A TM01-TE11 mode converter for a twisted rectangular waveguide

Abstract

The application discloses a TM01-TE11 mode converter for twisting a rectangular waveguide, wherein a TM01-TE10 structure of an input section is a circle composed of four arc surfaces, the four arc surfaces are connected with a circular-arc-to-rectangular waveguide transition section; two adjacent output ports of the circular-arc-to-rectangular waveguide transition section are connected with a rectangular waveguide, and the other two adjacent output ports are connected with a 180-degree twisted rectangular waveguide section; four output ports of the rectangular waveguide and the 180-degree twisted rectangular waveguide section are respectively connected with four input ports of a bending waveguide section; the four output ports of the bending waveguide section are opposite to each other, the four output ports of the bending waveguide section are extended to intersect, and the intersection is connected with a combined output section for output. The application has high mode purity, high mode suppression degree, better isolation, high conversion efficiency and large relative bandwidth.

Description

Technical Field

[0001] This invention belongs to the field of microwave technology and relates to a TM01-TE11 mode converter with a twisted rectangular waveguide. Background Technology

[0002] High-power microwave generating devices, such as relativistic antiwave tubes and virtual cathode oscillators, typically output electromagnetic wave modes that are low-order and angularly uniformly distributed, such as the circular waveguide TM01 mode, TE01 mode, and coaxial TEM mode. While these modes facilitate the operation of the generating devices, they are not ideal for practical applications. This is because their electromagnetic fields diverge uniformly outward from the center, leading to low radiation efficiency, energy dispersion, and high sidelobe levels. These problems make them unsuitable for scenarios requiring efficient utilization of electromagnetic energy, such as heating plasma or long-distance transmission.

[0003] In contrast, circular waveguide TE11 mode electromagnetic waves are more commonly used in practical applications. These waves have concentrated energy in a vertical beam, resulting in high radiation efficiency, long transmission distance, and can be directly radiated using a horn antenna. Furthermore, in the high-power microwave field, there are many situations where it is necessary to convert the TM01 mode generated by the microwave source into other waveguide and mode forms. For example, during microwave transmission and coupling, it is often necessary to switch between circular and rectangular waveguides and generate rectangular TE10 modes to control the mode and increase power; some high-power microwave radiating antennas also require excitation with rectangular TE10 modes.

[0004] While common high-power waveguide mode converters can all achieve high-efficiency electromagnetic wave mode conversion, they still have different drawbacks such as narrow bandwidth, insufficient power capacity, large size, complex structure that is not easy to manufacture, and a large number of coupled high-order hybrid modes. Summary of the Invention

[0005] To address the shortcomings of the existing TM01-TE10 mode converter, such as narrow operating bandwidth and low noise mode suppression, a TM01-TE11 mode converter based on a twisted rectangular waveguide is proposed. Since the 180-degree phase twist of the signal in the twisted rectangular waveguide has broadband characteristics, the TM01-TE11 mode converter has the advantages of ultra-wideband and high efficiency.

[0006] A mode converter utilizing a torsion rectangular waveguide structure, wherein the torsion rectangular waveguide is applied in the mode converter, the mode converter includes an input segment TM01-TE10 structure, an arc-to-rectangular waveguide transition segment, a rectangular waveguide and a 180-degree torsion rectangular waveguide segment, a bent waveguide segment and a synthesized output segment.

[0007] The input segment TM01-TE10 is a standard circular waveguide. The output of the input segment TM01-TE10 is a circle composed of four arc-shaped surfaces, which connect to a transition section from a circular arc to a rectangular waveguide. Two adjacent output ports of the transition section connect to the rectangular waveguide, and the other two adjacent output ports connect to a 180-degree twisted rectangular waveguide segment. The rectangular waveguide and the 180-degree twisted rectangular waveguide segment have the same length. The four output ports of the rectangular waveguide and the 180-degree twisted rectangular waveguide segment are then connected to the four input ports of a bent waveguide segment. The four output ports of the bent waveguide segment are paired and extended until they intersect, where they are connected to a combined output segment.

[0008] Furthermore, a metal frustum is provided inward at the output end of the input segment TM01-TE10 structure, and a cross-shaped metal insert is inserted at the center of the bottom of the frustum.

[0009] Furthermore, the bent waveguide segment consists of a sequentially connected 90-degree outward-bending waveguide and two 90-degree inward-bending waveguides, with each pair of the three 90-degree bent waveguides connected by a straight waveguide. The three 90-degree bent waveguides are of identical dimensions.

