Coaxial-Rectangular Waveguide Mode Converter

Abstract

The present invention relates to the technical field of waveguides, and discloses a coaxial-rectangular waveguide mode converter to achieve bandwidth expansion and miniaturization of a back-fed T-type converter. The present invention includes: a rectangular waveguide with one end open and one end closed with a gap left for inserting a coaxial connector; a transition section structure disposed inside the rectangular waveguide; the coaxial connector includes a coaxial probe and a dielectric material embedded in the gap at the closed end of the rectangular waveguide, and the coaxial probe is connected to the transition section structure inside the rectangular waveguide; the transition section structure includes: a front rectangular impedance matching stub connected to the coaxial probe, the other end of the front rectangular impedance matching stub is connected to the rectangular gradient structure, and a part of the gradient spiral transition structure is embedded in the rectangular gradient structure; wherein, the layers of the suspended part of the gradient spiral transition structure extend outward in a trend from large to small, and the extension direction is parallel to the extension direction of the coaxial probe.

Description

Technical Field

[0001] The present invention relates to the technical field of waveguides, and particularly to a coaxial-rectangular waveguide mode converter. Background Art

[0002] The X-band (8 - 12 GHz) is a key research working frequency band in the field of high-power microwave antenna design. Within this frequency band, the state has stipulated two national standards for the port dimensions of rectangular waveguides, namely BJ-84 (6.57 - 9.99 GHz) and BJ-100 (8.2 - 12.5 GHz). The port dimensions of the BJ-84 standard waveguide are larger than those of the BJ-100 standard waveguide. For the application of a large-scale antenna array system operating in the target frequency band of 7.9 - 8.9 GHz, on the one hand, the rectangular waveguide with a BJ-84 port will greatly increase the size of the system, resulting in a reduction in the number of array elements of the high-power microwave antenna array, thereby reducing the gain of the array antenna; on the other hand, it will significantly increase the overall weight of the high-power microwave system, greatly restricting the portability of the high-power microwave system and the flexibility of the carrier platform. Therefore, a rectangular waveguide with a more compact BJ-100 standard port is used to feed the radiating antenna operating in the target frequency band of 7.9 - 8.9 GHz.

[0003] The existing -15 dB impedance bandwidth of the ladder structure converter designed based on the BJ-100 standard waveguide port can often cover a working frequency band of 2 - 4 GHz or even wider within the X-band. As an antenna is a passive band-pass filter, if its working frequency band is too wide, it will cause the antenna to receive electromagnetic waves in other frequency bands, or the electromagnetic waves emitted by the antenna will be received by terminals in other frequency bands, resulting in unnecessary electromagnetic interference. Therefore, it is necessary to design a special electromagnetic wave mode conversion device for the antenna operating in the target frequency band.

[0004] The existing coaxial-rectangular waveguide converter design generally uses a coaxial probe mounted directly above the waveguide for vertical top-feed feeding. In the application of a large antenna array system, this type of coaxial-rectangular waveguide is not conducive to the integration with the devices at the back end of the high-power microwave system equipped with complex wire harnesses. Therefore, it is necessary to design a back-feed coaxial-rectangular waveguide converter.

[0005] The electromagnetic wave radiation modes and characteristic impedances required for different microwave transmission lines are different. The coaxial line requires TEM mode radiation with a characteristic impedance of 50 Ω, while the rectangular waveguide requires TE10 mode radiation with a characteristic impedance usually greater than 120 Ω. Directly integrating the coaxial line in a back-feed manner behind the rectangular waveguide cannot effectively excite the TE10 mode radiation of the rectangular waveguide. Therefore, it is necessary to specifically design a transition structure between the coaxial and rectangular waveguides to achieve impedance matching and mode conversion between different transmission lines.

[0006] By summarizing the research on the publicly available high-power microwave coaxial-rectangular waveguide mode converters, it is found that the existing high-power microwave converters are divided into two methods: one is the T-type converter with a T-type structure set inside the rectangular waveguide. When using the vertical top-feed feeding method, the T-type converter cannot be integrated with a large antenna array; while when using the back-feed feeding method, the bandwidth of the T-type converter is too narrow to meet the basic bandwidth requirements of the target frequency band. To achieve a back-fed high-power broadband performance mode conversion device, the general method is to design an N-order stepped structure based on the Chebyshev response N-order λ⁄4 impedance transformation method to achieve broadband TEM-TE10 mode conversion between the coaxial line and the rectangular waveguide. The implementation principle is as follows:

