Compact grating-loaded circular waveguide TM 01 -TE 01 Mode converter

Abstract

The application discloses a grating-loaded compact circular waveguide TM01-TE01 mode converter and belongs to the technical field of microwave waveguides. The structure comprises coaxial and bottom-to-top circular waveguide input sections, first transition sections, coaxial waveguide transition sections, reflective grating mode conversion sections and circular waveguide output sections; wherein the reflective grating mode conversion section comprises a radial line structure and a mode conversion transition section; the inner conductor of the radial line structure comprises a first second-order circular truncated cone, a transition cylinder and a second second-order circular truncated cone; the inner wall of the outer conductor of the radial line structure is provided with a plurality of curved surface metal reflective grating grooves which are uniformly arranged in the circumferential direction. The application combines the radial line theory, the reflective grating theory and the waveguide mode transmission theory, and has the advantages of compact structure, coaxial input and output ports, high conversion efficiency, large power capacity, easy processing and the like.

Description

Technical Field

[0001] This invention belongs to the field of microwave waveguide technology, specifically relating to a compact circular waveguide™ with grating loading that features high conversion efficiency, large power capacity, compact structure, and easy fabrication. 01 -TE 01 Radial line mode converter. Background Technology

[0002] Circular waveguide™ 01 Mode is a common output mode of high-power microwave sources, circular waveguide™ 01 The mode exhibits the strongest longitudinal component of the electric field along the waveguide axis, effectively exchanging energy with the axially moving electron beam. However, as the frequency increases, the heat loss of the waveguide wall rises, which is detrimental to the transmission of high-power microwaves. Circular waveguide TE 01 This mode has no longitudinal electric field component along the waveguide axis, its loss is minimal compared to other modes, and it lacks polarization degeneracy and has relatively few competing modes, making it suitable for long-distance millimeter-wave waveguide transmission. Therefore, to meet the requirements of long-distance, low-loss waveguide transmission, a circular waveguide™ outputting a high-power microwave source is needed. 01 Mode conversion to circular waveguide TE 01 mold.

[0003] Currently, circular waveguide™ 01 Mode conversion to circular waveguide TE 01 The main methods employed are introducing transition modes and introducing transmission grating-type conversion structures. Three typical transition modes are rectangular waveguide TE... 10 Mode, Circular Waveguide TE 11 Modes and Circular Waveguide™ 11 model.

[0004] Rectangular waveguide TE 10 Mode: Circular waveguide™ 01 Mode conversion to rectangular waveguide TE 10 mode, then the rectangular waveguide TE 10 Mode conversion to circular waveguide TE 01 The technical approach to pattern conversion typically involves first performing task division and then combining. For example... Figure 1 As shown in (a), the circular waveguide TM is first connected through two curved rectangular waveguides. 01 Mode conversion to rectangular waveguide TE 10 The mode, through the unequal length design of two curved rectangular waveguides, enables the two-way output rectangular waveguide TE... 10 The electric field distribution of the mode is reversed at the output port, and finally connected to the output circular waveguide, it is converted into a circular waveguide TE. 01 model.

[0005] Circular waveguide TE 11Modes and Circular Waveguide™ 11 Mode: Circular waveguide™ 01 Mode conversion to circular waveguide TE 11 mode, then the circular waveguide TE 11 Mode conversion to circular waveguide™ 11 The mode, finally the circular waveguide™ 11 Mode conversion to circular waveguide TE 01 Mode conversion techniques typically involve introducing perturbation structures. For example... Figure 1 As shown in (b), the circular waveguide TM is first connected via a coaxial insert plate. 01 Mode conversion to circular waveguide TE 11 The pattern is then implemented using a corrugated structure to connect the circular waveguide TE. 11 Mode conversion to circular waveguide™ 11 The mode, finally, uses a curved waveguide to connect the circular waveguide TM. 11 Mode conversion to circular waveguide TE 01 model.

[0006] Introducing a transmission grating-type conversion structure: Introducing a transmission grating-type conversion structure to the circular waveguide TM 01 Mode conversion to circular waveguide TE 01 The technical approach for this mode is based on the theory of transmission gratings and the theory of waveguide mode transmission. For example... Figure 1 As shown in (c), the circular waveguide TM 01 The beam is fed in from the input port and passes through a transmission grating conversion structure to realize a circular waveguide™. 01 Mode radial polarization direction to circular waveguide TE 01 The mode angle is converted to the polarization direction and finally output from the output port.

