A folded waveguide slow-wave structure and vacuum electron tube

Abstract

The embodiment of the present application provides a folded waveguide slow-wave structure and a vacuum electron tube. The slow-wave structure includes a folded waveguide unit, which includes: a smoothly curved waveguide segment; a first and a second straight waveguide segment, respectively located at both ends of the smoothly curved waveguide segment; the first and second curved waveguide segments, the first curved waveguide segment is located at the end of the first straight waveguide segment, and the second curved waveguide segment is located at the end of the second straight waveguide segment; the first curved waveguide segment, the first straight waveguide segment, the smooth curved waveguide segment, the second straight waveguide segment and the second curved waveguide segment are smoothly connected in sequence, the width of the smooth curved waveguide segment is not less than the width of the straight waveguide segment, and the width of at least part of the smooth curved waveguide segment is greater than the width of the straight waveguide segment. The embodiment of the present application improves the coupling impedance, increases the total output power, reduces the slow-wave line length required for power saturation, realizes high-power miniaturization, and has a first-order continuous gradient, small reflection coefficient and transmission loss, which is conducive to improving processing accuracy and quality.

Description

Technical Field

[0001] The present application relates to the field of vacuum electronic devices, and in particular to a folded waveguide slow-wave structure and a vacuum electron tube. Background Art

[0002] Currently, the main slow-wave structures being studied in terahertz traveling-wave tubes (TWTs) include folded waveguides, rectangular staggered double gratings, and double-row rectangular gratings. Terahertz waves operate at very short wavelengths, and due to the size co-transit effect, high-frequency systems become very small, making fabrication difficult and requiring low precision, resulting in high reflections and losses. Folded waveguide slow-wave structures offer wide bandwidth, low loss, high thermal conductivity, and ease of fabrication and assembly, making them widely used as TWT slow-wave structures.

[0003] However, the electric field strength of the conventional folded waveguide slow-wave structure in the direction of electromagnetic wave transmission is relatively weak, so its coupling impedance is small, resulting in defects such as low output power and interaction efficiency, low gain and long saturation interaction length of the folded waveguide traveling wave tube, which is not conducive to miniaturization; or, the waveguide boundary is not smoothly connected, has mutation points, does not have first-order continuity and gradualness, the reflection coefficient is relatively large, and the electric field is concentrated at the mutation point, resulting in excessive electromagnetic wave transmission loss. During processing, the force at the mutation point is uneven, affecting the processing accuracy and quality. Summary of the Invention

[0004] The embodiments of the present application provide a folded waveguide slow-wave structure and a vacuum electron tube, which can improve the coupling impedance, increase the total output power, and reduce the slow-wave line length required when the power is saturated, thereby achieving the purpose of high-power miniaturization. At the same time, it has a first-order continuous gradient, a small reflection coefficient and transmission loss, and is conducive to improving processing accuracy and processing quality.

[0005] To this end, the embodiments of the present application adopt the following technical solutions:

[0006] In a first aspect, an embodiment of the present application provides a folded waveguide slow-wave structure, the folded waveguide slow-wave structure comprising one or at least two folded waveguide units connected in sequence, the folded waveguide unit comprising: a smoothly curved waveguide segment having a mid-axis plane and being symmetrical about the mid-axis plane; a first straight waveguide segment and a second straight waveguide segment, respectively located at both ends of the smooth curved waveguide segment and symmetrical about the mid-axis plane; a first curved waveguide segment and a second curved waveguide segment, the first curved waveguide segment being located at an end of the first straight waveguide segment away from the smooth curved waveguide segment, and the second curved waveguide segment being located at an end of the second straight waveguide segment away from the smooth curved waveguide segment. The ends of the curved waveguide segments are symmetrical about the central axis plane; wherein the inner surfaces of the first curved waveguide segment, the first straight waveguide segment, the smooth curved waveguide segment, the second straight waveguide segment and the second curved waveguide segment are smoothly connected in sequence and their outer surfaces are smoothly connected in sequence, the width between the inner surface and the outer surface of the smooth curved waveguide segment is not less than the width between the inner surface and the outer surface of the first straight waveguide segment or the second straight waveguide segment, and the width of at least part of the smooth curved waveguide segment is greater than the width of the first straight waveguide segment or the second straight waveguide segment.

[0007] In the embodiment of the present application, the inner surfaces and outer surfaces of the plurality of waveguide segments arranged in sequence are smoothly connected, the width of the smoothly curved waveguide segment is not less than the width of the straight waveguide segment, and the width of at least some of the smoothly curved waveguide segments is greater than the width of the straight waveguide segment. This makes the electric field strength in the direction of electromagnetic wave transmission relatively strong, improves the coupling impedance, increases the total output power, reduces the length of the slow-wave line required for power saturation, and helps achieve the purpose of high-power miniaturization. At the same time, it has a first-order continuous gradient. On the one hand, the reflection coefficient and transmission loss are small, and on the other hand, it is conducive to improving processing accuracy and processing quality. In addition, it should be noted that the central axis plane is perpendicular to the arrangement direction of at least two folded units. The folded waveguide slow-wave structure is a hollow structure processed on the metal, and it needs to be vacuumed before operation.

[0008] In one possible implementation, the tangent lines at both ends of the inner and outer curvature lines of the cross section of the smoothly curved waveguide segment are aligned with the extension direction of the central axis of the cross section of the smoothly curved waveguide segment, so that the two ends of the smoothly curved waveguide segment are smoothly connected to the first straight waveguide segment and the second straight waveguide segment in a tangential manner, respectively. The width of the smoothly curved waveguide segment is maximum at the mid-axis plane or at the middle portion along the curvature direction between the mid-axis plane and the ends of the smoothly curved waveguide segment. That is, the two ends of the outer surface of the smoothly curved waveguide segment are tangentially connected to the outer surface of the first straight waveguide segment and the outer surface of the second straight waveguide segment, respectively, and the two ends of the inner surface of the smoothly curved waveguide segment are tangentially connected to the inner surface of the first straight waveguide segment and the inner surface of the second straight waveguide segment, respectively. Thus, the widths of the two ends of the smoothly curved waveguide segment are equal to the width of the waveguide segment. Furthermore, when the width of the smoothly curved waveguide segment is greatest at the mid-axis plane, the width of the smoothly curved waveguide segment may increase along the direction from both ends of the smoothly curved waveguide segment to the mid-axis plane. When the width of the smoothly curved waveguide segment is greatest at the middle portion along the curvature direction between the mid-axis plane and the ends of the smoothly curved waveguide segment, the width of the smoothly curved waveguide segment may increase from the ends of the smoothly curved waveguide segment and the mid-axis plane toward each other along the curvature direction. Furthermore, it is understood that, provided that usage requirements are met, the width of the smoothly curved waveguide segment may also be greatest at locations other than the mid-axis plane and the middle portion mentioned above.

[0009] In one possible implementation, the widths of both ends of the smoothly curved waveguide segment are equal to the widths of the first straight waveguide segment or the second straight waveguide segment, and the width of the smoothly curved waveguide segment increases from both ends of the smoothly curved waveguide segment to the central axis, wherein: the longitudinal dimension of the outer curvature line of the cross-section of the smoothly curved waveguide segment along the central axis is greater than the transverse dimension perpendicular to the central axis, and the longitudinal dimension of the inner curvature line of the cross-section of the smoothly curved waveguide segment along the central axis is greater than, equal to, or less than the transverse dimension perpendicular to the central axis; or, the longitudinal dimension of the outer curvature line of the cross-section of the smoothly curved waveguide segment along the central axis is equal to or less than the transverse dimension perpendicular to the central axis, and the longitudinal dimension of the inner curvature line of the cross-section of the smoothly curved waveguide segment along the central axis is less than the transverse dimension perpendicular to the central axis. That is, when the width of the smoothly curved waveguide segment is maximum at the central axis, the following two situations may occur. The first case is that the longitudinal dimension of the outer bending line may be greater than the transverse dimension, for example, the outer bending line may be a first semi-elliptical line; at this time, the longitudinal dimension of the inner bending line may be greater than the transverse dimension, for example, the inner bending line may be a second semi-elliptical line, and the second semi-elliptical line is different from the first semi-elliptical line; or the longitudinal dimension of the inner bending line may be equal to the transverse dimension, for example, the inner bending line may be a semicircular arc line; or, the longitudinal dimension of the inner bending line may be smaller than the transverse dimension, for example, the inner bending line may be a combination of two circular arc lines and a cosine line connected between the two circular arc lines. The second case is that the longitudinal dimension of the outer curvature is equal to or smaller than the transverse dimension. When the longitudinal dimension of the outer curvature is equal to the transverse dimension, the outer curvature can be, for example, a semicircular arc. When the longitudinal dimension of the outer curvature is smaller than the transverse dimension, the outer curvature can be, for example, a combination of two first circular arcs and a first cosine line. In this case, the longitudinal dimension of the inner curvature can be smaller than the transverse dimension. For example, the inner curvature can be a combination of two second circular arcs and a second cosine line, and the radius of the first circular arc is larger than the radius of the second circular arc. The first cosine line and the second cosine line can be the same or different. In addition, it should be noted that both of the above cases must meet the following requirements: the width of the smoothly curved waveguide segment is not less than the width of the first straight waveguide segment or the second straight waveguide segment, and the width of at least part of the smoothly curved waveguide segment is greater than the width of the first straight waveguide segment or the second straight waveguide segment.

