The specific implementation modes of the present invention will be further described in detail below in conjunction with 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 structural schematic diagram of a conventional folded waveguide slow-wave structure.

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

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

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

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

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

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

[0035] Fig. 9 It is a dispersion comparison curve diagram corresponding to the parameter ra of the folded waveguide slow-wave structure of the present invention.

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

[0037] Fig.11 It is a dispersion comparison curve diagram corresponding to the parameter rb of the folded waveguide slow-wave structure of the present invention.

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

[0039] Fig.13 It is a normalized phase velocity curve diagram corresponding to the folded waveguide slow-wave structure of the present invention under different α conditions.

[0040] Fig.14 It is a coupling impedance curve diagram corresponding to the folded waveguide slow-wave structure of the present invention under different α conditions. DETAILED DESCRIPTION

[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 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] In order to improve the broadband performance of the folded waveguide slow-wave structure. The present invention provides a folded waveguide slow-wave structure, which is applied to a traveling wave tube in the short millimeter wave and terahertz frequency bands. Figures 1 to 14 As shown, the folded waveguide slow-wave structure specifically comprises: a plurality of folded waveguide units and an electron injection channel of a periodic structure, wherein the folded waveguide unit comprises a straight waveguide section 3 and a waveguide connecting section 2. In the direction of the electron injection channel 1 toward the waveguide connecting section 2, two adjacent straight waveguide sections 3 are arranged in an inclined symmetrical manner; Figure 4A As shown, the angle formed by the axes L1 and L2 of two adjacent straight waveguide sections 3 is α; 10°≤α≤60°.

[0047] The slow-wave structure has the characteristics of large bandwidth and high design flexibility. On the basis of the conventional folded waveguide, the present invention tilts the straight waveguide section 3 so that the axes of the two adjacent straight waveguide sections 3 form an angle α, 10°≤α≤60°. Within this angle range, there will not be too many high-order modes generated and it is beneficial to dispersion adjustment, which can improve the bandwidth of the folded waveguide slow-wave structure and improve the power and efficiency of the device. The values ​​of the parameters a, b, p, and h of the slow-wave structure provided by the present invention are determined by adjusting the structural dimensions of the conventional folded waveguide slow-wave structure when the center frequency is 78 GHz.

[0048] In the above embodiment, within one period (2p), two adjacent straight waveguide sections 3 are symmetrically tilted outward. That is to say, along the radial direction of the electron injection channel 1 toward the waveguide connecting section 2, the distance between the two adjacent straight waveguide sections 3 gradually decreases. The folded waveguide slow-wave structure of the present invention is optimized on the basis of the conventional folded waveguide. The waveguide connecting section 2 is designed as an elliptical cavity structure, and the original folded waveguide straight waveguide section is tilted outward to form the folded waveguide slow-wave structure of the present invention. Compared with the conventional folded waveguide slow-wave structure, the straight waveguide section 3 is tilted in the present invention, so that the dispersion curve of the waveguide is flat, and the elliptical cavity structure is designed to increase the inner cavity of the waveguide connecting section 2, which can change the field strength distribution inside the existing folded waveguide, and increase the field strength near the electron injection channel, so as to further improve the coupling impedance of the slow-wave structure. Finally, after optimization, the dispersion difference can be reduced by more than 77% in the 71-96GHz frequency band.

[0049] Further, in a specific embodiment, in the height direction of the slow-wave structure, the boundary formed by the vertical cross section of the waveguide connecting section 2 is elliptical, forming an elliptical cavity structure, and the long axis of the elliptical cavity is parallel to the axis of the electron injection channel. The axial direction of the electron injection 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. The vertical cross section of the waveguide connecting section 2 here refers to the cross section of the waveguide connecting section 2 on the XY plane. In this embodiment, by designing the waveguide connecting section 2 as an elliptical cavity structure, the inner cavity of the waveguide connecting section 2 is enlarged, the field strength distribution inside the existing folded waveguide is changed, and the field strength of the electron injection channel is improved, so that the coupling impedance amplitude of the slow-wave structure can be further improved, and the coupling impedance decrease is maintained at a small level while the bandwidth is increased.