[0007] Whether it's a power splitting and then combining approach or a perturbation structure approach, the technical route involves introducing a rectangular waveguide TE. 10 Mode, Circular Waveguide TE 11 Modes and Circular Waveguide™ 11 Intermediate transition modes, such as single-mode converters, and other typical transition structures, lead to problems such as large axial dimensions, non-coaxial input and output ports, and difficulties in manufacturing processes, which are detrimental to practical applications. While introducing a transmission grating-type conversion structure offers coaxial input and output ports, it suffers from low power capacity and low conversion efficiency, limiting its practical application. Summary of the Invention

[0008] This invention proposes a grating-loaded compact circular waveguide™ 01 -TE 01The mode converter combines radial line theory, reflection grating theory and waveguide mode transmission theory. It has the advantages of compact structure, coaxial input and output ports, high conversion efficiency, large power capacity and easy processing. It solves the problems of large transition section structure, difficult manufacturing process and non-coaxial input and output ports of previous mode converters, and provides a new idea for the design of mode converters.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A grating-loaded compact circular waveguide™ 01 -TE 01 A mode converter is characterized by comprising a circular waveguide input section, a first transition section, a coaxial waveguide transition section, a reflective grating mode conversion section, and a circular waveguide output section arranged coaxially from bottom to top.

[0011] Among them, circular waveguide TM 01 The mode is fed into the coaxial waveguide transition section after passing through the circular waveguide input section and the first transition section; Circular waveguide TM 01 The mode is converted to a coaxial TEM mode in the coaxial waveguide transition section and fed into the reflective grating mode conversion section; the coaxial TEM mode is converted to a circular waveguide TE mode in the reflective grating mode conversion section. 01 The mode is finally output through the circular waveguide output segment.

[0012] The reflected grating-type mode conversion section includes a radial line structure and a mode conversion transition section.

[0013] The radial line structure includes an inner radial line conductor and an outer radial line conductor.

[0014] The radial conductor includes, from bottom to top, a first frustum of second order, a transition cylinder, and a second frustum of second order; wherein, in the first frustum of second order: the top surface radius of the first frustum is R1, the radius of the connecting surface between the first and second frustums is R2, and the bottom surface radius of the second frustum is R3; in the second frustum of second order: the top surface radius of the first frustum is R4, the radius of the connecting surface between the first and second frustums is R5, and the bottom surface radius of the second frustum is R6; the radius of the transition cylinder is R3; and satisfies R1 <R2<R3、R4<R5<R6<R3。

[0015] The inner wall of the radial outer conductor is provided with several curved metal reflective grating grooves with the same structure, which are evenly arranged around the angular direction; the grooves of the curved metal reflective grating have the same depth, and the two sides are planes that are parallel to each other and form an angle of 45° with the axial direction.

[0016] The mode transition section is a circular waveguide with a gradually decreasing radius.

[0017] Furthermore, in the radial line structure, the lower side thickness d1 of the transition cylinder is less than its upper side thickness d2.

[0018] Furthermore, at least a portion of the first-order frustum of the second second-order frustum is located in the mode transition section.

[0019] Furthermore, the depth H of the groove of the metal reflective grating is in the range of H = (0.24~0.26)λ, and the width L is in the range of L < λ / 2, where λ represents the working wavelength.

[0020] Furthermore, the coaxial waveguide transition section consists of a coaxial outer conductor, a coaxial inner conductor, and two sets of support structures; wherein, the coaxial outer conductor consists of a linearly tapered section and a uniformly tapered section; the coaxial inner conductor consists of a first linearly tapered section, a second linearly tapered section, and a cylindrical section; the lower side of the first linearly tapered section extends into the first transition section, and the top surface of the extended portion is provided with a frustum-shaped groove.

[0021] Furthermore, the support structure is located between the uniformly radii of the coaxial outer conductor and the cylindrical segment of the coaxial inner conductor; one set of the support structure consists of several fan-shaped columns evenly arranged along the angular direction; and the two sets of support structures are arranged in the same angular direction.

[0022] Furthermore, a trapezoidal groove is provided in the uniformly radii segment between a pair of adjacent sector columns; the trapezoidal groove has a trapezoidal shape in any cross section along the central axis.

[0023] Common reflective grating structures such as Figure 4 As shown, when in angle When the polarization direction of the incident linearly polarized wave makes an angle θ with the tangential direction of the grating strip, the beam can be decomposed into two mutually perpendicular components, namely the electric field E perpendicular to the tangential direction of the grating strip. ⊥ and a magnetic field H parallel to the tangential direction of the grating strips / / The electric field E that forms the TM wave and is parallel to the tangential direction of the grating stripe. / / and a magnetic field H perpendicular to the tangential direction of the grating strips ⊥ The TE wave is formed. The TM wave is reflected back after penetrating to the bottom of the grating groove, while the TE wave is reflected at the surface of the grating groove. Therefore, after reflection by the metal grating, the TE wave and the TM wave will form a certain phase difference. By selecting an appropriate included angle θ and grating strip depth, the synthesized polarized wave can be made into the desired form.