[0010] In one possible implementation, the inner curvature line and the outer curvature line each include one of the following types: two arcs and a cosine line connected between the two arcs; two arcs and a top portion of a parabola connected between the two arcs; two arcs and a top portion of a semi-ellipse connected between the two arcs; wherein the tangents of the ends of the two arcs of the outer curvature line and the inner curvature line away from each other along the curvature direction are consistent with the extension direction of the central axis, so that the two ends of the smoothly curved waveguide section are smoothly connected to the first straight waveguide section and the second straight waveguide section in a tangential manner. That is, the portion between the two arcs of the outer curvature line can be the same as or different from the portion between the two arcs of the inner curvature line. When the portion between the two arcs of the outer curvature line is the same as the portion between the two arcs of the inner curvature line, the inner curvature line and the outer curvature line are of the same type. For example, the inner curvature line and the outer curvature line are both two arcs and a cosine line connected between the two arcs. When the portion between the two arcs of the outer curve line is different from the portion between the two arcs of the inner curve line, the inner and outer curve lines are of different types. For example, the inner curve line is composed of two arcs and a cosine line connected between the two arcs, while the outer curve line is composed of two arcs and the top portion of a parabola connected between the two arcs. Furthermore, the radius of the two arcs of the outer curve line is greater than the radius of the two arcs of the inner curve line. Furthermore, the portion between the two arcs may be composed of other continuous curve types besides cosine lines, parabolas, and elliptical lines.

[0011] In one possible implementation, the inner and outer curvatures are of the same type, and the portion between the two arcs of the outer curvature is obtained by translating the top portion of a cosine line, a parabola, or a semi-ellipse between the two arcs of the inner curvature; and / or the central angle of the arc of the inner curvature is the same as the central angle of the arc of the outer curvature. That is, translating the portion between the two arcs of the inner curvature can obtain the portion between the two arcs of the outer curvature. In this case, the portion between the two arcs of the inner curvature and the portion between the two arcs of the outer curvature have the same size along the arrangement direction of at least two folded waveguide units. Furthermore, through reasonable design, the central angle of the arc of the inner curvature can be made different from that of the arc of the outer curvature, or the central angle of the arc of the inner curvature can be made the same as that of the arc of the outer curvature.

[0012] In a possible implementation, the central angles of the arcs of the inner and outer bending lines are both 45°, that is, one eighth of a circle. The radius of the arc line of the outer bending line The portion between the two arcs of the outer curvature line is obtained by translating the portion between the two arcs of the inner curvature line, and the translation distance is Among them, b is the width of the first straight waveguide segment or the second straight waveguide segment, p is the distance between the central axis plane of the first straight waveguide segment and the central axis plane of the second straight waveguide segment, and s is the dimension of the part between the two arc lines of the inner bending line along the arrangement direction of the two folded waveguide units.

[0013] In one possible implementation, the inner curvature is a first semi-elliptical line, and the outer curvature is a second semi-elliptical line. The tangent lines at both ends of the first semi-elliptical line and the second semi-elliptical line are consistent with the extension direction of the central axis, thereby achieving a smooth and tangential connection between the two ends of the smoothly curved waveguide segment and the first straight waveguide segment and the second straight waveguide segment, respectively. In other words, the inner curvature and the outer curvature are both semi-elliptical lines, and their sizes are different. This ensures that the two ends of the first semi-elliptical line, which serves as the inner curvature, can be tangentially connected to the inner side surface of the first straight waveguide segment and the inner side surface of the second straight waveguide segment, respectively, and the two ends of the second semi-elliptical line, which serves as the outer curvature, can be tangentially connected to the outer side surface of the first straight waveguide segment and the outer side surface of the second straight waveguide segment, respectively, thereby achieving a smooth connection between the two ends of the smoothly curved waveguide segment and the first straight waveguide segment and the second straight waveguide segment, respectively.

[0014] In one possible implementation, one of the inner and outer curvature lines includes two circular arcs and a curvature line connected between the two circular arcs, and the other includes a semi-ellipse, wherein the curvature line includes one of a cosine line, a top portion of a parabola, and a top portion of a semi-ellipse; and the tangents of the ends of the two circular arcs away from each other along the curvature direction and the tangents of the two ends of the semi-ellipse are consistent with the extension direction of the central axis of the cross section of the smoothly curved waveguide segment, so that the two ends of the smoothly curved waveguide segment are smoothly connected to the first straight waveguide segment and the second straight waveguide segment in a tangential manner. That is, the types of the inner and outer curvature lines can be different, one of the two can be a combination of two circular arcs and a curvature line, and the other can be a semi-ellipse, and the ends of the two circular arcs can be tangentially connected to the outer side surface or the inner side surface of the straight waveguide segment, and the two ends of the semi-ellipse can be tangentially connected to the inner side surface or the outer side surface of the straight waveguide segment.

[0015] In one possible implementation, the outer bending line includes two circular arc lines and a bending line connected between the two circular arc lines or includes a semi-elliptical line, and the bending line includes one of a cosine line, the top part of a parabola and the top part of a semi-elliptical line; the inner bending line includes two cosine lines, and the first ends of the two cosine lines are smoothly connected. The tangents of the second ends of the two cosine lines and the tangents of the ends of the two circular arc lines away from each other along the bending direction or the tangents of the two ends of the semi-elliptical line are consistent with the extension direction of the central axis of the cross-section of the smoothly curved waveguide section, so that the two ends of the smoothly curved waveguide section are smoothly connected to the first straight waveguide section and the second straight waveguide section in a tangential manner. That is to say, the types of the inner bending line and the outer bending line may be different, the inner bending line may be two cosine lines, the outer bending line may be a combination of two circular arc lines and a bending line or may be a semi-elliptical line, and the ends of the two cosine lines away from each other along the bending direction can be connected tangentially to the inner side surface of the straight waveguide section, the ends of the two circular arc lines away from each other along the bending direction or the two ends of the semi-elliptical line can be connected tangentially to the outer side surface of the straight waveguide section.

[0016] In one possible implementation, the inner bending line is a semicircular arc line, the longitudinal dimension of the outer bending line along the central axis is larger than the transverse dimension along the direction perpendicular to the central axis, and the outer bending line includes two circular arc lines and a bending line or includes a semi-elliptical line; or, the outer bending line is a semicircular arc line, the longitudinal dimension of the inner bending line along the central axis is smaller than the transverse dimension along the direction perpendicular to the central axis, and the inner bending line includes two circular arc lines and a bending line or includes a semi-elliptical line; wherein the bending line is connected between the two circular arc lines and includes one of a cosine line, a top part of a parabola, and a top part of a semi-elliptical line. That is to say, the types of the inner bending line and the outer bending line may be different, and one of them may be a semicircular arc line, wherein: when the inner bending line is a semicircular arc line, if it is to be ensured that at least part of the width of the smoothly curved waveguide section is greater than the width of the straight waveguide section, the longitudinal dimension of the outer bending line needs to be greater than the transverse dimension, and the outer bending line may include two circular arc lines and a bending line or may include a semi-elliptical line; when the outer bending line is a semicircular arc line, if it is to be ensured that at least part of the width of the smoothly curved waveguide section is greater than the width of the straight waveguide section, the longitudinal dimension of the inner bending line needs to be smaller than the transverse dimension, and the inner bending line may include two circular arc lines and a bending line or include a semi-elliptical line.

[0017] In one possible implementation, the widths of both ends of the smoothly curved waveguide segment are equal to the widths of the first straight waveguide segment or the second straight waveguide segment, the width of the smooth curved waveguide segment at the mid-axis plane is greater than or equal to the widths of the first straight waveguide segment or the second straight waveguide segment, and the width of the smoothly curved waveguide segment increases from the ends of the smoothly curved waveguide segment and the mid-axis plane toward each other along the bending direction. In other words, the width of the smoothly curved waveguide segment reaches a maximum at a midpoint between the mid-axis plane and the ends of the smoothly curved waveguide segment along the bending direction. Specifically, the width of the smoothly curved waveguide segment is maximum at a cross section that has an angle of 45 degrees with the mid-axis plane and passes through the midpoints between the two ends of the smoothly curved waveguide segment. In this way, the width of the smoothly curved waveguide segment increases from the ends of the smoothly curved waveguide segment to the cross section, and the width of the smoothly curved waveguide segment increases from the mid-axis plane of the smoothly curved waveguide segment to the cross section.

[0018] In one possible implementation, the inner curvature of the cross section of the smoothly curved waveguide segment is a semicircular arc, and the outer curvature of the cross section of the smoothly curved waveguide segment has a longitudinal dimension along the central axis that is equal to the transverse dimension along the direction perpendicular to the central axis. The outer curvature includes two cosine lines, the first ends of the two cosine lines are tangentially connected, and the tangents of the second ends of the two cosine lines and the tangents of the two ends of the semicircular arc are consistent with the extension direction of the central axis, so that the two ends of the smoothly curved waveguide segment are smoothly connected to the first straight waveguide segment and the second straight waveguide segment in a tangential manner. In other words, the inner curvature can be a semicircular arc, and the outer curvature can be two cosine lines. The width of the cross section of the smoothly curved waveguide segment formed by the two can increase from the central axis plane and the ends of the smoothly curved waveguide segment toward each other along the bending direction, and is the largest in the middle between the central axis plane and the ends of the smoothly curved waveguide segment along the bending direction.

