A weakly reflective folded waveguide slow-wave structure

Abstract

The present invention discloses a weak-reflection folded waveguide slow-wave structure, comprising a straight waveguide section and a bending region, wherein an impedance matching region is provided between the straight waveguide section and the bending region for impedance matching connection between the straight waveguide section and the bending region. Since the weak-reflection folded slow-wave structure of the present invention introduces an impedance matching section, good impedance matching is achieved, and thus the slow-wave structure has good radio frequency transmission characteristics; at the same time, compared with conventional folded waveguides and eccentric arc folded waveguide slow-wave structures of the same physical dimensions, the solution of the present invention has excellent reflection performance; and compared with conventional folded waveguides of the same physical dimensions, the coupling impedance of the present invention is significantly improved compared with conventional folded waveguides. The traveling wave tube based on the present invention will have physical performance advantages such as greater output power, higher interaction efficiency, and lower oscillation risk.

Description

Technical Field

[0001] The invention relates to the field of microwave vacuum electronic technology, in particular to a weak reflection type folded waveguide slow-wave structure. Background Art

[0002] Traveling wave tubes (TWTs), based on vacuum electronics principles, have broad application prospects in areas such as radar detection, broadband satellite communications, and electronic countermeasures. Compared to amplifiers based on solid-state electronics, they boast high output power, wide bandwidth, and high efficiency, meeting the needs of most current high-power electromagnetic transmission systems. Generally speaking, a TWT consists primarily of a slow-wave structure (slow-wave line), an electron gun, a magnetic focusing system, an energy input and output coupling structure, and a step-down collection stage. The slow-wave structure is the core component of the TWT; it is the primary site for energy conversion between the electron beam and the electromagnetic wave, and its physical properties directly determine the device's performance.

[0003] In the microwave frequency band, common slow-wave structures mainly include helical structures and coupled-cavity structures. Helical slow-wave structures offer advantages such as operating bandwidth, low synchronization voltage, and high interaction efficiency. However, due to the dimensional co-inherence effect, they are difficult to fabricate in the millimeter-wave and terahertz bands. Coupled-cavity slow-wave structures are all-metal cavities with high coupling impedance, capable of handling large power and dissipating heat effectively. However, their narrow operating bandwidth limits their application in broadband scenarios. Folded-waveguide slow-wave structures offer advantages such as wide bandwidth and ease of fabrication, making them widely used in the design of millimeter-wave and terahertz traveling-wave tubes. However, due to the weak longitudinal electric field strength within the electron injection channel, the coupling impedance of conventional folded-waveguide slow-wave structures is relatively low, which in turn limits the output power and electronic efficiency of traveling-wave tubes based on these structures. To further improve the coupling impedance of folded-waveguide slow-wave structures, deformed folded-waveguide slow-wave structures, such as ridge-loaded folded waveguides and eccentric circular arc folded waveguides, have been proposed for the design of millimeter-wave and terahertz traveling-wave tubes.

[0004] refer to Figure 1 The ridge-loaded folded waveguide slow-wave structure is constructed by adding metal ridges to the inner wall of the straight waveguide section of the folded waveguide slow-wave structure. Then, holes are punched through the metal wall along the slow-wave structure's axis of symmetry, forming an electron beam channel. The ridge loading enhances the field in the waveguide gap to a certain extent. As the electron beam propagates through the waveguide gap along the electron beam channel, it is subjected to a stronger electromagnetic force, resulting in more efficient energy exchange between the electromagnetic field and the electron beam, effectively amplifying the high-frequency field energy.

[0005] The inventors discovered that a disadvantage of ridge-loaded folded waveguide slow-wave structures is that the addition of metal ridges to the inner wall of the straight waveguide introduces impedance discontinuities, causing impedance mismatch within the slow-wave structure. This results in reflections during electromagnetic wave transmission, deteriorating the transmission characteristics of this structure. Therefore, compared to folded waveguide traveling wave tubes (FWTs), ridge-loaded FWTs have a limited operating bandwidth and a higher risk of self-oscillation.

