TM11 mode filtering device suitable for circular waveguide

Abstract

The invention discloses a TM11 mode filtering device suitable for a circular waveguide, and relates to the technical field of microwave waveguides. The device consists of four mode filtering units, wherein the two mode filtering units are arranged in the same direction to form a group of mode extracting and filtering structures; the two mode extraction filtering structures are arranged on the circular waveguide transmission system in an orthogonal cascade mode; and the mode filtering unit comprises a circular waveguide, a choke ring coupling structure coaxially arranged with the circular waveguide, two rectangular waveguide elbow structures, a four-section rectangular straight waveguide structure and an E-T joint mode selection structure. Based on a mode conversion principle, the filter is suitable for filtering a high-order TM mode in a circular waveguide transmission system, and has the advantages of small size, easiness in processing, low loss and large power capacity.

Description

Technical Field

[0001] The 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, with the demand for higher power microwaves (HPM) from further technological innovation, the power capacity of devices has gradually become a limitation for the development of microwave sources to higher power. The use of over-moded structure to design microwave sources can effectively improve the power capacity of microwave sources, but this will also generate higher-order parasitic modes in the system. The existence of parasitic modes will not only reduce the mode purity in high-power microwave transmission systems, but will also increase system losses, reduce transmission efficiency, and may increase unnecessary resonances in the system. Therefore, how to filter out parasitic modes and ensure that the main mode single-mode transmission is maintained in the system is a major problem in the current application field.

[0003] In order to deal with this kind of problem, the research on the suppression and filtering of specific modes in waveguide transmission systems has gradually received attention. In the typical application scenario of high-power microwave systems, the main mode of the microwave source output in the circular waveguide transmission system is the TM01 mode, while the higher-order mixed modes are mainly TM11 mode and various TE modes such as TE11, TE01, and TE02. According to the electromagnetic wave mode to be filtered out, the filters used in the circular waveguide system can be classified into circular waveguide TE filters and circular waveguide TM filters. Among them, the circular waveguide TE filter can be designed using the field distribution characteristics of the TE mode in the circular waveguide, and the principle of cutting the wall current by the ridge structure is adopted to achieve the filtering of the corresponding mode. However, since there is no difference in the axial wall current distribution in the field distribution of each TM mode, the principle of cutting the current line cannot be applied. Therefore, the design of the circular waveguide TM filter is more complicated, and there is a lack of research on the filtering method of the TM higher-order mode in the circular waveguide. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a TM11 mode filtering device suitable for circular waveguides. The present invention is based on the mode conversion principle and is suitable for filtering out high-order TM modes in circular waveguide transmission systems. It has the advantages of small size, easy processing, low loss and large power capacity.

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

[0006] A TM11 mode filtering device suitable for a circular waveguide is composed of four mode filtering units; wherein 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 a 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] Wherein, 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 are respectively connected to the symmetrical outer side surfaces of the choke ring coupling structure through a section of 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 section of rectangular straight waveguide structure;

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

[0012] Furthermore, in a set of mode extraction and filtering structures, the midpoint distance between two mode filtering units is D 1 , D 1 The value range is λ±5mm, where λ is the wavelength; the midpoint distance between the two sets of mode extraction and filtering structures is D 2 , D 2 The value range is Where n is a positive integer.

[0013] Furthermore, the radius r of the circular waveguide 0 Determined by the waveguide transmission system, it meets the over-mode transmission conditions of electromagnetic waves at the operating frequency.

[0014] Furthermore, the rectangular straight waveguide structure is a WR90 standard rectangular waveguide, with a width of a, a height of b, and a length of L. 1 ; L 1 The value of is chosen to make the electromagnetic field form a standing wave in the straight waveguide section of the rectangular waveguide, so as to increase the energy coupling efficiency of the device.

[0015] Furthermore, the outer radius of the choke ring coupling structure is r 1 , height b, r 1 The value range is 35mm~40mm.

[0016] Furthermore, the rectangular waveguide elbow structure has a width a, a height b, and an inner radius r. 2 , r 2 The value range is 23mm~25mm.

[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 over-moded circular waveguide is transmitted to the choke ring, resonance is generated. Since the wide side of the rectangular waveguide and the polarization direction of the TM mode electric field of the circular waveguide are perpendicular to each other, the electromagnetic waves of the TM mode are coupled into the rectangular waveguide from two symmetrical ports, while the TE mode is cut off. By controlling the sum of the length of the straight waveguide structure of the rectangular waveguide and the radius of the choke ring to be approximately an integer multiple of the wavelength, the electromagnetic field forms a standing wave in the rectangular straight waveguide section, thereby increasing the energy coupling efficiency of the device.

