A power-extracting coupling structure for staggered grid slow wave circuit and a design method thereof

Abstract

The application provides an energy transmission coupling structure for staggered grid slow wave circuit and a design method thereof, the energy transmission coupling structure comprising a three-branch waveguide coupling structure, the three-branch waveguide coupling structure comprising a first branch waveguide for microwave transmission and a second branch waveguide and a third branch waveguide arranged along the direction of electron beam travel; a ridge load arranged on the first branch waveguide along the height direction of the three-branch waveguide coupling structure; and a slot load arranged at the intersection area of the three-branch waveguide coupling structure along the height direction of the three-branch waveguide coupling structure. The energy transmission coupling structure can solve the problems of the existing H-plane coupling structure, such as too long overall length and complex structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum electron devices. More particularly, it relates to an energy transfer coupling structure for staggered grating slow wave circuit and a design method thereof. BACKGROUND

[0002] Millimeter wave / terahertz technology has important application value in the field of future communication, imaging, radar, etc. The main obstacle restricting its development at present is the lack of compact structure, moderate power level, wideband coherent radiation source. Traveling wave tube is a kind of vacuum electron device, which can realize the generation or amplification of millimeter wave / terahertz signal. Compared with other types of devices, traveling wave tube is one of the few devices that have the ability of wideband, high gain, large power at millimeter wave and terahertz frequency band, and compact structure. The traditional system of traveling wave tube device is limited by the size of the effect of crossing the river. With the increase of frequency, the output power decreases with the square of the frequency, which greatly limits the ability of traveling wave tube to work at high frequency. The technology of strip electron beam is an effective technical way to overcome this problem, and is currently one of the research hotspots in the field of terahertz vacuum electron devices.

[0003] Staggered grating circuit is a full-metal slow wave structure suitable for strip electron beam, which has the advantages of large power capacity and wide frequency band, and its basic structure is shown in Figure 1 Although the inherent performance of staggered grating slow wave structure is excellent, especially the bandwidth, the relative bandwidth can reach 30% in theory, but because the electromagnetic wave transmission path and the electron beam transmission path cannot be naturally separated, the input and output coupling structure must be carefully designed in the actual device to realize the effective feeding and extraction of electromagnetic wave signal.

[0004] The existing coupling structure is divided into E-plane and H-plane structures, and the lead-out direction of the waveguide is along the Y and X directions shown in Figure 1 respectively. Figure 2 and Figure 3respectively, are the most common E-plane and H-plane coupling structures. Each of the two coupling methods has its advantages and disadvantages. The E-plane coupling structure is relatively simple and compact in axial (Z-direction) length, and can achieve good performance after matching design. However, the biggest defect is that the coupling direction conflicts with the plane where the periodic focusing magnetic field is located, resulting in that the output waveguide needs to be introduced vertically through the magnetic field system. This brings great difficulty to the design and debugging of the magnetic field system. Especially for the strip beam device, the transmission characteristics of the electron beam are very sensitive to the magnetic field change. Therefore, in actual use, the E-plane coupling structure is generally not used. The H-plane coupling structure has the waveguide output direction parallel to the plane of the magnetic field system, and is introduced from the middle of the upper and lower magnetic field planes, which makes the coupling system and the magnetic field system not affect each other. However, the H-plane coupling structure needs more complex transition design, including slow wave structure end taper, output waveguide matching and isolator design. Finally, the coupling system that meets the performance requirements is often too long and complex in structure. SUMMARY

[0005] In view of the above problems, the present application provides an energy coupling structure for staggered grid slow wave circuit to solve the problem of the existing H-plane coupling structure that the overall length is too long and the structure is complex.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] The present application provides an energy coupling structure for staggered grid slow wave circuit, comprising:

[0008] The three-branch waveguide coupling structure comprises a first branch waveguide for microwave transmission, and a second branch waveguide and a third branch waveguide arranged along the direction of electron beam travel;

[0009] A ridge loading is arranged on the first branch waveguide along the height direction of the three-branch waveguide coupling structure, and a groove loading is arranged at the intersection area of the three-branch waveguide coupling structure along the height direction of the three-branch waveguide coupling structure.

