Rectangular waveguide TE10-circular waveguide TE01 mode conversion device

Abstract

The invention discloses a rectangular waveguide TE10-circular waveguide TE01 mode conversion device, and belongs to the technical field of high-power microwaves. The whole device is of a mirror symmetry structure, and comprises an input rectangular waveguide, a rectangular coupling window, a first periodic arc loading resonant cavity, a cross slot coupling window, a second periodic arc loading resonant cavity, a *-shaped slot coupling window and an output circular waveguide. A TE10 mode input from the input rectangular waveguide passes through the two-order periodic arc loading resonant cavity, and finally the circular waveguide TE01 mode is excited through the *-shaped slot coupling window, so that conversion from the rectangular waveguide TE10 mode to the circular waveguide TE01 mode is realized. According to the invention, a circular waveguide TE01 mode can be excited by a rectangular waveguide TE10 mode in an X wave band, the size of a conversion three-dimensional structure is greatly reduced by using a resonant working principle, and the converter has the advantages of high power, miniaturization, low insertion loss and high foreign mode suppression degree.

Description

Technical Field

[0001] This invention belongs to the field of high-power microwave technology, specifically relating to a high-power compact rectangular waveguide TE10-circular waveguide TE01 mode conversion device. Background Technology

[0002] The operation of high-power microwave systems relies heavily on the transmission structure of high-power microwaves, among which the mode conversion device, as the connection between the microwave source and various transmission lines, is particularly important. In the application of high-power microwave devices, interconnection between different devices and interfaces is very common. When the required waveform mode differs from the existing waveform mode, a mode conversion device is needed. The circular waveguide TE01 mode has the characteristic of low ohmic loss, ensuring the efficiency of electromagnetic wave signal transmission; at the same time, circular waveguide transmission lines have higher power capacity than rectangular waveguide transmission lines. Given that rectangular waveguide structures are predominantly used in microwave engineering, effectively converting the rectangular waveguide TE10 mode into a high-purity circular waveguide TE01 mode is of great significance for further improving the power capacity of the feeder link, reducing transmission loss, and improving transmission efficiency.

[0003] The most commonly used operating modes in circular waveguide transmission lines are TE11, TM01, and TE01 modes. Among them, the TE11 mode has the longest cutoff wavelength and is the dominant mode in circular waveguides. However, it suffers from polarization degeneracy, causing instability in the polarization direction of the waveguide field. If the wave encounters inhomogeneities within the waveguide during propagation, a degenerate polarization mode will occur. The TM01 mode is the secondary dominant mode in circular waveguides. Its electromagnetic field does not change along the circumference, and its field distribution exhibits axisymmetry, with the strongest electric field component along the waveguide axis. These characteristics allow the TM01 mode to effectively exchange energy with electron beams moving along the axis, and it is frequently used in microwave tubes and linear electron accelerators. The TE01 mode has no change in either the electric or magnetic field along the angular direction, exhibiting a circularly symmetrical structure. At the waveguide wall, the magnetic field of the TE01 mode only has a z-axis component; therefore, the high-frequency current at the waveguide wall only has an angular component and no longitudinal wall current. When the transmission power is constant, the waveguide loss decreases and the attenuation constant decreases with increasing frequency. However, the TE01 mode is not the main mode and is degenerate with the TM11 mode, so other interference modes need to be suppressed when using it.