[0019] In a possible implementation, the inner curvature line and the outer curvature line of the cross section of the smoothly curved waveguide section respectively include one of the following types: two cosine lines, the first ends of the respective cosine lines are smoothly connected, and the tangents of the second ends of the respective cosine lines are consistent with the extension direction of the central axis of the cross section of the smoothly curved waveguide section, so that the two ends of the smoothly curved waveguide section are respectively smoothly connected to the first straight waveguide section and the second straight waveguide section in a tangential manner; the top parts of two parabolas, the first ends of the respective top parts of the two parabolas are smoothly connected, and the top parts of the two parabolas are respectively The tangent of the second end of the smooth curved waveguide section is consistent with the extension direction of the central axis of the cross section of the smooth curved waveguide section, so that the two ends of the smooth curved waveguide section are smoothly connected to the first straight waveguide section and the second straight waveguide section in a tangential manner; the top portions of the two semi-elliptical lines, the first ends of the top portions of the two semi-elliptical lines are smoothly connected, and the tangent of the second end of the top portions of the two semi-elliptical lines is consistent with the extension direction of the central axis of the cross section of the smooth curved waveguide section, so that the two ends of the smooth curved waveguide section are smoothly connected to the first straight waveguide section and the second straight waveguide section in a tangential manner. In other words, the inner and outer curved lines of the cross section of the smooth curved waveguide section can be of different types, for example, one is two cosine lines and the other is two parabolas; or the inner and outer curved lines of the cross section of the smooth curved waveguide section can be of the same type, for example, both are two cosine lines. It should be noted that regardless of whether the two types are the same or different, the following conditions must be met: the width of the smoothly curved waveguide segment is not less than the width of the first straight waveguide segment or the second straight waveguide segment, and the width of at least part of the smoothly curved waveguide segment is greater than the width of the first straight waveguide segment or the second straight waveguide segment.

[0020] In one possible implementation, the first curved waveguide segment and half of the smoothly curved waveguide segment are centrally symmetrical structures about the center of the first straight waveguide segment; the second curved waveguide segment and the other half of the smoothly curved waveguide segment are centrally symmetrical structures about the center of the second straight waveguide segment; and / or, electron injection channels are respectively provided on the first straight waveguide segment and the second straight waveguide segment, and the cross-sectional shape of the electron injection channels is circular or rectangular.

[0021] In a second aspect, an embodiment of the present application provides a vacuum electron tube, comprising the folded waveguide slow-wave structure provided in the first aspect. The vacuum electron tube may be one of a traveling wave tube, a backward wave tube, a klystron, and a magnetron.

[0022] Other features and advantages of the embodiments of the present application will be described in detail in the subsequent specific embodiments section. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following is a brief introduction to the drawings required for describing the embodiments or prior art.

[0024] Figure 1 This is a schematic diagram of the three-dimensional structure of a common folded waveguide slow-wave structure;

[0025] Figure 2A A schematic diagram of the three-dimensional structure of a folded waveguide slow-wave structure;

[0026] Figure 2B A schematic diagram of the three-dimensional structure of another folded waveguide slow-wave structure;

[0027] Figure 3A A schematic structural diagram of a folded waveguide unit of a folded waveguide slow-wave structure;

[0028] Figure 3B It is a structural schematic diagram of a folded waveguide unit of another folded waveguide slow-wave structure;

[0029] Figure 3C A schematic structural diagram of a folded waveguide unit of another folded waveguide slow-wave structure;

[0030] Figure 3D Schematic diagram of the cross section of another folded waveguide slow-wave structure;

[0031] Figure 4 A schematic diagram of the three-dimensional structure of a folded waveguide slow-wave structure provided in an embodiment of the present application;

[0032] Figure 5A for Figure 4 An exemplary structural diagram of a folded waveguide unit of a folded waveguide slow-wave structure is shown;

[0033] Figure 5B for Figure 4 An exemplary actual structural diagram of the folded waveguide slow-wave structure is shown;

[0034] Figure 5C for Figure 4 The cosine-bent folded waveguide slow-wave structure shown is similar to Figure 1 The comparison diagram of the interaction impedance-frequency of the common folded waveguide slow-wave structure is shown;

[0035] Figure 5D for Figure 4 The cosine-bent folded waveguide slow-wave structure shown is similar to Figure 1 The output power-frequency comparison diagram of the common folded waveguide slow-wave structure is shown;

[0036] Figure 5E for Figure 4 The cosine-bent folded waveguide slow-wave structure shown is similar to Figure 1The comparison diagram of the device length required for the power saturation of the common folded waveguide slow-wave structure shown;

[0037] Figure 6 Another exemplary structural diagram of the folded waveguide unit of the folded waveguide slow-wave structure according to an embodiment of the present application;

[0038] Figure 7 This is another exemplary structural diagram of the folded waveguide unit of the folded waveguide slow-wave structure of an embodiment of the present application. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0040] In the description of this application, the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limiting this application.

[0041] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "install", "connect" and "connect" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, a conflicting connection or an integrated connection. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0042] In the description of this specification, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0043] The following is a detailed introduction to the abbreviations and key terms used in the embodiments of this application:

[0044] A traveling wave tube (TWT) is a microwave electron tube that achieves amplification by continuously modulating the speed of an electron beam. In a TWT, the electron beam interacts with the microwave field traveling in a slow-wave circuit. Within the slow-wave circuit, which can be 6 to 40 wavelengths long, the electron beam continuously transfers kinetic energy to the microwave signal field, thereby amplifying the signal. Due to the long duration of the action, the gain is very high, and the lack of a resonant cavity significantly increases the operating bandwidth. In other words, the function of a TWT is to amplify microwave signals. The microwave signal to be amplified enters the slow-wave circuit through an input energy coupler and travels along the slow-wave circuit. The electrons exchange energy with the traveling microwave field, amplifying the microwave signal.

[0045] Terahertz technology. Terahertz radiation is electromagnetic radiation in the 0.1-10 THz range. Its frequency lies between radio waves and light waves, millimeter waves and infrared light, and its energy lies between electrons and photons. As the pinnacle of the new scientific and technological revolution, terahertz technology is thriving in both military and civilian fields, driving the advancement of human society. In the military, terahertz technology can be applied to high-resolution radar imaging, electronic countermeasures, deep space exploration, deep space communications, ultra-wideband satellite communications, and electromagnetic weapons. In the civilian sector, with the accelerated evolution of the information age, people's growing communication needs require greater communication capabilities to meet them. Terahertz waves, with their high frequency, wide bandwidth, and strong penetration, have broad application prospects in autonomous driving, nondestructive testing, medical imaging, remote sensing and telemetry, security inspections, radio astronomy, rock exploration, and many other areas, providing strong support for future upgrades in the communications industry.

[0046] Slow-wave structures are devices designed to enhance the interaction between moving electrons and electromagnetic fields in traveling-wave electronic devices, allowing the energy of the electron flow to be more efficiently converted into high-frequency electromagnetic energy. Because electromagnetic waves propagate at the speed of light in a vacuum, while the speed of an electron beam in a vacuum is much slower than that, specific high-frequency structures must be used to slow the motion of the electromagnetic wave's isophase plane in order to enable interaction between the electromagnetic wave and the electron beam. This means that the phase velocity of the electromagnetic wave must be slowed, requiring the electron's travel speed to approach that of the electromagnetic wave to meet synchronization requirements.

[0047] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0048] Traveling wave tubes (TWTs) are widely used in radar, electronic countermeasures, communications, and other fields, serving as core components for microwave power amplification. Coupled-cavity slow-wave TWTs, in particular, are widely used in fire control, search, and warning radars due to their high peak and average power output capabilities, high efficiency, and large duty cycle.

[0049] Currently, the main slow-wave structures being studied in terahertz-band traveling-wave tubes (TWTs) include folded waveguides, rectangular staggered double gratings, and double-row rectangular gratings. Terahertz waves operate at very short wavelengths, and due to the size co-transitivity effect, high-frequency systems must be very small. This makes processing difficult and inaccurate, resulting in high reflections and losses. Folded waveguide slow-wave structures offer wide bandwidth, low loss, high thermal conductivity, and ease of processing and assembly, making them widely used as TWT slow-wave structures. Conventional folded waveguide slow-wave structures are typically hollow structures formed using micromachining techniques in metal materials, requiring evacuation of the hollow structure for operation. Existing folded waveguide slow-wave structures exhibit relatively weak electric field strength in the direction of electromagnetic wave transmission, resulting in low coupling impedance. This results in drawbacks such as low output power, interaction efficiency, gain, and a long saturation interaction length for TWTs.

[0050] The following describes several related technologies of folded waveguide slow-wave structures with reference to the accompanying drawings.

[0051] Figure 1 This is a schematic diagram of the three-dimensional structure of a common folded waveguide slow-wave structure. Figure 1 As shown, this folded waveguide slow-wave line is a type of all-metal slow-wave line. It is formed by periodically bending a rectangular waveguide into a U-shaped meander line along the electric field. The bend is semicircular. The wide side of the rectangular waveguide is a, the narrow side dimension / waveguide thickness is b, the geometric period is 2p, and the straight waveguide height is h. Circular or square through-holes are opened in the waveguide wall along the central axis of the slow-wave structure. Then, a metal tube with the same aperture size is used to connect the two through-holes in each periodic U-shaped groove of the slow-wave structure, thereby forming an electron injection channel with a radius of r. c .

[0052] The electric field strength of the folded waveguide slow-wave structure in the direction of electromagnetic wave transmission is relatively weak, so its coupling impedance is small, resulting in small output power, interaction efficiency, gain and long saturation interaction length of the folded waveguide traveling wave tube.

[0053] Figure 2A This is a schematic diagram of the three-dimensional structure of a folded waveguide slow-wave structure. Figure 2A As shown, the folded waveguide slow-wave structure is an undulating waveguide, which is deformed from an ordinary rectangular waveguide with a wide side dimension a and a narrow side dimension b. The interior is a hollow structure for installing a strip electron beam. Figure 2A The upper or lower surface of the undulating waveguide shown in FIG) is periodically undulating, and the H surface (such as Figure 2AThe side surface of the undulating waveguide shown (perpendicular to the upper or lower surface of the undulating waveguide) is flat, and the intersection of the E-plane and the H-plane is a wavy line with a period length of P and an undulation height of h. The wavy line can be a sine curve, a cosine curve, a triangular waveform curve, or a semicircular arc curve.

