Miniaturized periodic permanent magnet focused metamaterial backward wave oscillator

Abstract

The invention discloses a miniaturized periodic permanent magnet focusing metamaterial backward wave oscillator, which comprises a metamaterial slow wave structure, a coupling cavity, a periodic permanent magnet focusing system and a coaxial output interface, the metamaterial slow-wave structure comprises a waveguide shell, a periodic resonance structure and a first vacuum gap; the coupling cavity comprises a coupling cavity shell, a coupling cavity inner conductor and a second vacuum gap; the coupling cavity inner conductor is connected with the periodic resonance structure and the coaxial output interface; the periodic permanent magnet focusing system comprises a first permanent magnet focusing structure and a second permanent magnet focusing structure which are asymmetrically arranged up and down, and the metamaterial slow wave structure is arranged between the first permanent magnet focusing structure and the second permanent magnet focusing structure. According to the backward wave oscillator, the metamaterial slow wave structure and the periodic permanent magnet focusing system are arranged, and the coupled cavity is multiplexed as the collector, so that the size of the backward wave oscillator is reduced. And an asymmetric focusing magnetic field is generated through the asymmetrically arranged periodic permanent magnet focusing system, so that electron beams can perform energy exchange better.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of vacuum electron devices, in particular to a miniaturized periodic permanent magnet focusing metamaterial backward wave oscillator. BACKGROUND

[0002] Vacuum electron devices, such as backward wave oscillators and traveling wave tubes, have been applied in the fields of accelerators, plasma science, radars, etc. due to their high output power. It is well known that the output power of a backward wave oscillator is always higher than that of a solid-state device. In a vacuum environment, electrons exhibit higher mobility, and the excellent heat dissipation performance of vacuum electron devices enables them to achieve high power output even in high-frequency working conditions. In contrast, the efficiency and power of solid-state devices will be greatly reduced as the working frequency increases. If an attempt is made to achieve the power level of a single vacuum electron device by integration, the overall system efficiency will be seriously dragged down by problems such as heat dissipation, and the advantages of solid-state devices in terms of size and mass will also be lost. Therefore, in the current application scenarios of high power and high frequency, microwave vacuum electron devices still maintain an unparalleled advantage.

[0003] Miniaturization is a long-term development goal and trend of vacuum electron devices. In order to achieve the goal of miniaturization of vacuum electron devices, the size of components, including but not limited to the slow wave structure, the output structure, the electron gun, and the magnetic focusing system, needs to be gradually reduced. High-power microwave sources are an important application of backward wave oscillators, and miniaturized backward wave oscillators can reduce costs and device size. Moreover, the slow wave structure of traditional backward wave oscillators is relatively large in size, which is not conducive to the overall miniaturization of the device. In addition, current metamaterial backward wave oscillators usually use a uniform magnetic field generated by a solenoid or a permanent magnet to focus the electron beam, which is not conducive to the miniaturization of the focusing system and the electron beam focusing effect is not good. SUMMARY

[0004] In order to solve the problems of large size of conventional backward wave oscillators and poor electron beam focusing effect, the present application proposes a miniaturized periodic permanent magnet focusing metamaterial backward wave oscillator, which uses metamaterial as the slow wave structure and a new type of periodic permanent magnet focusing system. The coupling cavity is multiplexed as a collector, has a smaller size, and generates an asymmetric focusing magnetic field through the asymmetrically arranged periodic permanent magnet focusing system, which facilitates better energy exchange of the electron beam to solve the above problems.

[0005] The present application discloses a miniaturized periodic permanent magnet focusing metamaterial backward wave oscillator, which comprises a metamaterial slow wave structure, a coupling cavity, a periodic permanent magnet focusing system, and a coaxial output interface. The metamaterial slow wave structure comprises a waveguide shell, a periodic resonant structure, and a first vacuum gap arranged in the waveguide shell. The coupling cavity is connected with the metamaterial slow wave structure at one end and connected with the coaxial output interface at the other end, and the coupling cavity comprises a coupling cavity shell, the coupling cavity shell is provided with a coupling cavity inner conductor and a second vacuum gap, the coupling cavity inner conductor comprises an inner conductor first section, an inner conductor second section and an inner conductor third section, the inner conductor first section is connected with the periodic resonant structure, and the inner conductor third section is connected with the coaxial output interface. The periodic permanent magnet focusing system comprises the first permanent magnet focusing structure and the second permanent magnet focusing structure which are asymmetrically arranged upwards and downwards, and the metamaterial slow wave structure is arranged between the first permanent magnet focusing structure and the second permanent magnet focusing structure.

