Low-frequency-band convolution backward wave tube structure

Abstract

A low-frequency-band convolution backward wave tube structure disclosed by the present invention comprises a cut-off transition section, an interaction section and an output transition section which are coaxially connected in sequence, the cut-off transition section is internally provided with a cathode structure, the interaction section is cylindrical, the interior of the interaction section is in a vacuum state, the interior of the interaction section is connected with a metamaterial unit sequence, and the output transition section is internally connected with a collector. The metamaterial unit sequence comprises a plurality of three-elliptical-ring metamaterial units which are connected at intervals in the axial direction of the interaction section, a dislocation angle is formed between every two adjacent three-elliptical-ring metamaterial units, the metamaterial unit sequence provides backward waves in the interaction section, and under the action of an external voltage and an axial magnetic field, the metamaterial unit sequence can generate a three-elliptical-ring metamaterial. The cut-off transition section reflects the backward wave back to the interaction section and cuts off the wave with the frequency lower than 2.41 GHz, the metamaterial unit sequence enables electromagnetic energy to be directed to a TE11 mode, the output transition section radiates the electromagnetic energy in the TE11 mode, and a miniaturized structure of the TE11 mode can be achieved at a low frequency band.

Description

Technical Field

[0001] The present invention relates to the technical field of metamaterials, and in particular to a low-frequency gyrotron backward wave tube structure. Background Art

[0002] As a high-power microwave device in the traditional frequency band of microwave technology, the S-band (2-4 GHz) gyrotron has demonstrated unique advantages in radar communications, particle accelerator driving sources, and other fields. However, compared with high-frequency bands (such as 28 GHz and 95 GHz), research on S-band gyrotrons is relatively less, but its high power demand in specific scenarios still drives the development of related technologies. 11 The mode has the lowest cutoff frequency in the circular waveguide and is suitable for low-loss transmission of high-power microwave or radio frequency signals. It is often used in radar, satellite communication and other systems. 11 The mode can form a narrow beam and low sidelobe radiation characteristic, which is suitable for high-precision radar, directional communication or radio telescope feed. In addition, in nuclear fusion devices (such as tokamaks), TE 11 Gaussian beam can be used for plasma heating to achieve efficient energy injection. 11 Mode Gaussian beam plays an important role in efficient transmission, directional radiation and specific technical scenarios, and is an important bridge connecting waveguide technology and free space optics. The diffraction output structure of the gyrotron is beneficial to TE 11 mode is generated, so the novel electromagnetic properties of the three-elliptical ring metamaterial are used to construct a gyrotron slow-wave structure, which can eliminate the traditional gyrotron front-stage transverse electron velocity acceleration device and improve the compactness of the gyrotron.

[0003] Currently TE 11 Mode generation is typically achieved by adding a mode conversion structure to a high-power microwave device. Mode conversion structures are prone to breakdown and discharge in the presence of high power and strong electromagnetic fields. Furthermore, the mode conversion structure itself increases the size and weight of the high-power microwave device, hindering its lightweight and miniaturization. Furthermore, for high-power microwave devices that require frequency tuning over a wide bandwidth, the mode conversion structure itself is not conducive to frequency agility. Currently, lightweight and compact high-power microwave systems can be installed on interceptor drones. These mobile platforms can actively search for and approach target drones, activating electromagnetic sources within a range of tens of meters. Therefore, lightweighting and miniaturizing high-power microwave systems to enable their mobile deployment is a new trend in the current development of high-power microwave sources.

[0004] (Physics of Plasma 26(10):103301 (2019) DOI:org / 10.1063 / 1.5097319), in 2024, He Chaoxiong et al. from the University of Electronic Science and Technology of China proposed a compact magnetron radiation TE11 mode, with an efficiency of 61%, by inserting a mode converter into the relativistic magnetron cavity to achieve TEM-TE 11 Mode conversion. (IEEE TPS 52 (2), pp. 285-290, DOI:10.1109 / TPS.2024.3369932), but the use of a mode converter increases the volume of the structure. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a low-frequency gyrotron wave tube structure that can achieve TE at low frequencies. 11 Miniaturized structure of the pattern.