[0010] Furthermore, the synthesized output segment is composed of a synthesized segment, a radius expansion segment, and an output segment connected in sequence. The synthesized segment is a four-way synthesizer. The four input terminals of the synthesized segment are extensions of the output terminals of the bent waveguide segment. A metal matching block is set at the intersection center of the synthesized segment and the extended output terminals of the bent waveguide segment. The output terminal is a circular waveguide.

[0011] Furthermore, the radius of the synthesized segment is smaller than the cutoff wavelength of the TE11 mode transmitted within the synthesized segment. The radius of the synthesized segment is expanded to match that of the output segment through the radius expansion segment. The radius of the output segment is consistent with the radius of the input segment TM01-TE10 structure, thus achieving consistent dimensions of the input and output circular waveguides of the mode converter.

[0012] Advantages or beneficial effects of this application:

[0013] This invention proposes a novel TM01-TE11 mode converter. This mode converter utilizes a torn rectangular waveguide to alter the electromagnetic wave polarization direction, ensuring that the electromagnetic wave polarization directions at the four output ports of the bent waveguide section satisfy the TE11 mode synthesis conditions. Simultaneously, the rectangular waveguide offers advantages such as single propagation within the operating frequency range, high mode purity, high clutter mode suppression, and better isolation. Furthermore, the torn and bent waveguide sections enable coaxial operation of the input and output ports, making it better suited for high-power microwave transmission and application.

[0014] Introducing a torsion rectangular waveguide into the design of a mode converter provides a solution to common problems in mode converters, such as low mode conversion efficiency, poor suppression of higher-order modes, and narrow operating bandwidth. Furthermore, this structure is simple to design and easy to fabricate and assemble. This mode converter boasts advantages such as high conversion efficiency and relatively large bandwidth. Compared to traditional three-bend mode converters, it offers advantages such as simpler design and easier operation for different operating frequencies. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the mode converter;

[0016] Figure 2 Right view of the input segment TM01-TE10 structure;

[0017] Figure 3 This is a schematic diagram of the input segment TM01-TE10;

[0018] Figure 4 Schematic diagram of a 180-degree twisted rectangular waveguide;

[0019] Figure 5 Schematic diagram of the bent waveguide section and the synthesized output section;

[0020] Figure 6 Right view of the synthesized output segment;

[0021] Figure 7 The electric field distribution diagram of the mode converter;

[0022] Figure 8 The simulation results for S11 and S21 of the mode converter are shown in the figure. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in conjunction with the following specific embodiments and the accompanying drawings. These embodiments are merely illustrative, and the claims are not limited to these embodiments.

[0024] This embodiment provides a mode converter for a circular waveguide TM01 to TE11 with a center frequency of 9 GHz, and the input structure is as follows. Figure 1 As shown, it includes an input segment TM01-TE10 structure 1, a metal frustum 2 and a cross-shaped metal insert 3 inside the input segment circular waveguide, a transition structure 4 from circular arc to rectangular waveguide, a rectangular waveguide structure 5 and a 180-degree twisted rectangular waveguide structure 6, an inwardly bent 90-degree waveguide structure 7, inwardly bent 90-degree waveguide structures 8 and 9, a straight waveguide segment 10 and a synthesis structure 12, a matching block 11 for mode synthesis conversion inside the synthesis structure, a radius expansion structure 13 and an output port 14.

[0025] The input segment TM01-TE10 structure 1 includes a circular waveguide input port and four arc-shaped TE10 mode output ports. A metal frustum is positioned inwards from the circular waveguide output port of the input segment TM01-TE10 structure to convert the TM01 mode input from the circular waveguide. A cross-shaped metal plate is inserted at the center of the bottom of the frustum to evenly divide the converted mode into four equal parts. The electric field distribution of the input TM01 mode is axisymmetric, with only r and z components in the cylindrical coordinate system. Upon encountering the metal frustum built into the circular waveguide, a small amount of electromagnetic wave is reflected, while the remainder is converted into the TEM mode after passing through the metal frustum. The electric field distribution of the TEM mode has only a r component in the cylindrical coordinate system. The TEM mode is then divided into four equal arc-shaped TE10 modes by the cross-shaped metal plate. A transition section from the arc to the rectangular waveguide is connected at the output end.

