CN108808179A - A kind of novel coaxial plate higher order mode driver - Google Patents

Abstract

The invention discloses a kind of novel coaxial plate higher order mode drivers, belong to mode exciter field.The mode exciter includes the coaxial TE of TEM coaxial-sector₁₀Power splitter, fan-shaped coaxial TE₁₀Coaxial TE₆₁Mode converter, coaxial TE₆₁Circular waveguide TE₆₁Mode converter, circular waveguide TE₆₁Circular waveguide TE₆₂Mode converter.Its mode transition procedure is：The fan-shaped coaxial TE of TEM-₁₀Fan-shaped coaxial TE₂₀Coaxial TE₆₁Circle TE₆₁Circle TE₆₂.The present invention realizes fan-shaped coaxial TE using the bat wave coupling process of cosine metallic walls₁₀Coaxial TE₆₁Pattern is converted, and small, high conversion efficiency is reflected, with roomy.Compact overall structure of the present invention, each section can inhibit parasitic mode, and high conversion efficiency, mode purity is high, has good application prospect.

Description

A Novel Coaxial Board High-Order Mode Exciter

technical field

The invention belongs to the field of mode exciters, and in particular relates to a novel coaxial board high-order mode exciter.

Background technique

As a new type of electric vacuum device, the gyrotron has very important applications in thermonuclear fusion control, high-power electromagnetic heating and millimeter-wave radar. The working mode in the gyrotron is usually a high-order side corridor mode or a high-order bulk mode. Such high-order modes are not convenient for direct use and transmission. Quasi-optical mode converters are usually used to convert them into low-order modes that are easy to use and transmit. In order to accurately test the performance of the quasi-optical mode converter, it is necessary to design a high-purity circularly polarized high-order mode exciter to simulate the output mode of the gyrotron.

At present, there are mainly two types of high-order exciters. The first type uses a waveguide structure. In "High Power Laser and Particle Beams", September 2012, Volume 24, Issue 9, a curved type is proposed. The waveguide mode exciter uses a folded waveguide to realize mode conversion. Although the size of the mode exciter is shortened, the conversion efficiency is very low due to the large reflection introduced by folding. In the article "A TE ₀₁ Generator Excited by TEM" (ISAPE), a waveguide mode exciter using TEM to excite the TE ₀₁ mode is proposed, which consists of large-sized coaxial waveguides, circular waveguides, and twisted waveguides , at the center frequency of 35GHz, the conversion efficiency is 97.5%, and the mode purity is 99%, but the bandwidth is only 0.1GHz, and the conversion efficiency is not high enough. In the article "High-Efficiency, Broadband Converter From A Rectangular Waveguide TE ₁₀ Mode to A Circular Waveguide TM ₀₁ Mode for Overmoded Device Measurement", a rectangular waveguide TE ₁₀ mode excites a circular waveguide TM ₀₁ mode waveguide mode exciter, although The conversion efficiency reaches 99% with a bandwidth of 0.5GHz, but the mode exciter only works well between low-order modes, and the input and output are not coaxial. The second type is to use a quasi-optical structure. In "CHINESE JOURNAL OF VACUUM SCIENCE-AND TECHNOLOGY", Volume 34, No. 11, November 2014, a quasi-optical high-order mode exciter was proposed. The mode exciter uses a three-section coaxial resonant cavity with holes in the side wall to excite the high-order mode TE ₆₂ , but its maximum mode conversion efficiency is only 95%, and the mode purity is lower than 98%. In addition, in the article "A High-Efficiency Quasi-Optical Mode Converter for a 140-GHz 1-MW CW Gyrotron", a high-efficiency quasi-optical mode exciter is proposed, which consists of a corrugated wall waveguide radiator, Composed of a quasi-elliptical mirror and two annular mirrors, the TE _28,8 mode can be converted into a basic Gaussian beam at 140GHz, and the conversion efficiency can reach 98%. .

Contents of the invention

Aiming at the problems of the existing high-order mode exciter with complicated structure, high requirement for assembly precision, low conversion efficiency and mode purity, the invention proposes a novel high-order exciter for coaxial board.

In order to solve the above problems, the present invention is achieved through the following technical solutions:

A new coaxial board high-order mode exciter, including coaxial TEM-sector coaxial TE ₁₀ power splitter, sector coaxial TE ₁₀ -coaxial TE ₆₁ mode converter, coaxial TE ₆₁ -circular waveguide TE ₆₁ Mode converters, circular waveguide TE ₆₁ - circular waveguide TE ₆₂ mode converters.