[0006] The present invention provides a low-frequency band gyroscopic backward wave tube structure, comprising a cutoff gradient section, an interaction section and an output gradient section coaxially connected in sequence, wherein a cathode structure is arranged in the cutoff gradient section, the interaction section is cylindrical and in a vacuum state, and is internally connected to a metamaterial unit sequence structure, and the output gradient section is connected to a collecting electrode; the metamaterial unit sequence structure comprises a plurality of three-elliptical ring metamaterial units spaced apart along the axial direction of the interaction section, and there is an offset angle between two adjacent three-elliptical ring metamaterial units, and the metamaterial unit sequence structure provides a backward wave in the interaction section; under the action of an external voltage and an axial magnetic field, the cutoff gradient section reflects the backward wave back to the interaction section, and at the same time cuts off the frequency below 2.41 GHz, and the metamaterial unit sequence structure directs the electromagnetic energy to the TE 11 Mode, the output gradient section converts electromagnetic energy into TE 11 The pattern radiates out.

[0007] Optionally, the misalignment angle between two adjacent tri-elliptical ring metamaterial units is .

[0008] Optionally, the spacing between two adjacent three-elliptical ring metamaterial units is P, and P satisfies the following formula: in, For TE 11 mode wavelength at 2.41 GHz.

[0009] Optionally, the pitch P is 11.7 mm.

[0010] Optionally, the thickness d of the three-elliptical ring metamaterial unit is 1.71 mm.

[0011] Optionally, the major axis of each ellipse of the three-elliptical ring metamaterial unit , short axis ,radius , the angle between the three ellipses .

[0012] Optionally, two adjacent three-elliptical ring meta-material units and a three-elliptical ring meta-material unit and the interaction segment are fixedly connected by metal rods.

[0013] Optionally, the radius of the interaction segment is smaller than TE 11 mode wavelength at 2.41 GHz.

[0014] Optionally, the cathode structure includes a cylindrical support plate and an annular cathode mounted thereon, the cut-off gradient section is cylindrical, a cavity is opened in the center of the cut-off gradient section, and the cylindrical support plate is fixed in the cavity.

[0015] Optionally, the outer diameters of the cut-off gradient section and the interaction section are consistent, and the outer diameter of the output gradient section gradually increases from one end close to the interaction section to the other end.