[0007] Insert the coaxial line into the rectangular waveguide to excite the TEM characteristic impedance value of the coaxial line in the rectangular waveguide, which is:

[0008] ;

[0009] Where, and are the input impedance of the coaxial line and the relative permittivity of the dielectric material of the coaxial line respectively, and are the inner diameter and outer diameter of the coaxial line respectively. The characteristic impedance of the main mode TE10 inside the rectangular waveguide is calculated as:

[0010] ;

[0011] Where, λ is the relative wavelength when the microwave device is working. From the Chebyshev response N-order λ⁄4 impedance transformation method, the transformation ratio of the characteristic impedance from the coaxial line to the rectangular waveguide can be obtained as:

[0012] ;

[0013] The relative bandwidth is:

[0014] ;

[0015] Where, and represent the relative wavelengths corresponding to the starting and cut-off frequencies respectively. The above formulas can determine the order N of the Chebyshev-type impedance converter as:

[0016] ;

[0017] Where, is the maximum reflection coefficient in the frequency band, is the floor function, is the inverse hyperbolic cosine function, It is a cosecant function.

[0018] The advantages of the N - order stepped - structure impedance transformation converter are simple structure and easy to process in kind. However, its disadvantage is that the number of steps N is generally 3 or 4, which considerably increases the longitudinal dimension of the rectangular waveguide and causes a relatively large burden in terms of size and weight when applied in an array system.

[0019] Therefore, it is necessary to design a new structure to optimize or even replace the traditional N - order rectangular stepped structure. Summary of the Invention

[0020] The object of the present invention is to disclose a coaxial - rectangular waveguide mode converter to achieve bandwidth expansion and miniaturization of a back - fed T - type converter.

[0021] To achieve the above object, the coaxial - rectangular waveguide mode converter disclosed by the present invention includes:

[0022] A rectangular waveguide with one end open and the other end closed with a gap left for inserting a coaxial connector;

[0023] A transition - section structure disposed inside the rectangular waveguide;

[0024] The coaxial connector includes a coaxial probe and a dielectric material embedded in the gap at the closed end of the rectangular waveguide, and the coaxial probe is connected to the transition - section structure inside the rectangular waveguide;

[0025] The transition - section structure includes: a pre - set rectangular impedance - matching stub connected to the coaxial probe, the other end of the pre - set rectangular impedance - matching stub is connected to a rectangular tapering structure, and a part of a gradually - varying spiral - type transition structure is embedded in the rectangular tapering structure; wherein, the circles of the suspended part of the gradually - varying spiral - type transition structure extend outward in a trend from large to small, and the extending direction is parallel to the extending direction of the coaxial probe.

[0026] Preferably, the rectangular tapering structure includes a first rectangular impedance - matching stub connected to the rectangular waveguide, a second rectangular impedance - matching stub sleeved around the middle part of the first rectangular impedance - matching stub, the bottom surface of the second rectangular impedance - matching stub is connected to a third rectangular impedance - matching stub, the side surface of the second rectangular impedance - matching stub is connected to the pre - set rectangular impedance - matching stub, and the bottom surface of the third rectangular impedance - matching stub is connected to a fourth rectangular impedance - matching stub; the areas of the horizontal cross - sections of the fourth rectangular impedance - matching stub, the third rectangular impedance - matching stub, and the second rectangular impedance - matching stub gradually change in a trend from small to large; and the gradually - varying spiral - type transition structure is embedded in the second rectangular impedance - matching stub.

[0027] Preferably, the gradually - varying spiral equation of the spiral - type transition structure is:

[0028] ;

[0029] Among them, is the initial radius of the helix, is the helix rising angle, is the number of turns of the helix coil, , and respectively represent the three directions of the three-dimensional coordinate system. The origin of the coordinate system is the center point of the closed end of the rectangular waveguide. The direction is the direction in which the layers of the suspended part of the tapered spiral transition structure perpendicular to the closed end extend outward in a trend from large to small.

[0030] Preferably, the number of turns of the tapered spiral transition structure is between 3 and 4.

[0031] Preferably, the tapered spiral transition structure and the second rectangular impedance matching stub form two fixed fulcrums, and the number of turns of the helix is 3.2.

[0032] Preferably, the area of the vertical cross-section of the front rectangular impedance matching stub is smaller than the area of the vertical cross-section of the second rectangular impedance matching stub.