[0054] Figure 2B This is a schematic diagram of the three-dimensional structure of another folded waveguide slow-wave structure. Figure 2B As shown, the folded waveguide slow-wave structure is a flat-top sinusoidal waveguide with a wide side dimension a and a narrow side dimension b. P is the period length. Based on the sinusoidal slow-wave structure, the flat-top sinusoidal waveguide slow-wave structure appropriately compresses the narrow side dimension b. The compression size is equal to the height hs of the truncated tops of the periodic strip-shaped undulations of the upper and lower sinusoidal lines, so that the size parameters satisfy: b<h b +2h, where h b is the height of the band-shaped electron beam channel, and h is the height of the sinusoidal periodic band-shaped fluctuation.

[0055] Figure 2A and Figure 2B The folded waveguide slow-wave structures shown all require a strip electron beam as an energy source. The strip electron beam can be, for example, an electron beam with a rectangular cross-section. However, focusing the strip electron beam and ensuring its stable transmission is a great challenge, resulting in greater design difficulty.

[0056] Figure 3A The folded waveguide slow-wave structure may include one or more folded waveguide units, such as Figure 3A As shown, the folded waveguide slow-wave structure is an arc-shaped curved waveguide boundary folded waveguide slow-wave structure, which includes a periodic structure of a series of straight waveguides and arc-shaped curved waveguides. The inner boundary C of the curved waveguide in and outer boundary C out The non-semicircular arc is formed by adjusting the position of the arc center and the radius to increase the width of the curved waveguide, so as to enhance the electromagnetic field in the electron beam direction of the straight waveguide gap.

[0057] Figure 3B FIG. 1 is a schematic structural diagram of a folded waveguide unit of another folded waveguide slow-wave structure. The folded waveguide slow-wave structure may include one or more folded waveguide units, such as Figure 3B As shown, the folded waveguide slow-wave structure is a rectangular folded waveguide slow-wave structure, which includes a straight waveguide segment forming a plurality of geometric periodic structures, a waveguide connecting segment, and an electron injection channel located at the center axis of the slow-wave structure; the intersection of the outer top wall of the waveguide connecting segment and the outer side wall of the straight waveguide segment is the outer axis O out In the direction of extension of the central axis of the slow-wave structure, the waveguide connecting section includes an outer axis O formed on at least one side end of the outer side of the waveguide connecting section outIt is a fan-shaped outer lug structure of the central shaft.

[0058] Figure 3C FIG. 1 is a structural diagram of a folded waveguide unit of another folded waveguide slow-wave structure. The folded waveguide slow-wave structure may include one or more folded waveguide units, such as Figure 3C As shown, the folded waveguide slow-wave structure is a non-semicircular binaural folded waveguide slow-wave structure, which includes a plurality of geometric periodic structures defined by a plurality of grating bodies distributed staggered with each other, each geometric periodic structure includes a straight waveguide segment and a curved waveguide connecting segment. The curved waveguide connecting segment includes an outer arc boundary C out1 The first arc segment and the outer arc boundary C out2 The second arc segment; the outer arc boundary C out1 and the outer arc boundary C out2 The outer arc boundary of the semicircular curved waveguide connecting section bulges toward both sides with the corresponding grid body center line as the midline.

[0059] Figure 3D FIG. 1 is a schematic diagram of the cross section of another folded waveguide slow-wave structure. Figure 3D As shown, the folded waveguide slow-wave structure is a dome-trapezoidal staggered double-grid slow-wave structure, which includes two undulating parts located on the upper and lower sides. The undulating parts are mainly composed of a plurality of trapezoidal parts, circular groove parts and dome parts. The plurality of trapezoidal parts are arranged in sequence and spaced apart in the transverse direction, and adjacent trapezoidal parts are transitioned through the circular groove parts. In the longitudinal cross-section parallel to the transverse direction, the trapezoidal parts are isosceles trapezoids with their height extending in the longitudinal direction. The upper bases of the upper and lower isosceles trapezoids are both arranged on the side close to the strip-shaped electron injection channel. The dome part is connected to the upper base of the isosceles trapezoid. The lower bases of two adjacent trapezoidal parts in the transverse direction are transitioned through the circular groove part between them.

[0060] Figure 3A 、 Figure 3B 、 Figure 3C and Figure 3D The folded waveguide slow-wave structure shown has a non-smoothly connected waveguide boundary, has a mutation point, does not have first-order continuity and gradient, and has a relatively large reflection coefficient; the electric field is concentrated at the mutation point, resulting in excessive electromagnetic wave transmission loss; during processing, the mutation point is subjected to uneven force, which affects the processing accuracy and quality and causes processing difficulties.

[0061] In view of this, an embodiment of the present application provides a folded waveguide slow-wave structure and a vacuum electron tube. The vacuum electron tube includes a folded waveguide slow-wave structure and an electron beam. In the embodiment of the present application, since two adjacent waveguide segments arranged in sequence are smoothly connected, the width of the smoothly curved waveguide segment is not less than the width of the straight waveguide segment, and the width of at least part of the smoothly curved waveguide segment is greater than the width of the straight waveguide segment, thereby making the electric field strength in the direction of electromagnetic wave transmission relatively strong, improving the coupling impedance, increasing the total output power, reducing the slow-wave line length required for power saturation, and achieving the purpose of high-power miniaturization. At the same time, it has a first-order continuous gradient, a small reflection coefficient and transmission loss, and is conducive to improving processing accuracy and processing quality.

[0062] The embodiments of the present application can be applied to high-frequency, high-power traveling wave tubes. Specifically, the vacuum tube can be a traveling wave tube. Furthermore, the vacuum tube can also be a backward wave tube, a klystron, or a magnetron. Specifically, the folded waveguide slow-wave structure of the embodiments of the present application can also serve as a waveguide structure for other types of vacuum tubes.

[0063] Figure 4 This is a schematic diagram of the three-dimensional structure of a folded waveguide slow-wave structure provided in an embodiment of the present application. Figure 4 As shown in FIG, the folded waveguide slow-wave structure includes one or at least two folded waveguide units 10 connected in sequence. Figure 4 , an electron note 20 is also shown.

[0064] The folded waveguide unit 10 includes a smoothly curved waveguide segment Q, a first straight waveguide segment Z1, a second straight waveguide segment Z2, a first curved waveguide segment W1, and a second curved waveguide segment W2. The smoothly curved waveguide segment Q has a central axis plane and is symmetrical about the central axis plane. The central axis plane is perpendicular to the arrangement direction of at least two folded units. Figure 4 The central axis X is shown in the figure and lies on the central axis plane. The first straight waveguide segment Z1 and the second straight waveguide segment Z2 are located at either end of the smoothly curved waveguide segment Q, respectively, and are symmetrical about the central axis plane. The first curved waveguide segment W1 is located at the end of the first straight waveguide segment Z1 away from the smoothly curved waveguide segment Q, and the second curved waveguide segment W2 is located at the end of the second straight waveguide segment Z2 away from the smoothly curved waveguide segment Q. The first curved waveguide segment W1 and the second curved waveguide segment W2 are symmetrical about the central axis plane. In other words, the folded waveguide unit 10 as a whole is a symmetrical structure about the central axis X.

[0065] Furthermore, the inner surfaces of the first curved waveguide segment W1, the first straight waveguide segment Z1, the smoothly curved waveguide segment Q, the second straight waveguide segment Z2, and the second curved waveguide segment W2 are smoothly connected in sequence, and their outer surfaces are smoothly connected in sequence. The width between the inner and outer surfaces of the smoothly curved waveguide segment Q is no less than the width between the inner and outer surfaces of the first straight waveguide segment Z1 or the second straight waveguide segment Z2, and the width of at least part of the smoothly curved waveguide segment Q is greater than the width of the first straight waveguide segment Z1 or the second straight waveguide segment Z2. This results in a relatively strong electric field intensity in the direction of electromagnetic wave transmission, improves coupling impedance, increases total output power, and reduces the slow-wave line length required for power saturation, achieving the goal of high-power miniaturization. Furthermore, the device exhibits first-order continuous gradient, low reflection coefficient and transmission loss, and is conducive to improving processing accuracy and quality.

[0066] Furthermore, the first curved waveguide segment W1 and half of the smoothly curved waveguide segment Q can be a centrally symmetrical structure about the center of the first straight waveguide segment Z1; the second curved waveguide segment W2 and the other half of the smoothly curved waveguide segment Q can be a centrally symmetrical structure about the center of the second straight waveguide segment Z2. In addition, electron injection channels are respectively provided on the first straight waveguide segment Z1 and the second straight waveguide segment Z2, and the cross-sectional shape of the electron injection channels is circular or rectangular. Since focusing a strip-shaped electron beam (an electron beam with a rectangular cross-section) and ensuring its stable transmission is very challenging, the folded waveguide slow-wave structure of the embodiment of the present application is applicable not only to electron injection channels with a rectangular cross-section, but also to electron injection channels with a circular cross-section. This helps to reduce the design difficulty and ensure that the electron beam can be stably transmitted.

[0067] In order to achieve a smooth connection between the two ends of the smoothly curved waveguide segment Q and the first straight waveguide segment Z1 and the second straight waveguide segment Z2 in a tangential manner, the tangent lines at both ends of the outer curved line Q2 of the cross section of the smoothly curved waveguide segment Q can be consistent with the extension direction of the central axis X of the cross section of the smoothly curved waveguide segment Q, so that the two ends of the outer surface of the smooth curved waveguide segment Q are tangentially connected to the outer surface of the first straight waveguide segment Z1 and the outer surface of the second straight waveguide segment Z2, and the tangent lines at both ends of the inner curved line Q1 of the cross section of the smoothly curved waveguide segment Q can be consistent with the extension direction of the central axis X of the cross section of the smoothly curved waveguide segment Q, so that the two ends of the inner surface of the smooth curved waveguide segment Q are tangentially connected to the inner surface of the first straight waveguide segment Z1 and the inner surface of the second straight waveguide segment Z2, so that the width of the two ends of the smoothly curved waveguide segment Q is equal to the width of the waveguide segment. At this time, the folded waveguide slow-wave structure of the present application can have but is not limited to the following two embodiments:

[0068] First embodiment - the width of the smoothly curved waveguide section Q is the largest at the mid-axis plane. In this case, the width of the smoothly curved waveguide section Q can be increased along the direction from both ends of the smoothly curved waveguide section Q to the mid-axis plane, such as Figure 4shown.

