A TM11 mode filtering device suitable for circular waveguides

Abstract

The present invention discloses a TM11 mode filtering device suitable for circular waveguides, relating to the field of microwave waveguide technology. The device comprises four mode filtering units, two of which are arranged in the same direction to form a mode extraction and filtering structure. The two mode extraction and filtering structures are arranged in an orthogonal cascade on a circular waveguide transmission system. The mode filtering units comprise a circular waveguide, a choke ring coupling structure coaxially arranged with the circular waveguide, two rectangular waveguide elbow structures, four sections of rectangular straight waveguide structures, and an E-T connector mode selection structure. Based on the principle of mode conversion, the present invention is suitable for filtering high-order TM modes in circular waveguide transmission systems. It has the advantages of small size, ease of processing, low loss, and high power capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave waveguides, and in particular to a TM11 mode filtering device suitable for circular waveguides. Background Art

[0002] In recent years, as further technological innovations have driven the demand for higher-power microwaves (HPM), the power handling capacity of components has gradually become a constraint on the development of higher-power microwave sources. Designing microwave sources with over-moded structures can effectively increase their power handling capacity, but this also comes with the generation of higher-order parasitic modes in the system. The presence of parasitic modes not only reduces the mode purity of high-power microwave transmission systems, but also increases system losses, reduces transmission efficiency, and potentially increases unnecessary resonances within the system. Therefore, filtering out parasitic modes and ensuring single-mode transmission of the primary mode within the system is a major challenge in current applications.

[0003] To address these issues, research on suppressing and filtering specific modes in waveguide transmission systems has gained increasing attention. In typical high-power microwave system applications, the dominant mode output by the microwave source in a circular waveguide transmission system is the TM01 mode, while higher-order mixed modes are primarily TM11 and various TE modes, such as TE11, TE01, and TE02. Based on the electromagnetic wave modes they filter out, filters used in circular waveguide systems can be categorized as circular waveguide TE filters and circular waveguide TM filters. Circular waveguide TE filters can be designed by leveraging the field distribution characteristics of TE modes in circular waveguides, employing the principle of wall current severance by a ridge structure to filter out the corresponding modes. However, since the field distributions of the various TM modes lack axial wall current differences, the current line severance principle cannot be applied. Therefore, the design of circular waveguide TM filters is more complex, and research on filtering methods for higher-order TM modes in circular waveguides is currently lacking. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention provides a TM11 mode filtering device suitable for circular waveguides. Based on the principle of mode conversion, the present invention is suitable for filtering out higher-order TM modes in circular waveguide transmission systems. It has the advantages of being compact, easy to process, low-loss, and having high power capacity.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A TM11 mode filtering device suitable for circular waveguides is composed of four mode filtering units. Two mode filtering units are arranged in the same direction to form a set of mode extraction and filtering structures. The two mode extraction and filtering structures are arranged in an orthogonal cascade manner on the circular waveguide transmission system to filter the TM11 mode of the circular waveguide.

[0007] The mode filtering unit is a left-right mirror-symmetrical structure, including: a circular waveguide, a choke ring coupling structure, two rectangular waveguide elbow structures, four sections of rectangular straight waveguide structures, and an ET connector mode selection structure;

[0008] The circular waveguide is an over-moded circular waveguide for transmitting electromagnetic waves in a transmission system, and the transmission modes include TM01 mode and TM11 mode;

[0009] The choke ring coupling structure is a circular cylindrical cavity coaxially arranged outside the circular waveguide;

[0010] The rectangular waveguide elbow structure is an H-plane waveguide elbow; one end of the two rectangular waveguide elbow structures is respectively connected to the symmetrical outer side surfaces of the choke ring coupling structure through a rectangular straight waveguide structure, and the other end is respectively connected to port 1 and port 2 of the ET connector mode selection structure through a rectangular straight waveguide structure;

[0011] Port 4 of the ET connector mode selection structure is connected to a matched load.

[0012] Furthermore, in one set of mode extraction and filtering structures, the midpoint distance between the two mode filtering units is D1, and the value range of D1 is λ±5mm, where λ is the wavelength; the midpoint distance between the two sets of mode extraction and filtering structures is D2, and the value range of D2 is Where n is a positive integer.