[0004] Under current technology, the TE10 mode conversion from the rectangular waveguide to the TE01 mode conversion from the circular waveguide can be achieved through several methods, including straight-line coupling, power-division sidewall coupling, and coaxial cavity-based annular coupling structures. A typical application of straight-line coupling is the Marie-type mode converter, which usually uses a waveguide structure with a gradually changing cross-section to change the input waveguide mode. The geometry of the mode converter achieved by this method is usually a straight line, with many structural variations, long dimensions, and large device volume. In particular, the field strength is high in the cross-shaped waveguide region when converting from the TE20 mode to the TE22 mode, which limits the power capacity of the device. Yong Xu et al. designed a Ka-band Marie mode converter based on a ridge-shaped twisted waveguide, with a total length of 26 electrical wavelengths. The fabrication process of the ridge-shaped twisted waveguide is relatively complex [Yong Xu, et al., “Design and Test of Broadband Rectangular Waveguide TE10 to Circular Waveguide TE21 and TE01 Mode Converters”, IEEE Transactions on Electron Devices, vol.66, no.8, Aug.2019]. Power-dividing sidewall coupling generates the TE01 mode through symmetrical excitation by creating coupling holes on the sidewall of a circular waveguide. This method is characterized by high conversion efficiency and ensures the purity of the TE01 mode. However, its drawback is that multiple coupling holes on the sidewall input equal-amplitude TE10 modes, necessitating the design of a multi-path power divider that meets structural requirements, resulting in a relatively large device size. Zhenwei Liu et al. proposed a quadrupole waveguide TE01 mode conversion structure with a gradually varying cross-sectional area operating in the K-band, which can effectively suppress other modes. The rectangular waveguide TE10 mode is first divided into four equal-amplitude TE10 modes through a two-stage T-branch waveguide structure. These four signals then converge within a quadrupole waveguide TE01 mode conversion structure to excite the TE01 mode. Finally, a tapered waveguide transitions the signal into a circular waveguide to form the TE01 mode [Zhenwei Liu, et al., “ABroadband Circular TE01 Mode Converter Using HighlyDeformed Circular Waveguide”, IEEE Transactions on Electron Devices, vol.71, no.12, Dec.2024]. Although the quadrupole waveguide TE01 mode conversion structure improves conversion purity and operating bandwidth, the maximum length of the T-branch waveguide structure in the conversion device reaches 14 electrical wavelengths, and the height of the tapered waveguide reaches 7.5 electrical wavelengths.Zhengxiao Lai et al. achieved mode conversion using a coaxial cavity and annular coupling slot. They utilized a branching structure to split the input rectangular waveguide TE10 mode into two identical signals, and then input several equal-amplitude, in-phase microwave signals into the inner conductor through the rectangular coupling slot within the coaxial cavity, thereby exciting the TE01 mode [Zhengxiao Lai, Dongfeng Li, Kairong Chu, “Design of S-band 200MW High Peak Power Klystron Mode Converter”, Journal of Microwaves, vol.41, no.2, Apr.2025]. Results showed that this design achieved a conversion purity of over 99% in the S-band, but the relative bandwidth with a return loss greater than 20dB was only 1%. The diameter of the coaxial cavity reached 2.1 electrical wavelengths, resulting in a power capacity of 200MW in the S-band. Therefore, they estimated the power capacity in the X-band to be approximately 2.5MW. Zhengxiao Lai et al. also compared the coaxial cavity-structured mode converter with an S-band petal-shaped mode converter. The petal-shaped mode converter splits the input rectangular waveguide TE10 mode into two equal-amplitude, in-phase signals. These signals are then coupled into a circular waveguide via four petal-shaped coupling holes on the two rectangular waveguides. Finally, a waveform suppressor outputs a high-purity circular waveguide TE01 mode. At the same input power, the petal-shaped mode converter increases the field strength by 20.9% compared to the former, but also increases the risk of microwave breakdown. Furthermore, the petal-shaped mode converter's suppression of unwanted modes is relatively poor compared to coaxial cavities and coupling slots. Summary of the Invention

[0005] To address the shortcomings of existing rectangular waveguide TE10 to circular waveguide TE01 mode conversion devices, such as insufficient power capacity and non-compact structure, this invention proposes a rectangular waveguide TE10 to circular waveguide TE01 mode conversion device. Based on a periodically arc-loaded circular waveguide TE011 mode resonant cavity structure, this invention not only effectively suppresses the TM111 degenerate interference mode but also possesses high power capacity.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A rectangular waveguide TE10 to circular waveguide TE01 mode conversion device is provided. The device has an overall mirror-symmetric structure and includes: an input rectangular waveguide, a rectangular coupling window, a first-period circular arc-loaded resonant cavity, a cross-slit coupling window, a second-period circular arc-loaded resonant cavity, a star-shaped slit coupling window, and an output circular waveguide.

