Directional coupler suitable for gradient circular waveguide microwave power measurement and power measurement method

Abstract

The invention discloses a directional coupler suitable for gradient circular waveguide microwave power measurement and a power measurement method.The directional coupler comprises a circular waveguide gradient transition section of a cone structure, the two ends of the gradient transition section are connected with circular straight waveguide sections of different diameters respectively, and a rectangular coupling cavity is formed in the upper portion of the outer wall of the circular waveguide gradient transition section; coaxial interfaces with different coupling degrees are respectively arranged at the two ends of the rectangular coupling cavity, and the rectangular coupling cavity is used for coupling microwave signals transmitted by the circular waveguide and coupling TE11 or TM01 mode microwaves transmitted by the circular waveguide to a coaxial TEM mode. The directional coupler has the advantages of being high in coupling degree, high in power capacity, good in directionality and the like, overcomes the defects that an existing directional coupler is complex in structure, low in coupling degree, low in power capacity, poor in directionality and the like, and can directly convert a TE11 mode or a TM01 mode transmitted by the circular waveguide into a coaxial TEM mode on the circular waveguide transition section to be coupled to a coaxial interface. And directional coupling and measurement of high-power microwaves are realized.

Description

Technical Field

[0001] The invention relates to the technical field of high-power microwave measurement, and in particular to a directional coupler suitable for gradual circular waveguide microwave power measurement and a power measurement method. Background Art

[0002] In microwave systems, directional couplers are a widely used microwave component. For example, directional couplers are used in power monitoring devices in signal generators and mixers in receivers. Couplers can be divided into waveguide, microstrip and other forms according to different structures. In power online measurement systems, waveguide coupling is often used to couple out some microwaves from the waveguide. According to different coupling methods, they can be divided into pinhole coupling, cross coupling, slot coupling and the like. Usually, directional couplers in waveguides through cross coupling, slot coupling and the like often have complex structures, resulting in high processing difficulties and narrow operating frequency bands. Pinhole coupling has the advantages of simple structure, good directivity and small coupling degree swing within the frequency band, and is more commonly used in waveguide couplers. The theoretical basis of the design of aperture directional couplers is mainly the small hole diffraction theory and the phase superposition principle. The small hole diffraction theory was proposed by HA Bethe [Bethe H A. Theory of diffraction by small holes], and R. Levy et al. [Levy R, Analysis and synthesis of waveguide multi-aperture directional couplers] conducted in-depth research on the aperture coupling theory and made a series of improvements and enhancements.

[0003] Although the research on directional couplers at home and abroad has been going on for a long time and there are many types, in the field of high-power microwaves, directional couplers need to have higher power capacity. There are few studies on small-hole directional couplers designed for circular waveguides, which are a commonly used microwave transmission form in high-power microwaves. There are also relatively few literatures on the use of hole-coupled directional couplers for high-power microwave measurements.

[0004] Cao Naisheng et al. [Design of circular waveguide-rectangular waveguide small hole coupled directional coupler] designed a circular waveguide-rectangular waveguide small hole directional coupler for high-power microwave output power measurement. They analyzed the coupling conditions using weak coupling theory and concluded that a multi-hole coupler can only have directional coupling if the reverse phase cancellation condition is met. They also designed a TE based on this structure. 01 -TE 10 Double hole directional coupler. However, the coupling degree of this structure is low, ranging from 33.8 to 36.5 dB, and is only applicable to circular waveguide TE 01 mode, not suitable for circular waveguide transmission, commonly used transmission main mode TE 11 and axisymmetric mode TM 01model.

[0005] Zhang Cuicui et al. [Design of high-power microwave broadband waveguide directional coupler] designed an X-band broadband waveguide coupler to meet the needs of high-power microwave measurement. The porous coupling structure was used and the Chebyshev distribution was optimized to obtain a coupler with a measured coupling degree of 38-39dB and a directivity better than 30dB. However, this structure is only suitable for rectangular waveguides and has a low power capacity, which can only meet the coupling measurement of MW-level power.