[0010] Preferably, the third branch waveguide and the second branch waveguide are coaxially arranged, and the groove loading is symmetrically arranged about the axis of the third branch waveguide.

[0011] Preferably, the axis of the third branch waveguide and the axis of the first branch waveguide are orthogonally arranged, and the ridge loading is symmetrically arranged about the axis of the first branch waveguide.

[0012] Preferably, the ridge loading is arranged close to the intersection area of the three-branch waveguide.

[0013] Preferably, the groove loading and the ridge loading are formed on two opposite sides of the three-branch waveguide coupling structure, respectively.

[0014] Preferably, the energy transfer coupling structure is configured to directly couple with the slow wave structure.

[0015] Preferably, the energy transfer coupling structure is an input coupling structure, further comprising a reflector arranged at the branch waveguide on the side of the electron gun of the traveling wave tube.

[0016] Preferably, the energy transfer coupling structure is an output coupling structure, further comprising a reflector arranged at the branch waveguide on the side of the collector of the traveling wave tube.

[0017] The present application also provides a design method of the energy transfer coupling structure of the staggered grid slow wave circuit, comprising: designing an initial three-branch waveguide coupling structure, the initial three-branch waveguide coupling structure comprising a first branch waveguide for microwave transmission and a second branch waveguide and a third branch waveguide arranged along the direction of the electron beam; arranging a ridge loading on the first branch waveguide along the height direction of the three-branch waveguide coupling structure; and arranging a groove loading at the intersection of the three-branch waveguide along the height direction of the three-branch waveguide coupling structure.

[0018] Preferably, the resonance frequency of the energy transfer coupling structure is adjusted by changing the height of the ridge loading or the depth of the groove loading, and the matching and isolation performance of the energy transfer coupling structure is optimized.

[0019] The present application has the following advantages:

[0020] The energy transfer coupling structure of the present application has a compact overall structure, in which the groove loading and the ridge loading, which are used to adjust the isolation and matching performance, are arranged on the three-branch waveguide coupling structure. Compared with the existing H-plane coupling structure which uses a multi-section stepped transition, the present application uses the in-situ addition of circuit elements, which does not increase the length of the coupling circuit, thereby maintaining the compactness of the structure. In addition, since the groove loading and the ridge loading have complementary electrical properties and good parameter adjustment characteristics, a single-section reflector can meet the performance requirements, thereby further shortening the length of the energy transfer coupling structure. The present application can achieve a matching performance better than -20 dB and an isolation performance better than -15 dB in the range of 205 GHz to 240 GHz, thereby further increasing the operating bandwidth of the energy transfer coupling structure to 35 GHz.

[0021] The groove loading and the ridge loading of the present application both have tunable characteristics, and the resonance frequency of the energy transfer coupling structure is adjusted by changing the height of the ridge loading or the depth of the groove loading, thereby optimizing the matching and isolation performance of the energy transfer coupling structure. This adds a useful fine-tuning mechanism for practical applications, which can compensate for the deterioration of the matching performance caused by the machining, assembly and welding processes. BRIEF DESCRIPTION OF DRAWINGS

[0022] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0023] Figure 1 is a structural schematic diagram of a conventional staggered grid slow wave circuit.

[0024] Figure 2 is a structural schematic diagram of an existing E-plane coupling structure.

[0025] Figure 3 is a structural schematic diagram of an existing H-plane coupling structure.

[0026] Figure 4 is a structural schematic diagram of an existing three-branch waveguide coupling structure.

[0027] Figure 5 is one of structural schematic diagrams of the energy transfer coupling structure of the present application.

[0028] Figure 6 is another structural schematic diagram of the energy transfer coupling structure of the present application.

[0029] Figure 7 is a S-parameter performance schematic diagram of the energy transfer coupling structure of the present application.

[0030] Figure 8 is a matching characteristic variation curve diagram of the energy transfer coupling structure of the present application when the slot loading depth is changed.