[0016] The technical solution provided by the embodiment of the present invention has the following advantages compared with the existing technology: The embodiment of the present invention provides a low-frequency gyrotron tube structure, which uses a three-elliptical ring metamaterial unit structure and its novel electromagnetic properties to eliminate the front-stage electron acceleration structure, thereby improving the compactness of the gyrotron tube structure. By combining the spacing arrangement and staggered angle combination in the interaction section, the low-frequency band and S-band dispersion relation can be controlled, and finally the TE in the entire device can be realized. 11 The excitation mode of the mode and its energy release. Under the action of external voltage and axial magnetic field, the generated electron motion is divided into three parts: on the one hand, it performs Larmor motion around the guide center, and on the other hand, it moves around the axial direction under the action of electric field and magnetic field. Finally, the electrons generated after the interaction are collected by the collector, so it is more compact in structure and easy to achieve lightweight and miniaturization. When the high-energy electrons emitted by the cathode structure enter the beam-wave interaction region in the interaction section, the electrons interact with the slow-wave structure of the three-elliptical ring metamaterial unit. The periodic slow-wave structure formed by the sequence structure of the three-elliptical ring metamaterial unit will change the scattering of the high-energy moving electrons generated by the cathode structure, thereby changing the distribution of working modes in the overall device, and realizing TE 11 The stimulation of the pattern. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic structural diagram of a low-frequency gyrotron backward wave tube structure provided by an embodiment of the present invention; Figure 2 A schematic diagram of relevant parameters of a low-frequency gyrotron backward wave tube structure provided by an embodiment of the present invention; Figure 3 The arrangement of nine triple elliptical ring metamaterial units in the interaction segment provided by the embodiment of the present invention; Figure 4A schematic structural diagram of a three-elliptical ring metamaterial unit provided by an embodiment of the present invention, wherein Figure 4 a is a schematic diagram of the structure of a three-elliptical ring metamaterial unit. Figure 4 b is Figure 4 a Schematic diagram of the structure of adjacent three-elliptical ring metamaterial units; Figure 5 The electromagnetic characteristic curve of the three-elliptical ring metamaterial unit provided by the embodiment of the present invention, wherein Figure 5 a is the curve of relative dielectric constant changing with frequency, Figure 5 b is the curve of relative magnetic permeability changing with frequency; Figure 6 A simulation diagram of the cyclotron motion of electrons emitted from a ring-shaped cathode provided by an embodiment of the present invention on the cathode surface; Figure 7 A simulation diagram of the overall axial motion of high-energy electrons generated by the cathode structure provided by an embodiment of the present invention; Figure 8 The radiation TE in the interaction section under loading of the three-elliptical ring metamaterial unit provided by the embodiment of the present invention 11 Mode electric field distribution diagram; Figure 9 Schematic diagram of electron spokes in a three-elliptical staggered slow-wave structure provided by an embodiment of the present invention, wherein: Figure 9 a is a schematic diagram of the electronic spoke at the axial position z=12mm at the same time. Figure 9 b is a schematic diagram of the electronic spoke at the axial position z = 48 mm at the same time; Figure 10 Schematic diagram of the axial distribution of high-energy electrons at different times in a cyclotron provided by an embodiment of the present invention, wherein: Figure 10 a is a schematic diagram of the axial distribution of high-energy electrons at t=2ns. Figure 10 b is a schematic diagram of the axial distribution of high-energy electrons at t=50ns. Figure 10 c is a schematic diagram of the axial distribution of high-energy electrons at t = 400 ns; Figure 11 For TE 11 Schematic diagram of the mode output power and electronic conversion efficiency changing with current and voltage, where: Figure 11 a is TE 11 Schematic diagram of the mode output power and electronic conversion efficiency changing with current, Figure 11 b is TE 11 Schematic diagram of the mode output power and electronic conversion efficiency changing with voltage; Figure 12 After optimization, TE 11 Schematic diagram of various parameters of the model; among them, Figure 12 a is the optimized TE 11The working electric field of the mode, Figure 12 b is the optimized TE 11 The output power of the mode is 450 MW. Figure 12 c is the optimized TE 11 The operating frequency of the mode is 2.41GHz. Figure 12 d is the optimized TE 11 The electron beam current of the mode is 1.77 kA.

[0018] Description of reference numerals: 1. Cut-off gradient section; 2. Interaction section; 3. Output gradient section; 4. Metamaterial unit sequence; 5. Collector; 6. Cathode structure. DETAILED DESCRIPTION

[0019] A specific embodiment of the present invention is described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiment.

[0020] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the technical solutions of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0021] The present invention is described below by means of several specific embodiments. To keep the following description of the embodiments of the present invention clear and concise, detailed descriptions of known functions and components may be omitted. When any component of an embodiment of the present invention appears in more than one drawing, the component may be represented by the same reference numeral in each drawing.