[0026] The arc-to-rectangular waveguide transition section 4 smoothly transitions the four-part arc surface output from the TM01-TE10 input structure to a rectangular shape, facilitating the subsequent design of waveguide torsion and combining structures. Simultaneously, the TE10 mode electromagnetic wave propagates singly within this structure, allowing for a low-loss transition of the TE10 mode output from the TM01-TE10 input structure into the rectangular waveguide. Two adjacent output ports of the arc-to-rectangular waveguide transition section connect to the rectangular waveguide 5, and the other two adjacent ports connect to the 180-degree torsion rectangular waveguide 6. The rectangular waveguide and the 180-degree torsion rectangular waveguide section have the same length.

[0027] The rectangular waveguide and 180-degree twisted rectangular waveguide segments consist of two straight rectangular waveguides and two 180-degree twisted rectangular waveguides, connecting the output ports of the transition section from the circular arc to the rectangular waveguide. The two straight rectangular waveguide segments are adjacent, and the two 180-degree twisted rectangular waveguide segments are adjacent. The 180-degree twisted rectangular waveguides alter the polarization direction of the propagating electromagnetic field, making it opposite to the polarization direction of the electromagnetic field output from the rectangular waveguide. Simultaneously, the loss of the 180-degree twisted rectangular waveguide is negligible compared to the rectangular waveguide. In the input segment TM01-TE10 structure, the input TM01 mode is divided and transformed into four equal parts, each with opposite polarization directions, forming the TE10 mode.

[0028] The four output ports of the rectangular waveguide and the 180-degree twisted rectangular waveguide segment are followed by a bent waveguide segment. The bent waveguide segment contains three 90-degree bent waveguides and two straight waveguides, achieving a 270-degree bend in the four output ports. The output surfaces of the four output ports face each other and are connected to the input of the synthesized output segment.

[0029] The bent waveguide consists of one outwardly bent 90-degree waveguide and two inwardly bent 90-degree waveguides connected in sequence, with each pair of the three 90-degree bent waveguides connected by a straight waveguide. The three 90-degree bent waveguides are of the same size.

[0030] The synthesizing section is a four-way synthesizer. Its four inputs are extensions of the output of the bent waveguide section. A metal matching block is placed at the intersection of the synthesizing section and the extended output of the bent waveguide section. The output is a circular waveguide. The synthesizing output section contains a matching block 11 for synthesizing and conversion. The matching block structure consists of a metal cylinder at the bottom and a metal cone on top of the cylinder. The radius of the synthesizing output section is smaller than the radius of the input section TM01-TE10 structure. Then, a radius-enlarging section 13 expands the radius to match the radius of the input section TM01-TE10 structure, ensuring that the input and output dimensions are identical.

[0031] In this example, the input and output circular waveguide radii of the mode converter are both 24.75 mm, which is a standard overmode circular waveguide size. The input port circular waveguide section incorporates a metal frustum for mode conversion, the structure of which is as follows... Figure 2 As shown in structure 2, the frustum has a top radius of 10mm, a bottom radius of 14mm, and a height of 16mm. When the input electromagnetic wave signal encounters the metal frustum, a small amount of electromagnetic waves are reflected, while the rest are converted into TEM mode. A cross-shaped metal insert is embedded at the end of the frustum, as shown in the structure. Figure 2 As shown in structure 3, the insert plate is 0.5mm thick and has a curved front end, as... Figure 3 Structure 3 has an embedding depth of 2mm. The curved insert can more easily connect the arc to the rectangular waveguide transition section and the input section TM01-TE10 structure, while avoiding excessively high field strength inside the waveguide, which would lead to a decrease in power capacity.

[0032] A small portion of the electromagnetic waves is reflected by the cross-shaped metal plate, while the remaining waves are divided into four equal circular arcs, forming the TE01 mode. A transition section from the circular arcs to the rectangular waveguide connects these four arc segments. This transition section converts the circular arc TE10 mode to the rectangular TE10 mode. The rectangular waveguide has a cross-section of 23mm in length and 10.7mm in width, slightly larger than the standard rectangular WR90, ensuring electromagnetic wave propagation within the mode converter's operating frequency range. The output end of the transition section is vertically higher than the input end to ensure that adjacent twisted waveguides avoid structural interference when the subsequent rectangular waveguide is twisted 180 degrees.

[0033] like Figures 4 to 6As shown, after the arc-to-rectangular waveguide transition section, a rectangular waveguide and a 180-degree twisted rectangular waveguide section are connected. The cross-sectional dimensions of the waveguides remain consistent. The 180-degree twisted rectangular waveguide can change the polarization direction of the TE10 mode. The introduction of the 180-degree twisted rectangular waveguide into the design of this mode converter, after matching the size of the subsequent synthesized output section, also gives the mode converter a large operating bandwidth. Three 90-degree bent waveguides and a straight waveguide are connected to the output port to change the direction of the output port so that it can be connected to the input of the synthesized output section.