[0008] The input rectangular waveguide is used to input the TE10 mode of the rectangular waveguide into the rectangular coupling window;

[0009] The rectangular coupling window has a width that is the same as the height of the first periodic circular arc loading resonant cavity. One end is connected to the input rectangular waveguide, and the other end is connected to the space between the two circular arcs of the first periodic circular arc loading resonant cavity. By using electrical coupling, the TE10 mode in the input rectangular waveguide can effectively excite the TE011 mode of the first periodic circular arc loading resonant cavity.

[0010] The first periodic circular arc loading resonant cavity is a rotationally symmetric structure, consisting of a large cylindrical cavity and six small cylindrical cavities equidistantly embedded along the circumference of the large cylindrical cavity. The central axis of the large cylindrical cavity is perpendicular to the central axis of the rectangular coupling window.

[0011] The central axis of the cross-shaped coupling window coincides with the central axis of the large cylindrical cavity, and one of its arms is parallel to the central axis of the rectangular coupling window. This is used to couple the TE011 mode in the first-period circular arc-loaded resonant cavity to the second-period circular arc-loaded resonant cavity and suppress degenerate modes.

[0012] The cross-section of the second periodic circular arc loading resonant cavity is the same as that of the first periodic circular arc loading resonant cavity;

[0013] The central axis of the star-shaped coupling window coincides with the central axis of the large cylindrical cavity. The included angles of its two adjacent arms are the same, and one of the arms is parallel to the central axis of the rectangular coupling window, so that the TE011 mode in the second periodic arc-loaded resonant cavity excites the TE01 mode in the output circular waveguide.

[0014] The output circular waveguide is used to output the TE01 mode to the subsequent devices.

[0015] Furthermore, the radius of the large cylindrical cavity is defined as R, the radius of the small cylindrical cavity as r, and the center distance between the large and small cylindrical cavities is defined as d, where d is in the range of Rr < d < 2r.

[0016] Furthermore, the radius R of the large cylindrical cavity and the height of the two-order periodic circular arc-loaded resonant cavity are determined by the resonant frequency.

[0017] Furthermore, the arm length of the cross-shaped coupling window ranges from 30mm to 40mm, the arm width ranges from 4mm to 10mm, and the height ranges from 1mm to 5mm.

[0018] Furthermore, the arm length of the cross-shaped coupling window ranges from 30mm to 40mm, the arm width ranges from 1mm to 5mm, and the height ranges from 1mm to 5mm.

[0019] Furthermore, within the X-band, the radius R of the large cylindrical cavity ranges from 15mm to 40mm.

[0020] Furthermore, the edges of the cross-shaped coupling window and the star-shaped coupling window are chamfered and smoothed to facilitate processing and avoid concentration of edge electric field intensity.

[0021] Furthermore, the mode conversion device is made of all-metal materials.

[0022] The working principle of this invention is as follows:

[0023] Since the electromagnetic field of the TE011 mode in the circular waveguide resonator remains constant along the circumference and the electric field is almost zero at the cavity edge, while the TM111 mode has a strong magnetic field component at the cavity edge, changing the edge structure of the circular waveguide resonator has different effects on the two modes. This allows for the separation of the resonant frequencies of the two degenerate modes and also improves the mode isolation between the TE011 mode and other adjacent interfering modes. The TE10 mode, input from the rectangular waveguide, is fed into the first-period circular arc-loaded resonator through a rectangular coupling window and excites the TE011 mode. A cross-slit coupling window structure is used between the two-order periodic circular arc-loaded resonators. The first-period circular arc-loaded resonator excites the TE011 mode of the second-period circular arc-loaded resonator through the cross-slit coupling window. The second-period circular arc-loaded resonator and the output circular waveguide are coupled through a star-shaped slit coupling window, located at the center of the second-period circular arc-loaded resonator, using magnetic coupling to couple the TE01 mode in the output circular waveguide.