[0006] Preferably, the coaxial output interface comprises an interface shell, the interface shell is provided with a dielectric layer, the dielectric layer is provided with an interface probe, and the interface probe is connected with the inner conductor third section.

[0007] Preferably, the metamaterial slow wave structure is provided with an electron beam inlet at one end, and the electron gun is externally connected.

[0008] Preferably, the periodic resonant structure comprises a plurality of metamaterial unit structures arranged periodically.

[0009] Preferably, the periodic resonant structure is arranged on the inner wall of the waveguide shell in a biased manner.

[0010] Preferably, the first vacuum gap and the second vacuum gap are communicated, one end of the coupling cavity shell is connected with the waveguide shell, and the other end of the coupling cavity shell is connected with the interface shell.

[0011] Preferably, the radius of the inner conductor second section is greater than that of the inner conductor first section and the inner conductor third section.

[0012] Preferably, the first permanent magnet focusing structure and the second permanent magnet focusing structure each comprise a fourth pole shoe, the fourth pole shoe is provided with a second pole shoe in a side-to-side opposite manner, the first pole shoe and the third pole shoe are arranged periodically and alternately between the second pole shoes, and the first pole shoe and the third pole shoe in the first permanent magnet focusing structure are provided with a pole shoe gasket below, and the first pole shoe and the third pole shoe in the second permanent magnet focusing structure are provided with a pole shoe gasket above.

[0013] Preferably, a plurality of cavities are formed between the first pole shoe, the second pole shoe, the third pole shoe and the fourth pole shoe, a central magnet is arranged in the cavity, and a periodically arranged edge magnet is arranged outside the second pole shoe.

[0014] Preferably, the lateral dimension of the edge magnet in the first permanent magnet focusing structure is smaller than the lateral dimension of the edge magnet in the second permanent magnet focusing structure.

[0015] The beneficial effects of the present application are as follows: (1) The superstructure material is used as a slow wave structure in the application, and compared with a traditional backward wave oscillator, the superstructure material has a subwavelength characteristic, so that the size is smaller.

[0016] (2) The coupling cavity of the application can realize good matching of the signal output structure and multiplexing as a collecting electrode of the backward wave oscillator, compared with the traditional backward wave oscillator, the structure multiplexing is realized, and the size of the device is further reduced.

[0017] (3) A novel periodic permanent magnet focusing system is used in the application, compared with the solenoid focusing system, the application does not need an additional power supply and an auxiliary coil and its fixing device, so that the weight and size are greatly reduced. Meanwhile, under the condition of the same electron beam parameters, the required magnetic field peak value of the periodic magnetic field is smaller than that of the uniform magnetic field, so that the size of the periodic permanent magnet focusing system is also smaller than that of the uniform permanent magnet focusing system.

[0018] (4) The edge magnet of the periodic permanent magnet focusing system of the application is asymmetrically arranged, which can balance and offset the asymmetric distribution of the space charge field on the upper and lower surfaces of the electron beam caused by the periodic resonant structure, so as to better focus the electron beam. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A structure schematic diagram of the miniaturized periodic permanent magnet focusing superstructure material backward wave oscillator of the embodiment of the application is shown in the figure. Figure 2 A cross-sectional view of the miniaturized periodic permanent magnet focusing superstructure material backward wave oscillator of the embodiment of the application is shown in the figure. Figure 3 A cross-sectional view of the superstructure material slow wave structure of the embodiment of the application is shown in the figure. Figure 4 A schematic diagram of the superstructure material unit structure of the embodiment of the application is shown in the figure. Figure 5 A cross-sectional view of the coupling cavity and coaxial output interface of the embodiment of the application is shown in the figure. Figure 6 A structure schematic diagram of the periodic permanent magnet focusing system of the embodiment of the application is shown in the figure. Figure 7 A cross-sectional view of the periodic permanent magnet focusing system of the embodiment of the application is shown in the figure. Figure 8 A schematic diagram of the electron focusing result of the miniaturized periodic permanent magnet focusing superstructure material backward wave oscillator of the embodiment of the application is shown in the figure.