[0006] Sun Jun et al. [Application of circular waveguide directional coupler in high-power microwave measurement] established an X-band circular waveguide directional coupler with a six-aperture coupling model based on multi-aperture coupling technology. In the designed 9.2-10 GHz frequency band, the coupling degree is stable within (55±2) dB, the isolation is greater than 80 dB, and the power capacity can meet the GW-level measurement requirements. Liu Guo et al. [Design of high-power circular waveguide multi-aperture array directional coupler] proposed the design concept of composite aperture array by combining the characteristics of equal aperture distribution and Chebyshev distribution, and completed the analysis of the 8-aperture special aperture array distribution, which not only ensured that the coupling degree had a small fluctuation within the band, but also took into account the requirements of directivity. However, the above structure only couples simple circular straight waveguides, and has not yet considered the coupling measurement of the transition gradient section of the circular waveguide in the form of a cone section (the input and output port diameters are inconsistent).

[0007] Chinese patent application 202121390132.1 discloses a microwave broadband cavity coupler. Although directional coupling is achieved in the range of 700 to 6000 MHz, the main waveguide is small in size, so the power capacity is only in the kW range. Chinese patent application 201610586421.6 discloses a directional coupler for measuring microwave power of a gyrotron traveling wave tube and a manufacturing method for the directional coupler. The main waveguide is a circular waveguide, the auxiliary waveguide is a rectangular waveguide, the power capacity is in the order of hundreds of kilowatts, and the coupled output end is a rectangular waveguide. After power coupling is achieved, waveguide coaxial conversion is required to perform power measurement, and the structure is relatively complex.

[0008] In summary, there are few studies on circular waveguide directional couplers based on hole coupling theory at home and abroad, and they generally have defects such as low power capacity, low coupling degree or complex structure, which are not suitable for simple measurement of GW-level high-power microwaves. In addition, the designed circular waveguide directional couplers can only be used for simple circular straight waveguides, and the directional coupling measurement of irregular circular waveguide transition sections is not considered. Summary of the invention

[0009] The technical problem to be solved by the present invention is to overcome the shortcomings of circular waveguide directional couplers such as complex structure, low power capacity, low coupling degree, and poor directivity, and to provide a circular waveguide high-power microwave directional coupler and a power measurement method which is suitable for a transition gradient section structure and has a simple auxiliary waveguide structure and can directly perform power coupling measurement, and which combines the gradient circular waveguide directional coupling with the stripline structure so that the electromagnetic field TE transmitted by the gradient circular waveguide is 11 ,TM 01 The modes are coupled and converted into TEM modes on the coaxial interface of the stripline structure, realizing simple online coupling measurement of high-power microwaves.

[0010] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0011] A directional coupler suitable for measuring microwave power of a tapered circular waveguide comprises a first circular straight waveguide section, a circular waveguide tapered transition section and a second circular straight waveguide section which are connected in sequence, wherein the circular waveguide tapered transition section is in a cone structure and is used to realize the transition of microwave transmission of circular waveguides with different diameters, a rectangular coupling cavity is arranged above the outer wall of the circular waveguide tapered transition section, a first coaxial interface and a second coaxial interface are arranged at two ends of the rectangular coupling cavity, the rectangular coupling cavity is used to couple the microwave signal transmitted by the circular waveguide, and make the TE of the circular waveguide transmission 11 or TM 01 The microwaves of the mode are coupled to the first coaxial interface and the second coaxial interface and converted into the TEM mode; the first coaxial interface and the second coaxial interface are used to connect the directional coupler with the external measurement interface, and the first coaxial interface and the second coaxial interface are respectively coupled with microwaves through different coupling degrees to realize the directionality of the coupler.

[0012] As a further improvement of the present invention, a plurality of equidistantly distributed coupling holes are provided between the circular waveguide gradual transition section and the rectangular coupling cavity, and the apertures and depths of the coupling holes are different, and microwave energy is coupled by hole coupling.

[0013] As a further improvement of the present invention, chamfers are provided on both inner and outer wall surfaces of the coupling hole located in the circular waveguide gradual transition section.

[0014] As a further improvement of the present invention, the rectangular coupling cavity includes an inner conductor and an outer conductor, the outer conductor adopts a rectangular waveguide structure, the inner conductor is arranged inside the outer conductor, and the two ends of the inner conductor are respectively connected to the first coaxial interface and the second coaxial interface to realize the microwave electromagnetic field mode of waveguide transmission by the circular waveguide TE 11 or TM 01 mode is converted to coaxial TEM mode.

[0015] As a further improvement of the present invention, the first coaxial interface includes a first coaxial cylindrical inner core, a first medium and a first coaxial cylindrical outer conductor, the first coaxial cylindrical inner core is connected to the end of the inner conductor, and the first coaxial cylindrical inner core is nested inside the first coaxial cylindrical outer conductor through the first medium.