One end of the coaxial TEM-sector coaxial TE ₁₀ power divider is the coaxial input end, and the other end is provided with 6 straight metal plates evenly distributed in the angular direction between the inner and outer conductors to divide the coaxial waveguide into six identical The fan-shaped waveguide can divide the input TEM mode into 6 fan-shaped coaxial TE ₁₀ modes. Between the coaxial input end and the straight metal board, there are 6 metal support rods connected to the inner and outer conductors, which are used to stably support the coaxial inner and outer conductors and match and offset the reflection caused by the straight metal board at the input port.

The fan-shaped coaxial TE ₁₀ -coaxial TE ₆₁ mode converter has 6 cosines smoothly connected to the straight metal plate in the coaxial TEM-fan-shaped coaxial TE ₁₀ power divider, which are evenly arranged between the inner and outer conductors in the angular direction The metal plug-in board converts the fan-shaped coaxial TE ₁₀ into the fan-shaped coaxial TE ₂₀ , wherein each fan-shaped coaxial mode converter only disturbs the propagation direction of the mode in the fan-shaped waveguide, and does not change the transverse dimension of the waveguide. Each cosine metal board extends a second straight metal board to the rear end to smoothly transition the coaxial TE ₂₀ mode and stabilize the output. After the second straight metal plug-in board is cut off at the same time, the fan-shaped coaxial TE ₂₀ is merged and converted into a coaxial TE ₆₁ output.

In the coaxial TE ₆₁ -circular waveguide TE ₆₁ mode converter, the radius of the inner conductor is gradually reduced to form a conical section, while the outer conductor is gradually enlarged, and the end of the conical section is truncated and transitioned to the circular waveguide output circular waveguide TE ₆₁ .

The circular waveguide TE ₆₁ -circular waveguide TE ₆₂ mode converter consists of a circular waveguide with gradually changing radius along the axial direction and a section of uniform straight circular waveguide connected at the end.

Further, the six metal direct-plug boards in the coaxial TEM-sector coaxial TE ₁₀ power divider occupy an angle of 2°.

Further, the starting point and the ending point of the cosine metal plug-in plate are kept in smooth contact with the longitudinal direct plug-in plate.

Further, the truncation of the end of the conical section of the inner conductor of the coaxial TE ₆₁ -circular waveguide TE ₆₁ mode converter adopts a chamfered structure.

Advantages of the present invention:

(1) The metal support rod is used, which can not only adjust the reflection formed by the shielding wave propagation at the front end of the plug board, but also stably support the inner and outer conductors to ensure the coaxiality of the input and output;

(2) The board transition is very smooth, so only the direction of wave propagation is changed, and the reflection is very small during the propagation along the board. And the overall model has a compact structure, and each part can suppress miscellaneous modes;

(3) The transition part from the coaxial to the circular waveguide, the truncation of the end of the conical section adopts a chamfer design to make the structure smoother and effectively reduce the concentration of field strength;

(4) The mode conversion realized by the beat-wave coupling method of the cosine metal wall has small reflection, high conversion efficiency and wide bandwidth, which is very suitable for exciting other higher-order modes and has a good application prospect.

Description of drawings

Figure 1 is a schematic diagram of the overall structure of the mode exciter:

Figure 2 is a schematic diagram of the overall mode conversion of the mode exciter;

Figure 3 is a schematic diagram of a coaxial TEM-sector coaxial TE ₁₀ six-way power splitter;

Fig. 4 is a schematic diagram of sector coaxial TE ₁₀ - sector coaxial TE ₂₀ - coaxial TE ₆₁ mode converter;

Fig. 5 is a schematic diagram of a coaxial TE ₆₁ -circular waveguide TE ₆₁ mode converter;

Fig. 6 is a schematic diagram of a circular waveguide TE ₆₁ -circular waveguide TE ₆₂ mode converter;

Figure 7 is a schematic diagram of the overall mode conversion efficiency of the coaxial TEM-circular waveguide TE ₆₂ mode exciter;

Figure 8 is a schematic diagram of the overall mode purity of the coaxial TEM-circular waveguide TE ₆₂ mode exciter;

Fig. 9 is a schematic diagram of the overall reflection of the coaxial TEM-circular waveguide TE ₆₂ mode exciter.

Description of reference numerals: I first part (1) metal support bar (2) straight metal plate; II second part (3) cosine metal plate (4) second straight metal plate; III third part (5) Conical segment (6) end of the conical segment; IV fourth part (7) radius-period gradient circular waveguide (8) straight circular waveguide.