[0020] The reference signs are as follows: 1-metamaterial slow-wave structure, 101-periodic resonant structure, 102-waveguide housing, 103-first vacuum gap, 104-electron injection port, 2-coupling cavity, 201-coupling cavity housing, 202-first section of inner conductor, 203-second section of inner conductor, 204-third section of inner conductor, 205-second vacuum gap, 3-periodic permanent magnet focusing system, 301-first iron pole shoe, 302-second iron pole shoe, 303-third iron pole shoe, 304-fourth iron pole shoe, 305-center magnet, 306-edge magnet, 307-iron pole shoe gasket, 4-coaxial output interface, 401-interface probe, 402-dielectric layer, 403-interface housing. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of this application more clear, the application is further described in detail below with reference to the accompanying drawings and examples.

[0022] The embodiment of the present application discloses a miniaturized periodic permanent magnet focused metamaterial backward wave oscillator, the structure of which is as follows: Figure 1 , metamaterial slow-wave structure 1, coupling cavity 2, periodic permanent magnet focusing system 3 and coaxial output interface 4. The backward wave oscillator interacts with the slow-wave structure through the electron beam, causing the electron beam to slow down and give up energy, thereby stimulating high-power coherent electromagnetic radiation. The metamaterial backward wave oscillator includes the following main components: metamaterial slow-wave structure: formed by metamaterial units arranged periodically in the direction of electron beam travel, used to provide a place for energy exchange; signal output structure (including coupling cavity and SMA coaxial output structure): outputs the high-power signal generated by the system; periodic permanent magnet focusing system, used to ensure that the electron beam is not diverged by the space charge field; collecting pole (reused by the coupling cavity), used to collect the remaining electrons after the interaction.

[0023] like Figure 2As shown, the metamaterial slow wave structure 1 includes a periodic resonant structure 101, a waveguide shell 102, a first real space gap 103, and an electron beam inlet 104. The periodic resonant structure 101 is arranged on the inner wall of the waveguide shell 102, the first real space gap 103 is arranged inside the waveguide shell 102, and the electron beam inlet 104 is arranged on the left side of the waveguide shell 102. The periodic resonant structure 101 includes a plurality of metamaterial unit structures arranged periodically, and the number of metamaterial unit structures can be adjusted. In this embodiment, there are 12 metamaterial unit structures. An electron gun is connected to the electron beam inlet 104, and the electrons are emitted from the opening into the metamaterial slow wave structure 1. The tail end of the periodic resonant structure 101 is connected to the inner conductor of the coupling cavity in the coupling cavity 2, and extends into the cavity for a distance to enhance the impedance matching of the coupling cavity 2. The periodic resonant structure 101 is arranged offset on the inner wall of the waveguide shell 102, so that the electron beam can avoid the periodic resonant structure 101 when injected, and the magnetic field generated by the periodic permanent magnet focusing system 3 can produce the same magnetic field force on the upper and lower surfaces of the electron beam, reducing the difficulty of magnetic field focusing.

[0024] In this embodiment, the cross-sectional view of the metamaterial slow wave structure 1 and the dimensions of each structure are as shown in the following table: Figure 3 As shown in the table, the dimensions (in mm) are as follows: a =14.5, by =4, ty =2, tz =2.5, ar =5, wl =131, wge =4.5, offs =3, t =1.2, gap =2. Wherein, the transverse dimension of the inner cavity of the metamaterial slow wave structure 1 is a × a . bx The height of the cathode inlet (electron beam inlet 104) for emitting the electron beam 。ty and tz are the thicknesses of the cavity wall of the metamaterial slow wave structure 1 in the vertical plane and the horizontal plane, respectively. ar is the distance of the periodic resonant structure 101 from the cathode inlet. offs is the distance between the periodic resonant structure 101 and the center of the electron beam (i.e., the position of the periodic resonant structure 101 arranged offset on the inner wall of the waveguide shell 102). gap is the distance of the periodic resonant structure 101 from the upper surface of the electron beam. t is the thickness of the periodic resonant structure 101. wl is the length of the cavity of the metamaterial slow wave structure 1, wge is the length of the periodic resonant structure 101 extending into the coupling cavity 2. Figure 4Fig. 1 is a schematic diagram of a periodic resonant structure 101 composed of periodically arranged super-material unit structures in the embodiment, Figure 4 Fig. 2 is a schematic diagram of a super-material unit structure used in the embodiment.