[0013] Furthermore, the radius r0 of the circular waveguide is determined by the waveguide transmission system and meets the over-mode transmission condition of electromagnetic waves at the operating frequency.

[0014] Furthermore, the rectangular straight waveguide structure is a WR90 standard rectangular waveguide, with a width a, a height b, and a length L1; the value of L1 satisfies the requirement that the electromagnetic field forms a standing wave in the straight waveguide section of the rectangular waveguide to increase the energy coupling efficiency of the device.

[0015] Furthermore, the outer radius of the choke ring coupling structure is r1, and the height is b, and the value range of r1 is 35mm to 40mm.

[0016] Furthermore, the rectangular waveguide elbow structure has a width of a, a height of b, an inner radius of r2, and a value range of r2 is 23 mm to 25 mm.

[0017] Furthermore, the width of port 1 and port 2 of the ET connector mode selection structure is a, and the height is b.

[0018] The principles and beneficial effects of the present invention are as follows:

[0019] When the electromagnetic field in the overmoded circular waveguide is transmitted to the choke ring, resonance occurs. Because the wide side of the rectangular waveguide and the TM mode electric field polarization directions of the circular waveguide are perpendicular to each other, the TM mode electromagnetic waves are coupled into the rectangular waveguide from two symmetrical ports, while the TE mode is cut off. By controlling the sum of the straight waveguide length and the choke ring radius to be approximately an integer multiple of the wavelength, the electromagnetic field forms a standing wave in the straight rectangular waveguide section, increasing the device's energy coupling efficiency.

[0020] The two rectangular waveguide elbow structures are symmetrically arranged about the plane of the circular waveguide transmission structure's central axis. They connect Ports 1 and 2 of the ET connector's mode selection structure via another straight rectangular waveguide. Because the waveguide structures are completely symmetrical, the electromagnetic field distribution characteristics of the circular waveguide indicate that electromagnetic field components propagating in the TM01 mode will propagate through the waveguides on both sides with equal amplitude and in phase, while electromagnetic field components propagating in the TM11 mode will propagate through the waveguides on both sides with equal amplitude and in phase, ultimately entering the ET connector structure.

[0021] According to the basic principle of the magic-T structure, the electromagnetic wave components of equal amplitude and phase coupled from the TM01 mode enter the ET connector via a symmetrical rectangular waveguide elbow, forming standing wave voltage antinodes at the symmetrical plane. These antinodes are then reflected back into the main circular waveguide, ensuring forward transmission of the TM01 mode. This means that the coupled wave from the TM01 mode is almost completely reflected, thus eliminating energy loss in the main mode. Meanwhile, the electromagnetic wave components of equal amplitude and antiphase coupled from the TM11 mode are output from port 4 of the ET connector and absorbed by the matched load, effectively extracting and eliminating energy from higher-order mode components. Therefore, the device of the present invention can achieve highly efficient filtering of the TM11 mode components in a circular waveguide overmoded transmission system while ensuring low-loss transmission of the TM01 mode components. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a pattern extraction and filtering unit according to an embodiment of the present invention;

[0023] Figure 2 2. It is a top view of a pattern extraction and filtering unit according to an embodiment of the present invention;

[0024] Figure 3 is a front view of a pattern extraction and filtering unit according to an embodiment of the present invention;

[0025] Figure 4 1 is a schematic diagram of a pattern extraction and filtering structure composed of two pattern extraction and filtering units in an embodiment of the present invention;

[0026] Figure 5 Schematic diagram of a device composed of a set of pattern extraction and filtering structures in an embodiment of the present invention;

[0027] Figure 6This is a schematic diagram of the TM11 mode filtering effect according to an embodiment of the present invention;

[0028] Figure 7 This is a schematic diagram of the transmission efficiency of the TM01 mode according to an embodiment of the present invention.

[0029] Explanation of the accompanying symbols: 1. Choke ring coupling structure, 2. Rectangular straight waveguide structure, 3. Rectangular waveguide elbow structure, 4. Rectangular straight waveguide structure, 5. ET connector mode selection structure. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and technical problem solved by the present invention clearer, the present invention is further described below with reference to the accompanying drawings and specific examples.