[0024] Applying grating theory to the mode converter of this invention, since the beam propagation direction in the radial line is uniformly distributed radially and angularly, the grating strain should be arranged angularly around the circumference, such as... Figure 6As shown. If the tangent direction of the grating strip is exactly 45° to the polarization direction of the electric field at the outer edge of the radial line, according to grating theory, the beam can be decomposed into two mutually perpendicular components with equal phase and amplitude. The TM wave and the TE wave, two different and orthogonal modes, form a phase difference after being reflected by the metal grating strip. By selecting an appropriate depth of the metal grating strip so that the reflected TE wave and TM wave satisfy the phase difference δ = 2nπ + π, the polarization direction of the synthesized wave can be twisted by 90°, thus achieving the purpose of polarization twisting. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a common waveguide mode converter structure.

[0026] Figure 2 This is a schematic diagram of the mode converter according to an embodiment of the present invention.

[0027] Figure 3 This is a cross-sectional schematic diagram of the mode converter according to an embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram of the structure of a common metal grating.

[0029] Figure 5 This is a schematic diagram of the coaxial support structure according to an embodiment of the present invention.

[0030] Figure 6 This is a schematic diagram of the reflective grating conversion structure according to an embodiment of the present invention.

[0031] Figure 7 Circular waveguide TM as an embodiment of the present invention 01 - Circular waveguide TE 01 The conversion efficiency diagram.

[0032] Figure 8 The figure shows the simulation results of the power capacity at the operating frequency of 9.7 GHz in this embodiment of the invention.

[0033] The reference numerals in the attached diagrams are as follows: 1. Circular waveguide input section; 2. First transition section; 3. Coaxial waveguide transition section; 31. Coaxial waveguide outer conductor; 32. Coaxial waveguide inner conductor; 33. Fan-shaped support column; 34. Coaxial outer conductor groove; 4. Reflective grating mode conversion section; 41. Radial inner conductor; 42. Radial outer conductor; 43. Mode transition section; 44. Metal reflective grating groove; 5. Circular waveguide output section. Detailed Implementation

[0034] To better illustrate the purpose, advantages, and technical concept of this invention, the technical solution of this invention will be further clearly and completely described below in conjunction with the accompanying drawings and specific examples.

[0035] This embodiment uses a TM loaded with a radial grating at a center frequency of 9.7 GHz. 01 -TE 01 For example, a mode converter, such as Figure 2 , Figure 3 As shown, it includes a circular waveguide input section, a first transition section, a coaxial waveguide transition section, a reflective grating mode conversion section, and a circular waveguide output section arranged coaxially from bottom to top, all made of PEC.

[0036] Among them, circular waveguide TM 01 The mode is fed into the coaxial waveguide transition section after passing through the circular waveguide input section and the first transition section; Circular waveguide TM 01 The mode is converted to a coaxial TEM mode in the coaxial waveguide transition section and fed into the reflective grating mode conversion section; the coaxial TEM mode is converted to a circular waveguide TE mode in the reflective grating mode conversion section. 01 The mode is finally output through the circular waveguide output segment.

[0037] The reflected grating-type mode conversion section includes a radial line structure and a mode conversion transition section.

[0038] The radial line structure includes an inner radial line conductor and an outer radial line conductor.

[0039] The radial conductor includes a first frustum of second order, a transition cylinder, and a second frustum of second order arranged sequentially from bottom to top. Specifically, in the first frustum of second order: the top surface radius of the first frustum is R1 = 78 mm, the radius of the connecting surface between the first and second frustums is R2 = 95 mm, and the bottom surface radius of the second frustum is R3 = 152 mm; in the second frustum of second order: the top surface radius of the first frustum is R4 = 17 mm, the radius of the connecting surface between the first and second frustums is R5 = 25 mm, and the bottom surface radius of the second frustum is R6 = 57 mm; the transition cylinder has a radius of R3 = 152 mm and an axial length of d3 = 5 mm; in the radial structure, the lower side thickness of the transition cylinder is d1 = 18 mm, and the upper side thickness is d2 = 25 mm.