[0069] Second embodiment: The width of the smoothly curved waveguide segment Q is largest in the middle portion along the curvature direction between the mid-axis plane and the ends of the smoothly curved waveguide segment Q. In this case, the width of the smoothly curved waveguide segment Q can increase from the ends of the smoothly curved waveguide segment Q and the mid-axis plane toward each other along the curvature direction, as described below. Figure 7 shown.

[0070] In addition, it can be understood that, under the premise of meeting the use requirements, the width of the smoothly curved waveguide segment Q can also reach the maximum at other positions besides the above-mentioned mid-axis plane and the middle.

[0071] Several exemplary specific solutions in the first embodiment are first introduced below.

[0072] The first scheme - the inner bending line Q1 and the outer bending line Q2 respectively include one of the following types: two circular arc lines and a cosine line connected between the two circular arc lines; two circular arc lines and the top part of a parabola connected between the two circular arc lines; two circular arc lines and the top part of a semi-ellipse connected between the two circular arc lines; wherein the tangents of the two circular arc lines of the outer bending line Q2 and the inner bending line Q1 at the ends away from each other along the bending direction are consistent with the extension direction of the central axis X, so that the two ends of the smoothly curved waveguide segment Q are smoothly connected to the first straight waveguide segment Z1 and the second straight waveguide segment Z2 in a tangential manner.

[0073] That is, the portion between the two arcs of the outer curvature Q2 may be the same as or different from the portion between the two arcs of the inner curvature Q1. When the portion between the two arcs of the outer curvature Q2 is the same as the portion between the two arcs of the inner curvature Q1, the inner curvature Q1 and the outer curvature Q2 are of the same type. For example, both the inner curvature Q1 and the outer curvature Q2 are composed of two arcs and a cosine line connecting the two arcs. When the portion between the two arcs of the outer curvature Q2 is different from the portion between the two arcs of the inner curvature Q1, the inner curvature Q1 and the outer curvature Q2 are of different types. For example, the inner curvature Q1 is composed of two arcs and a cosine line connecting the two arcs, while the outer curvature Q2 is composed of two arcs and the top portion of a parabola connecting the two arcs. Furthermore, the radius of the two arcs of the outer curvature Q2 is greater than the radius of the two arcs of the inner curvature Q1. Furthermore, the portion between the two circular arcs may be replaced by other continuous curved lines in addition to cosine lines, parabolas, and elliptical lines.

[0074] The central angle of the inner curved line Q1 and the central angle of the outer curved line Q2 can be different or the same. When the inner curved line Q1 and the outer curved line Q2 are of the same type, the portion between the two arcs of the outer curved line Q2 can be obtained by translating the top portion of a cosine curve, a parabola, or a semi-ellipse between the two arcs of the inner curved line Q1. In this case, the portion between the two arcs of the inner curved line Q1 and the portion between the two arcs of the outer curved line Q2 have the same size along the arrangement direction of at least two folded waveguide units 10.

[0075] The following is a specific description using an example in which the inner bending line Q1 and the outer bending line Q2 are of the same type and the portion between the two arc lines is a cosine line.

[0076] Figure 5A for Figure 4 An exemplary structural diagram of the folded waveguide unit of the folded waveguide slow-wave structure is shown. Figure 5A As shown, the central angles of the arcs of the inner bending line Q1 and the outer bending line Q2 can be, for example, both 45°. The bending line between the two arcs of the outer bending line Q2 is obtained by partially translating the arcs between the two arcs of the inner bending line Q1. In this case, the radius of the arc of the inner bending line Q1 is The radius of the arc of the outer bending line Q2 And translation distance Among them, b is the width of the first straight waveguide segment Z1 or the second straight waveguide segment Z2, the half-cycle length p is the distance between the central axis plane of the first straight waveguide segment Z1 and the central axis plane of the second straight waveguide segment Z2, and s is the part between the two arc lines of the inner bending line Q1, that is, the dimension of the bending line along the arrangement direction of the two folded waveguide units 10.

[0077] That is to say, Figure 5A The folded waveguide slow-wave structure shown is Figure 1 Based on the conventional folded waveguide slow-wave structure shown, the semicircular curved waveguide segment is replaced with a structured curved waveguide consisting of two eighth-circular curved waveguides and a cosine waveguide. In other words, the intersection of the electric field and magnetic field surfaces of the structured curved waveguide is a combination of an eighth-circle and a cosine waveform. This structured curved waveguide smoothly connects to the straight waveguide, forming a cosine-curved folded waveguide slow-wave structure. Its boundary exhibits first-order continuity, creating a gradual transition.

[0078] Among them, the entire slow-wave structure is jointly determined by the width dimension a of the rectangular waveguide in the straight waveguide section, the narrow-side dimension b of the rectangular waveguide in the straight waveguide section, the half-period length p, the length h of the straight waveguide section, the radius dimension r0 of the electron beam channel, the axial length s of the cosine waveguide, etc. The cross-section of this slow-wave structure is a rectangle with a width dimension of a and a varying narrow-side dimension. Also, to ensure that the electron beam channel can be completely arranged in the straight waveguide section, it is necessary to satisfy: h > 2r0; to ensure that there are arc lines on both sides of the cosine line, it is necessary to satisfy: s < p - b. In the D-band, the structural dimensions of a specific implementation scheme of the cosine-curved folded waveguide slow-wave structure can be (unit: mm): a = 1.12, b = 0.2, p = 0.36, h = 0.32, r0 = 0.15, s = 0.14. Among them, the frequency range of the D-band is 110 GHz - 170 GHz, and the wavelength range is 2.73 mm - 1.76 mm, belonging to the millimeter wave (extremely high frequency) level band.

[0079] In addition, it should be noted that the folded waveguide slow-wave structure is a hollow structure processed on metal, and it needs to be evacuated first during operation. The product implementation method can be precision machining of metal parts. The machining method can mainly be high-speed milling, combined with electrical discharge machining and slow wire electrical discharge machining processes to ensure the accuracy, surface finish, and consistency of the slow-wave line.

[0080] Figure 5B For Figure 4 an exemplary actual structure diagram of the folded waveguide slow-wave structure shown. That is, to obtain Figure 4 the folded waveguide slow-wave structure shown, it is necessary to fabricate Figure 5B the structure shown during the actual machining process. As Figure 5B shown, this folded waveguide slow-wave structure can include an upper grid body and a lower grid body. Both the upper grid body and the lower grid body are made of metal. Protrusions and depressions are respectively arranged at intervals on the upper grid body and the lower grid body. The protrusions on the upper grid body correspond to the depressions on the lower grid body, and the depressions on the upper grid body correspond to the protrusions on the lower grid body, that is, they are staggered and need to be spaced a certain distance apart, so that the spaced space can form Figure 4 the folded waveguide slow-wave structure shown.

[0081] The cosine-curved folded waveguide slow-wave structure can be simulated using three-dimensional electromagnetic simulation software and traveling-wave tube beam-wave interaction simulation software. Its coupling impedance, output power, bandwidth, device length required at power saturation, etc. can be obtained. By comparing with the ordinary folded waveguide slow-wave structure, it can be known that Figure 4 the cosine-curved folded waveguide slow-wave structure shown has a higher coupling impedance than the ordinary folded waveguide slow-wave structure and can output power higher than that of the ordinary folded waveguide slow-wave structure with a smaller volume. The following will be specifically described in combination with Figure 5C , Figure 5D and Figure 5E for specific illustration.

[0082] Figure 5C for Figure 4 The cosine-bent folded waveguide slow-wave structure shown is similar to Figure 1 The comparison diagram of the interaction impedance-frequency of the common folded waveguide slow wave structure is shown in FIG. Figure 5C In the figure, curve 1 is Figure 4 The coupling impedance characteristics of the cosine-bent folded waveguide slow-wave structure shown in FIG2 are as follows; Curve 2 is Figure 1 The coupling impedance characteristics of a common folded waveguide slow-wave structure are shown in Figure 1. Comparison of curves 1 and 2 shows that the coupling impedance of the cosine-bend folded waveguide slow-wave structure is higher than that of the common folded waveguide slow-wave structure at the same frequency across the entire operating frequency band, meaning it can more effectively support the beam-wave interaction, thereby increasing the output power of the slow-wave line.

[0083] Figure 5D for Figure 4 The cosine-bent folded waveguide slow-wave structure shown is similar to Figure 1 The output power-frequency comparison diagram of the ordinary folded waveguide slow wave structure is shown in the figure. Among them, the difference between the maximum frequency and the minimum frequency is the bandwidth, so Figure 5D Bandwidth performance can also be displayed. Figure 5D In the figure, curve 3 is Figure 4 The output power and bandwidth performance of the cosine-bent folded waveguide slow-wave structure shown in FIG4; Curve 4 is Figure 1 The output power and bandwidth performance of the common folded waveguide slow-wave structure are shown in Figure 3. From the comparison between curve 3 and curve 4, it can be clearly seen that the output power of the cosine-bent folded waveguide slow-wave structure is generally higher than that of the common folded waveguide slow-wave structure.