[0033] Preferably, the coaxial probe uses a cylindrical metal rod, and the dielectric material uses PTFE (Polytetrafluoroethylene) with a dielectric constant of 2.2.

[0034] Preferably, the port of the rectangular waveguide conforms to the national standard of the BJ-100 model, and a chamfer for preventing electric breakdown is provided at the open end.

[0035] Preferably, the part other than the spiral transition structure is symmetric about the left and right.

[0036] Preferably, the rectangular waveguide has a longitudinal length of 18.3 mm in the direction;

[0037] The coaxial probe uses a cylindrical metal rod with a radius of 0.61 mm, and the insertion depth into the rectangular waveguide is 3 mm;

[0038] The front rectangular impedance matching stub has dimensions of 9.85 mm, 2.1 mm, and 2.45 mm in the , and directions respectively;

[0039] The first rectangular impedance matching stub has dimensions of , and The dimensions in the

[0040] direction are 22.86 mm, 1.6 mm and 5 mm respectively; , and The dimensions in the

[0041] direction are 16 mm, 2 mm and 6.2 mm respectively; , and The dimensions in the

[0042] direction are 17.2 mm, 2.3 mm and 4.3 mm respectively; , and The dimensions in the

[0043] direction are 9.84 mm, 4.26 mm and 2.45 mm respectively; The initial radius, cross-sectional length, cross-sectional width, rising angle and number of turns of the tapered spiral transition structure are 10 mm, 0.3 mm, 0.15 mm, 19° and 3.2 turns respectively; The starting point coordinates are (6.37 mm, 0 mm, 9.7 mm).

[0044] The present invention has the following beneficial effects:

[0045] 1. It can achieve impedance matching between a coaxial cable and a rectangular waveguide with BJ-100 port standard within the X-band (7.9 - 8.9 GHz), and provide a suitable electromagnetic wave radiation pattern for the radiating antenna.

[0046] 2. By using a tapered spiral structure to replace the traditional N-order rectangular stepped structure and loading it on the T-type converter, the problems that the vertical top-fed T-type coaxial-rectangular waveguide converter cannot be applied in a large high-power microwave array and the back-fed T-type coaxial-rectangular waveguide converter has a too narrow bandwidth are solved. Compared with the traditional N-order stepped transition section, the longitudinal dimension of the rectangular waveguide is reduced, and the miniaturization of the back-fed converter is realized.

[0047] 3. The technology of the present invention can be extended to applications in high-power microwave scenarios such as radar detection, directed energy illumination, and high-energy particle radio frequency acceleration. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0049] Figure 1It is a three-dimensional solid diagram of the coaxial-rectangular waveguide mode converter disclosed in the embodiments of the present invention.

[0050] Figure 2 It is a left sectional view of the coaxial-rectangular waveguide mode converter disclosed in the embodiments of the present invention.

[0051] Figure 3 It is a front view of the coaxial-rectangular waveguide mode converter disclosed in the embodiments of the present invention.

[0052] Figure 4 It is a top view of the coaxial-rectangular waveguide mode converter disclosed in the embodiments of the present invention.

[0053] Figure 5 It is a schematic diagram of the simulation results of the S-parameters (i.e., return loss) of the solution disclosed in the embodiments of the present invention and the comparative embodiments. Among them, the anchor points numbered 1 and 2 respectively represent the simulation results corresponding to the starting frequency and the cut-off frequency at which the converter operates.

[0054] Figure 6 It is a schematic diagram of the simulation results of the variation of the maximum electric field strength with frequency in the single-support and double-support modes disclosed in the embodiments of the present invention. Detailed implementation manners

[0055] The following will describe the embodiments of the present invention in detail with reference to the accompanying drawings. However, the present invention can be implemented in many different ways defined and covered by the claims.

[0056] Embodiment 1

[0057] Based on the back-fed T-type converter, this embodiment draws on the design idea of the Chebyshev N-order stepped transition section, realizing the bandwidth expansion of the back-fed T-type converter and the miniaturization of the device relative to the N-order stepped transition section, so as to facilitate integration in the antenna system.

[0058] Refer to Figures 1 to 4 , the coaxial-rectangular waveguide mode converter 100 in this embodiment includes:

[0059] A rectangular waveguide 1 with one end open and the other end closed with a gap for inserting a coaxial connector. Preferably, a chamfer is provided at the open end to prevent electric breakdown.

[0060] A transition section structure disposed inside the rectangular waveguide.