[0031] This embodiment provides a mode filtering device for a circular waveguide transmission system, such as Figure 4-5 As shown, the TM11 mode filtering device consists of four mode filtering units; two of these units are arranged in the same direction, forming a mode extraction and filtering structure. These two mode extraction and filtering structures are arranged in an orthogonal cascade on a circular waveguide transmission system to filter the circular waveguide's TM11 mode. In this embodiment, the midpoint spacing D1 between the two mode filtering units in one mode extraction and filtering structure is 38.3 mm, and the midpoint spacing D2 between the two sets of mode extraction and filtering structures is 64.5 mm. The spacing between the two mode extraction and filtering units creates a reflective standing wave structure between them. The principle of λ / 4 reflection cancellation eliminates the reflection of the TM11 mode electromagnetic field component, causing it to resonate between the two units. This increases the coupling between the TM11 and choke ring structures, further improving TM11 mode filtering efficiency. Furthermore, the spacing D2 allows for absorption of TM11 higher-order propagation modes of any polarization direction, further improving mode filtering efficiency.

[0032] The pattern filtering unit, such as Figure 1-3 As shown, it is a left-right mirror-symmetrical structure, including: a circular waveguide, a choke ring coupling structure, two rectangular waveguide elbow structures, a four-section rectangular straight waveguide structure, and an ET connector mode selection structure.

[0033] The circular waveguide is an over-moded circular waveguide for transmitting electromagnetic waves in the transmission system, with a radius r0 of 24.5 mm and an operating center frequency of 9.7 GHz. According to the cutoff size, it can be seen that electromagnetic waves can propagate in the over-moded circular waveguide in the form of TM01 mode, TM11 mode, and several TE modes.

[0034] The choke ring coupling structure is a circular cylindrical cavity coaxially arranged outside the circular waveguide.

[0035] The rectangular waveguide elbow structure is an H-plane waveguide elbow; one end of the two rectangular waveguide elbow structures is respectively connected to the symmetrical outer side surfaces of the choke ring coupling structure through a rectangular straight waveguide structure, and the other end is respectively connected to port 1 and port 2 of the ET connector mode selection structure through a rectangular straight waveguide structure.

[0036] The width a of the rectangular waveguide elbow structure, the rectangular straight waveguide structure, and ports 1 and 2 is 22.86 mm, and the height b is 10.16 mm, meeting the WR90 standard for rectangular waveguide dimensions. The inner radius r2 of the rectangular waveguide elbow is 24.29 mm, and the outer radius r3 is 47.15 mm. The length L1 of the rectangular straight waveguide structure connected to the choke coupling structure is 20 mm, and the length L2 of the rectangular straight waveguide structure connected to the ET connector mode selector structure is 89 mm. Appropriate values ​​for L1 and L2 are selected to ensure that the electromagnetic field forms a standing wave within the straight waveguide segment, thereby maximizing the device's energy coupling efficiency.

[0037] Port 4 of the ET connector mode selection structure is connected to a matching load, and the width of port 4 is b and the height h is 19 mm.

[0038] When the electromagnetic field propagates along a circular waveguide structure, the principle of electromagnetic field distribution within a circular waveguide indicates that, on the circular waveguide cross-section, the field component transmitted in the TM01 mode exhibits equal amplitude and in-phase distribution near the boundary, along the diameter of the circular waveguide at both ends. The field component transmitted in the TM11 mode exhibits equal amplitude and in-phase distribution near the boundary, along the diameter of the circular waveguide at both ends. The electromagnetic field resonates at the choke ring structure and is extracted by the rectangular waveguide, ultimately entering the rectangular straight waveguide connected by two semicircular arc rectangular waveguides and entering the ET connector structure from both sides.