[0016] As a further improvement of the present invention, the second coaxial interface includes a second coaxial cylindrical inner core, a second medium and a second coaxial cylindrical outer conductor, the second coaxial cylindrical inner core is connected to the end of the inner conductor, and the second coaxial cylindrical inner core is nested inside the second coaxial cylindrical outer conductor through the second medium.

[0017] As a further improvement of the present invention, both the first medium and the second medium are made of polytetrafluoroethylene material.

[0018] As a further improvement of the present invention, the inner conductor is in a "concave"-shaped structure, and chamfers are provided at outer corners of the inner conductor.

[0019] As a further improvement of the present invention, chamfers are provided at the inner wall corners of the outer conductor.

[0020] As a further improvement of the present invention, the diameters of the first circular straight waveguide section and the second circular straight waveguide section are inconsistent, the first circular straight waveguide section is used to connect the microwave source input end, and the second circular straight waveguide section is used to connect the microwave output end.

[0021] As a general technical concept, the present invention also provides a power measurement method based on the above-mentioned directional coupler suitable for gradient circular waveguide microwave power measurement, wherein the first coaxial interface is connected to the microwave cable, and the output power P1 and coupling degree C0 of the first coaxial interface are tested, thereby calculating the transmission power P0 of the main waveguide.

[0022] P0=P1×10 -C0 / 10 .

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] 1. The directional coupler for measuring microwave power of a tapered circular waveguide is characterized in that the first straight circular waveguide section and the second straight circular waveguide section are connected at both ends of the tapered circular waveguide tapered transition section, and a rectangular coupling cavity is provided above the outer wall of the circular waveguide tapered transition section, and the first coaxial interface and the second coaxial interface are provided at both ends of the rectangular coupling cavity, so that a circular waveguide high-power microwave directional coupler with a simple and compact structure is formed, which can be directly applied to the circular waveguide transition section and is also suitable for circular waveguide TE 11 and TM 01 The coupling measurement of the mode realizes the circular waveguide TE 11 or TM 01The directional coupler of the present invention has broad application prospects in high-power microwave measurement applications due to the efficient coupling transmission of the mode to the coaxial TEM mode.

[0025] 2. The directional coupler of the present invention, which is suitable for measuring microwave power in a gradient circular waveguide, connects a rectangular coupling cavity by drilling equidistantly distributed coupling holes of different radii on the outer wall of the circular waveguide, and places an inner conductor in the coupling cavity to connect two coaxial interfaces. The coupling degree of the coupler is improved by hole coupling, and the two coaxial interfaces are microwave coupled by different coupling degrees respectively, thereby achieving good directionality of the coupler.

[0026] 3. The power measurement method of the present invention is implemented based on the above-mentioned circular waveguide high-power microwave directional coupler. It has a simple principle and convenient operation. It can carry out power measurement without connecting an additional waveguide coaxial converter, thereby improving the efficiency of power measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is an isometric principle schematic diagram of a circular waveguide directional coupler in a specific embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the side view structure principle of a circular waveguide directional coupler in a specific embodiment of the present invention

[0029] Figure 3 for Figure 2 Schematic diagram of the cross-sectional structure principle in the middle AA direction;

[0030] Figure 4 It is a schematic diagram of the isometric principle of connecting the conductor in the rectangular coupling cavity and the coaxial interface in a specific embodiment of the present invention;

[0031] Figure 5 The circular waveguide transmission TE in the specific embodiment of the present invention 11 Reflection coefficient diagram when in mode;

[0032] Figure 6 The circular waveguide transmission TM in the specific embodiment of the present invention 01 Reflection coefficient diagram when in mode;

[0033] Figure 7 The circular waveguide transmission TE in the specific embodiment of the present invention 11 Transmission coefficient diagram when in mode;

[0034] Figure 8 The circular waveguide transmission TM in the specific embodiment of the present invention 01 Transmission coefficient diagram when in mode;

[0035] Fig. 9 The circular waveguide transmission TE in the specific embodiment of the present invention 11Coupling coefficient diagram of two coaxial interfaces in mode;

[0036] Fig.10 The circular waveguide transmission TM in the specific embodiment of the present invention 01 Coupling coefficient diagram of two coaxial interfaces in mode;

[0037] Fig.11 The circular waveguide transmission TE in the specific embodiment of the present invention 11 Internal electric field distribution diagram of directional coupler in mode;

[0038] Fig.12 The circular waveguide transmission TM in the specific embodiment of the present invention 01 Internal electric field distribution diagram of the directional coupler in mode.