[0022] refer to Figure 1 , Figure 1 A schematic diagram of a low-frequency gyrotron wave tube structure provided by an embodiment of the present invention is shown in FIG. Figure 1As shown, an embodiment of the present invention provides a low-frequency gyrotron wave tube structure, which is mainly used for the efficient generation and directional radiation of low-frequency (<2.41GHz) electromagnetic waves, including a cutoff gradient section 1, an interaction section 2 and an output gradient section 3 coaxially connected in sequence. A cathode structure 6 is provided in the cutoff gradient section 1. The cutoff gradient section 1 can reflect electromagnetic waves below the cutoff frequency (2.41GHz) through a gradient waveguide structure (such as a cone or a step shape), and only high-frequency waves are allowed to pass through. In conjunction with the cathode structure 6, the lateral diffusion of the electron beam is constrained to ensure that it stably enters the interaction section. The cutoff gradient section 1 usually adopts a metal-dielectric composite structure to reduce reflection loss by impedance matching. The cutoff frequency is determined by the waveguide size and the dielectric constant of the material, and requires precise Designed to meet the needs of low-frequency filtering, the interaction section 2 is cylindrical and in a vacuum state inside, and is connected to a metamaterial unit sequence 4 inside. The interaction section 2 needs to maintain a vacuum environment: to avoid energy loss caused by collisions between electron beams and gas molecules; metamaterial unit sequence 4: consists of multiple three-elliptical ring metamaterial units arranged axially, and each unit is composed of three nested elliptical rings (which may be metal or dielectric materials), with staggered angle design: adjacent units are rotated by a certain angle (such as 30°) to break the symmetry to enhance non-reciprocal coupling and promote backward wave generation; physical mechanism: the cyclotron motion of the electron beam is coupled with the electromagnetic mode of the metamaterial unit to excite backward wave oscillation; the equivalent negative refractive index characteristics of the metamaterial can regulate the phase velocity to achieve directional energy transmission to TE 11 Mode, the output gradient section 3 is connected with the collector 5, the output gradient section 3 function: Mode purification: filter out the stray mode (such as TM01) through the gradient waveguide to ensure TE 11 Main mode output; impedance matching: reduce reflection between waveguide and free space, improve radiation efficiency; the collecting electrode 5 is located at the end of the output section, absorbs residual electron beam energy, and prevents secondary reflection from interfering with the main wave. The metamaterial unit sequence 4 includes multiple three-elliptical ring metamaterial units connected along the axial direction of the interaction section 2. There is a staggered angle between two adjacent three-elliptical ring metamaterial units. The metamaterial unit sequence 4 provides a return wave in the interaction section 2. Under the action of the external voltage and axial magnetic field, the cutoff gradient section 1 reflects the return wave back to the interaction section 2, and at the same time cuts off the frequency below 2.41GHz. The metamaterial unit sequence 4 directs the electromagnetic energy to the TE 11 Mode, output gradient section 3 converts electromagnetic energy into TE 11The overall workflow is as follows: Electron beam excitation: The cathode structure 6 emits an electron beam. Under the action of an external axial magnetic field and voltage, the electrons perform cyclotron motion in the interaction segment 2. Backward wave generation and reflection: The metamaterial unit sequence 4 forms a periodic electromagnetic coupling in the interaction segment 2, generating a backward wave. The cutoff gradient segment 1 reflects waves with frequencies below 2.41GHz back to the interaction segment, while allowing high-frequency waves to pass through; Mode conversion and radiation: The metamaterial unit sequence 4 directionally couples electromagnetic energy to the TE 11 mode, and finally outputs gradient segment 3 with TE 11模式 Radiate out.

[0023] The embodiment of the present invention provides a low-frequency gyrotron tube structure, which uses a three-elliptical ring metamaterial unit structure and its novel electromagnetic properties to eliminate the front-stage electron acceleration structure, thereby improving the compactness of the gyrotron tube structure. By combining the spacing arrangement and staggered angle combination in the interaction section, the low-frequency band and S-band dispersion relation can be controlled, and finally the TE in the entire device can be realized. 11 The excitation mode of the mode and its energy release. Under the action of external voltage and axial magnetic field, the generated electron motion is divided into three parts: on the one hand, it performs Larmor motion around the guide center, and on the other hand, it moves around the axial direction under the action of electric field and magnetic field. Finally, the electrons generated after the interaction are collected by the collector, so it is more compact in structure and easy to achieve lightweight and miniaturization. When the high-energy electrons emitted by the cathode structure enter the beam-wave interaction region in the interaction section, the electrons interact with the slow-wave structure of the three-elliptical ring metamaterial unit. The periodic slow-wave structure formed by the sequence structure of the three-elliptical ring metamaterial unit will change the scattering of the high-energy moving electrons generated by the cathode structure, thereby changing the distribution of working modes in the overall device, and realizing TE 11 The stimulation of the pattern.