[0031] Figure 9 is a frequency response curve diagram of the slot loading and ridge loading of the present application.

[0032] Reference numerals: 1, first branch waveguide, 2, second branch waveguide, 3, third branch waveguide, 4, ridge loading, 5, slot loading, 6, reflector, 7, three-branch waveguide intersection area. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions, and numerical values set forth in these embodiments are not limiting to the scope of the present application unless otherwise specifically stated.

[0034] The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the scope of the application its application or uses.

[0035] Techniques and equipment known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered part of the specification where appropriate.

[0036] In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0037] It should be noted that like reference numerals and letters refer to like items in the several views, and as a result, further discussion of such items is not necessary in the subsequent views once such items are defined in one view.

[0038] Because of the complex transmission characteristics of the strip electron beam and the difficulty of long distance transmission, the strip beam traveling wave tube design hopes that the circuit is as short as possible to minimize the electron beam interception. Therefore, an excessively long coupling system is undesirable. This is also one of the key problems that researchers have been trying to solve in the current strip beam traveling wave tube development. In addition, an excessively complex structure will bring difficulties in processing implementation. In particular in the terahertz frequency band, the optimal size in the electrical performance design is often difficult to strictly implement in actual processing, which leads to the difficulty in highly matching the design and the actual measurement. Therefore, in terms of structure, the coupler also needs to be as simple as possible.

[0039] In summary, the problems of the existing coupling structure can be summarized as follows: 1) the existing E-plane coupling structure design has a conflict with the direction of the magnetic field system and is difficult to be practical; 2) the existing H-plane coupling structure meets the practical requirements, but the structure is too complex and too long, and if the transition design is simplified, the performance is often not satisfactory.

[0040] In order to solve the above problems, the present application provides an energy coupling structure for an interleaved grid slow wave circuit, which is used to directly couple with the slow wave structure of a traveling wave tube. In combination Figures 1 to 9 As shown, specifically, the energy coupling structure for the interleaved grid slow wave circuit includes a three-branch waveguide coupling structure, the three-branch waveguide coupling structure includes a first branch waveguide 1 for microwave transmission and a second branch waveguide 2 and a third branch waveguide 3 arranged along the electron beam running direction, a ridge loading 4 arranged on the first branch waveguide 1 along the height direction of the three-branch waveguide coupling structure, and a slot loading 5 arranged at the three-branch waveguide intersection area 7 along the height direction of the three-branch waveguide coupling structure. The height direction of the three-branch waveguide coupling structure refers to the Y direction, the electron beam running direction refers to the Z direction, and the X direction is perpendicular to the Y direction and the Z direction. The overall length of the energy coupling structure is short, the structure is compact, and the performance can meet the practical requirements. The energy coupling structure can simultaneously realize good characteristics of matching, reflection and isolation without using a complex transition, solving the problem that the existing coupling structure cannot simultaneously realize H-plane extraction, simple and compact structure and excellent performance.

[0041] Figure 4is a three-branch waveguide coupling structure with a reflector 6, the first port is marked as the electromagnetic wave input or output port, corresponding to the first branch waveguide 1. The second port is the port to the slow wave structure, corresponding to the second branch waveguide 2. The third port is the port to the traveling wave tube electron gun or the collector, corresponding to the third branch waveguide 3. It can be understood that the reflector and the three-branch waveguide coupling structure in the figure are connected cavities. Ideally, it is desirable to achieve matching of the first port and the second port, while both are isolated from the third port. In terms of specific indicators, the reflection characteristic S 11 , 22 <-10dB, the isolation characteristic S 31 , 32 <-10dB. The above indicators are for the final actual circuit, considering the error and characteristic change in the process of circuit processing, assembly and welding, and sufficient margin is required in the design. Therefore, the design requirements are generally: the reflection characteristic S 11 , 22 <-20dB, the isolation characteristic S 31 , 32 <-15dB, that is, the reflection characteristic S 11 <-20dB, the reflection characteristic S 22 <-20dB. The isolation characteristic S 31 <-15dB, the isolation characteristic S 32 <-15dB. However, the pure three-branch waveguide coupling structure cannot meet the above requirements by simply changing the waveguide size without introducing additional circuit elements in the natural state. At this time, additional circuit elements need to be introduced. In order to achieve the isolation characteristic of the third port, a reflector is added between the third port and the other two ports. The principle of the reflector is to simulate the open load of the transmission line, and form an equivalent electrical boundary at the appropriate position, so as to realize total reflection of the electromagnetic wave signal, which requires adjustment of the structural parameters of the reflector and the distance between the first and second ports. However, a single-stage reflector cannot generally meet the matching characteristics of the first port and the second port while meeting the isolation characteristic, that is, it is necessary to ensure that the signal from the second port is reflected along the first port after transmission, and the signal from the first port is reflected to the second port. Therefore, the usual way is to use multiple levels, that is, Figure 3 , the way of using multiple reflectors (also known as Bragg reflectors) is shown, which increases the length of the circuit. In order to maintain a compact structure, the present application adds circuit elements in situ, that is, adds circuit elements to the three-branch waveguide coupling structure to obtain double improvement of matching and isolation effect.