[0025] The coupling cavity 2 is connected to the super-material slow wave structure 1 at one end and connected to a Sub Miniature version A (SMA) coaxial output interface 4 at the other end. The coaxial output interface 4 includes an interface shell 403, a dielectric layer 402 arranged in the interface shell 403, and an interface probe 401 arranged in the dielectric layer. The coupling cavity 2 includes a coupling cavity shell 201, a coupling cavity inner conductor, and a second free space gap 205. The coupling cavity inner conductor is arranged inside the coupling cavity shell 201 and includes an inner conductor first section 202, an inner conductor second section 203, and an inner conductor third section 204. The inner conductor first section 202 is connected to the periodic resonant structure 101, and the inner conductor third section 204 is connected to the interface probe 401 of the coaxial output interface 4 for outputting signals. The inner conductor second section 203 is arranged between the inner conductor first section 202 and the inner conductor third section 204, and the radius of the inner conductor second section 203 is slightly larger than that of the inner conductor first section 202 and the inner conductor third section 204, which can adjust the impedance matching of the signal output structure and is easier to assemble. The first free space gap 103 is in communication with the second free space gap 205. One end of the coupling cavity shell 201 is connected to the waveguide shell 102, and the other end is connected to the interface shell 403 of the coaxial output interface 4.

[0026] The cross-sectional view of the coupling cavity 2 and the coaxial output interface 4 and the dimensions of the structures in the embodiment are shown in Fig. 3. The dimensions (in mm) in the figure are as follows: Figure 5 li1 =33, li2 =10, el =52.5, ri1 =0.8, lo =4, ro =2.1, ri =0.6, t =2. Wherein, the internal dimensions of the coupling cavity 2 are ea × ea ×e l . l is the total length of the cavity inside, li1 is the length of the inner conductor first section 202, li2 is the length of the inner conductor first section 202 plus the inner conductor second section 203, ri1 is the radius of the inner conductor second section 203, ri is the radius of the inner conductor first section 202, the inner conductor third section 204, and the interface probe 401, lo is the length of the coaxial output interface 4, ro ​The radius of the medium layer 402 in the coaxial output interface 4, t The thickness of the interface shell 403 of the coaxial output interface 4.

[0027] As Figure 6 shown, the periodic magnetic focusing system (PMF) 3 includes a first permanent magnetic focusing structure arranged above the metamaterial slow wave structure 1 and a second permanent magnetic focusing structure arranged below the metamaterial slow wave structure 1, the metamaterial slow wave structure 1 is arranged between the first permanent magnetic focusing structure and the second permanent magnetic focusing structure, and the first permanent magnetic focusing structure and the second permanent magnetic focusing structure are asymmetrically arranged.

[0028] The first permanent magnetic focusing structure and the second permanent magnetic focusing structure each include a fourth pole shoe 304, a second pole shoe 302 is arranged opposite to each other on the right side of the fourth pole shoe 304, a first pole shoe 301 and a third pole shoe 303 are arranged in a periodic and alternating manner between the second pole shoes 302, and a pole shoe gasket 307 is arranged below the first pole shoe 301 and below the third pole shoe 303 in the first permanent magnetic focusing structure and above the first pole shoe 301 and above the third pole shoe 303 in the second permanent magnetic focusing structure. A plurality of cavities are formed between the first pole shoe 301, the second pole shoe 302, the third pole shoe 303 and the fourth pole shoe 304, and a center magnet 305 is arranged in the cavities. The second pole shoe 302 is provided with a periodically arranged edge magnet 306 on the front and rear outer sides, thereby generating a periodic magnetic field to control the focusing of electrons. The third pole shoe 303 passes through the second pole shoe 302 and is used to limit the edge magnet 306. The edge magnets 306 in the first permanent magnetic focusing structure and the second permanent magnetic focusing structure are asymmetrically arranged, the transverse size of the edge magnet 306 in the first permanent magnetic focusing structure is smaller than the transverse size of the edge magnet 306 in the second permanent magnetic focusing structure, which is used to generate an asymmetric magnetic field to offset the interference magnetic field generated by the periodic resonant structure 101, so as to facilitate the energy exchange of the electron beam. According to the needs, the periods of each structure and the magnetic field strength of each material in the periodic magnetic focusing system 3 can be adjusted to control the focusing position and degree of the electrons. In the embodiment, the number of periods formed by the first pole shoe 301, the third pole shoe 303, the second pole shoe 302 and the fourth pole shoe 304 in the first permanent magnetic focusing structure and the second permanent magnetic focusing structure is 15, the number of periods of the center magnet 305 is 14, and the number of periods of the edge magnet 306 is 7. The magnetic field strength of the first center magnet 305 is different from that of the last center magnet 305, which facilitates the focusing of the initial stage and the final stage of the energy exchange of the electron beam.