Detailed ways

In order to make the technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

A new type of coaxial board high-order mode exciter, as shown in Figure 1, the high-order mode exciter includes four parts connected in sequence along the axial direction, the first part is the coaxial TEM-sector coaxial TE ₁₀ power points The second part is sector coaxial TE ₁₀ - coaxial TE ₆₁ mode converter, the third part is coaxial TE ₆₁ - circular waveguide TE ₆₁ mode converter, the fourth part is circular waveguide TE ₆₁ - circular waveguide TE ₆₂ Mode changer.

(1) The first part is the coaxial TEM-sector coaxial TE ₁₀ power splitter, which divides the coaxial waveguide TEM mode with an outer diameter of 40mm and an inner diameter of 35mm into 6 fan-shaped coaxial TE ₁₀ modes along the axial direction. Referring to Figure 3, six straight metal plug-in boards distributed angularly symmetrically between the inner and outer diameters of the coaxial waveguide at the coaxial output end are arranged to divide the coaxial output end into six identical fan-shaped waveguides, and then the front end of the straight metal plug-in board Correspondingly set six metal support rods. Metal support rods are used to add reflection, and when the phase difference between the reflection of the metal support rod at the port and the reflection of the board is close to 180°, the superposition and cancellation of the total port reflection reaches the minimum. Further fine-tuning the thickness of the metal support rods to keep the vertical shielding area the same as that of the plugboard can keep the power of the TE ₁₀ modules output by the six ports relatively stable and even. Among them, the straight metal plug-in board is 2mm thick and 20mm long. The distance between the front end and the coaxial input port is 30mm. The distance between the six metal support rods and the six straight metal plug-in boards is 18.75mm. Finally, the six output ports of the first part are used as the second section. of six input ports.

(2) The second part is the sector coaxial TE ₁₀ -sector coaxial TE ₂₀ -coaxial TE ₆₁ mode converter. Referring to Fig. 4, according to the beat wave coupling method, the metal plate with cosine corrugation is used as the waveguide side wall, and the propagation direction of the mode in the fan-shaped coaxial waveguide is disturbed to realize the conversion of TE ₁₀ -TE ₂₀ mode, and finally in the second part of the coaxial The output end of the waveguide sectorized coaxial TE ₂₀ merges into a coaxial TE ₆₁ .

The sidewall perturbation parameter equation of the fan-shaped coaxial waveguide is:

Φ(z)＝a ₁ *cos((β ₁ -β ₂ )*z)-a ₂ *sin((β ₂ -β ₃ )*z)

0≤z≤n*T

a ₁ represents the excitation term amplitude of the cosine corrugated wall disturbance, a ₂ represents the suppression term amplitude; β ₁ represents the phase constant of the input mode TE ₁₀ ; β ₂ represents the phase constant of the TE ₂₀ to be excited; β ₃ represents the first The phase constant of a higher order mode. is the geometric period of the cosine wave, n is the period number of the cosine wave, and z is the axial position of the cosine board. The angle of each metal board occupies 2°, so each fan-shaped waveguide is actually 58°. During propagation, the lateral dimension of the fan-shaped waveguide remains unchanged, and only the longitudinal propagation direction is disturbed along the sidewall, so the reflection in this section is very small. By adjusting and optimizing the period number n of the fan-shaped side wall, the geometric period length T, the amplitude a ₁ of the excitation item and the amplitude a ₂ of the suppression item, the fan-shaped coaxial TE ₁₀ is converted into a fan-shaped coaxial TE ₂₀ mode, and after the metal plate is cut off, A complete coaxial TE ₆₁ mode is obtained at the output. Wherein, n=1, T=293mm, a ₁ =8.5mm, a ₂ =0.8mm.

(3) The third part is the coaxial TE ₆₁ -circular waveguide TE ₆₁ mode converter. Referring to FIG. 5 , this part realizes the transformation from the coaxial TE ₆₁ to the circular waveguide TE ₆₁ . The eigenvalue of the coaxial TE ₆₁ mode increases with the increase of the ratio C of the coaxial inner and outer radii. When C is greater than 2.5, its eigenvalue remains almost unchanged and is approximately equal to the eigenvalue of the circular waveguide TE ₆₁ mode. That is, when C is greater than 2.5, by further optimizing the length of the transition section and the radius of the end of the inner shaft, the coaxial waveguide can be directly transformed into a circular waveguide, thereby reducing the reflection caused by the disappearance of the inner shaft. As shown in Figure 5, the outer diameter of the coaxial shaft is gradually expanded to 44.7mm, and the inner radius of the inner shaft is shrunk to about 12mm. Shaft TE ₆₁ mode is converted to circular waveguide TE ₆₁ mode.