[0042] Further, the compensation circuit element adopted by the present application is a slot loading and ridge loading with complementary electromagnetic characteristics. Referring to Figure 5As shown, the third branch waveguide 3 and the second branch waveguide 2 are coaxially arranged, and the axis L2 of the third branch waveguide 3 and the axis L1 of the first branch waveguide 1 are orthogonally arranged. The first branch waveguide 1 is formed with a first port, the second branch waveguide 2 is formed with a second port, and the third branch waveguide 3 is formed with a third port. The slot loading 5 is located at the three-branch waveguide intersection area 7, and the slot loading 5 is symmetrically arranged about the axis L2 of the third branch waveguide 3. Since the slot loading 5 can improve the cutoff frequency of the waveguide, whether the signal transmitted from the second port or the first port, when transmitted to the third port, will experience the improvement of the waveguide cutoff frequency due to the influence of the slot loading 5, thereby enhancing the isolation effect of the third port. The ridge loading 4 is arranged on the first branch waveguide 1, and the ridge loading 4 is symmetrically arranged about the axis L1 of the first branch waveguide 1 and arranged close to the three-branch waveguide intersection area 7. Since the ridge loading 4 can reduce the cutoff frequency of the waveguide, the transmission matching characteristics between the first port and the second port can be improved.

[0043] Specifically, the ridge loading 4 is equivalent to adding a matching network on the path from the first port to the three-branch waveguide intersection area 7. The network can add an additional reactance to the three-branch waveguide intersection area 7, to a certain extent, offset the loading effect of the three-branch waveguide intersection area 7 itself, and also change the impedance of the waveguide at the connection between the first port and the three-branch waveguide intersection area 7, so that the impedance matching condition meets the requirements.

[0044] The slot loading 5 has no effect on the impedance of the waveguide connecting the first port and the second port, and its role is completely to change the equivalent impedance of the three-branch waveguide intersection area 7. The slot loading 5 is close to the reflector 6, so it has a certain influence on the third branch waveguide 3. The slot loading 5 can form a weak resonance effect with the reflector 6, and theoretically this effect is positive, which can make the isolation of the third port better.

[0045] More specifically, the ridge loading 4 is to match the first port and the second port, but the equivalent impedance of the three-branch waveguide intersection area 7 and the equivalent impedance of the matching network are not a fixed constant. Their values and whether they are inductive or capacitive (i.e. the sign) change with frequency. When a very wide bandwidth is required, for example, more than 30GHz, it is difficult to meet the requirements by relying on a ridge loading alone. At this time, a second loading element needs to be introduced, but a ridge loading cannot be introduced again, because when the frequency range is very wide, the inductance / capacitance of the ridge loading at some frequencies is the same as that of the three-branch waveguide intersection area 7, so it not only cannot offset the reactance of the three-branch waveguide intersection area 7, but also enhances it. Therefore, a loading element opposite to the characteristics of the ridge loading 4 needs to be introduced, that is, a slot loading 5 is introduced at the three-branch waveguide intersection area 7. By "opposite characteristics" it is meant that the frequency response trend is opposite. By comparing the frequency response curves of the slot loading 5 and the ridge loading 4 in the frequency band of interest, it can be clearly seen that the slot loading 5 and the ridge loading 4 have opposite effects on S Figure 9 The frequency response curves of the slot loading 5 and the ridge loading 4 given in the frequency band of interest can clearly see that the slot loading 5 and the ridge loading 4 have opposite effects on S11 The influence is opposite, especially at the high frequency end, forming two opposite peaks.