[0061] The coaxial connector includes a coaxial probe 2 and a dielectric material 3 embedded in the gap at the closed end of the rectangular waveguide. The coaxial probe is connected to the transition section structure inside the rectangular waveguide. The coaxial probe can be a cylindrical metal rod, and the dielectric material and the coaxial probe are combined to form a coaxial connector to realize a 50Ω feeding structure. Optionally, there is a circular groove with the same size as the dielectric sleeve at the closed end of the rectangular waveguide, and the dielectric sleeve contacts the closed end of the rectangular waveguide through the circular groove.

[0062] The transition section structure includes: a front rectangular impedance matching stub 4 connected to a coaxial probe, the other end of the front rectangular impedance matching stub is connected to a rectangular tapered structure, and a partial structure of a tapered spiral transition structure 9 is embedded in the rectangular tapered structure; wherein, the layers of the suspended part of the tapered spiral transition structure extend outward in a trend from large to small, and the extending direction is parallel to the extending direction of the coaxial probe, that is: extending in the Z-axis direction from large size to small size.

[0063] Preferably, the rectangular tapered structure of this embodiment includes a first rectangular impedance matching stub 6 connected to a rectangular waveguide, a second rectangular impedance matching stub 5 sleeved around the middle part of the first rectangular impedance matching stub (in other words, both ends of the first rectangular impedance matching stub penetrate through the second rectangular impedance matching stub and are connected to the rectangular waveguide), the bottom surface of the second rectangular impedance matching stub is connected to a third rectangular impedance matching stub 7, the side surface of the second rectangular impedance matching stub is connected to the front rectangular impedance matching stub, and the bottom surface of the third rectangular impedance matching stub is connected to a fourth rectangular impedance matching stub 8; the areas of the horizontal cross-sections of the fourth rectangular impedance matching stub, the third rectangular impedance matching stub, and the second rectangular impedance matching stub gradually change in a trend from small to large; the tapered spiral transition structure is embedded in the second rectangular impedance matching stub.

[0064] In this embodiment, the tapered spiral equation of the spiral transition structure is:

[0065] ;

[0066] wherein, is the initial radius of the spiral, is the spiral rising angle, is the number of spiral turns, , and respectively represent the three directions of the three-dimensional coordinate system, the origin of the coordinate system is the center point of the closed end of the rectangular waveguide, The direction is the extending direction in which the layers of the suspended part of the tapered spiral transition structure perpendicular to the closed end extend outward in a trend from large to small.

[0067] Preferably, the part of the coaxial-rectangular waveguide mode converter disclosed in this embodiment, except for the spiral transition structure, is of a left-right symmetric structure, and the tapered spiral transition structure and the second rectangular impedance matching stub form two fixed fulcrums. Compared with the method of only fixing the starting end, on the one hand, the connection stability between the structures is strengthened. On the other hand, the double fulcrum has a higher power capacity and more excellent bandwidth performance than the single fulcrum (the bandwidth of the return loss of the single fulcrum support design is significantly smaller than the working bandwidth of the double support).

[0068] Preferably, the coaxial-rectangular waveguide mode converter in this embodiment is formed into a final product with the following dimensions.

[0069] The port of the rectangular waveguide conforms to the national standard of the BJ-100 model. The coaxial probe uses a cylindrical metal rod, and the dielectric material uses PTFE with a dielectric constant of 2.2.

[0070] The rectangular waveguide has a longitudinal length of 18.3 mm in the

[0071] The coaxial probe uses a cylindrical metal rod with a radius of 0.61 mm and is inserted into the rectangular waveguide to a depth of 3 mm.

[0072] The front rectangular impedance matching stub has dimensions of 9.85 mm, 2.1 mm, and 2.45 mm in the , and directions respectively.

[0073] The first rectangular impedance matching stub has dimensions of 22.86 mm, 1.6 mm, and 5 mm in the , and directions respectively.

[0074] The second rectangular impedance matching stub has dimensions of 16 mm, 2 mm, and 6.2 mm in the , and directions respectively.

[0075] The third rectangular impedance matching stub has dimensions of 17.2 mm, 2.3 mm, and 4.3 mm in the , and directions respectively.

[0076] The fourth rectangular impedance matching stub has dimensions of 9.84 mm, 4.26 mm, and 2.45 mm in the , and directions respectively.

[0077] The initial radius, cross-sectional length, cross-sectional width, rising angle, and number of turns of the tapered spiral transition structure are 10 mm, 0.3 mm, 0.15 mm, 19°, and 3.2 turns respectively; the starting point coordinates are (6.37 mm, 0 mm, 9.7 mm).