[0020] The two rectangular waveguide elbow structures are symmetrically distributed with respect to the plane where the central axis of the circular waveguide transmission structure is located, and are connected to port 1 and port 2 of the ET connector mode selection structure through another rectangular straight waveguide. Since the waveguide structures on both sides are completely symmetrical, according to the electromagnetic field distribution characteristics in the circular waveguide structure, the electromagnetic field components propagating in the TM01 mode will propagate in the waveguide structures on both sides in the form of equal amplitude and in phase, and the electromagnetic field components propagating in the TM11 mode will propagate in the waveguide structures on both sides in the form of equal amplitude and anti-phase, and enter 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 will enter the ET connector with the help of the symmetrical rectangular waveguide elbow, and form the antinode of the standing wave voltage at the symmetrical plane position, and finally reflect back to the main circular waveguide to ensure the forward transmission of the TM01 mode, that is, the coupled wave of the TM01 mode is almost completely reflected, so there will be no energy loss of the main mode. The electromagnetic wave components of equal amplitude and anti-phase coupled from the TM11 mode will be output from port 4 of the ET connector and absorbed by the matching load, that is, the energy of the high-order mode components is extracted and eliminated. Therefore, the device of the present invention can achieve high-efficiency filtering of the TM11 mode components in the circular waveguide over-modulation transmission system, and at the same time ensure low-loss transmission of the TM01 mode components. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0023] Figure 2 is a top view of a mode extraction and filtering unit of an embodiment of the present invention;

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

[0025] Figure 4 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 is a schematic diagram of a device composed of a group of pattern extraction and filtering structures in an embodiment of the present invention;

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

[0028] Figure 7 It 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 drawings: 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 in conjunction with 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 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 circular waveguide TM11 mode. In this embodiment, in a set of mode extraction and filtering structures, the midpoint spacing D between the two mode filtering units is 1 The midpoint distance D between the two groups of patterns for extracting and filtering structures is 38.3 mm. 2 The distance between the two mode extraction and filtering units is selected to form a reflection standing wave structure between the two units. The reflection of the electromagnetic field component of the TM11 mode is eliminated by the principle of λ / 4 reflection cancellation, so that it resonates between the two units, increasing the coupling degree of TM11 to the choke ring structure, and further improving the TM11 mode filtering efficiency. At the same time, the spacing D 2 The selection of can realize the absorption of TM11 high-order propagation mode in any polarization direction, and further improve the mode filtering efficiency.

[0032] The mode 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, and its radius r 0It is 24.5mm and the working center frequency is 9.7GHz. According to the cutoff size, it can be known that electromagnetic waves can propagate in the overmoded 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 are respectively connected to the symmetrical outer side surfaces of the choke ring coupling structure through a section of 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 section of rectangular straight waveguide structure.

[0036] The width a of the rectangular waveguide elbow structure, the rectangular straight waveguide structure, and the port 1 and port 2 is 22.86 mm, and the height b is 10.16 mm, which conforms to the rectangular waveguide WR90 standard size. The inner radius r of the rectangular waveguide elbow structure 2 24.29mm, outer radius r 3 The length L of the rectangular straight waveguide structure connected to the choke ring coupling structure is 47.15 mm. 1 The length L of the rectangular straight waveguide structure connected to the ET connector mode selection structure is 20 mm. 2 is 89mm; select the appropriate L 1 and L 2 The value of makes the electromagnetic field form a standing wave in the straight waveguide section of the rectangular waveguide, so as to increase the energy coupling efficiency of the device.

[0037] Port 4 of the ET joint 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 is transmitted along the circular waveguide structure, according to the electromagnetic field distribution principle in the circular waveguide, on the circular waveguide cross section, the field component transmitted in the TM01 mode is distributed in equal amplitude and phase at both ends along the diameter direction of the circular waveguide near the boundary, and the field component transmitted in the TM11 mode is distributed in equal amplitude and anti-phase at both ends along the diameter direction of the circular waveguide near the boundary. The electromagnetic field resonates at the choke ring structure and is extracted by the rectangular waveguide, and finally enters the rectangular straight waveguide connected by two semicircular arc rectangular waveguides, and enters the ET connector structure from both sides.

[0039] According to the basic principle of the magic T structure, the electromagnetic field component of the TM01 mode enters the rectangular waveguide structure from both ends of the circular waveguide transmission structure in an equal amplitude and in-phase propagation mode, and enters the ET joint structure from both ends in an equal amplitude and in-phase propagation mode after the same propagation distance, and will not propagate from the branch port to enter the matching destructive structure; the electromagnetic field component of the TM11 mode enters the rectangular waveguide structure from both ends of the circular waveguide transmission structure in an equal amplitude and in-phase propagation mode, and enters the ET joint structure from both ends in an equal amplitude and in-phase propagation mode after the same propagation distance, and its energy will completely propagate from the branch port to enter the matching destructive structure. Through the selective characteristics of the structure, the device achieves the filtering of the TM11 mode in the circular waveguide transmission structure, and effectively controls 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 circular waveguide transmission system mode filtering device of this embodiment can achieve efficient transmission of the TM01 mode in the frequency band of 9.5 GHz to 9.9 GHz, and the transmission loss is less than -0.14 dB.

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

Claims

1. A TM11 mode filtering device suitable for a circular waveguide, characterized in that: It consists of 4 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 on the circular waveguide transmission system in an orthogonal cascade manner to filter the circular waveguide TM11 mode; 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; Wherein, 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 are respectively connected to the symmetrical outer side surfaces of the choke ring coupling structure through a section of 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 section of 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 as claimed in 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 as claimed in 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 working 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 of a, a height of b, and a length of 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.

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 35 mm to 40 mm.

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, an inner radius of r2, and a value range of r2 of 23 mm to 25 mm.

7. A TM11 mode filtering device suitable for a circular waveguide as claimed in 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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