[0046] In a specific embodiment, the width a of the three-branch waveguide of the energy transmission coupling structure in the X direction and the height b in the Y direction are 0.78 mm and 0.35 mm respectively, the radius of the ridge loading is 0.208 mm, the height of the ridge loading in the Y direction is 0.0694 mm, the distance between the center of the ridge loading and the intersection area of the three-branch waveguide is 0.185 mm, the radius of the groove loading is 0.3 mm, the depth of the groove loading in the Y direction is 0.35 mm, and the distance between the center of the groove loading and the reflector is 0.73 mm.

[0047] Referring to Figure 7 It can be known that the matching characteristics S11, S22 <-20 dB, and the isolation characteristics S31, S32 <-15 dB in the range of 205 GHz to 240 GHz, which can fully meet the practical requirements. The energy transmission coupling structure provided by the application has a performance better than the bandwidth range of -20 dB, reaching 35 GHz from 205 GHz to 240 GHz, thereby further widening the working bandwidth of the energy transmission coupling structure, improving the matching characteristics, and having a positive impact on the isolation performance.

[0048] Combining Figure 5 and Figure 6 It can be known that the groove loading 5 and the ridge loading 4 can be arranged on the opposite sides or the same side of the three-branch waveguide coupling structure. Further, in order to avoid interference between the groove loading 5 and the ridge loading 4 due to machining precision when the groove loading 5 and the ridge loading 4 are machined, the groove loading 5 and the ridge loading 4 are formed on the two opposite sides of the three-branch waveguide coupling structure respectively.

[0049] More specifically, the energy transmission coupling structure can be an input coupling structure or an output coupling structure. When the energy transmission coupling structure is an input coupling structure, a reflector arranged on the side of the branch waveguide of the electron gun of the traveling wave tube is further included. When the energy transmission coupling structure is an output coupling structure, a reflector arranged on the side of the branch waveguide of the collector of the traveling wave tube is further included. The horizontal cross sections of the ridge loading and the groove loading can both be circular or can be other shapes respectively, and the application does not limit this. In the specific machining process, two circuit halves are provided, a groove channel constituting the three-branch waveguide coupling structure is machined on the two circuit halves by using a high-speed precision milling machine, a convex circular ridge meeting the design requirements is machined on one of the two circuit halves, a concave circular groove meeting the design requirements is machined on the other circuit half, and finally the two circuit halves are clamped and welded into a whole by a mold.

[0050] The present invention also provides a design method for a power transmission coupling structure for an interleaved gate slow wave circuit. The method includes: designing an initial three-branch waveguide coupling structure, the initial three-branch waveguide coupling structure including a first branch waveguide 1 for microwave transmission and a second branch waveguide 2 and a third branch waveguide 3 arranged along the electron beam travel direction; setting a ridge loading 4 on the first branch waveguide 1 along the height direction of the three-branch waveguide coupling structure; and setting a slot loading 5 in the three-branch waveguide intersection area 7 along the height direction of the three-branch waveguide coupling structure.

[0051] Furthermore, in combination Figure 8 As shown in the figure, dh represents the depth of slot loading 5 (unit: mm). This invention can adjust the resonant frequency of the power transmission coupling structure by changing the height of ridge loading 4 or the depth of slot loading 5, thereby optimizing the matching and isolation performance of the power transmission coupling structure. In the terahertz band, due to the larger size of the slot loading, it is more suitable as a tuning hole and used in conjunction with tuning pins for tuning, while the ridge loading, due to its relatively smaller size, is more suitable for direct integral processing to ensure accuracy.