[0078] To prove the structural rationality and performance superiority of the above design dimensions of this embodiment, the following several groups of comparative tests were conducted:

[0079] Comparative Experiment 1: Conduct an electric field simulation and power capacity comparison between the single - support and double - support fixation modes of the gradient spiral transition structure and the second rectangular impedance - matching stub. Among them, in the single - support mode, the spiral line passes through the reserved channel of the second rectangular impedance - matching stub without contact; in the double - support mode, the middle section of the spiral line passing through the second rectangular impedance - matching stub after the starting point is integrated with the second rectangular impedance - matching stub.

[0080] Comparative Experiment 2: Conduct an electric field simulation comparison between the gradient spiral transition structure with single - support and double - support modes in this embodiment and a comparative product without using a gradient spiral transition structure.

[0081] Comparative Experiment 3: Conduct an electric field simulation comparison between this embodiment and a gradient spiral transition structure with a double - support mode without a pre - set rectangular impedance - matching stub.

[0082] Refer to Figure 5 and Figure 6 , through modeling and simulation comparison experiments, it can be obtained that:

[0083] 1. Adopting the technical solution of the present invention, both the double - support and single - support can meet the requirement that the - 15 dB impedance bandwidth can cover 7.36 - 9 GHz, meeting the target frequency band requirement index. When there is no pre - set rectangular impedance - matching stub or no spiral transition structure inside the mode converter, the return loss value of the mode converter cannot reach - 15 dB within the frequency band, so it cannot meet the requirement of mode conversion.

[0084] 2. The bandwidth of the return loss of the single - support design of the spiral transition structure on the rectangular transition structure is significantly smaller than the working bandwidth of the double - support (the present invention), that is, the superiority of the single - support mode in Comparative Experiment 1 is inferior to that of the double - support mode in terms of performance.

[0085] 3. Based on the simulation results of the electric field distribution at each frequency point of the embodiment and the comparative design, as well as the simulation results of the relationship between the power capacity value of the present invention and the frequency change. According to the calculation formula of the power capacity of the rectangular waveguide:

[0086]

[0087] Among them, is the input power, which is set to 0.5 W in the electromagnetic simulation software; is the breakdown field strength of air, which is 3×10^6 V / m; is the maximum electric field strength value inside the rectangular waveguide of the mode converter.

[0088] In this embodiment, the maximum simulated electric field value of the double-support mode within the target frequency band of 7.9 - 8.9 GHz is 23519 V / m. Therefore, according to the rectangular waveguide power capacity calculation formula, the lowest power capacity at each frequency point in this embodiment is 8135 W, which meets the design requirement of 8000 W for the high-power microwave system. Therefore, the present invention has a relatively high power capacity and conforms to the theoretical tolerance value in high-power microwave applications. For the single-support mode, within the target frequency band of 7.9 - 8.9 GHz, its maximum power capacity is 7081 W, which does not meet the requirement of the high-power microwave system for the power capacity of microwave devices.

[0089] In summary, the coaxial-rectangular waveguide mode converter disclosed in the embodiments of the present invention has at least the following beneficial effects:

[0090] 1. It can achieve impedance matching from the coaxial line to the rectangular waveguide of the BJ-100 port standard within the X-band (7.9 - 8.9 GHz) and provide a suitable electromagnetic wave radiation mode for the radiating antenna.

[0091] 2. By using a tapered spiral structure to replace the traditional N-order-rectangular step structure and loading it on the T-type converter, it solves the problems that the vertically top-fed T-type coaxial-rectangular waveguide converter cannot be applied in large high-power microwave arrays and the bandwidth of the back-fed T-type coaxial-rectangular waveguide converter is too narrow. Compared with the traditional N-order-step transition section, it reduces the longitudinal size of the rectangular waveguide and realizes the miniaturization of the back-fed converter.

[0092] 3. It can be extended to high-power microwave scenarios such as radar detection, directed energy irradiation, and high-energy particle radio frequency acceleration for application.