[0084] Figure 5E for Figure 4 The cosine-bent folded waveguide slow-wave structure shown is similar to Figure 1 The comparison diagram of the device length required for the power saturation of the common folded waveguide slow wave structure is shown in the figure. Figure 5E The left side view is Figure 1 The simulation results of the device length required when the power of the ordinary folded waveguide slow wave structure is saturated are shown; the right side view is Figure 4 The simulation results of the device length required for the cosine-bend folded waveguide slow-wave structure at power saturation are shown. Comparison of the two figures shows that the device length required for the cosine-bend folded waveguide slow-wave structure of the present embodiment at power saturation is much shorter than that of a conventional folded waveguide slow-wave structure, significantly reducing the device size and facilitating the goal of high-power miniaturization.

[0085] Figure 4The cosine curved folded waveguide slow wave structure shown is composed of a rectangular straight waveguide section and a structural curved waveguide. The straight waveguide section can be processed into an electron injection channel. The structural curved waveguide consists of two one-eighth circular curved waveguides and a cosine waveguide. Figures 5A-5E It can be seen that the coupling impedance of this cosine-curved folded waveguide slow-wave structure is higher than that of a conventional folded waveguide slow-wave structure at the same frequency across the entire operating frequency band, meaning it can more effectively support injection-wave interaction, thereby significantly increasing the output power of the slow-wave line. Furthermore, the entire slow-wave structure is smoothly connected, without any abrupt changes, and its boundaries have first-order continuity. The reflection coefficient and transmission loss are low, and the processing accuracy and quality are high. Furthermore, the device length required for power saturation of this cosine-curved folded waveguide slow-wave structure is much shorter than that of a conventional folded waveguide slow-wave structure, significantly reducing the device size and achieving high-power miniaturization requirements.

[0086] The second solution is that the inner curved line Q1 is the first semi-elliptical line, and the outer curved line Q2 is the second semi-elliptical line. The tangents at both ends of the first semi-elliptical line and the second semi-elliptical line are consistent with the extension direction of the central axis X, so that the two ends of the smoothly curved waveguide segment Q are smoothly connected to the first straight waveguide segment Z1 and the second straight waveguide segment Z2 in a tangential manner.

[0087] Figure 6 FIG. 1 is another exemplary structural diagram of the folded waveguide unit of the folded waveguide slow-wave structure according to an embodiment of the present application. Figure 6 As shown, the inner curvature line Q1 and the outer curvature line Q2 are both semi-elliptical lines, and have different sizes, but the midpoints of both ends of the inner curvature line Q1 and the outer curvature line Q2 are K. This ensures that the two ends of the first semi-elliptical line, which serves as the inner curvature line Q1, can be tangentially connected to the inner side surfaces of the first straight waveguide segment Z1 and the inner side surfaces of the second straight waveguide segment Z2, respectively. At the same time, it ensures that the two ends of the second semi-elliptical line, which serves as the outer curvature line Q2, can be tangentially connected to the outer side surfaces of the first straight waveguide segment Z1 and the outer side surfaces of the second straight waveguide segment Z2, respectively. This achieves a smooth connection between the two ends of the smoothly curved waveguide segment Q and the first straight waveguide segment Z1 and the second straight waveguide segment Z2, respectively.

[0088] The third solution - one of the inner curved line Q1 and the outer curved line Q2 includes two circular arcs and a curved line connected between the two circular arcs, and the other includes a semi-elliptical line, and the curved line includes a cosine line, the top part of a parabola, and the top part of a semi-elliptical line; and the tangents of the ends of the two circular arcs away from each other along the bending direction and the tangents of the two ends of the semi-elliptical line are consistent with the extension direction of the central axis X of the cross section of the smoothly curved waveguide segment Q, so that the two ends of the smoothly curved waveguide segment Q are smoothly connected to the first straight waveguide segment Z1 and the second straight waveguide segment Z2 in a tangential manner.

[0089] That is to say, the types of the inner bending line Q1 and the outer bending line Q2 may be different, one of them may be a combination of two circular arcs and a bending line, and the other may be a semi-elliptical line, and the ends of the two circular arcs can be connected tangentially to the outer side surface or the inner side surface of the straight waveguide segment, and the two ends of the semi-elliptical line can be connected tangentially to the inner side surface or the outer side surface of the straight waveguide segment.

[0090] The fourth scheme - the outer curved line Q2 includes two circular arcs and a curved line connected between the two circular arcs or includes a semi-elliptical line, and the curved line includes a cosine line, the top part of a parabola and the top part of a semi-elliptical line; the inner curved line Q1 includes two cosine lines, and the first ends of the two cosine lines are smoothly connected, for example, tangently connected, and the tangents of the second ends of the two cosine lines and the tangents of the ends of the two circular arcs away from each other along the bending direction or the tangents of the two ends of the semi-elliptical line are consistent with the extension direction of the central axis X of the cross section of the smoothly curved waveguide segment Q, so that the two ends of the smoothly curved waveguide segment Q are smoothly connected to the first straight waveguide segment Z1 and the second straight waveguide segment Z2 in a tangential manner.

[0091] That is to say, the types of the inner bending line Q1 and the outer bending line Q2 may be different. The inner bending line Q1 may be two cosine lines, and the outer bending line Q2 may be a combination of two circular arc lines and a bending line, or may be a semi-elliptical line, and the ends of the two cosine lines away from each other along the bending direction can be connected tangentially to the inner side surface of the straight waveguide section, and the ends of the two circular arc lines away from each other along the bending direction or the two ends of the semi-elliptical line can be connected tangentially to the outer side surface of the straight waveguide section.

[0092] Fifth Solution: The inner curvature line Q1 is a semicircular arc, the outer curvature line Q2 has a longitudinal dimension along the central axis X direction greater than its transverse dimension along the direction perpendicular to the central axis X, and the outer curvature line Q2 includes two circular arcs and a curved line, or includes a semi-elliptical line. Alternatively, the outer curvature line Q2 is a semicircular arc, the inner curvature line Q1 has a longitudinal dimension along the central axis X direction less than its transverse dimension along the direction perpendicular to the central axis X, and the inner curvature line Q1 includes two circular arcs and a curved line, or includes a semi-elliptical line. The curved line connects the two circular arcs and includes one of a cosine line, the top portion of a parabola, and the top portion of a semi-elliptical line.

[0093] That is, the inner and outer curve lines Q1 and Q2 may be of different types, and one of them may be a semicircular arc. When the inner curve line Q1 is a semicircular arc, to ensure that at least a portion of the width of the smoothly curved waveguide segment Q is greater than the width of the straight waveguide segment, the longitudinal dimension of the outer curve line Q2 must be greater than the transverse dimension. The outer curve line Q2 may include two circular arcs and a curved line, or may include a semi-elliptical line. When the outer curve line Q2 is a semicircular arc, to ensure that at least a portion of the width of the smoothly curved waveguide segment Q is greater than the width of the straight waveguide segment, the longitudinal dimension of the inner curve line Q1 must be less than the transverse dimension. The inner curve line Q1 may include two circular arcs and a curved line, or may include a semi-elliptical line.

[0094] In the above-mentioned several schemes of the folded waveguide slow-wave structure of the first embodiment of the present application, the widths of the two ends of the smoothly curved waveguide segment Q are equal to the widths of the first straight waveguide segment Z1 or the second straight waveguide segment Z2, and the width of the smoothly curved waveguide segment Q increases along the direction from the two ends of the smooth curved waveguide segment Q to the central axis plane, wherein: the longitudinal dimension of the outer curved line Q2 of the cross section of the smooth curved waveguide segment Q along the central axis X is greater than the lateral dimension perpendicular to the central axis X, and the longitudinal dimension of the inner curved line Q1 of the cross section of the smooth curved waveguide segment Q along the central axis X is greater than or equal to or less than the lateral dimension perpendicular to the central axis X; or, the longitudinal dimension of the outer curved line Q2 of the cross section of the smooth curved waveguide segment Q along the central axis X is equal to or less than the lateral dimension perpendicular to the central axis X, and the longitudinal dimension of the inner curved line Q1 of the cross section of the smooth curved waveguide segment Q along the central axis X is less than the lateral dimension perpendicular to the central axis X. That is to say, when the width of the smoothly curved waveguide segment Q is the largest at the mid-axis plane, there may be the following two situations: the first situation is that the longitudinal dimension of the outer curved line Q2 may be greater than the transverse dimension, for example, the outer curved line Q2 may be a first semi-elliptical line; at this time, the longitudinal dimension of the inner curved line Q1 may be greater than the transverse dimension, for example, the inner curved line Q1 may be a second semi-elliptical line, and the second semi-elliptical line is different from the first semi-elliptical line; or the longitudinal dimension of the inner curved line Q1 may be equal to the transverse dimension, for example, the inner curved line Q1 may be a semicircular arc line; or, the longitudinal dimension of the inner curved line Q1 may be smaller than the transverse dimension, for example, the inner curved line Q1 may be a combination of two circular arc lines and a cosine line. The second scenario is that the longitudinal dimension of the outer curvature Q2 is equal to or smaller than the transverse dimension. When the longitudinal dimension of the outer curvature Q2 is equal to the transverse dimension, the outer curvature Q2 can, for example, be a semicircular arc. When the longitudinal dimension of the outer curvature Q2 is smaller than the transverse dimension, the outer curvature Q2 can, for example, be a combination of two first circular arcs and a first cosine line. In this case, the longitudinal dimension of the inner curvature Q1 is smaller than the transverse dimension. For example, the inner curvature Q1 can be a combination of two second circular arcs and a second cosine line, with the radius of the first circular arc being greater than the radius of the second circular arc, and the first and second cosine lines being the same. Furthermore, it should be noted that both of the above scenarios require that the width of the smoothly curved waveguide segment Q is no less than the width of the first straight waveguide segment Z1 or the second straight waveguide segment Z2, and that the width of at least some of the smoothly curved waveguide segments Q is greater than the width of the first straight waveguide segment Z1 or the second straight waveguide segment Z2.