[0039] Based on the basic principle of the magic-T structure, the TM01 mode electromagnetic field component propagates from both ends of the circular waveguide transmission structure into the rectangular waveguide structure with equal amplitude and in-phase. After traveling the same distance, it propagates from both ends with equal amplitude and in-phase, and does not propagate from the branch port into the matching destructive structure. The TM11 mode electromagnetic field component propagates from both ends of the circular waveguide transmission structure with equal amplitude and in-phase, and after traveling the same distance, it propagates from both ends with equal amplitude and in-phase, and its energy propagates completely from the branch port into the matching destructive structure. Through the selective characteristics of this structure, the device achieves filtering of the TM11 mode in the circular waveguide transmission structure while effectively controlling the loss of the TM01 mode.

[0040] like Figure 6 As shown, the mode filtering device of the circular waveguide transmission system of this embodiment can effectively filter out the TM11 mode in the frequency band of 9.55 GHz to 9.78 GHz, and the filtering effect is better than -10 dB.

[0041] like Figure 7 As shown, the mode filtering device of the circular waveguide transmission system of this embodiment can achieve efficient transmission of the TM01 mode in the frequency band of 9.5 GHz to 9.9 GHz, with a transmission loss lower than -0.14 dB.

[0042] The above description is only a preferred embodiment of the present invention and does not limit the scope of patent protection of the present invention. Any equivalent structural transformation made by using the contents of the description and drawings of the present invention, directly or indirectly applied to other related technical fields, is also included in the scope of protection of the present invention.

Claims

1. A TM11 mode filtering device suitable for a circular waveguide, characterized in that: It consists of four mode filtering units; two of them are arranged in the same direction to form a mode extraction and filtering structure; the two mode extraction and filtering structures are arranged in an orthogonal cascade on the circular waveguide transmission system to filter the TM11 mode of the circular waveguide; The mode filtering unit is a left-right mirror-symmetrical structure, including: a circular waveguide, a choke ring coupling structure, two rectangular waveguide elbow structures, four sections of rectangular straight waveguide structures, and an ET connector mode selection structure; The circular waveguide is an over-moded circular waveguide for transmitting electromagnetic waves in a transmission system, and the transmission modes include TM01 mode and TM11 mode; The choke ring coupling structure is a circular cylindrical cavity coaxially arranged outside the circular waveguide; The rectangular waveguide elbow structure is an H-plane waveguide elbow; one end of the two rectangular waveguide elbow structures is respectively connected to the symmetrical outer side surfaces of the choke ring coupling structure through a rectangular straight waveguide structure, and the other end is respectively connected to port 1 and port 2 of the ET connector mode selection structure through a rectangular straight waveguide structure; Port 4 of the ET connector mode selection structure is connected to a matched load.

2. A TM11 mode filtering device suitable for a circular waveguide according to claim 1, characterized in that: In one set of mode extraction and filtering structures, the midpoint distance between the two mode filtering units is D1, and the value range of D1 is λ±5mm, where λ is the wavelength; the midpoint distance between the two sets of mode extraction and filtering structures is D2, and the value range of D2 is Where n is a positive integer.

3. A TM11 mode filtering device suitable for a circular waveguide according to claim 2, characterized in that: The radius r0 of the circular waveguide is determined by the waveguide transmission system and meets the over-mode transmission condition of electromagnetic waves at the operating frequency.

4. A TM11 mode filtering device suitable for a circular waveguide as claimed in claim 3, characterized in that: The rectangular straight waveguide structure is a WR90 standard rectangular waveguide, with a width a, a height b, and a length L1; the value of L1 satisfies the requirement that the electromagnetic field forms a standing wave in the straight waveguide section of the rectangular waveguide, thereby increasing the energy coupling efficiency of the device.

5. A TM11 mode filtering device suitable for a circular waveguide as claimed in claim 4, characterized in that: The outer radius of the choke ring coupling structure is r1, and the height is b. The value range of r1 is 35mm to 40mm.

6. A TM11 mode filtering device suitable for a circular waveguide as claimed in claim 5, characterized in that: The rectangular waveguide elbow structure has a width of a, a height of b, and an inner radius of r2, and the value range of r2 is 23 mm to 25 mm.

7. A TM11 mode filtering device suitable for a circular waveguide according to claim 6, characterized in that: The width of port 1 and port 2 of the ET connector mode selection structure is a, and the height is b.

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