[0093] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A coaxial-rectangular waveguide mode converter, characterized in that: include: A rectangular waveguide, one end is open, the other end is closed and has a gap for the coaxial connector to be inserted; A transition section structure disposed inside the rectangular waveguide; The coaxial connector includes a coaxial probe and a dielectric material embedded in the closed end gap of the rectangular waveguide, and the coaxial probe is connected to the transition section structure inside the rectangular waveguide; The transition section structure includes: a front rectangular impedance matching branch connected to the coaxial probe, the other end of the front rectangular impedance matching branch is connected to a rectangular gradient structure, and a part of a gradient spiral transition structure is embedded in the rectangular gradient structure; wherein the circles of the suspended part of the gradient spiral transition structure extend outward in a trend from large to small, and the extension direction is parallel to the extension direction of the coaxial probe; the number of circles of the gradient spiral transition structure is a non-integer, and two fixed fulcrums are formed in the part embedded in the rectangular gradient structure, so that the lowest power capacity at each frequency point within the target frequency band of 7.9-8.9 GHz is greater than 8000 W.

2. The coaxial-rectangular waveguide mode converter according to claim 1, characterized in that: The rectangular gradient structure includes a first rectangular impedance matching branch connected to the rectangular waveguide, a second rectangular impedance matching branch sleeved on the periphery of the middle part of the first rectangular impedance matching branch, the bottom surface of the second rectangular impedance matching branch connected to the third rectangular impedance matching branch, the side surface of the second rectangular impedance matching branch connected to the front rectangular impedance matching branch, and the bottom surface of the third rectangular impedance matching branch connected to the fourth rectangular impedance matching branch; the horizontal cross-sectional areas of the fourth rectangular impedance matching branch, the third rectangular impedance matching branch and the second rectangular impedance matching branch gradually change from small to large; and the gradient spiral transition structure is embedded in the second rectangular impedance matching branch.

3. The coaxial-rectangular waveguide mode converter according to claim 2, characterized in that: The gradient spiral line equation of the gradient spiral transition structure is: ； in, is the initial radius of the helix, is the spiral rise angle, is the number of spiral coils, , and They represent the coordinates of the three directions of the three-dimensional coordinate system, respectively. The origin of the coordinate system is the center point of the closed end of the rectangular waveguide. The coordinate direction is the direction in which the circles of the suspended part of the gradual spiral transition structure perpendicular to the closed end extend outward in a trend from large to small.

4. The coaxial-rectangular waveguide mode converter according to claim 3, characterized in that: The number of spiral coils of the gradual spiral transition structure is between 3 and 4.

5. The coaxial-rectangular waveguide mode converter according to claim 4, characterized in that: The two fixed fulcrums are specifically formed by the gradual spiral transition structure and the second rectangular impedance matching branch, and the number of spiral coils is 3.

2.

6. The coaxial-rectangular waveguide mode converter according to claim 2, characterized in that: The area of ​​the vertical cross section of the front rectangular impedance matching branch is smaller than the area of ​​the vertical cross section of the second rectangular impedance matching branch.

7. The coaxial-rectangular waveguide mode converter according to any one of claims 2 to 6, characterized in that: The coaxial probe is a cylindrical metal rod, and the dielectric material is PTFE with a dielectric constant of 2.

2.

8. The coaxial-rectangular waveguide mode converter according to claim 7, characterized in that: The port of the rectangular waveguide complies with the national standard of the BJ-100 model, and the open end is provided with a chamfer to prevent electrical breakdown.

9. The coaxial-rectangular waveguide mode converter according to claim 8, characterized in that: The part other than the gradual spiral transition structure is a bilaterally symmetrical structure.

10. The coaxial-rectangular waveguide mode converter according to claim 9, characterized in that: The rectangular waveguide The longitudinal length in the direction is 18.3 mm; The coaxial probe is a cylindrical metal rod with a radius of 0.61 mm and is inserted into the rectangular waveguide to a depth of 3 mm; The front rectangular impedance matching branch is , and The dimensions in the directions are 9.85 mm, 2.1 mm, and 2.45 mm; The first rectangular impedance matching branch is , and The dimensions in the directions are 22.86 mm, 1.6 mm, and 5 mm; The second rectangular impedance matching branch is , and The dimensions in the directions are 16 mm, 2 mm, and 6.2 mm respectively; The third rectangular impedance matching branch is , and The dimensions in the directions are 17.2 mm, 2.3 mm, and 4.3 mm respectively; The fourth rectangular impedance matching branch is , and The dimensions in the directions are 9.84 mm, 4.26 mm, and 2.45 mm; The initial radius, section length, section width, rising angle and number of turns of the gradual spiral transition structure are 10 mm, 0.3 mm, 0.15 mm, 19° and 3.2 turns respectively; the starting point coordinates are (6.37 mm, 0 mm, 9.7 mm).

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