[0052] In summary, the power coupling structure of this invention has a compact overall structure, where both the slot loading and ridge loading, which adjust isolation and matching characteristics, are located on the three-branch waveguide coupling structure. Compared to the existing H-plane coupling structure that uses a multi-stage stepped transition, this invention uses this in-situ addition of circuit components, which does not increase the length of the coupling circuit and maintains the compactness of the structure. Furthermore, since the slot loading and ridge loading have complementary electrical properties and good parameter adjustment characteristics, a single reflector is sufficient to meet the performance requirements, thereby further shortening the length of the power coupling structure. This invention can achieve matching characteristics better than -20dB and isolation characteristics better than -15dB in the 205GHz to 240GHz range, thereby further increasing the operating bandwidth of the power coupling structure to 35GHz.

[0053] Both the slot loading and ridge loading of this invention have tunable characteristics. By changing the height of the ridge loading or the depth of the slot loading, the resonant frequency of the power transmission coupling structure can be adjusted, thereby optimizing the matching and isolation performance of the power transmission coupling structure. This adds a useful fine-tuning mechanism for practical applications, which can compensate for the deterioration of matching performance caused by processing, assembly, and welding processes.

[0054] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A power-extracting coupling structure for an interdigital slow wave circuit, characterized by, Comprise: A three-branch waveguide coupling structure, comprising a first branch waveguide for microwave transmission, and a second branch waveguide and a third branch waveguide arranged along the direction of the electron beam; A ridge load arranged on the first branch waveguide along the height direction of the three-branch waveguide coupling structure, and a groove load arranged at the intersection area of the three-branch waveguide along the height direction of the three-branch waveguide coupling structure.

2. The power-extracting coupling structure for an interdigital slow wave circuit according to claim 1, characterized by, The third branch waveguide and the second branch waveguide are coaxially arranged, and the groove load is symmetrically arranged about the axis of the third branch waveguide.

3. The power-extracting coupling structure for an interdigital slow wave circuit according to claim 1, characterized by, The axis of the third branch waveguide and the axis of the first branch waveguide are orthogonally arranged, and the ridge load is symmetrically arranged about the axis of the first branch waveguide.

4. The power-extracting coupling structure for an interdigital slow wave circuit according to claim 3, characterized by The ridge load is arranged close to the intersection area of the three-branch waveguide.

5. The power-extracting coupling structure for an interdigital slow wave circuit according to claim 1, characterized by, The groove load and the ridge load are respectively formed on two opposite sides of the three-branch waveguide coupling structure.

6. The power-extracting coupling structure for an interdigital slow wave circuit according to claim 1, characterized by The energy transfer coupling structure is used to directly couple with the slow wave structure.

7. The power-extracting coupling structure for an interdigital slow wave circuit according to claim 1, characterized by The energy transfer coupling structure is an input coupling structure, further comprising a reflector arranged at the branch waveguide on the side of the electron gun of the traveling wave tube.

8. The power-extracting coupling structure for an interdigital slow wave circuit according to claim 1, characterized by, The energy transfer coupling structure is an output coupling structure, further comprising a reflector arranged at the branch waveguide on the side of the collector of the traveling wave tube.

9. A design method of a power coupling structure for an interdigital slow wave circuit, characterized by, The method comprises: designing an initial three-branch waveguide coupling structure, the initial three-branch waveguide coupling structure comprising a first branch waveguide for microwave transmission, and a second branch waveguide and a third branch waveguide arranged along the direction of the electron beam; arranging a ridge load on the first branch waveguide along the height direction of the three-branch waveguide coupling structure; arranging a groove load at the intersection area of the three-branch waveguide along the height direction of the three-branch waveguide coupling structure.

10. The design method of claim 9, wherein, The resonance frequency of the energy transfer coupling structure is adjusted by changing the height of the ridge load or the depth of the groove load, and the matching and isolation performance of the energy transfer coupling structure is optimized.

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