[0006] In order to improve the coupling impedance of conventional folded waveguide and change the frequency range of the first stop band, an eccentric arc folded waveguide slow wave structure (such as Figure 2 A ridge-loaded folded waveguide slow-wave structure (Folded Waveguide Slow Wave Structure With Modified Circular Bends, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 61, NO. 10, OCTOBER 2014) was proposed. Similar to the ridge-loaded folded waveguide slow-wave structure, this slow-wave structure improves the coupling impedance by changing the longitudinal electric field distribution within the electron beam channel.

[0007] However, the inventors discovered through research that a disadvantage of this eccentric arc folded waveguide slow-wave structure is that, due to the different cross-sections of the straight waveguide section and the eccentric arc bent section, there is a tendency for impedance mismatch between the straight waveguide section and the eccentric arc bent section, resulting in significant transmission reflections. Similar to the ridge-loaded folded waveguide slow-wave structure, the eccentric arc folded waveguide traveling wave tube has a limited operating bandwidth compared to a folded waveguide traveling wave tube, and also has a higher risk of self-oscillation.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] The object of the present invention is to provide a weakly reflective folded waveguide slow-wave structure, which improves the coupling impedance of a conventional folded waveguide slow-wave structure and reduces the reflection coefficient in the slow-wave structure.

[0010] To solve the above problems, an embodiment of the present invention provides a weakly reflective folded waveguide slow-wave structure, comprising a straight waveguide section and a bending area, wherein an impedance matching area is provided between the straight waveguide section and the bending area for impedance matching connection between the straight waveguide section and the bending area.

[0011] Furthermore, the cross section of the impedance matching region formed on a section perpendicular to the wide surface of the straight waveguide section is triangular.

[0012] Furthermore, the bending area includes an inner arc and an outer arc, the inner arc is eccentric toward a side close to the electron injection channel of the slow-wave structure, and the outer arc is a non-eccentric arc of 180 degrees.

[0013] Furthermore, the slow-wave structure is constructed according to the following geometric constraints:

[0014]

[0015] Where a is the width of the wide side of the folded waveguide, b is the width of the narrow side of the folded waveguide, p is the half-period length of the folded waveguide, h1 is the length of the impedance matching area, h in The inward eccentric distance used for the inner arc of the bending area.

[0016] Furthermore, the slow-wave structure also satisfies the following geometric constraints: h1 = h out , where h out is the eccentric distance of the center of the outer arc of the bending area.

[0017] Furthermore, the radius R of the outer arc of the bending area out Satisfaction: R out =0.5(p+b).

[0018] Furthermore, the radius R of the eccentric inner arc of the bending area in satisfy:

[0019] Since the weakly reflective folded slow-wave structure in the scheme of the present invention introduces an impedance matching section, good impedance matching is achieved, and therefore the slow-wave structure has good RF transmission characteristics; at the same time, compared with conventional folded waveguides and eccentric arc folded waveguide slow-wave structures of the same physical dimensions, the scheme of the present invention has excellent reflection performance; and compared with conventional folded waveguides of the same physical dimensions, the coupling impedance of the scheme of the present invention is significantly improved compared with conventional folded waveguides. The traveling wave tube based on the scheme of the present invention will have physical performance advantages such as greater output power, higher interaction efficiency, and lower oscillation risk. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the structure of an existing ridge-loaded folded waveguide slow-wave structure;

[0021] Figure 2 Schematic diagram of the structure of an existing eccentric arc folded waveguide slow-wave structure;

[0022] Figure 3 A schematic side cross-sectional view of a weakly reflective folded waveguide slow-wave structure provided by an embodiment of the present invention;

[0023] Figure 4A schematic diagram of the three-dimensional structure of a weakly reflective folded waveguide slow-wave structure provided by an embodiment of the present invention;

[0024] Figure 5 A comparison diagram of the normalized phase velocity between the slow-wave structure according to an embodiment of the present invention and a conventional folded waveguide;

[0025] Figure 6 1 is a comparison diagram of the coupling impedance between the slow-wave structure of an embodiment of the present invention and a conventional folded waveguide;

[0026] Figure 7 This is a comparison diagram of reflection parameters of the slow-wave structure of an embodiment of the present invention, a conventional folded waveguide, and an eccentric arc folded waveguide slow-wave structure.