[0095] Several specific solutions of the folded waveguide slow-wave structure of the first embodiment of the present application are introduced above. The specific solution of the folded waveguide slow-wave structure of the second embodiment of the present application is introduced below.

[0096] The first solution is that the inner bending line Q1 of the cross section of the smoothly curved waveguide segment Q is a semicircular arc line, and the outer bending line Q2 of the cross section of the smoothly curved waveguide segment Q has a longitudinal dimension along the direction of the central axis X that is equal to the lateral dimension along the direction perpendicular to the central axis X. The outer bending line Q2 includes two cosine lines, and the first ends of the two cosine lines are smoothly connected, for example, tangentially connected. The tangents of the second ends of the two cosine lines and the tangents of the two ends of the semicircular arc line are consistent with the extension direction of the central axis X, so that the two ends of the smoothly curved waveguide segment Q are smoothly connected to the first straight waveguide segment Z1 and the second straight waveguide segment Z2 in a tangential manner.

[0097] That is to say, the inner bending line Q1 can be a semicircular arc line, and the outer bending line Q2 can be two cosine lines. The width of the cross section of the smoothly curved waveguide segment Q formed by the two can increase from the central axis plane and the end of the smoothly curved waveguide segment Q along the bending direction toward each other, and is the largest in the middle along the bending direction between the central axis plane and the end of the smoothly curved waveguide segment Q.

[0098] The second solution is that the inner bending line Q1 and the outer bending line Q2 of the cross section of the smoothly curved waveguide segment Q each include one of the following types:

[0099] Two cosine lines, each of which has a smoothly connected first end, and each of which has a tangent line at its second end aligned with the extension direction of the central axis of the cross section of the smoothly curved waveguide segment Q, so that both ends of the smoothly curved waveguide segment Q are smoothly connected to the first straight waveguide segment and the second straight waveguide segment in a tangential manner.

[0100] The top portions of the two parabolas are smoothly connected at their respective first ends, and the tangents of the respective second ends of the top portions of the two parabolas are aligned with the extension direction of the central axis of the cross section of the smoothly curved waveguide segment Q, so that the two ends of the smoothly curved waveguide segment Q are smoothly connected to the first straight waveguide segment and the second straight waveguide segment in a tangential manner.

[0101] The top parts of the two semi-elliptical lines, the first ends of the respective top parts of the two semi-elliptical lines are smoothly connected, and the tangents of the second ends of the respective top parts of the two semi-elliptical lines are consistent with the extension direction of the central axis of the cross section of the smoothly curved waveguide segment Q, so that the two ends of the smoothly curved waveguide segment Q are smoothly connected to the first straight waveguide segment and the second straight waveguide segment in a tangential manner.

[0102] That is, the inner curved line Q1 and the outer curved line Q2 of the cross section of the smoothly curved waveguide segment Q can be of different types, for example, one can be two cosine lines and the other can be two parabolas. Alternatively, the inner curved line Q1 and the outer curved line Q2 of the cross section of the smoothly curved waveguide segment Q can be of the same type, for example, both can be two cosine lines. It should be noted that regardless of whether the two types are the same or different, the following conditions must be met: the width of the smoothly curved waveguide segment Q is not less than the width of the first straight waveguide segment Z1 or the second straight waveguide segment Z2, and the width of at least part of the smoothly curved waveguide segment Q is greater than the width of the first straight waveguide segment Z1 or the second straight waveguide segment Z2.

[0103] Figure 7 FIG. 1 is another exemplary structural diagram of the folded waveguide unit of the folded waveguide slow-wave structure of the embodiment of the present application. Figure 7 As shown, the inner curved line Q1 can be two first cosine lines, the two first cosine lines are symmetrical about the central axis X, and the first ends of the two first cosine lines can be smoothly connected, for example, tangentially connected, and the second ends of the two first cosine lines can be tangentially connected to the inner side surface of the first straight waveguide segment Z1 and the inner side surface of the second straight waveguide segment Z2, respectively; the outer curved line Q2 can be two second cosine lines, the two second cosine lines are symmetrical about the central axis X, and the first ends of the two second cosine lines can be smoothly connected, for example, tangentially connected, and the second ends of the two second cosine lines can be tangentially connected to the outer side surface of the first straight waveguide segment Z1 and the outer side surface of the second straight waveguide segment Z2, respectively, and the first cosine line and the second cosine line have different sizes, so that the two ends of the smoothly curved waveguide segment are smoothly connected to the first straight waveguide segment and the second straight waveguide segment in a tangential manner. In this way, the width of the cross section of the smoothly curved waveguide segment Q formed by the inner curved line Q1 and the outer curved line Q2 can increase from the central axis plane and the end of the smoothly curved waveguide segment Q toward each other along the bending direction, and is the largest in the middle along the bending direction between the central axis plane and the end of the smoothly curved waveguide segment Q.

[0104] In one example, the middle width may be b is the width of the first straight waveguide segment Z1 or the second straight waveguide segment Z2. As described above, the inner curved line Q1 and the outer curved line Q2 can be composed not only of two cosine lines but also of the top portions of two parabolas or two semi-ellipses. In this case, the width of the middle portion will vary depending on the specific shapes of the two parabolas or two semi-ellipses and can be designed based on actual work needs.

[0105] In the above-mentioned scheme of the folded waveguide slow-wave structure of the second embodiment of the present application, the widths of the two ends of the smoothly curved waveguide segment Q are equal to the widths of the first straight waveguide segment Z1 or the second straight waveguide segment Z2, the width of the smooth curved waveguide segment Q at the mid-axis plane is greater than or equal to the widths of the first straight waveguide segment Z1 or the second straight waveguide segment Z2, and the width of the smoothly curved waveguide segment Q increases from the ends and the mid-axis plane of the smoothly curved waveguide segment Q toward each other along the bending direction. That is, the width of the smoothly curved waveguide segment Q is 45 degrees from the mid-axis plane and passes through the midpoint K at the two ends of the smoothly curved waveguide segment Q (such as Figure 7 Thus, the width of the smoothly curved waveguide segment Q increases from the end of the smoothly curved waveguide segment Q to the cross-section; and the width of the smoothly curved waveguide segment Q increases from the mid-axis plane of the smoothly curved waveguide segment Q to the cross-section.

[0106] In summary, the stacked waveguide slow-wave structure of the embodiment of the present application improves the field distribution in the conventional folded waveguide slow-wave line, increases the coupling impedance, and overcomes the problem of low coupling impedance of the folded waveguide in the prior art; solves the limitation of the low coupling impedance of the conventional folded waveguide slow-wave structure on the output power and gain, and improves the gain reduction and bandwidth limitation problems caused by the continuous decrease in coupling impedance in the high-frequency region of the passband, thereby increasing the power gain per unit length in the slow-wave line, thereby increasing the total output power and reducing the slow-wave line length required for power saturation, achieving the purpose of high-power miniaturization; at the same time, the boundary connection of the slow-wave structure is smooth and has a first-order continuous gradient, which on the one hand reduces the reflection coefficient and transmission loss, and on the other hand is also conducive to improving processing accuracy and processing quality.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and do not limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A folded waveguide slow-wave structure, characterized in that: The invention comprises one or at least two folded waveguide units (10) connected in sequence, wherein the folded waveguide unit (10) comprises: a smoothly curved waveguide segment (Q) having a median axis and being symmetrical about the median axis; The first straight waveguide section (Z1) and the second straight waveguide section (Z2) are respectively located at two ends of the smoothly curved waveguide section (Q) and are symmetrical about the central axis; a first curved waveguide segment (W1) and a second curved waveguide segment (W2), wherein the first curved waveguide segment (W1) is located at an end of the first straight waveguide segment (Z1) away from the smoothly curved waveguide segment (Q), and the second curved waveguide segment (W2) is located at an end of the second straight waveguide segment (Z2) away from the smoothly curved waveguide segment (Q), and the first curved waveguide segment (W1) and the second curved waveguide segment (W2) are symmetrical about the central axis plane; wherein the inner surfaces of the first curved waveguide segment (W1), the first straight waveguide segment (Z1), the smooth curved waveguide segment (Q), the second straight waveguide segment (Z2) and the second curved waveguide segment (W2) are smoothly connected in sequence and their outer surfaces are smoothly connected in sequence; the width between the inner surface and the outer surface of the smooth curved waveguide segment (Q) is not less than the width between the inner surface and the outer surface of the first straight waveguide segment (Z1) or the second straight waveguide segment (Z2); and the width of at least part of the smooth curved waveguide segment (Q) is greater than the width of the first straight waveguide segment (Z1) or the second straight waveguide segment (Z2); The widths of both ends of the smoothly curved waveguide segment (Q) are equal to the width of the first straight waveguide segment (Z1) or the second straight waveguide segment (Z2), and the width of the smoothly curved waveguide segment (Q) increases along the direction from both ends of the smoothly curved waveguide segment (Q) to the mid-axis plane; The inner bending line (Q1) and the outer bending line (Q2) of the smooth bending waveguide section (Q) each include one of the following types: Two circular arcs and a cosine line connecting the two circular arcs; two circular arcs and a top portion of a parabola connected between the two circular arcs; Two circular arcs and a top portion of a semi-elliptical line connected between the two circular arcs; The tangent lines of the two arcs of each of the outer curved line (Q2) and the inner curved line (Q1) at their ends away from each other along the bending direction are consistent with the extension direction of the central axis (X), so that the two ends of the smoothly curved waveguide section (Q) are smoothly connected to the first straight waveguide section (Z1) and the second straight waveguide section (Z2) in a tangential manner. The structure of the folded waveguide unit is determined by the wide side dimension a of the first or second straight waveguide segment, the narrow side dimension b of the first or second straight waveguide segment, the half-period length p, the length h of the first or second straight waveguide segment, the radius dimension r0 of the electron beam channel, and the axial length s of the cosine waveguide segment; wherein the cosine waveguide segment is the waveguide segment where the cosine line in the smoothly curved waveguide segment (Q) is located; The structural parameters of the folded waveguide unit satisfy: h>2r0, s<(pb).