[0039] Legend: 1. First circular straight waveguide section; 2. Circular waveguide gradual transition section; 3. Second circular straight waveguide section; 4. Rectangular coupling cavity; 41. First coupling hole; 42. Second coupling hole; 43. Third coupling hole; 44. Fourth coupling hole; 45. Inner conductor; 46. Outer conductor; 5. First coaxial interface; 51. First coaxial cylindrical inner core; 52. First dielectric; 53. First coaxial cylindrical outer conductor; 6. Second coaxial interface; 61. Second coaxial cylindrical inner core; 62. Second dielectric; 63. Second coaxial cylindrical outer conductor; R1. Chamfer of the outer corner of the conductor in the rectangular coupling cavity; R2. Chamfer of the inner wall corner of the conductor outside the rectangular coupling cavity; R3. Chamfer of the side surface of the outer wall of the small-hole circular waveguide; R4. Chamfer of the side surface of the inner wall of the small-hole circular waveguide. DETAILED DESCRIPTION

[0040] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0041] In the description of the present invention, it should be understood that the terms "side", "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0042] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or suggesting relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0043] Example

[0044] like Figure 1 , Figure 2 and Figure 3 As shown, the directional coupler of the present invention suitable for measuring microwave power of a gradient circular waveguide comprises a first circular straight waveguide section 1, a circular waveguide gradient transition section 2, and a second circular straight waveguide section 3 which are connected in sequence from left to right. The circular waveguide gradient transition section 2 is a cone structure. The diameters of the first circular straight waveguide section 1 and the second circular straight waveguide section 3 are inconsistent. The first circular straight waveguide section 1 is used to connect the microwave source input end, and the second circular straight waveguide section 3 is used to connect the microwave output end, so as to realize the transition of microwave transmission of circular waveguides with different diameters. A rectangular coupling cavity 4 is provided above the outer wall of the circular waveguide gradient transition section 2. The two ends of the rectangular coupling cavity 4 are respectively provided with a first coaxial interface 5 and a second coaxial interface 6. The rectangular coupling cavity 4 is used to couple microwave signals transmitted from the circular waveguide, and make the TE of the circular waveguide transmission 11 or TM 01 The microwaves in the mode are finally coupled to the first coaxial interface 5 and the second coaxial interface 6 and converted into TEM mode. The first coaxial interface 5 and the second coaxial interface 6 are used to connect the directional coupler with the external measurement interface. Microwave coupling is performed through different coupling degrees to realize online monitoring and measurement of high-power microwaves transmitted by circular waveguide.

[0045] like Figure 3 As shown, in this embodiment, a first coupling hole 41, a second coupling hole 42, a third coupling hole 43 and a fourth coupling hole 44 are equidistantly distributed between the circular waveguide gradual transition section 2 and the rectangular coupling cavity 4, and the apertures and depths of the four coupling holes are different, and microwave energy is coupled by hole coupling.

[0046] By arranging the coupling holes between the circular waveguide gradual transition section 2 and the rectangular coupling cavity 4 at reasonable and equidistant intervals, the structure is made simple and easy to process while ensuring the coupling performance. Since different coupling holes are located at different positions on the circular waveguide gradual transition section 2, the depths after being opened are also different, and the coupling performance will deteriorate. In order to ensure that the present invention still has the characteristics of a waveguide hole coupler, the coupling characteristics of holes of different depths are achieved by adjusting different apertures. Without adding additional structures, the structure still retains the functional characteristics of a directional coupler, that is, good coupling and directionality, and ultimately achieves different coupling degrees on different coaxial interfaces.

[0047] like Figure 3 and Figure 4 As shown, the rectangular coupling cavity 4 includes an inner conductor 45 and an outer conductor 46. The outer conductor 46 adopts a rectangular waveguide structure. The inner conductor 45 is in a "concave" shape. The inner conductor 45 is arranged inside the outer conductor 46. The two ends of the inner conductor 45 are respectively connected to the first coaxial interface 5 and the second coaxial interface 6 to realize the microwave electromagnetic field mode of waveguide transmission by the circular waveguide TE 11 or TM 01 mode is converted to coaxial TEM mode.