[0050] In order to match the waveguide connecting section 2 with an elliptical cross section, the angle formed by the axes of the two adjacent straight waveguide sections 3 is α, 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 bandwidth of the device.

[0051] Fig.13This is the normalized phase velocity diagram of the folded waveguide slow-wave structure corresponding to different α. α increases from 30° to 50°, an increase of 66.6%. At 71GHz, the normalized phase velocity increases from 0.242 to 0.273, an increase of 12.88%. At 86GHz, the normalized phase velocity increases from 0.243 to 0.27, an increase of 11.1%. The normalized phase velocity curve is almost a translation trend, but the upper cutoff frequency also decreases, and the anomalous dispersion phenomenon weakens. Overall, it has little effect on the dispersion smoothness within the working frequency band.

[0052] Fig.14 The figure below shows the coupling impedance of the folded waveguide slow-wave structure for different α. When α increases from 30° to 50°, the coupling impedance remains basically unchanged at 71GHz, and increases from 1.08Ω to 1.22Ω at 86GHz, an increase of 24.39%. As α increases, the coupling impedance increases at the end of the operating band.

[0053] Adjusting the size of α can affect the up and down translation of the phase light velocity ratio curve and adjust the size of the coupling impedance at the high-frequency end. Based on this, the slow-wave structure parameters can be better adjusted according to needs.

[0054] In a specific embodiment, the major axis length of the waveguide connecting section 2 is denoted as ra, and the minor axis length is denoted as rb, 0.5<rb / ra<1, and the value of rb / ra within this range makes the parameter adjustment more obviously different from the conventional structure change.

[0055] In a specific embodiment, the waveguide connecting section 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 section 3 is located on the long axis of the waveguide connecting section. The portion of the straight waveguide section 3 that contacts the elliptical cavity is selected as the end point of the long axis of the elliptical cavity. When the size of α is adjusted, no new structure is generated. Unlike the conventional folded waveguide, the folded waveguide slow-wave structure of the present invention changes the inclination angle of the straight waveguide section 3, reduces the degree of fluctuation in the longitudinal dimension of the slow-wave structure, can adjust the dispersion curve, and enhance broadband performance. It can be understood that the position of the connection point between the outer elliptical arc boundary and the straight waveguide section is higher than the position of the connection point between the inner elliptical arc boundary and the straight waveguide section in the radial direction of the electron injection channel.

[0056] In a specific embodiment, the inner elliptical arc boundary of the waveguide connecting section 2 is located within the boundary defined by the electron injection channel 1. This arrangement 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 the present invention are set as (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°. The folded waveguide model is established using the three-dimensional electromagnetic software CST, and the conventional folded waveguide and the folded waveguide of the present invention are modeled and simulated, and the performances are compared and analyzed. In order to calculate the dispersion curve of the folded waveguide slow-wave structure, the structural parameters are adjusted so that the center frequency coupling impedance (Kc) of the folded waveguide slow-wave structure of the present invention is similar to that of the conventional folded waveguide. Figure 7 and Figure 8 The coupling impedance and dispersion comparison curves of the folded waveguide slow-wave structure of the present invention and the conventional folded waveguide slow-wave structure are shown in FIG. Compared with the conventional folded waveguide slow-wave structure, the phase light velocity ratio difference of the folded waveguide slow-wave structure of the present invention in the 71-96GHz band is reduced by more than 70%. Therefore, under the condition that other conditions remain unchanged, with the folded waveguide slow-wave structure of the present invention as the interaction circuit, the microwave electric vacuum device can achieve a larger bandwidth due to the flatter dispersion.

[0058] Fig. 9 and Fig.10 is the comparison curve of the present invention when the parameter ra is different, Fig.11 and Fig.12 This is a comparison curve of the present invention when the parameter rb is different. ra has a smaller effect, and rb adjusts the upper cutoff frequency when the coupling impedance changes slightly. Excluding the structural parameters (a, b, p, h) similar to those of conventional folded waveguides, by adjusting ra, the anomalous dispersion characteristics of the dispersion curve can be adjusted, and by adjusting rb, the upper cutoff frequency can be adjusted when the coupling impedance changes slightly, and adjusting α affects the up and down translation of the phase light velocity ratio curve and adjusts the coupling impedance size at the high-frequency end. Based on this, the slow-wave structural parameters can be better adjusted according to needs.