[0024] refer to Figure 4 , Figure 4 A schematic structural diagram of a three-elliptical ring metamaterial unit provided by an embodiment of the present invention, wherein Figure 4 a is a schematic diagram of the structure of a three-elliptical ring metamaterial unit. Figure 4 b is Figure 4 a Schematic diagram of the structure of adjacent three-elliptical ring metamaterial units, as shown in Figure 4 As shown, the misalignment angle between two adjacent three-elliptical ring metamaterial units is , The misalignment angle achieves the optimal solution between mode purity, coupling efficiency and process feasibility through precise symmetry breaking and periodic design, and is the core of the miniaturization of low-frequency gyrotron backward wave tubes.

[0025] Specifically, refer to Figure 2 、 Figure 3 and Figure 5 , Figure 2 A schematic diagram of relevant parameters of a low-frequency gyrotron wave tube structure provided by an embodiment of the present invention. Figure 3 The arrangement of 9 triple elliptical ring metamaterial units in the interaction segment provided by the embodiment of the present invention is as follows: Figure 5 The electromagnetic characteristic curve of the three-elliptical ring metamaterial unit provided by the embodiment of the present invention, wherein Figure 5 a is the curve of relative dielectric constant changing with frequency, Figure 5 b is the curve of relative permeability changing with frequency, such as Figure 2 、 Figure 3 and Figure 5 As shown, the spacing between two adjacent three-elliptical ring metamaterial units is P, and P satisfies the following formula: in, For TE 11 The wavelength of the mode is at 2.41GHz. Therefore, the equivalent dielectric constant and equivalent permeability of the three-elliptical ring metamaterial unit can be solved using the equivalent medium theory, and the optimization is carried out under the above constraints. value to improve beam-wave interaction.

[0026] Specifically, as the optimal effect, the pitch P is 11.7 mm.

[0027] Optionally, the thickness d of the three-elliptical ring metamaterial unit is 1.71 mm.

[0028] Optionally, the major axis of each ellipse of the three-elliptical ring metamaterial unit , short axis ,radius , the angle between the three ellipses .

[0029] refer to Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 and Figure 12 As shown, Figure 6 This is a simulation diagram of the cyclotron motion of electrons emitted from a ring-shaped cathode provided by an embodiment of the present invention. Figure 7 This is a simulation diagram of the overall axial motion of high-energy electrons generated by the cathode structure provided by an embodiment of the present invention. Figure 8 The radiation TE in the interaction section under loading of the three-elliptical ring metamaterial unit provided by the embodiment of the present invention 11 Mode electric field distribution diagram, Figure 9 Schematic diagram of electron spokes in a three-elliptical staggered slow-wave structure provided by an embodiment of the present invention, wherein: Figure 9a is a schematic diagram of the electronic spoke at the axial position z=12mm at the same time. Figure 9 b is a schematic diagram of the electronic spoke at the axial position z=48mm at the same time. Figure 10 Schematic diagram of the axial distribution of high-energy electrons at different times in a cyclotron provided by an embodiment of the present invention, wherein: Figure 10 a is a schematic diagram of the axial distribution of high-energy electrons at t=2ns. Figure 10 b is a schematic diagram of the axial distribution of high-energy electrons at t=50ns. Figure 10 c is a schematic diagram of the axial distribution of high-energy electrons at t=400ns. Figure 11 For TE 11 Schematic diagram of the mode output power and electronic conversion efficiency changing with current and voltage, where: Figure 11 a is TE 11 Schematic diagram of the mode output power and electronic conversion efficiency changing with current, Figure 11 b is TE 11 Schematic diagram of the mode output power and electronic conversion efficiency changing with voltage, Figure 12 After optimization, TE 11 Schematic diagram of various parameters of the model; among them, Figure 12 a is the optimized TE 11 The working electric field of the mode, Figure 12 b is the optimized TE 11 The output power of the mode is 450 MW. Figure 12 c is the optimized TE 11 The operating frequency of the mode is 2.41GHz. Figure 12 d is the optimized TE 11 The electron beam current of the mode is 1.77kA, such as Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 and Figure 12 As shown, when the high-energy electrons emitted by the cathode structure 6 enter the beam-wave interaction region in the interaction section 2, the electrons interact with the slow-wave structure of the three-elliptical ring metamaterial unit. When the spacing P changes, the electromagnetic characteristic parameters of the anode structure 6 will change, and the scattering of the high-energy moving electrons generated by the cathode structure 6 by the periodic slow-wave structure formed by the metamaterial unit sequence 4 will change, thereby changing the distribution of working modes in the metamaterial unit sequence 4. Therefore, TE can be achieved by optimizing and designing the metamaterial unit sequence 4. 11 The excitation of the mode. And by optimizing the design of the metamaterial unit structure 4, the beam-wave interaction efficiency can be improved. There is no mode conversion device. Particle simulation confirms that when working at 2.41GHz, TE 11 The mode electron conversion efficiency can reach 67.8%.