[0029] The cross-sectional view of the periodic magnetic focusing system 3 and the dimensions of each structure in the embodiment are shown in Figure 7 The dimensions (unit: mm) in the figure are as follows: y1 =15.5,z1 = 2.5, tz = 4, y = 15, iz = 1, mz1 = 8, my1 = 15, mz2 = 17, my2 = 15.5, gz = 126, ty = 0.5, x = 30, x1 = 38, gx = 1, xt = 1.5, xb = 3. Wherein the size of the leftmost fourth pole shoe 304 is x1 × y1 × z1 , the size of the first pole shoe 301 is x × my1 × iz , the size of the third pole shoe 303 is gx × y × gz , the size of the second pole shoe 302 is xt × y × iz , and the size of the pole shoe gasket 307 is x × ty × tz . The size of the upper and lower center magnet 305 is x × my1 × mz1 , the size of the edge magnet 306 outside the upper first permanent magnetic focusing structure is xt × my2 × mz2 , the size of the edge magnet 306 outside the lower second permanent magnetic focusing structure is xb × my2 × mz2 , and the distance from the leftmost first pole shoe 301 to the last first pole shoe 301 is gz .

[0030] The miniaturization advantage of the embodiment is that the size of the metamaterial slow wave structure 1 is subwavelength, which is smaller than the conventional slow wave structure. The coupling cavity 2 can be reused as a collector, and the device does not need to additionally increase the collector, further reducing the size of the device. Compared with other metamaterial backward wave oscillators, the periodic resonant structure is placed in the center of the waveguide, and the electron beam inlet is placed below. In the embodiment, the periodic resonant structure 1 is biased upward, and the electron beam inlet 104 is placed in the center of the metamaterial waveguide. This can make the upper and lower surfaces of the electron beam obtain the same focusing magnetic field under the focusing of the periodic permanent magnet system. Therefore, the application can adopt the periodic permanent magnet focusing system 3, thereby having the advantage of miniaturization. By introducing the periodic permanent magnet focusing system 3, the disadvantage of large size of the focusing system caused by the solenoid is solved. By periodically arranging the magnets and pole shoes, the related parameters of the periodic permanent magnet focusing system 3 can be adjusted to generate a focusing magnetic field for electrons, and the purpose of reducing the size of the system is also achieved. Moreover, the periodic permanent magnet focusing system 3 adopts an asymmetric design to generate an asymmetric focusing magnetic field to balance and offset the asymmetric space charge field on the surface of the electron beam caused by the periodic resonant structure, thereby facilitating better focusing of the electron beam. Finally, the high-power signal generated by the coupling of the coupling cavity 2 is output through the SMA coaxial output interface 4.

[0031] In summary, the backward wave oscillator shown in the embodiment uses a metamaterial slow wave structure 1, and based on the subwavelength characteristics of the metamaterial, the miniaturization of the slow wave structure of the backward wave oscillator is achieved. Moreover, the periodic permanent magnet focusing system 3 is introduced, which avoids the use of a large-size solenoid compared with the conventional solenoid focusing system, reduces the size of the system, enhances the integrity of the system, and the edge magnets 306 on the upper and lower sides are asymmetrically arranged to generate an asymmetric magnetic field to balance and offset the asymmetric space charge field on the upper and lower surfaces of the electron beam caused by the periodic resonant structure 101, thereby facilitating better focusing of the electron beam, as shown in Figure 8 The miniaturized periodic permanent magnet focusing metamaterial backward wave oscillator proposed in the embodiment can focus the electron beam through simulation.