[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. When the axial coupling impedance is reduced by 3.8%, the phase light velocity ratio difference is reduced by more than 77%. It is suitable for improving the broadband performance of E-band devices.

[0060] The present invention also provides a traveling wave tube, which comprises the folded waveguide slow-wave structure as described above.

[0061] The present 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, wherein the initial folded waveguide slow-wave structure includes a connected straight waveguide section, a waveguide connecting section, and an electron injection channel; in the direction of the electron injection channel toward the waveguide connecting section, two adjacent straight waveguide sections are tilted and symmetrically arranged; and the angle formed by the axes of the two adjacent straight waveguide sections is designed to be α, 10°≤α≤60°.

[0062] In summary, the folded waveguide slow-wave structure provided by the present invention is optimized on the basis of the conventional folded waveguide slow-wave structure. The straight waveguide section is tilted so that the angle formed between the axes of two adjacent straight waveguide sections is α. Compared with the conventional folded waveguide slow-wave structure, by changing the tilt angle of the straight waveguide, the fluctuation degree of the slow-wave structure in the longitudinal dimension is reduced, so that the dispersion curve can be adjusted to make the dispersion curve of the slow-wave structure smooth, thereby enhancing the broadband performance. By designing the waveguide connecting section as an elliptical cavity structure, the inner cavity of the waveguide connecting section can be enlarged, the field strength distribution inside the existing folded waveguide is changed, and the field strength near the electron injection channel is increased, so that the coupling impedance of the slow-wave structure can be improved. The final optimization can achieve a dispersion difference reduction of more than 77% in the 71-96GHz frequency band. The present invention is suitable for 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 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 folded waveguide slow-wave structure, characterized in that: include: Multiple folded waveguide units and electron injection channels of periodic structure; The folded waveguide unit comprises a straight waveguide section and a waveguide connecting section; In the direction from the electron injection channel to the waveguide connecting section, two adjacent straight waveguide sections are arranged in an oblique symmetric manner; The included angle formed by the axes of two adjacent straight waveguide sections is α; 10°≤α≤60°.

2. The folded waveguide slow-wave structure according to claim 1, characterized in that: In one period, two adjacent straight waveguide sections are symmetrical and tilted outward.

3. The folded waveguide slow-wave structure according to claim 1, characterized in that: In the height direction of the slow-wave structure, the boundary formed by the vertical cross section of the waveguide connecting section is elliptical, and the major axis of the ellipse is parallel to the axis of the electron injection channel.

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

5. The folded waveguide slow-wave structure according to claim 3, characterized in that: The major axis length of the waveguide connecting section is denoted as ra, and the minor axis length is denoted as rb, and 0.5<rb / ra<1.

6. The folded waveguide slow-wave structure according to claim 3, characterized in that: The waveguide connecting section 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 section is located on the major axis of the waveguide connection section.

7. The folded waveguide slow-wave structure according to claim 6, characterized in that: The inner elliptical arc boundary of the waveguide connecting section is located within the boundary defined by the electron injection channel.

8. The 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 short millimeter wave and terahertz frequency bands.

9. A traveling wave tube, characterized in that: It comprises a folded waveguide slow-wave structure as described in any one of claims 1 to 8.

10. A design method for a folded waveguide slow-wave structure, characterized in that: The following steps are involved: Designing an initial folded waveguide slow-wave structure according to needs, the initial folded waveguide slow-wave structure comprises a connected straight waveguide section, a waveguide connecting section and an electron injection channel; In the direction from the electron injection channel to the waveguide connecting section, two adjacent straight waveguide sections are arranged obliquely and symmetrically; The angle formed by the axes of two adjacent straight waveguide sections is designed to be α, 10°≤α≤60°.

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