[0040] Figure 6 This is the embodiment TM 01 -TE 01 A schematic diagram of the reflective grating conversion structure of the mode converter is shown. The inner wall of the radial outer conductor has 25 identical curved metal reflective grating grooves evenly arranged around the angular axis. The material is PEC. The two sides of the metal reflective grating grooves are parallel planes forming a 45° angle with the axial direction. The inner wall radius of the radial outer conductor is R = 104 mm, the groove depth is H = 7.76 mm ≈ λ / 4, and the groove width is L = 13 mm.

[0041] The mode conversion transition section is a circular waveguide with a gradually decreasing radius, with an upper radius of 26 mm and a lower radius of 32 mm. The axial length of the portion of the second second-order frustum extending into the mode conversion transition section is 6 mm.

[0042] The coaxial waveguide transition section consists of a coaxial outer conductor, a coaxial inner conductor, and two sets of support structures. The coaxial outer conductor consists of a linearly tapered section and a uniformly tapered section. The coaxial inner conductor consists of a first linearly tapered section, a second linearly tapered section, and a cylindrical section. The lower side of the first linearly tapered section extends into the first transition section, and the top surface of the extended portion is provided with a frustum-shaped groove, with the outer corner of the top surface rounded.

[0043] Figure 5 This embodiment uses a circular waveguide™ 01 -TE 01 A schematic diagram of the support structure of the mode converter, as shown below. Figure 5 As shown, the support structure is located between the uniformly radii of the coaxial outer conductor and the cylindrical segment of the coaxial inner conductor; one set of the support structure consists of 10 sector-shaped columns evenly arranged along the angular direction; and the two sets of support structures have the same arrangement in the angular direction. The sector-shaped columns are made of PEC, with an inner diameter Φ1 = 78.4 mm and an outer diameter Φ2 = 100 mm.

[0044] Since the two side planes of the grating groove are parallel to each other and form a 45° angle with the mode converter axis, and the transmission direction of the radially transmitted cylindrical TEM mode is uniformly distributed radially and angularly, and the polarization direction is along the mode converter axis, this structure can be compared with the ordinary parallel metal grating structure when the polarization direction is incident at a 45° angle with the metal grating strip.

[0045] According to the principle of reflection gratings, when the tangent direction of the grating strip forms a 45° angle with the polarization direction of the electric field at the outer edge of the radial line, the beam can be divided into two different modes with the same amplitude: TM wave and TE wave. Since the TM wave is reflected back after penetrating to the bottom of the grating groove, while the TE wave is reflected at the surface of the grating groove, by selecting an appropriate depth of the metal grating strip to create a 180° phase difference between the TM wave and the TE wave, the polarization direction of the synthesized wave can be twisted by 90°, thereby achieving the cylindrical TEM mode-radial TE mode. 01 The purpose of analog-to-digital conversion.

[0046] A trapezoidal groove is provided in a uniformly radii-equivalent section between a pair of adjacent sector columns. Any cross-section of the trapezoidal groove along the central axis is trapezoidal, with a lower base length of 45mm, an upper base length of 11mm, and a height of 3mm. Based on the relationship between electric field and power capacity, the introduction of the trapezoidal groove increases the vacuum cross-sectional area of ​​the supporting structure section, thereby reducing the electric field energy density and lowering the local electric field, resulting in a larger power capacity.

[0047] Circular waveguide™ 01 The mode is fed into the first transition section via the circular waveguide input section. Part of the TM mode is reflected at the frustum, superimposed on the incident wave, forming an electromagnetic wave with a circular energy distribution. At this point, the energy at the inner conductor port of the coaxial line is relatively low, with the energy mainly distributed in the outer ring, achieving minimal reflection and controlling the circular waveguide TM. 01 Mode transmission, for circular waveguide™ 01 The transition from the mode to the coaxial TEM mode provides a good foundation, while also bringing greater power capacity.

[0048] Based on the theoretical analysis of the support rods in the coaxial waveguide extraction region, if the first cutoff mode of the coaxial waveguide is Hn1, then n sector-shaped support rods should be selected. In this case, since only the coaxial TEM mode can be transmitted among the modes generated by the support rods, higher-order modes are all cut off, minimizing mode disturbance. Furthermore, numerical calculations show that setting up two layers of identical n sector-shaped support rods can reduce the reflection caused by a single-layer support rod. Based on the above theory, a coaxial waveguide support structure composed of two layers of n identical sector-shaped rods can minimize the impact on the internal field of the waveguide while achieving the supporting function.

[0049] The coaxial TEM mode is fed in through the coaxial waveguide transition section, and after passing through the first and second order frustums, it is converted into a cylindrical TEM mode and fed into the grating groove. After passing through the grating groove, it is converted into a radial TEM mode. 01 The mode feed into the mode conversion transition section is converted to a coaxial TE via the second second-order frustum. 01 A circular waveguide with a gradually decreasing mode feed radius is converted into a circular waveguide TE. 01 The mode is then fed into the circular waveguide output section to achieve mode conversion.