2. The folded waveguide slow-wave structure according to claim 1, characterized in that: The tangent lines at both ends of the inner bending line (Q1) and the outer bending line (Q2) of the cross section of the smoothly curved waveguide segment (Q) are consistent with the extension direction of the central axis (X) of the cross section of the smoothly curved waveguide segment (Q), so that the two ends of the smoothly curved waveguide segment (Q) are smoothly connected to the first straight waveguide segment (Z1) and the second straight waveguide segment (Z2) in a tangential manner, respectively, wherein: the width of the smoothly curved waveguide segment (Q) is maximum at the mid-axis plane or maximum in the middle along the bending direction between the mid-axis plane and the end of the smoothly curved waveguide segment (Q).

3. The folded waveguide slow-wave structure according to claim 1, characterized in that: The longitudinal dimension of the outer bending line (Q2) of the cross section of the smoothly curved waveguide section (Q) along the central axis (X) is greater than the transverse dimension perpendicular to the central axis (X), and the longitudinal dimension of the inner bending line (Q1) of the cross section of the smoothly curved waveguide section (Q) along the central axis (X) is greater than, equal to, or less than the transverse dimension perpendicular to the central axis (X); or, The longitudinal dimension of the outer bending line (Q2) of the cross section of the smoothly curved waveguide section (Q) along the central axis (X) is equal to or smaller than the transverse dimension perpendicular to the central axis (X), and the longitudinal dimension of the inner bending line (Q1) of the cross section of the smoothly curved waveguide section (Q) along the central axis (X) is smaller than the transverse dimension perpendicular to the central axis (X).

4. The folded waveguide slow-wave structure according to claim 1, wherein: The inner curvature line (Q1) and the outer curvature line (Q2) are of the same type, and the portion between the two arcs of the outer curvature line (Q2) is obtained by translating the top portion of a cosine line, a parabola, or a semi-ellipse between the two arcs of the inner curvature line (Q1); and / or, The degree of the central angle of the arc line of the inner bending line (Q1) is the same as the degree of the central angle of the arc line of the outer bending line (Q2).

5. The folded waveguide slow-wave structure according to claim 1, characterized in that: The central angles of the arcs of the inner bending line (Q1) and the outer bending line (Q2) are both 45°, and the radius of the arc of the inner bending line (Q1) is The radius of the arc of the outer bending line (Q2) The portion between the two arcs of the outer curvature line (Q2) is obtained by translating the portion between the two arcs of the inner curvature line (Q1), and the translation distance is Wherein, b is the width of the first straight waveguide segment (Z1) or the second straight waveguide segment (Z2), p is the distance between the mid-axis plane of the first straight waveguide segment (Z1) and the mid-axis plane of the second straight waveguide segment (Z2), and s is the dimension of the portion between the two arc lines of the inner bending line (Q1) along the arrangement direction of the two folded waveguide units (10).

6. The folded waveguide slow-wave structure according to claim 1, characterized in that: The inner curvature line (Q1) is a first semi-elliptical line, the outer curvature line (Q2) is a second semi-elliptical line, and the tangent lines at both ends of the first semi-elliptical line and the second semi-elliptical line are consistent with the extension direction of the central axis (X), so that the two ends of the smoothly curved waveguide section (Q) are smoothly connected to the first straight waveguide section (Z1) and the second straight waveguide section (Z2) in a tangential manner.

7. The folded waveguide slow-wave structure according to claim 1, characterized in that: One of the inner curvature line (Q1) and the outer curvature line (Q2) includes two circular arcs and a curvature line connected between the two circular arcs, and the other includes a semi-ellipse line, the curvature line including one of a cosine line, a top portion of a parabola, and a top portion of a semi-ellipse line; Furthermore, the tangents of the ends of the two arc lines that are away from each other along the bending direction and the tangents of the two ends of the semi-elliptical line are consistent with the extension direction of the central axis (X) of the cross section of the smoothly curved waveguide segment (Q), so that the two ends of the smoothly curved waveguide segment (Q) are smoothly connected to the first straight waveguide segment (Z1) and the second straight waveguide segment (Z2) in a tangential manner.

8. The folded waveguide slow-wave structure according to claim 1, characterized in that: The outer curvature line (Q2) includes two arc lines and a curvature line connected between the two arc lines or includes a semi-ellipse line, and the curvature line includes one of a cosine line, a top portion of a parabola, and a top portion of a semi-ellipse line; The inner bending line (Q1) includes two cosine lines, the first ends of each of the two cosine lines are smoothly connected, and the tangents of the second ends of each of the two cosine lines and the tangents of the ends of the two arc lines away from each other along the bending direction or the tangents of the two ends of the semi-elliptical line are consistent with the extension direction of the central axis (X) of the cross section of the smoothly curved waveguide section (Q), so that the two ends of the smoothly curved waveguide section (Q) are smoothly connected to the first straight waveguide section (Z1) and the second straight waveguide section (Z2) in a tangential manner.

9. The folded waveguide slow-wave structure according to claim 1, characterized in that: The inner bending line (Q1) is a semicircular arc line, the longitudinal dimension of the outer bending line (Q2) along the central axis (X) is greater than the transverse dimension along the direction perpendicular to the central axis (X), and the outer bending line (Q2) includes two circular arc lines and a bending line or includes a semi-elliptical line; or, The outer bending line (Q2) is a semicircular arc line, the longitudinal dimension of the inner bending line (Q1) along the central axis (X) is smaller than the transverse dimension along the direction perpendicular to the central axis (X), and the inner bending line (Q1) includes two circular arc lines and a bending line or includes a semi-elliptical line; The bending line is connected between the two arc lines and includes one of a cosine line, a top portion of a parabola, and a top portion of a semi-ellipse line.

10. The folded waveguide slow-wave structure according to claim 1, characterized in that: The widths of both ends of the smoothly curved waveguide segment (Q) are equal to the width of the first straight waveguide segment (Z1) or the second straight waveguide segment (Z2), the width of the smoothly curved waveguide segment (Q) at the mid-axis plane is greater than or equal to the width of the first straight waveguide segment (Z1) or the second straight waveguide segment (Z2), and the width of the smoothly curved waveguide segment (Q) increases from the ends of the smoothly curved waveguide segment (Q) and the mid-axis plane toward each other along the bending direction.

11. The folded waveguide slow-wave structure according to claim 10, characterized in that: The inner bending line (Q1) of the cross section of the smoothly curved waveguide section (Q) is a semicircular arc line, the longitudinal dimension of the outer bending line (Q2) of the cross section of the smoothly curved waveguide section (Q) along the direction of the central axis (X) is equal to the transverse dimension along the direction perpendicular to the central axis (X), the outer bending line (Q2) includes two cosine lines, the first ends of the two cosine lines are smoothly connected, the tangents of the second ends of the two cosine lines and the tangents of the two ends of the semicircular arc line are consistent with the extension direction of the central axis (X), so that the two ends of the smoothly curved waveguide section (Q) are smoothly connected to the first straight waveguide section (Z1) and the second straight waveguide section (Z2) in a tangential manner.

12. The folded waveguide slow-wave structure according to claim 10, characterized in that: The inner bending line (Q1) and the outer bending line (Q2) of the cross section of the smooth curved waveguide section (Q) each include one of the following types: Two cosine lines, wherein the first ends of the respective cosine lines are smoothly connected, and the tangent lines of the second ends of the respective cosine lines are consistent with the extension direction of the central axis (X) of the cross section of the smoothly curved waveguide section (Q), so that the two ends of the smoothly curved waveguide section (Q) are smoothly connected to the first straight waveguide section (Z1) and the second straight waveguide section (Z2) in a tangential manner; Two parabolic top portions, wherein the first ends of the respective top portions of the two parabolas are smoothly connected, and the tangent lines of the second ends of the respective top portions of the two parabolas are consistent with the extension direction of the central axis (X) of the cross section of the smoothly curved waveguide segment (Q), so that the two ends of the smoothly curved waveguide segment (Q) are smoothly connected to the first straight waveguide segment (Z1) and the second straight waveguide segment (Z2) in a tangential manner; The top parts of the two semi-elliptical lines are smoothly connected at their respective first ends, and the tangent lines of the second ends of the top parts of the two semi-elliptical lines are consistent with the extension direction of the central axis (X) of the cross section of the smoothly curved waveguide segment (Q), so that the two ends of the smoothly curved waveguide segment (Q) are smoothly connected to the first straight waveguide segment (Z1) and the second straight waveguide segment (Z2) in a tangential manner.

13. The folded waveguide slow-wave structure according to any one of claims 1 to 12, characterized in that: The first curved waveguide segment (W1) and half of the smoothly curved waveguide segment (Q) are centrosymmetrical structures about the center of the first straight waveguide segment (Z1); the second curved waveguide segment (W2) and the other half of the smoothly curved waveguide segment (Q) are centrosymmetrical structures about the center of the second straight waveguide segment (Z2); and / or, The first straight waveguide section (Z1) and the second straight waveguide section (Z2) are respectively provided with electron injection channels, and the cross-sectional shape of the electron injection channels is circular or rectangular.

14. A vacuum electron tube, characterized in that: The invention comprises a folded waveguide slow-wave structure as claimed in any one of claims 1 to 13.

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