(4) The fourth part is the circular waveguide TE ₆₁ -circular waveguide TE ₆₂ mode converter. Referring to Fig. 6, according to the radius gradient coupling theory, when the waveguide mode only changes radially during propagation, this change will only affect the radial index n in TE _mn and TM _mn , but not the angular index of the mode m, so when the circular waveguide TE ₆₁ mode is used to excite the circular waveguide TE ₆₂ mode, the angular index of the mode is 6. In order to suppress the spurious mode and improve the mode conversion efficiency, the following coupling structure can be adopted according to the theory of radius gradient coupling and phase rematching techniques:

R(z) is the contour function of the radial variation of the circular waveguide along the axial direction, z is the axial position of the circular waveguide with gradually changing radius, a ₀ is the initial radius of the waveguide, and ε ₁ and ε ₂ are the perturbation parameters. In order to completely convert one mode to another mode, the length L of the mode converter needs to satisfy L=N*λ _ω , where N is the geometric period of the inner wall fluctuation, select an appropriate period number N, and adjust the length of the geometric period λ _ω , further By optimizing the parameters, increasing the excitation and suppressing the miscellaneous modes, the high-efficiency conversion from the circular TE ₆₁ to the circular TE ₆₂ can be realized. Where a ₀ =44.7mm, ε ₁ =46.5mm, ε ₂ =6mm, and the number of cycles N=5.

To sum up, referring to FIG. 2 , the mode conversion process of the waveguide mode excitation device in this embodiment is: TEM-sector coaxial TE ₁₀ -sector coaxial TE ₂₀ -coaxial TE ₆₁ -circular TE ₆₁ -circular TE ₆₂ .

Referring to Fig. 7 and Fig. 8, the highest conversion efficiency of this embodiment reaches 99.11%, the highest mode purity reaches 99.41%, and both the mode conversion efficiency and the mode purity are very high. Referring to Figure 9, the overall reflection of the mode exciter is less than 20dB with a bandwidth of about 0.35GHz.

Based on the above description, those skilled in the art should have a clear understanding of the device of the present invention. The above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention, such as adding metal inserts with periodic corrugated walls The use of the plate to realize mode conversion on the rectangular waveguide and the coaxial waveguide should be included in the protection scope of the present invention.

Claims (4)

1. a kind of novel coaxial plate higher order mode driver, it is characterised in that：Including the coaxial TE of TEM coaxial-sector₁₀Work(point Device, fan-shaped coaxial TE₁₀Coaxial TE₆₁Mode converter, coaxial TE₆₁Circular waveguide TE₆₁Mode converter, circular waveguide TE₆₁Circle wave Lead TE₆₂Mode converter；

The coaxial TE of TEM coaxial-sector₁₀Power splitter one end is coaxle input end, and 6 are provided between other end internal and external conductor Angular equally distributed straight metal backing, is divided into six pieces of identical fan-shaped waveguides, by the TEM mould deciles of input by coaxial waveguide At the fan-shaped coaxial TE in 6 tunnels₁₀Mould；It is also correspondingly arranged on 6 between coaxle input end and straight metal backing and connects internal and external conductor Metallic support rod；

The coaxial TE of sector₁₀Coaxial TE₆₁Mode converter is angularly evenly arranged between internal and external conductor and TEM coaxial- Fan-shaped coaxial TE₁₀6 cosine metal backings that straight metal backing is smoothly connected in power splitter, by fan-shaped coaxial TE₁₀Be converted to fan Just as axis TE₂₀；Every cosine metal backing extends one section of second straight metal backing to the back-end, by coaxial TE₂₀Mould smoothly transits simultaneously Stablize output；After second straight metal backing blocks simultaneously, fan-shaped coaxial TE₂₀Merging is converted to coaxial TE₆₁Output；

The coaxial TE₆₁Circular waveguide TE₆₁Mode converter, inner wire radius is gradually reduced to form conical section, while outer conductor It is gradually expanded, conical section end, which is blocked, is transitioned into circular waveguide output circular waveguide TE₆₁；

The circular waveguide TE₆₁Circular waveguide TE₆₂Mode converter is connected by radius period gradual change circular waveguide in an axial direction and end One section of uniform straight circular waveguide composition.

2. a kind of novel coaxial plate higher order mode driver as described in claim 1, it is characterised in that：The TEM coaxial- Fan-shaped coaxial TE₁₀Six pieces of metal straight cutting plate angles are to accounting for 2 ° of angle in power splitter.

3. a kind of novel coaxial plate higher order mode driver as described in claim 1, it is characterised in that：The cosine metal The beginning and end of plate keeps smoothly connecting with longitudinal straight cutting version.

4. a kind of novel coaxial plate higher order mode driver as described in claim 1, it is characterised in that：The coaxial TE₆₁- Circular waveguide TE₆₁Take chamfering structure in mode converter inner wire conical section end truncated position.