[0027] In the figure: 1-straight waveguide section; 2-bending area; 3-impedance matching area; 4-electron injection channel. DETAILED DESCRIPTION

[0028] The principles and spirit of the present invention will be described below with reference to several exemplary embodiments shown in the accompanying drawings. It should be understood that these embodiments are described only to enable those skilled in the art to better understand and implement the present invention, and are not intended to limit the scope of the present invention in any way.

[0029] In the description of the embodiments of the present invention, the term "including" and similar terms should be understood as open inclusion, i.e., "including but not limited to." The term "based on" should be understood as "based at least in part on." The term "one embodiment" or "the embodiment" should be understood as "at least one embodiment." The terms "first," "second," etc. may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0030] As previously mentioned, both ridge-loaded and eccentric arc-shaped folded waveguide slow-wave structures have their own shortcomings. However, prior to the present invention providing the following technical solutions to address these shortcomings and problems, neither the aforementioned issues nor the underlying causes of these problems were identified in the prior art.

[0031] In view of this, the inventors not only discovered the technical problems existing in the above two slow-wave structures, but also carried out research and analysis on the above technical problems. After research, the inventors found the underlying causes of the above problems and solved them with ingenious technical ideas.

[0032] Below, the technical solution of the present invention will be introduced in conjunction with the thinking process of the inventor when making improvements to the present invention. It should be understood that the part related to the thinking process is also part of the inventor's creative work.

[0033] The slow-wave structure provided in the embodiments of the present invention is a component of a traveling wave tube (TWT). The TWT is primarily composed of a slow-wave structure, an electron gun, a magnetic focusing system, a high-frequency input-output structure, and a step-down collection stage. During TWT operation, the electron gun emits an electron beam, which exchanges energy with the electromagnetic field in the slow-wave structure. In the magnetic focusing system, the magnetic field force is used to offset the space charge repulsion in the electron beam, constraining the electron beam so that it can pass smoothly through the entire slow-wave structure without being intercepted. The slow-wave structure's primary function is to transmit high-frequency electromagnetic waves and reduce their phase velocity to a value close to the injection velocity of the electron beam. It is the primary site for beam-wave interaction, modulating the electron beam so that it transfers energy to the high-frequency electromagnetic field. The high-frequency input-output structure's primary function is to couple the high-frequency input signal energy into the slow-wave structure and couple the amplified high-frequency signal energy to the output circuit. The collection stage is used to collect electrons that have already exchanged energy with the electromagnetic field. When the electrons hit the collection stage, they are converted into heat energy and dissipated.

[0034] As mentioned earlier, the slow-wave structure is a core component of a traveling wave tube (TWT). Its dispersion characteristics, coupling impedance, and RF transmission characteristics play a key role in the device's performance. Dispersion characteristics are one of the key characteristics of the slow-wave structure, which can determine the TWT's synchronous operating voltage, operating bandwidth, and other indicators. Coupling impedance is another key characteristic of the slow-wave structure. It usually depends on parameters such as the longitudinal electric field strength and transmission power flow within the electron beam channel. Coupling impedance is related to a series of important indicators such as the TWT's output power, interaction efficiency, and output gain. In addition, the transmission performance of the slow-wave structure deteriorates significantly in the millimeter wave and terahertz bands. Increased transmission loss reduces the device's interaction efficiency and gain, while deteriorating reflection performance increases the risk of self-oscillation in high-gain TWTs. Therefore, the RF transmission characteristics of the slow-wave structure itself also largely determine the device's physical performance.

[0035] The inventors found that the conventional folded waveguide slow-wave structure has suitable RF transmission performance, but its coupling impedance is relatively low, resulting in low output power and electronic efficiency of the conventional folded waveguide traveling wave tube; the inventors also found that the ridge-loaded folded waveguide slow-wave structure and the eccentric arc folded waveguide slow-wave structure proposed in the prior art can both achieve longitudinal electric field enhancement inside the electron injection channel, but due to the impedance mismatch between the curved section and the straight waveguide section of the slow-wave structure, the reflection coefficient will increase, resulting in an increased risk of self-oscillation of the traveling wave tube based on such slow-wave structure.