[0030] Optionally, two adjacent three-elliptical ring metamaterial units and the three-elliptical ring metamaterial unit and the interaction segment 2 are fixedly connected by metal rods. The metal rods (usually copper or stainless steel) connect the adjacent three-elliptical ring units and the interaction segment wall in an axial penetration manner to provide anti-vibration / anti-deformation support to ensure the structural integrity of the metamaterial sequence in a vacuum environment. Electromagnetic coupling assists: the metal rods can act as parallel inductors to adjust the equivalent circuit parameters between units (such as increasing the series inductance by about 0.5nH) and optimize the phase synchronization of the return wave.

[0031] Optionally, the radius of the interaction segment 2 is smaller than TE 11 mode wavelength at 2.41 GHz.

[0032] Specifically, the cathode structure 6 includes a cylindrical supporting plate and an annular cathode mounted thereon. The cut-off gradient section 1 is cylindrical, and a cavity is opened in the center of the cut-off gradient section 1. The cylindrical supporting plate is fixed in the cavity.

[0033] Optionally, the outer diameters of the cut-off gradient section 1 and the interaction section 2 are consistent, and the outer diameter of the output gradient section 3 gradually increases from one end close to the interaction section 2 to the other end.

[0034] The overall size design is as follows: like Figure 1 As shown, the radius of the interaction segment 2 is determined based on the expected response frequency of the metamaterial unit 4 in the S band. The period P is determined by optimizing the arrangement of the three elliptical ring metamaterial units, and the maximum opening diameter of the output gradient section 3 is determined according to the operating frequency. , and the radius of output gradient segment 3 , further optimize the gap between the cathode and anode to obtain the radius of the cathode structure 6 Finally, a low-frequency gyrotron backward wave tube structure provided by an embodiment of the present invention is obtained, comprising: The gyrotron consists of three main parts: the first part is the cutoff gradient section 1, which is used to reflect the backward wave back to the interaction section 2 and cut off the frequency below 2.41GHz; the second part is the interaction section 2, in which the metamaterial unit 4 is installed, and the three elliptical ring metamaterial unit is conducive to HE 31 (HE 31 =TE 21 +TE 11 ) mode exists by optimizing the staggered angles of three staggered ellipses , so that the metamaterial unit 4 is preferably TE 11 mode as its working mode, in which the equivalent permeability of the three-elliptical ring metamaterial unit is negative near the expected working frequency of 2.41 GHz (see Figure 4 (b) shows that the inner radius of the interaction segment 2 is TE 11 The expected operating frequency of the mode is 2.41GHz. The cutoff provides a negative equivalent dielectric constant, so that the added metamaterial unit 4 interaction section 2 provides a return wave. The metamaterial unit sequence 4 realizes the control of the dispersion relation and enhances the beam-wave interaction, so that the electromagnetic energy is directed to the TE 11 Mode, the third part outputs the gradient segment 3, making the electromagnetic energy TE 11 The pattern radiates out. The annular cathode used here is used to generate high-energy electrons. The high-energy electrons generated by the cathode structure 6, on the one hand, perform Larmor cyclotron motion around the center of the cathode, on the other hand, rotate as a whole along the axial direction under the action of the external electromagnetic field, and on the other hand, the electrons that complete the energy transfer are finally recovered by the collector 5. The metamaterial unit sequence 4 is arranged in the interaction section 2. The units of the three elliptical ring metamaterial units are connected together by metal rods at intervals up and down. There is a 60° offset angle between two adjacent units, and the interval between each unit is , making For TE 11 The wavelength of the mode is at 2.41 GHz. Therefore, the equivalent dielectric constant and equivalent permeability of the three-elliptical ring metamaterial unit can be solved using the equivalent medium theory. Optimize under the above constraints The value is used to improve the interaction between beam waves and vacuum is drawn in the middle. The cathode structure 6 is placed in the hollow part of the transition section 1. The cathode structure 6 is composed of a cylindrical support plate with a ring cathode emitter installed on it. The external voltage is applied through Figure 1 The cut-off gradient section 1 is applied between the anode waveguide structure and the annular cathode column on the left side. Figure 2 The mid-period P is optimized to 11.7 mm, and the thickness d of a single three-elliptical ring metamaterial unit is optimized to 1.71 mm. Figure 4 a) The long axis of the three elliptical ring metamaterial unit , short axis ,radius , the angle between the three ellipses , Figure 4 The misalignment angle between two adjacent three-elliptical ring metamaterial units in b .