[0048] By arranging a concave inner conductor 45 in the rectangular coupling cavity 4 to connect the first coaxial interface 5 and the second coaxial interface 6, the rectangular coupling cavity also presents a coaxial inner and outer conductor structure, which is conducive to the conversion of the microwave mode to the TEM mode, improves the transmission performance of the microwave in the coupling cavity, and realizes the conversion of the microwave mode from the circular waveguide TE mode to the TEM mode. 11 or TM 01 Good transition from transmission mode to coaxial TEM mode.

[0049] like Figure 3 As shown, the first coaxial interface 5 includes a first coaxial cylindrical inner core 51, a first dielectric 52 and a first coaxial cylindrical outer conductor 53. The first coaxial cylindrical inner core 51 is connected to the end of the inner conductor 45, and the first coaxial cylindrical inner core 51 is nested inside the first coaxial cylindrical outer conductor 53 through the first dielectric 52.

[0050] The second coaxial interface 6 includes a second coaxial cylindrical inner core 61, a second dielectric 62 and a second coaxial cylindrical outer conductor 63. The second coaxial cylindrical inner core 61 is connected to the end of the inner conductor 45, and the second coaxial cylindrical inner core 61 is nested inside the second coaxial cylindrical outer conductor 63 through the second dielectric 62.

[0051] Furthermore, the first medium 52 and the second medium 62 are both made of polytetrafluoroethylene material.

[0052] In this embodiment, in order to achieve support for the first coaxial cylindrical inner core 51, the second coaxial cylindrical inner core 61 and the inner conductor 45, the first medium 52 and the second medium 62 made of polytetrafluoroethylene are inserted, and the first medium 52 and the second medium 62 are respectively embedded in the first coaxial cylindrical outer conductor 53 and the second coaxial cylindrical outer conductor 63, and respectively wrap the first coaxial cylindrical inner core 51 and the second coaxial cylindrical inner core 61, thereby achieving stable fixed support without affecting the transmission performance of the first coaxial interface 5 and the second coaxial interface 6.

[0053] In this embodiment, in order to improve the power capacity of the circular waveguide high-power microwave directional coupler and ensure that the field strength inside the cavity is not too large at the sharp point to cause internal breakdown and affect microwave transmission, the first coupling hole 41, the second coupling hole 42, the third coupling hole 43 and the fourth coupling hole 44 are chamfered at the outer wall surface R3 and the inner wall surface R4 connected to the circular waveguide gradual transition section 2, and the outer corner R1 of the inner conductor 45 and the inner wall corner R2 of the outer conductor 46 are also chamfered, thereby achieving a higher power capacity of the circular waveguide directional coupler.

[0054] In this embodiment, the input port of the first circular straight waveguide section 1 and the output port of the second circular straight waveguide section 3 of the circular waveguide high-power directional coupler are respectively connected to the microwave source and the radiation antenna through a flange, and the test cable and the oscilloscope are connected through the first coaxial interface 5 or the second coaxial interface 6 to realize online monitoring and measurement of microwaves during transmission.

[0055] In this embodiment, a power measurement method based on the above-mentioned directional coupler suitable for gradient circular waveguide microwave power measurement is also provided. Since the first coaxial interface 5 has the same size as the conventional microwave cable interface, the first coaxial interface 5 can be directly connected to the microwave cable, and power measurement can be carried out without connecting an additional waveguide coaxial converter. By testing the output power P1 and coupling degree C0 of the first coaxial interface 5, the transmission power P0 of the main waveguide is calculated.

[0056] P0=P1×10 -C0 / 10 .

[0057] The measurement method of this embodiment has a simple principle and is easy to operate, and significantly improves the efficiency and accuracy of power measurement.

[0058] The working principle of the directional coupler suitable for measuring microwave power in a tapered circular waveguide of this embodiment is as follows:

[0059] The microwave signal is fed into the input port of the first circular waveguide section 1 and the transmission circular waveguide TE 11 or TM 01 Mode, microwave transmission passes through the circular waveguide gradual transition section 2, and the energy is coupled to the rectangular coupling cavity 4 above through the first coupling hole 41, the second coupling hole 42, the third coupling hole 43 and the fourth coupling hole 44 opened on the inner and outer walls of the circular waveguide gradual transition section 2. The first coupling hole 41, the second coupling hole 42, the third coupling hole 43 and the fourth coupling hole 44 are equidistantly distributed, and the coupling holes of different depths are adjusted by different apertures to achieve good coupling characteristics. After the microwave is coupled into the rectangular coupling cavity 4, the transmission performance of the microwave in the rectangular coupling cavity 4 is improved through the concave inner conductor 45. Since the coupling holes and the inner conductor 45 are chamfered, the breakdown caused by the large field strength at the sharp point is avoided, the power capacity of the directional coupler is improved, and the circular waveguide TE is realized.11 or TM 01 The microwave transmission mode makes a good transition to the coaxial TEM mode. Finally, the microwave is transmitted to the coaxial interface above the rectangular coupling cavity 4 in the form of TEM mode. The two coaxial interfaces can perform microwave coupling through different coupling degrees respectively to achieve the directionality of the coupler. Finally, the oscilloscope is connected through a test cable connected to the coaxial interface to realize the online monitoring and measurement of high-power microwaves transmitted by the circular waveguide.

[0060] The circular waveguide directional coupler proposed in the present invention can overcome the shortcomings of the previous coupler, such as complex structure, low power capacity, low coupling degree, and poor directivity. It has a simple and compact structure and has the advantages of high power capacity, high coupling degree, and high directivity. It can be directly applied to the transition section structure of the circular waveguide to transmit the electromagnetic field TE of the circular waveguide. 11 ,TM 01 The mode is coupled and converted into the TEM mode on the coaxial interface to achieve online coupling measurement of high-power microwaves. In a specific embodiment, a power capacity of more than 2GW can be achieved, a coupling degree of more than 60dB, a directivity of 20dB, and it is also applicable to circular waveguide TE 11 and TM 01 The above technical effects make the present invention have broad application prospects in high-power microwave measurement applications.

[0061] Inspired by the above disclosed technical features, the following is described through a specific application embodiment:

[0062] like Figures 1 to 12 As shown, the specific application example:

[0063] In this embodiment, the inner diameter of the first circular straight waveguide section 1 is 110 mm and the outer diameter is 120 mm. The inner diameter of the second circular straight waveguide section 3 is 120 mm and the outer diameter is 130 mm. The length of the circular waveguide gradual transition section 2 is 185 mm, and the waveguide wall thickness is 5 mm. The coupling holes connecting the circular waveguide gradual transition section 2 and the rectangular waveguide coupling cavity 4 are equidistantly distributed with a spacing of 51.71 mm. The distances between the centers of the first coupling hole 41, the second coupling hole 42, the third coupling hole 43 and the fourth coupling hole 44 and the input port of the circular waveguide gradual transition section 2 are 14.93 mm, 66.64 mm, 118.36 mm and 170.07 mm, respectively. The hole diameters are 7.32 mm, 10.1 mm, 6.68 mm and 5.04 mm, respectively. The chamfers R3 and R4 at the inner and outer wall surfaces of the hole waveguide are both 2 mm.

[0064] The overall length, width and height of the outer wall of the rectangular coupling cavity 4 are 180 mm, 30 mm and 24 mm respectively, and the wall thickness is 5 mm. The chamfer R2 at the inner corner of the outer conductor 46 is 3 mm, the inner conductor 45 is 149 mm long and 4 mm wide, and the thickness of the transverse long strip structure inner conductor 45 is 5.04 mm. The thickness of the block structure inner conductor at both ends of the inner conductor 45 connected to the first coaxial cylindrical inner core 51 and the second coaxial cylindrical inner core 61 is 4.2 mm, and the chamfer R1 at the outer corner of the inner conductor 45 is 3 mm.

[0065] The first coaxial interface 5 and the second coaxial interface 6 have the same size. The diameters of the first coaxial cylindrical inner core 51 and the second coaxial cylindrical inner core 61 are both 3.04 mm, and the inner core lengths are both 28.5 mm. The inner diameters of the first coaxial cylindrical outer conductor 53 and the second coaxial cylindrical outer conductor 63 are both 7 mm, the outer diameters are both 13 mm, and the wall thicknesses are both 3 mm. A first medium 52 and a second medium 62 made of polytetrafluoroethylene are inserted from a depth of 10 mm on the mouth of the first coaxial interface 5 and the second coaxial interface 6 to the inner wall of the outer conductor 46 to support and fix the first coaxial cylindrical inner core 51 and the second coaxial cylindrical inner core 61 and the inner conductor 45. The inner diameters of the first medium 52 and the second medium 62 are both 3.04 mm, and the outer diameters are both 10 mm. The depth of embedding into the inner walls of the first coaxial cylindrical outer conductor 53 and the second coaxial cylindrical outer conductor 63 is both 1.5 mm.