[0036] In view of this, an embodiment of the present invention provides a weak reflection type folded waveguide slow wave structure, such as Figure 3 and Figure 4As shown in . Different from the prior art, the embodiment of the present invention adds an impedance matching region 3 with a triangular cross-section between the straight waveguide section 1 and the bending region 2 of the folded waveguide slow-wave structure (the cross-section is a cross-section cut vertically, that is, the cross-section is perpendicular to the wide surface of the straight waveguide section 1, and overlaps or is parallel to the axis of the electron injection channel 4), which is used to achieve an impedance matching connection between the straight waveguide section 1 and the bending region 2 to reduce transmission reflections in the slow-wave structure. In one embodiment, the impedance matching region 3 is a cavity structure with an outer wall made of metal material. In addition, in one embodiment, the bottom surface of the impedance matching region 3 is a continuous plane formed by extending from the top edge of one side of the inner wall of the straight waveguide section 1 to the top edge of the other side, and the vertical surface of the impedance matching region 3 is a continuous plane formed by extending upward from the top edge of the inner wall of the straight waveguide section 1 close to the outside of the slow-wave structure according to the designed length. The inclined surface of the impedance matching region 3 is a continuous plane extending from the top edge of the vertical surface of the impedance matching region 3 to the edge of the bottom surface of the impedance matching region 3 close to the inner side of the slow-wave structure, so that the cross-section of the impedance matching region 3 forms a triangle.

[0037] Furthermore, in order to enhance the longitudinal electric field strength of the slow-wave structure within the electron injection channel 4, the inner arc of the bending region 2 adopts an inwardly eccentric arc design (the center of the circle is close to the electron injection channel side), while the outer arc of the bending region 2 adopts a non-eccentric 180-degree arc curve to achieve a smooth connection with the impedance matching area, ensuring that the reflection does not deteriorate while the coupling impedance of the slow-wave structure is improved.

[0038] In one embodiment, the dimensions of the weakly reflective folded waveguide slow-wave structure of the present invention are as follows: Figure 3 、 Figure 4 As shown in , the wide side of the folded waveguide is a, the narrow side of the folded waveguide is b, the length of the straight waveguide section is h, the half-period length of the folded waveguide is p, the diameter of the electron beam channel is d, the length of the impedance matching area is h1, and the inner arc of the bending area adopts an inward eccentric distance (OO1) of h in , the eccentric distance (OO2) of the center of the outer arc of the bending area is h out , the radius of the arc in the bending area is R in , the radius of the arc outside the bending area is R out O is the center point between the top edges of the outer walls of adjacent straight waveguide segments, which is the center point of the inner arc of the bending zone if it is constructed as a 180-degree arc without eccentricity. O2 is the center point of the outer arc of the bending zone, and O1 is the center point of the inner arc of the bending zone.

[0039] The above structural parameters must satisfy the following geometric constraints:

[0040] 1. To ensure that the electromagnetic wave maintains the main mode TE during transmission 10 Mode transmission and impedance matching area can achieve impedance matching effect. The length h1 of the impedance matching area needs to satisfy the following relationship:

[0041]

[0042] 2. To ensure smooth connection of the outer arc impedance matching zone in the bending area, the length h1 of the impedance matching zone must also meet the following requirements: h1 = h out ;

[0043] 3. The radius of the arc outside the bending area is R out Need to meet: R out =0.5(p+b);

[0044] 4. The radius of the eccentric inner arc in the bending area is R in Need to meet:

[0045] Example 1

[0046] Taking the slow wave structure of the W-band millimeter wave traveling wave tube as an example, the wide side length a is selected to be 1.8 mm, the narrow side b of the folded waveguide is selected to be 0.3 mm, the straight waveguide section length h is selected to be 0.52 mm, the folded waveguide half-period length p is selected to be 0.6 mm, the electron beam channel diameter d is selected to be 0.48 mm, the impedance matching area length h1 is selected to be 0.05 mm, and the inner arc of the bending area adopts an inward eccentric distance h in The eccentric distance h of the outer arc center of the bending area is 0.1mm. out It is 0.05mm.