[0032] The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the present application is not limited to the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A miniaturized periodic permanent magnet focused metamaterial backward wave oscillator, characterized in that, The superstructure material slow wave structure (1), the coupling cavity (2), the periodic permanent magnet focusing system (3) and the coaxial output interface (4) are arranged in sequence. The superstructure material slow wave structure (1) comprises a waveguide shell (102), and a periodic resonance structure (101) and a first real space gap (103) are arranged in the waveguide shell (102). The coupling cavity (2) is connected with the superstructure material slow wave structure (1) at one end and connected with the coaxial output interface (4) at the other end, and the coupling cavity (2) comprises a coupling cavity shell (201), and a coupling cavity inner conductor and a second real space gap (205) are arranged in the coupling cavity shell (201), the coupling cavity inner conductor comprises an inner conductor first section (202), an inner conductor second section (203) and an inner conductor third section (204), the inner conductor first section (202) is connected with the periodic resonance structure (101), and the inner conductor third section (204) is connected with the coaxial output interface (4). The periodic permanent magnet focusing system (3) comprises a first permanent magnet focusing structure and a second permanent magnet focusing structure which are arranged asymmetrically upwards and downwards, and the superstructure material slow wave structure (1) is arranged between the first permanent magnet focusing structure and the second permanent magnet focusing structure.

2. The compact cyclic permanent magnet focused metamaterial backward wave oscillator of claim 1, wherein, The coaxial output interface (4) comprises an interface shell (403), a dielectric layer (402) is arranged in the interface shell (403), an interface probe (401) is arranged in the dielectric layer, and the interface probe (401) is connected with the inner conductor third section (204).

3. The compact cyclic permanent magnet focused metamaterial backward wave oscillator of claim 2, wherein, One end of the superstructure material slow wave structure (1) is provided with an electron beam inlet (104) for externally connecting an electron gun.

4. The compact cyclic permanent magnet focused metamaterial backward wave oscillator of claim 3, wherein, The periodic resonance structure (101) comprises a plurality of superstructure material unit structures arranged periodically.

5. The compact cyclic permanent magnet focused metamaterial backward wave oscillator of claim 4, wherein, The periodic resonance structure (101) is arranged on the inner wall of the waveguide shell (102) in a biased manner.

6. The compact cyclic permanent magnet focused metamaterial backward wave oscillator of claim 5, wherein, The first real space gap (103) is communicated with the second real space gap (205), one end of the coupling cavity shell (201) is connected with the waveguide shell (102), and the other end is connected with the interface shell (403).

7. The compact cyclic permanent magnet focused metamaterial backward wave oscillator of claim 6, wherein, The radius of the inner conductor second section (203) is greater than that of the inner conductor first section (202) and the inner conductor third section (204).

8. The compact cyclic permanent magnet focused metamaterial backward wave oscillator of claim 7, wherein, The first permanent magnet focusing structure and the second permanent magnet focusing structure each comprise a fourth pole piece (304), second pole pieces (302) are arranged on the side surfaces of the fourth pole pieces (304) in a symmetrical manner, a first pole piece (301) and a third pole piece (303) are arranged periodically and alternately between the second pole pieces (302), and pole piece spacers (307) are arranged below the first pole pieces (301) and the third pole pieces (303) in the first permanent magnet focusing structure and above the first pole pieces (301) and the third pole pieces (303) in the second permanent magnet focusing structure.

9. The compact cyclic permanent magnet focused metamaterial backward wave oscillator of claim 8, wherein, A plurality of cavities are formed between the first pole piece (301), the second pole piece (302), the third pole piece (303) and the fourth pole piece (304), a center magnet (305) is arranged in each cavity, and edge magnets (306) are arranged periodically on the outer sides of the second pole pieces (302).

10. The compact cyclic permanent magnet focused metamaterial backward wave oscillator of claim 9, wherein, The lateral dimension of the edge magnet (306) in the first permanent magnetic focusing structure is smaller than the lateral dimension of the edge magnet (306) in the second permanent magnetic focusing structure.

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