[0066] The design demonstration results of this specific application embodiment are as follows:

[0067] The simulation results of the relationship between the input port reflection coefficient and frequency of the circular waveguide high-power microwave directional coupler applied to the transition gradient section of this embodiment are as follows: Figure 5 and Figure 6 As shown, they represent circular waveguide transmission TE 11 Mode and TM 01 The reflection coefficient in the 7.9 GHz to 8.1 GHz frequency band is lower than -35 dB. According to the formula VSWR = (1 + S 11 ) / (1-S 11 ) calculated that the in-band standing wave is no greater than 1.04.

[0068] The simulation results of the relationship between the transmission coefficient of the input port and the frequency are as follows: Figure 7 and Figure 8 As shown, they represent circular waveguide transmission TE 11 Mode and TM 01 The transmission coefficients in the 10-kHz mode, that is, the transmission coefficients in the frequency band of 7.9 GHz to 8.1 GHz, are all lower than -0.1 dB, indicating good transmission performance.

[0069] The simulation results of the coupling capability of the circular waveguide high-power microwave directional coupler are as follows: Fig. 9 and Fig.10 As shown, Fig. 9 Represents circular waveguide transmission TE 11 The coupling coefficient of the two coaxial interfaces in the mode is: Fig.10 Circular waveguide transmission TM 01 The coupling coefficient of the two coaxial interfaces in the mode is: Fig. 9 and Fig.10 Medium S 31 Both represent the coupling coefficient of the first coaxial interface 5, that is, the coaxial interface close to the input port, and S 41 Both represent the coupling coefficient of the second coaxial interface 6, that is, the coaxial interface close to the output port, and are Fig. 9 and Fig.10 It can be seen that in the specific embodiment, at the X-band 8 GHz frequency, TE 11 The coupling coefficients of the mode-TEM mode to the two ports are -61.5dB and -79dB respectively, the directivity is -17.5dB, and the TM 01 The coupling coefficients of the mode-TEM mode on the two ports are -60.4dB and -80.5dB respectively, and the directivity is -20.1dB. The first coaxial interface on the input side has 5 pairs of TE 11 Mode and TM 01 The coupling coefficient of the mode can be basically maintained at about -60dB in the frequency band of 7.9GHz to 8.1GHz, and the coupling fluctuation range is no more than 5dB. The second coaxial interface on the output side has 6 pairs of TE 11 Mode and TM 01 The coupling coefficient of the mode can be basically maintained at about -80dB in the frequency band of 7.95GHz to 8.05GHz, and the coupling fluctuation range is no more than 5dB, that is, the TE of circular waveguide transmission in this specific application embodiment is 11 Mode and TM 01 All modes showed good coupling stability and directionality.

[0070] The simulation results of the internal electric field distribution of the circular waveguide high-power microwave directional coupler are shown in Figure 2. Fig.11 and Fig.12 As shown, when the average power of the input excitation signal is 0.5W, TE 11 Mode and TM 01 The maximum internal electric field values ​​of the modes are 500V / m and 723V / m, respectively. The maximum field strengths corresponding to an input power of 2GW are 316kV / cm and 457kV / cm, respectively, which are lower than the breakdown field strength of 500kV / cm. That is, the power capacity of the directional coupler is not less than 2GW, and it has the characteristics of high power capacity.

[0071] In summary, the directional coupler suitable for measuring microwave power in a tapered circular waveguide proposed in this specific application embodiment has a simple and compact structure, has good reflection coefficient and transmission coefficient in the frequency band range of 7.9 GHz to 8.1 GHz in the X-band, and realizes low-loss transmission. The coaxial interfaces at both ends can respectively achieve coupling degrees of about 60 dB and 80 dB in the frequency band range, and directivity of about 20 dB, and are both suitable for TE transmission in circular waveguides. 11 Mode and TM 01 mode, showing high coupling degree, good coupling stability and directivity. The maximum electric field strength inside the directional coupler is 457kV / cm at 2GW input power, which is lower than the breakdown field strength and has the characteristics of high power capacity. That is, the directional coupler suitable for gradient circular waveguide microwave power measurement proposed in the present invention can overcome the shortcomings of the waveguide directional coupler in the prior art, such as complex structure, high processing difficulty, low power capacity, poor coupling stability, and poor directivity. It has the advantages of simple and compact structure, high power capacity, high coupling degree, good coupling stability and directivity, and strong versatility. The above advantages make the circular waveguide high-power microwave directional coupler proposed in the present invention have broad application prospects in the field of high-power microwave test and measurement.