[0035] The above inventions are only several specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A low-frequency gyrotron backward wave tube structure, characterized in that: The invention comprises a cut-off gradient section (1), an interaction section (2) and an output gradient section (3) which are coaxially connected in sequence, wherein a cathode structure (6) is provided in the cut-off gradient section (1), the interaction section (2) is cylindrical and is in a vacuum state, and is internally connected to a metamaterial unit sequence structure (4), and the output gradient section (3) is internally connected to a collecting electrode (5); The metamaterial unit sequence (4) comprises a plurality of three-elliptical ring metamaterial units spaced apart and connected along the axial direction of the interaction section (2), with a staggered angle between two adjacent three-elliptical ring metamaterial units, and the metamaterial unit sequence (4) provides a back wave in the interaction section (2); Under the action of external voltage and axial magnetic field, the cutoff gradient section (1) reflects the return wave back to the interaction section (2), and at the same time cuts off the frequency below 2.41 GHz. The metamaterial unit sequence (4) directs the electromagnetic energy to the TE 11 mode, the output gradient section (3) converts electromagnetic energy into TE 11 The pattern radiates out.

2. The low-frequency gyrotron wave tube structure according to claim 1, characterized in that: The misalignment angle between two adjacent three-elliptical ring metamaterial units is .

3. The low-frequency gyrotron wave tube structure according to claim 1, characterized in that: The spacing between two adjacent three-elliptical ring metamaterial units is P, and P satisfies the following formula: in, For TE 11 mode wavelength at 2.41 GHz.

4. The low-frequency gyrotron wave tube structure according to claim 3, characterized in that: The spacing P is 11.7 mm.

5. A low-frequency gyroscopic backward wave tube structure according to claim 1 or 4, characterized in that: The thickness d of the three-elliptical ring metamaterial unit is 1.71 mm.

6. The low-frequency gyrotron wave tube structure according to claim 5, characterized in that: Each elliptical major axis of the three-elliptical ring metamaterial unit , short axis ,radius , the angle between the three ellipses .

7. The low-frequency gyroscopic backward wave tube structure according to claim 1, characterized in that: Two adjacent three-elliptical ring metamaterial units and a three-elliptical ring metamaterial unit and an interaction segment (2) are fixedly connected via metal rods.

8. A low-frequency gyroscopic backward wave tube structure according to any one of claims 1 to 4, characterized in that: The radius of the interaction segment (2) is smaller than TE 11 mode wavelength at 2.41 GHz.

9. A low-frequency gyroscopic backward wave tube structure according to any one of claims 1 to 4, characterized in that: The cathode structure (6) comprises a cylindrical support plate and an annular cathode mounted thereon; the cut-off gradient section (1) is cylindrical; a cavity is opened at the center of the cut-off gradient section (1); and the cylindrical support plate is fixed in the cavity.

10. The low-frequency gyroscopic backward wave tube structure according to claim 1, characterized in that: The outer diameters of the cut-off gradient section (1) and the interaction section (2) are consistent, and the outer diameter of the output gradient section (3) gradually increases from one end close to the interaction section (2) to the other end.

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