[0024] The coupling window between the two-order periodic circular arc-loaded resonant cavities employs magnetic coupling, which effectively suppresses other interfering TE modes and avoids electric field concentration, thus improving the power capacity of the coupling gap. Furthermore, the symmetrical layout of the coupling window suppresses the excitation of asymmetric higher-order modes. In addition, the edges of the coupling window are appropriately chamfered and smoothed to avoid concentration of electric field intensity at the edges, thereby improving the power capacity of the conversion device.

[0025] The advantages of this invention compared to existing technologies are:

[0026] (1) The periodic circular arc loading resonant cavity proposed in this invention has a higher TE011 mode single-mode operating frequency range.

[0027] (2) The periodic circular arc loading resonant cavity structure designed in this invention greatly reduces the size of the device. The maximum radial dimension of the periodic circular arc loading resonant cavity in the X-band is only 1.6 electrical wavelengths, and the structure is compact.

[0028] (3) The present invention uses cross-slit coupling window and star-shaped coupling window to reduce the maximum field strength and increase the power capacity. With the typical microwave breakdown threshold of 1MV / cm in HPM system as a reference, the power capacity is about 45.12MW.

[0029] (4) The device of the present invention has a return loss of more than 20dB in the X-band, an operating bandwidth of 177MHz, an insertion loss of less than 0.1dB, and a noise mode suppression degree of more than 37dB.

[0030] (5) The mode conversion device of the present invention is made of all-metal material, which is easy to process and assemble and has good engineering applicability. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the mode conversion device according to an embodiment of the present invention.

[0032] Figure 2 This is a side view of the mode conversion device according to an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram of the horizontal cross-section of the periodic circular arc loading resonant cavity according to an embodiment of the present invention.

[0034] Figure 4 This is a schematic diagram of the cross-slit coupling window structure according to an embodiment of the present invention.

[0035] Figure 5 This is a schematic diagram of the cross-shaped coupling window structure according to an embodiment of the present invention.

[0036] Figure 6 These are the calculation results of the return loss, the output circular waveguide TE01 operating mode, and the partial interference mode S21 parameters provided in the embodiments of the present invention.

[0037] Figure 7 This is a schematic diagram of the electric field distribution of the mode conversion device according to an embodiment of the present invention.

[0038] Explanation of reference numerals in the attached figures: 1. Input rectangular waveguide, 2. Rectangular coupling window, 3. First-period circular arc-loaded resonant cavity, 4. Cross-slit coupling window, 5. Second-period circular arc-loaded resonant cavity, 6. Star-shaped slit coupling window, 7. Output circular waveguide. Detailed Implementation

[0039] To make the technical advantages and solutions of the present invention clearer, the implementation schemes of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0040] This embodiment provides an X-band high-power compact rectangular waveguide TE10 to circular waveguide TE01 mode conversion device with a center frequency of 8.725 GHz. Figure 1-2 As shown, it includes: an input rectangular waveguide, a rectangular coupling window, a first-period circular arc-loaded resonant cavity, a cross-slit coupling window, a second-period circular arc-loaded resonant cavity, a star-shaped slit coupling window, and an output circular waveguide.

[0041] The input rectangular waveguide is a standard BJ-32 rectangular waveguide, used to input the TE10 mode of the rectangular waveguide into the rectangular coupling window.