[0072] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A directional coupler suitable for measuring microwave power in a tapered circular waveguide, characterized in that: The invention comprises a main waveguide formed by a first circular straight waveguide section (1), a circular waveguide gradual transition section (2) and a second circular straight waveguide section (3) which are connected in sequence, wherein the circular waveguide gradual transition section (2) is in a cone structure and is used to realize the transition of microwave transmission of circular waveguides with different diameters, a rectangular coupling cavity (4) is provided above the outer wall of the circular waveguide gradual transition section (2), a first coaxial interface (5) and a second coaxial interface (6) are provided at two ends of the rectangular coupling cavity (4), and the rectangular coupling cavity (4) is used to couple microwave signals transmitted by the circular waveguide and make the TE of the circular waveguide transmission 11 or TM 01 The microwaves in the directional coupler mode are coupled to the first coaxial interface (5) and the second coaxial interface (6) to be converted into the TEM mode; the first coaxial interface (5) and the second coaxial interface (6) are used to connect the directional coupler with an external measurement interface, and the first coaxial interface (5) and the second coaxial interface (6) are respectively coupled with microwaves through different coupling degrees to achieve the directionality of the coupler.

2. The directional coupler suitable for measuring microwave power of a tapered circular waveguide according to claim 1, characterized in that: A plurality of equidistantly distributed coupling holes are provided between the circular waveguide gradual transition section (2) and the rectangular coupling cavity (4), wherein the apertures and depths of the coupling holes are different, and microwave energy is coupled by hole coupling.

3. The directional coupler suitable for measuring microwave power of a tapered circular waveguide according to claim 2, characterized in that: The coupling hole is located in the circular waveguide gradual transition section (2) and both inner and outer wall surfaces are chamfered.

4. The directional coupler suitable for measuring microwave power of a tapered circular waveguide according to claim 2, characterized in that: The rectangular coupling cavity (4) comprises an inner conductor (45) and an outer conductor (46); the outer conductor (46) adopts a rectangular waveguide structure; the inner conductor (45) is arranged inside the outer conductor (46); two ends of the inner conductor (45) are respectively connected to a first coaxial interface (5) and a second coaxial interface (6) to realize a microwave electromagnetic field mode of waveguide transmission by a circular waveguide TE 11 or TM 01 mode is converted to coaxial TEM mode.

5. The directional coupler suitable for measuring microwave power of a tapered circular waveguide according to claim 4, characterized in that: The first coaxial interface (5) comprises a first coaxial cylindrical inner core (51), a first dielectric (52) and a first coaxial cylindrical outer conductor (53); the first coaxial cylindrical inner core (51) is connected to the end of the inner conductor (45), and the first coaxial cylindrical inner core (51) is nested inside the first coaxial cylindrical outer conductor (53) through the first dielectric (52).

6. The directional coupler suitable for measuring microwave power of a tapered circular waveguide according to claim 5, characterized in that: The second coaxial interface (6) comprises a second coaxial cylindrical inner core (61), a second dielectric (62) and a second coaxial cylindrical outer conductor (63); the second coaxial cylindrical inner core (61) is connected to the end of the inner conductor (45), and the second coaxial cylindrical inner core (61) is nested inside the second coaxial cylindrical outer conductor (63) through the second dielectric (62).

7. The directional coupler suitable for measuring microwave power of a tapered circular waveguide according to claim 6, characterized in that: The first medium (52) and the second medium (62) are both made of polytetrafluoroethylene material.

8. The directional coupler suitable for measuring microwave power in a tapered circular waveguide according to any one of claims 4 to 7, characterized in that: The inner conductor (45) has a "concave"-shaped structure, and a chamfer is provided at an outer corner of the inner conductor (45).

9. The directional coupler for measuring microwave power in a tapered circular waveguide according to any one of claims 4 to 7, characterized in that: The inner wall corners of the outer conductor (46) are chamfered.

10. A power measurement method based on a directional coupler suitable for tapered circular waveguide microwave power measurement according to any one of claims 1 to 9, characterized in that: The first coaxial interface (5) is connected to the microwave cable, and the output power P1 and the coupling degree C0 of the first coaxial interface (5) are tested, thereby calculating the transmission power P0 of the main waveguide. P0=P1×10 -C0 / 10 。

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