Low-field-intensity design method of waveguide short circuit structure for high-power microwave

Abstract

The invention discloses a low-field-intensity and high-power-capacity design method for a microwave short-circuit structure, belongs to the field of high-power microwaves, and solves the problem that the power capacity of a device is restricted by an overhigh electric field at a waveguide short-circuit structure. Determining the aperture size R, the working mode TMmn and the injection power P of the circular waveguide; calculating standing wave electric field distribution in the circular waveguide when the tail end is connected with the straight waveguide metal plane short circuit structure with the length being L; drawing a corresponding standing wave field power line distribution diagram in the waveguide, and determining a power capacity weak point; a curved surface capable of forming a closed terminal with a waveguide wall is determined in a low-field-intensity area in the direction perpendicular to a power line, the curved surface is always perpendicular to an electric field and is an equivalent electric wall, and a metal short-circuit surface shape is designed along the curved surface; the straight wall short circuit structure is selected to correspond to the equivalent electric wall with the lowest surface electric field in the standing wave field, the frequency response characteristic of a reflection field is guaranteed, meanwhile, the maximum electric field intensity of the metal surface is remarkably reduced, and the power capacity of a device to which the waveguide short circuit structure belongs is effectively improved.

Description

Technical Field

[0001] The invention belongs to the field of high-power microwaves, and in particular relates to a method for designing low field intensity and high power capacity of a microwave short-circuit structure. Background Art

[0002] The metal waveguide short-circuit structure is a commonly used terminal structure in the field of high-power microwaves. It is used to reflect microwave signals with equal amplitude and opposite phase. It is usually combined with other transmission line structures, such as waveguide power division structure and waveguide coupling structure, to achieve transmission characteristics such as power distribution and mode conversion. The most common short-circuit structure is a metal straight wall or a metal structure with a stepped transition structure. The design focus of the reported short-circuit structure is to ensure that the final transmission characteristic parameters of the entire structure meet the requirements. However, according to the microwave transmission characteristics, there is usually a maximum electric field point at the short-circuit structure, and this value restricts the power capacity level of the entire structure. At present, there is no method reported for optimizing the design of low-field strength structures based on the electric field distribution characteristics of the short-circuit structure.

[0003] Prior art A metal straight wall short circuit structure used in a high power microwave square and round mode converter (Zhao Lishan, Yuan Chengwei, Zhang Jiande, Zhang Qiang, Design of low over-mode high power microwave square and round mode converter, High Power Laser and Particle Beams, 2011, 23 (11)), as shown in the attached Figure 1 As shown, it includes a circular waveguide (1), a rectangular waveguide (2), a mode coupling structure (3), and a straight wall short-circuit structure (4). The mode coupling structure (3) is a wide slot structure on the circular waveguide wall. The circular waveguide (1) is located at the front end of the structure. High-power microwaves are transmitted from here to the circular waveguide TM 01 Mode injection, the electric field is reflected at the straight wall short-circuit structure (4) at the end of the circular waveguide, so that an electric field distribution similar to a standing wave is formed in the circular waveguide, and a mode coupling structure (3) is used to excite a TE in the rectangular waveguide with an electric field direction parallel to the narrow side of the rectangular waveguide near the area where the electric field is parallel to the axis of the circular waveguide (1). 10 The circular waveguide TM is obtained by optimizing the size of the rectangular waveguide (2) and the distance between the rectangular waveguide (2) and the straight wall short-circuit structure (4). 01 Mode and TE of rectangular waveguide 10 High conversion efficiency between modes.

[0004] The prior art also discloses a metal short-circuit structure with a step transition structure used in a high-power power divider ( R.MONTEJO-GARAI,JORGE A.RUIZ-CRUZ, M.REBOLLAR1,A10-Way PowerDivider Based on a Transducer and a Radial Junction Operating in the CircularTM01 Mode, IEEE Access, 2019,7:127353), as attached Figure 2 As shown, it includes a circular waveguide (1), a metal short-circuit structure with a step transition (2), a radial line (3), and a rectangular waveguide (4). The circular waveguide (1) is located at the front end of the structure, and high-power microwaves are transmitted from here in the form of a circular waveguide TM 01 Mode injection, the metal short-circuit structure (2) with step transition will reflect the electric field and excite the radial line TEM mode in the radial line (3), and rectangular waveguides (4) are evenly distributed at equal angles around the circumference of the radial line (3) and excite the rectangular waveguide TE in it. 10 Circular waveguide TM is realized by optimizing the dimensions of radial line (3) and rectangular waveguide (4) and adjusting the dimensions of metal short-circuit step structure (2). 01 Mode to rectangular waveguide TE 10 High efficiency power splitter.

[0005] The main limitations and shortcomings of the above two metal waveguide short-circuit structures are that the electric field value on the surface of the metal short-circuit structure is significantly enhanced compared with the field strength on other metal surfaces. When the injected power is further increased, field-induced emission will occur at the metal short-circuit structure, and eventually develop into strong field breakdown, which restricts the power capacity of the microwave device. Summary of the invention

[0006] (I) Purpose of the invention

[0007] The purpose of the present invention is to provide a design method for a circular waveguide metal short-circuit structure with low surface electric field characteristics, so as to solve the problem that the electric field at the waveguide short-circuit structure is too high and restricts the power capacity of the device. The present invention is applicable to the design of a metal short-circuit structure whose working mode is the circular waveguide TMmn mode, and is not applicable to other working modes.