[0042] The central axis of the rectangular coupling window coincides with the central axis of the input rectangular waveguide, the wide side is the same height as the first periodic circular arc loading resonant cavity, and the narrow side dimension is 17.2mm. One end of the rectangular coupling window is connected to the input rectangular waveguide, and the other end is connected to the space between the two circular arcs of the first periodic circular arc loading resonant cavity, so that the TE10 mode in the input rectangular waveguide excites the TE011 mode of the first periodic circular arc loading resonant cavity.

[0043] like Figure 3 As shown, the first periodic circular arc-loaded resonant cavity is a rotationally symmetric structure, consisting of a large cylindrical cavity and six small cylindrical cavities equidistantly embedded along the circumference of the large cylindrical cavity. The central axis of the large cylindrical cavity is perpendicular to the central axis of the rectangular coupling window. In this embodiment, the radius of the large cylindrical cavity is R = 16 mm, the radius of the small cylindrical cavities is r = 10 mm, the distance from the center of the small cylindrical cavity to the center of the large cylindrical cavity is d = 18.5 mm, and the height is D1 = 26.2 mm. The periodic circular arc-loaded resonant cavity significantly improves the mode separation between the TE011 mode and its degenerate TM111 mode by introducing six small circular arcs on the outside of the circular waveguide to greatly perturb the circular waveguide boundary, and also improves the mode isolation between other adjacent interfering modes.

[0044] like Figure 4 As shown, the central axis of the cross-slit coupling window coincides with the central axis of the large cylindrical cavity, and one of its arms is parallel to the central axis of the rectangular coupling window. This is used to couple the TE011 mode in the first-period circular arc-loaded resonant cavity to the second-period circular arc-loaded resonant cavity and suppress degenerate modes. In this embodiment, the height of the cross-slit coupling window is b = 2 mm, the arm width is a = 7 mm, and the arm length is c = 33.3 mm.

[0045] The second periodic circular arc loading resonant cavity has the same cross-section as the first periodic circular arc loading resonant cavity, with a height D2 = 22.9 mm.

[0046] like Figure 5 As shown, the central axis of the star-shaped coupling window coincides with the central axis of the large cylindrical cavity, the included angles of its two adjacent arms are the same, and one of the arms is parallel to the central axis of the rectangular coupling window, so that the TE011 mode in the second periodic circular arc loading resonant cavity excites the TE01 mode in the output circular waveguide; in this embodiment, the height H of the star-shaped coupling window is 1mm, the arm width W is 1.5mm, and the arm length L is 36.8mm.

[0047] The output circular waveguide, with a radius of 24.9 mm, is used to output the TE01 mode to the subsequent devices.

[0048] Figure 6The calculation results for return loss, output circular waveguide TE01 operating mode, and some interference mode S21 parameters of this embodiment of the invention are presented. Analysis of the curves shows that the center frequency is 8.725 GHz, the return loss is greater than 20 dB, the relative bandwidth is 2%, and the in-band insertion loss is less than 0.1 dB. Within the operating frequency band, there are few interference modes, and the clutter mode suppression reaches over 37 dB.

[0049] Figure 7 A schematic diagram of the electric field distribution of an embodiment of the present invention is provided. The maximum field strength in the figure is 0.9999 MV / cm (input power 45.12 MW). Taking the typical microwave breakdown threshold of 1 MV / cm in the HPM system for calculation, the power capacity of the mode conversion device can reach 45.12 MW, which has a high power capacity.

[0050] Compared to direct coupling and power-dividing sidewall coupling, this invention eliminates the need for complex waveguide structures with gradually varying cross-sections and input power dividers. The TE011 operating mode inside the periodic boundary-loaded resonant cavity is directly excited by the input rectangular waveguide through a rectangular coupling window, resulting in a significant reduction in structural size. The cross-slit and star-shaped slit coupling window structures reduce insertion loss. By introducing a circular arc periodic perturbation to the circular waveguide metal boundary, the isolation between circular waveguide resonant modes is improved, and the resonant cavity coupling structure makes the conversion device compact. At the same time, the star-shaped slit coupling window structure reduces the maximum field strength of the device, further increasing the power capacity.