[0047] Through simulation results, we can find that (such as Figure 5 As shown in ), under the condition of the same size structure, the present invention has a higher normalized phase velocity and a flatter dispersion curve than the conventional folded waveguide, which indicates that the traveling wave tube with a slow-wave structure based on the present invention will have a higher synchronization voltage and a wider synchronization bandwidth.

[0048] like Figure 6 As shown in the figure, it can be seen that the coupling impedance of the slow-wave structure of the embodiment of the present invention is significantly higher than that of the conventional folded waveguide within the working frequency band, and the coupling impedance at the typical frequency of 94 GHz is about 37.5% higher than that of the conventional sinusoidal waveguide, which indicates that the traveling wave tube based on the slow-wave structure of the embodiment of the present invention will have greater output power, higher interaction efficiency and output gain.

[0049] Using the structural parameters of the weak reflection type folded slow wave structure in the embodiment of the present invention given above, the main period is selected as 23, and the effective conductivity is set to 2.25×10 7S / m. A transmission characteristic calculation model is established in the electromagnetic simulation software. Through the time domain simulation in the software, the simulation calculation results of the transmission parameters of the weak reflection type folded slow-wave structure can be obtained, and compared with the conventional folded waveguide and the eccentric arc folded waveguide slow-wave structure in the existing scheme-2, such as Figure 7 As shown in . In the operating frequency band of 88-102 GHz, the reflection parameter of the weak-reflection folded slow-wave structure is less than -23.7 dB, which is 10 dB lower than that of the conventional folded waveguide and the weak-reflection folded slow-wave structure. This shows that the weak-reflection folded slow-wave structure in the solution of the present invention has good RF transmission performance.

[0050] Through the simulation analysis results of the embodiments of the present invention, it can be seen that since the weak-reflection folded slow-wave structure in the scheme of the present invention introduces an impedance matching section to achieve good impedance matching, this slow-wave structure has good RF transmission characteristics; at the same time, compared with conventional folded waveguides and eccentric arc folded waveguide slow-wave structures of the same physical dimensions, the scheme of the present invention has excellent reflection performance; and compared with conventional folded waveguides of the same physical dimensions, the coupling impedance of the scheme of the present invention is significantly improved compared with conventional folded waveguides. The traveling wave tube based on the scheme of the present invention will have physical performance advantages such as greater output power, higher interaction efficiency, and lower oscillation risk.

[0051] This document uses specific examples to illustrate the inventive concept in detail. The above embodiments are only intended to help understand the core concept of the present invention. It should be noted that any obvious modifications, equivalent substitutions, or other improvements made by a person skilled in the art without departing from the inventive concept should be included within the scope of protection of the present invention.

Claims

1. A weakly reflective folded waveguide slow-wave structure, characterized in that: It comprises a straight waveguide section and a bending area, wherein an impedance matching area is provided between the straight waveguide section and the bending area for impedance matching connection between the straight waveguide section and the bending area; The bending area includes an inner arc and an outer arc, the inner arc is eccentric toward a side close to the electron injection channel of the slow-wave structure, and the outer arc is a non-eccentric arc of 180 degrees; The slow-wave structure is constructed according to the following geometric constraints: Where a is the width of the wide side of the folded waveguide, b is the width of the narrow side of the folded waveguide, p is the half-period length of the folded waveguide, h1 is the length of the impedance matching area, h in The inward eccentric distance used for the inner arc of the bending area.

2. The weakly reflective folded waveguide slow-wave structure according to claim 1, characterized in that: The cross section of the impedance matching region formed on a section perpendicular to the wide surface of the straight waveguide section is triangular.

3. The weakly reflective folded waveguide slow-wave structure according to claim 1, characterized in that: The slow-wave structure also satisfies the following geometric constraints: h1 = h out , where h out is the eccentric distance of the center of the outer arc of the bending area.

4. The weakly reflective folded waveguide slow-wave structure according to claim 3, characterized in that: The radius R of the outer arc of the bending area out Satisfaction: R out =0.5(p+b).

5. The weakly reflective folded waveguide slow-wave structure according to claim 4, characterized in that: Radius R of the eccentric inner arc of the bending area in satisfy:

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