[0008] (II) Technical solution

[0009] Step 1, determine the circular waveguide aperture size R, working mode TMmn and injection power P;

[0010] Step 2, select the length L of the straight waveguide section (L ≥ 5λ can be selected), and connect a metal plane short-circuit structure at the end to solve the standing wave electric field distribution in the circular waveguide in this state. The standing wave field distribution calculation formula of the TMmn mode in the circular waveguide is as follows:

[0011]

[0012] Where: E z is the longitudinal component of the electric field, and E r are the angular and radial components of the electric field, B is a constant, β is a propagation constant, z is the longitudinal coordinate of the circular waveguide, r is the radial coordinate of the circular waveguide, k c is the cut-off wave number, J n (x) is the first kind nth order Bessel function, λ is the microwave wavelength;

[0013] Step 3: Draw the corresponding standing wave field electric line distribution diagram in the waveguide according to the above calculation formula. By analyzing the periodic distribution law of the electric field, it can be known that there is a maximum standing wave electric field on the straight wall short-circuit surface, and this position is the weak link of power capacity.

[0014] Step 4: In order to reduce the electric field intensity on the metal wall surface and not destroy the existing standing wave field distribution characteristics, a curved surface that can form a closed terminal with the waveguide wall is determined in the low field strength area along the direction perpendicular to the electric line. The curved surface is always perpendicular to the electric field and is the equivalent electric wall. A metal short-circuit surface is designed along the curved surface, which can significantly reduce the electric field intensity on the metal surface without affecting the field distribution.

[0015] Step 5: Connect the metal plane and the metal transition wall to obtain a complete low-field strength waveguide short-circuit structure.

[0016] (III) Effective income

[0017] The shape design of the short-circuit surface of the present invention is based on a simple straight-wall short-circuit structure. The equivalent electric wall with the lowest surface electric field in the standing wave field corresponding to the straight-wall short-circuit structure is selected, and a method of designing a short-circuit terminal along the equivalent electric wall is adopted. This not only ensures the frequency response characteristics of the reflected field, but also significantly reduces the maximum electric field intensity on the metal surface, effectively improving the power capacity of the device to which the waveguide short-circuit structure belongs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Background technology 1 is a schematic diagram of a metal straight wall short circuit structure and electric field distribution used in a high power microwave square and round mode converter;

[0019] Figure 2 A schematic diagram of a metal short-circuit structure with a stepped transition structure and electric field distribution used in a high-power power divider as described in Background Technology 2;

[0020] Figure 3 A schematic diagram of equivalent electric wall distribution in a specific embodiment of the present invention;

[0021] Figure 4 A comparison diagram of the surface electric field corresponding to the short-circuit structure in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0022] The following is a detailed description of a low field strength design method for a waveguide short-circuit structure for high-power microwaves according to the present invention in conjunction with the accompanying drawings and embodiments.

[0023] A circular waveguide short-circuit structure working in the X-band (9GHz-10GHz), the main structural parameters are as follows: the circular waveguide radius is 24mm, the working mode is TM 01 The waveguide length is selected as 60 mm. First, the metal straight wall short-circuit structure is selected for the terminal. When TM is injected into the circular waveguide, 01 The standing wave electric field expression formed in the mode is:

[0024] E z =BJ n (k c r)(e -jβz +e -jβ(2L-z ))

[0025]

[0026] Where: E z is the longitudinal component of the electric field, E r is the transverse component of the electric field, B is a constant, β is the propagation constant, z is the longitudinal coordinate of the circular waveguide, r is the radial coordinate of the circular waveguide, k c is the cut-off wave number, J n (x) is the nth-order Bessel function of the first kind.

[0027] Draw the distribution diagram of the electric lines of the standing wave field according to the above formula, and determine the equivalent electric wall with the lowest surface electric field along the direction perpendicular to the electric lines, as shown in the attached figure. Figure 3 The metal short-circuit structure is designed based on the equivalent electric wall, and the electric fields corresponding to the two short-circuit structures are calculated, as shown in Figure 4 As shown in the figure, it can be seen that the electric field on the metal surface of the short-circuit structure designed along the equivalent electric wall is significantly reduced, which can greatly improve the power capacity of the device.

[0028] The above contents are further detailed descriptions of the present invention in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A low field strength design method for a waveguide short-circuit structure for high-power microwaves, characterized in that: Applicable to circular waveguide TM mn The specific steps of metal short-circuit structure design are as follows: Step 1: Determine the circular waveguide aperture size R and operating mode TM mn and the injected power P; Step 2, calculating the standing wave electric field distribution in the circular waveguide when the end connection length is L of the straight waveguide metal plane short-circuit structure; Step 3, according to the standing wave electric field distribution when the end of the calculation is connected to the straight waveguide metal plane short-circuit structure, the corresponding standing wave field power line distribution diagram in the waveguide is drawn, and the power capacity weak point is determined according to the existence of the standing wave electric field maximum value on the straight wall short-circuit surface; Step 4: In the low field intensity region, a curved surface is determined along the direction perpendicular to the electric lines of force, which can form a closed terminal with the waveguide wall. The curved surface is always perpendicular to the electric field and is an equivalent electric wall. The shape of the metal short-circuit surface is designed along the curved surface. Step 5: Connect the metal plane and the metal transition wall to obtain a complete low-field strength waveguide short-circuit structure.

2. The low field strength design method for a waveguide short-circuit structure for high-power microwaves as claimed in claim 1, characterized in that: Select L ≥ 5λ.

3. The low field strength design method for a waveguide short-circuit structure for high-power microwaves as claimed in claim 1, characterized in that: The standing wave field distribution calculation formula of the TMmn mode in the circular waveguide is as follows: Where: E z is the longitudinal component of the electric field, and E r are the angular and radial components of the electric field, B is a constant, β is a propagation constant, z is the longitudinal coordinate of the circular waveguide, r is the radial coordinate of the circular waveguide, k c is the cut-off wave number, J n (x) is the nth-order Bessel function of the first kind, and λ is the microwave wavelength.

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