[0034] The synthesized output section is limited by the size of the input port. The circular waveguide size of the output port is inconsistent with the circular waveguide size of the input port of the mode converter, which will lead to a port size mismatch when connected to the microwave system. By expanding the circular waveguide size of the synthesized output section to match that of the input port through a radius enlargement section, the transmitted mode is the circular waveguide master mode, so there is almost no loss.

[0035] The electric field strength of the mode converter at the center frequency is as follows: Figure 7 As shown, under the condition of a vacuum inside the mode converter, with a breakdown field strength of a smaller value of 100 MV / m, the power capacity of the mode converter is 697 MW. The simulation results of the mode converter are as follows... Figure 8 As shown, the frequency range with a conversion efficiency of over 98.5% is 7.83GHz-10.29GHz, with an absolute bandwidth of 2.46GHz and a relative bandwidth of 27.15%, achieving ultra-wideband mode conversion efficiency in the X-band, and a return loss S11 below -20dB. In summary, the circular waveguide TM01-TE11 mode converter provided in this embodiment achieves low-loss, ultra-wideband mode conversion from TM01 mode to TE11 mode. It has the advantages of simple design, easy fabrication, low energy leakage, high mode purity, low conversion loss, and ultra-wideband capability.

[0036] This invention divides the TM01 mode into four equal parts, forming the TE10 mode within a rectangular waveguide. A 180-degree twisted rectangular waveguide is used to change the polarization direction of the electromagnetic waves within the waveguide. The resulting output is then synthesized into the TE11 mode via a synthesis output segment, thus completing the conversion from TM01 to TE11 modes. By introducing a twisted rectangular waveguide structure into the mode converter, ultra-wideband mode conversion is achieved.

Claims

1. A TM01-TE11 mode converter based on a twisted rectangular waveguide, characterized in that, It includes the input segment TM01-TE10 structure, the arc-to-rectangular waveguide transition segment, the rectangular waveguide and 180-degree twisted rectangular waveguide segment, the bent waveguide segment, and the synthesized output segment; The input segment TM01-TE10 is a circular waveguide, consisting of four arc-shaped surfaces connected to a transition section from the circular arc to the rectangular waveguide. Two adjacent output ports of the transition section are connected to the rectangular waveguide, and the other two adjacent output ports are connected to a 180-degree twisted rectangular waveguide segment. The rectangular waveguide and the 180-degree twisted rectangular waveguide segment have the same length. The four output ports of the rectangular waveguide and the 180-degree twisted rectangular waveguide segment are connected to the four input ports of the bent waveguide segment. The four output ports of the bent waveguide segment are paired and extended to intersect, and a combined output segment is connected at the intersection.

2. The TM01-TE11 mode converter with a twisted rectangular waveguide according to claim 1, characterized in that, The output end of the input segment TM01-TE10 structure has a metal frustum facing inward, and a cross-shaped metal insert is inserted at the center of the bottom of the frustum.

3. The TM01-TE11 mode converter with a twisted rectangular waveguide according to claim 2, characterized in that, The bent waveguide segment consists of a 90-degree outward-bending waveguide and two 90-degree inward-bending waveguides connected in sequence, and the three 90-degree bent waveguides are connected to each other by a straight waveguide. The three 90-degree bend waveguides are the same size.

4. The TM01-TE11 mode converter with a twisted rectangular waveguide according to claim 3, characterized in that, The synthesized output segment consists of a synthesized segment, a radius expansion segment, and an output segment connected in sequence. The synthesized segment is a four-way synthesizer. The four input terminals of the synthesized segment are extensions of the output terminals of the bent waveguide segment. A metal matching block is set at the intersection center of the synthesized segment and the extended output terminals of the bent waveguide segment. The output terminal of the synthesized segment is a circular waveguide.

5. The TM01-TE11 mode converter with a twisted rectangular waveguide according to claim 4, characterized in that, The radius of the synthesized segment is smaller than the cutoff wavelength of the TE11 mode transmitted within the synthesized segment. The radius of the synthesized segment is expanded to match that of the output segment through the radius expansion segment. The radius of the output segment is consistent with the radius of the input segment TM01-TE10 structure, thus achieving consistent dimensions of the input and output circular waveguides of the mode converter.

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