[0050] Simulation results show that the conversion efficiency is 98.32% at an operating frequency of 9.7 GHz, and exceeds 90% in the 9.59–9.74 GHz frequency band. Figure 7 As shown.

[0051] Simulation results show that when a 4GW circular waveguide TM with an operating frequency of 9.7GHz is fed into the input port P1... 01 During the mode wave, the electric field intensity at the metal sidewalls is less than 0.6 MV / cm, such as Figure 8 As shown, the designed mode converter not only has high conversion efficiency, but also a power capacity of 4GW, a compact structure, an axial distance of 38mm, and coaxial input and output ports.

[0052] The above examples are only for illustrating the technical concept and features of the present invention, and are only used to specifically describe the present invention so that those skilled in the art can understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made according to the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A grating-loaded compact circular waveguide™ 01 -TE 01 Mode converter, characterized in that, It includes a circular waveguide input section, a first transition section, a coaxial waveguide transition section, a reflective grating mode conversion section, and a circular waveguide output section arranged sequentially from bottom to top, all coaxially. Among them, circular waveguide TM 01 The mode is fed into the coaxial waveguide transition section after passing through the circular waveguide input section and the first transition section; Circular waveguide TM 01 The mode is converted to a coaxial TEM mode in the coaxial waveguide transition section and fed into the reflective grating mode conversion section; the coaxial TEM mode is converted to a circular waveguide TE mode in the reflective grating mode conversion section. 01 The pattern is finally output through the circular waveguide output segment; The reflective grating-type mode conversion section includes a radial line structure and a mode conversion transition section; The radial line structure includes an inner radial line conductor and an outer radial line conductor; The radial conductor includes, from bottom to top, a first frustum of second order, a transition cylinder, and a second frustum of second order; wherein, in the first frustum of second order: the top surface radius of the first frustum is R1, the radius of the connecting surface between the first and second frustums is R2, and the bottom surface radius of the second frustum is R3; in the second frustum of second order: the top surface radius of the first frustum is R4, the radius of the connecting surface between the first and second frustums is R5, and the bottom surface radius of the second frustum is R6; the radius of the transition cylinder is R3; and satisfies R1 <R2<R3、R4<R5<R6<R3; The inner wall of the radial outer conductor is provided with several curved metal reflective grating grooves with the same structure, which are evenly arranged around the angular direction; the grooves of the curved metal reflective grating have the same depth, and the two sides are planes that are parallel to each other and form an angle of 45° with the axial direction. The mode transition section is a circular waveguide with a gradually decreasing radius.

2. A grating-loaded compact circular waveguide™ as described in claim 1 01 -TE 01 Mode converter, characterized in that, The depth H of the groove of the metal reflective grating is in the range of H = (0.24~0.26)λ, and the width L is in the range of L < λ / 2, where λ represents the working wavelength.

3. A grating-loaded compact circular waveguide™ as described in claim 2 01 -TE 01 Mode converter, characterized in that, In the radial line structure, the lower side thickness d1 of the transition cylinder is less than its upper side thickness d2.

4. A grating-loaded compact circular waveguide™ as described in claim 2 or 3 01 -TE 01 Mode converter, characterized in that, At least a portion of the first-order frustum of the second second-order frustum is located in the mode transition section.

5. A grating-loaded compact circular waveguide™ as described in claim 2 or 3 01 -TE 01 Mode converter, characterized in that, The coaxial waveguide transition section consists of a coaxial outer conductor, a coaxial inner conductor, and two sets of support structures; wherein, the coaxial outer conductor consists of a linearly tapered section and a uniformly tapered section; the coaxial inner conductor consists of a first linearly tapered section, a second linearly tapered section, and a cylindrical section; the lower side of the first linearly tapered section extends into the first transition section, and the top surface of the extended portion is provided with a frustum-shaped groove.

6. A grating-loaded compact circular waveguide™ as described in claim 5 01 -TE 01 Mode converter, characterized in that, The support structure is located between the uniformly radii of the coaxial outer conductor and the cylindrical segment of the coaxial inner conductor; one set of the support structure consists of several fan-shaped columns evenly arranged along the angular direction; and the two sets of support structures are arranged in the same angular direction.

7. A grating-loaded compact circular waveguide™ as described in claim 6 01 -TE 01 Mode converter, characterized in that, A trapezoidal groove is provided in a uniformly radii-spanning section between a pair of adjacent sector columns; any cross-section of the trapezoidal groove along the central axis is trapezoidal.

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