[0051] 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 merely specific embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A mode conversion device for a rectangular waveguide TE10 to a circular waveguide TE01, characterized in that, The device has a mirror-symmetric structure and includes: an input rectangular waveguide, a rectangular coupling window, a first-period circular arc-loaded resonant cavity, a cross-slit coupling window, a second-period circular arc-loaded resonant cavity, a star-shaped slit coupling window, and an output circular waveguide. The input rectangular waveguide is used to input the TE10 mode of the rectangular waveguide into the rectangular coupling window; The rectangular coupling window has a width that is the same as the height of the first periodic circular arc loading resonant cavity. One end is connected to the input rectangular waveguide, and the other end is connected to the space between the two arcs of the first periodic circular arc loading resonant cavity. By means of electrical coupling, the TE10 mode in the input rectangular waveguide excites the TE011 mode of the first periodic circular arc loading resonant cavity. The first periodic circular arc loading resonant cavity is a rotationally symmetric structure, consisting of a large cylindrical cavity and six small cylindrical cavities equidistantly embedded along the circumference of the large cylindrical cavity. The central axis of the large cylindrical cavity is perpendicular to the central axis of the rectangular coupling window. The central axis of the cross-shaped coupling window coincides with the central axis of the large cylindrical cavity, and one of its arms is parallel to the central axis of the rectangular coupling window. This is used to couple the TE011 mode in the first-period circular arc-loaded resonant cavity to the second-period circular arc-loaded resonant cavity and suppress degenerate modes. The cross-section of the second periodic circular arc loading resonant cavity is the same as that of the first periodic circular arc loading resonant cavity; The central axis of the star-shaped coupling window coincides with the central axis of the large cylindrical cavity. The included angles of its two adjacent arms are the same, and one of the arms is parallel to the central axis of the rectangular coupling window, so that the TE011 mode in the second periodic arc-loaded resonant cavity excites the TE01 mode in the output circular waveguide. The output circular waveguide is used to output the TE01 mode to the subsequent devices.

2. The rectangular waveguide TE10 to circular waveguide TE01 mode conversion device as described in claim 1, characterized in that, Let R be the radius of the large cylindrical cavity, r be the radius of the small cylindrical cavity, and d be the center distance between the large and small cylindrical cavities. The range of d is: Rr < d < 2r.

3. The rectangular waveguide TE10 to circular waveguide TE01 mode conversion device as described in claim 2, characterized in that, The radius R of the large cylindrical cavity and the height of the two-order periodic circular arc-loaded resonant cavity are determined by the resonant frequency.

4. The rectangular waveguide TE10 to circular waveguide TE01 mode conversion device as described in claim 3, characterized in that, In the X-band, the radius R of the large cylindrical cavity ranges from 15mm to 40mm.

5. The rectangular waveguide TE10 to circular waveguide TE01 mode conversion device as described in claim 4, characterized in that, The arm length of the cross-shaped coupling window ranges from 30mm to 40mm, the arm width ranges from 4mm to 10mm, and the height ranges from 1mm to 5mm.

6. The rectangular waveguide TE10 to circular waveguide TE01 mode conversion device as described in claim 4, characterized in that, The arm length of the cross-shaped coupling window ranges from 30mm to 40mm, the arm width ranges from 1mm to 5mm, and the height ranges from 1mm to 5mm.

7. A rectangular waveguide TE10 to circular waveguide TE01 mode conversion device as described in any one of claims 3-6, characterized in that, The edges of the cross-shaped coupling window and the star-shaped coupling window are chamfered and smoothed to facilitate processing and avoid concentration of edge electric field intensity.

8. The rectangular waveguide TE10 to circular waveguide TE01 mode conversion device as described in claim 7, characterized in that, The mode conversion device is made of all-metal materials.

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