An exponential function-based gradual change grid width type staggered double grid slow wave structure

Abstract

The application discloses an exponential function-based gradual change grid width type staggered double-grid slow wave structure which is formed by periodically arranging a plurality of single grid bodies in a rectangular waveguide; the single grid body is a double-grid structure in which an upper grid unit and a lower grid unit are staggered; a certain spacing is arranged between the upper grid unit and the lower grid unit, and a strip-shaped electron beam channel is formed; the upper grid unit and the lower grid unit are of the same structure, and the cross section shape of the upper / lower grid unit is as follows: the two ends are rectangular, and the cross section profile curve of the middle part is an exponential function. The longitudinal electric field amplitude is high under the premise that the phase velocities are similar, so that the coupling impedance is high, and the traveling wave tube can provide higher output power, gain and electron efficiency.

Description

Technical Field

[0001] This invention relates to slow wave structures, and more particularly to a gradient grating width type interleaved double grating slow wave structure based on an exponential function. Background Technology

[0002] Traveling wave tubes (TWTs) are widely used in communication satellites, radar, electronic warfare, and other fields due to their combination of high power and wide bandwidth, holding an irreplaceable position among many microwave vacuum electronic devices. A TWT mainly consists of five parts: an electron gun, a slow-wave structure, an input / output coupling structure, a collector, and a focusing system. The electron gun emits electrons at a certain speed. The slow-wave structure is the site where electrons interact with electromagnetic waves. It reduces the phase velocity of the transmitted electromagnetic waves to a synchronous speed, modulating the electrons with the electromagnetic field. The modulated electrons then surrender energy, amplifying the power of the electromagnetic waves—this is the working principle of the TWT. The input coupling structure couples high-frequency signals to the slow-wave line, and the output coupling structure couples the amplified high-frequency signal to the output circuit. The collector collects the electrons after they have undergone energy exchange with the electromagnetic field. The focusing system constrains the direction of electron flight, ensuring that electrons pass smoothly through the slow-wave structure without being intercepted. The slow-wave structure is the key component of the TWT, and its performance determines the overall performance of the device.

[0003] In recent years, with the development of vacuum electronic devices towards millimeter-wave and terahertz frequency bands, slow-wave structures have also shifted from helical and coupled-cavity types suitable for low-frequency bands to folded waveguide and interleaved double-grid types. Among them, the interleaved double-grid slow-wave structure is widely used in the terahertz frequency band due to its high power capacity, natural electron beam channel and easy fabrication. Traditional rectangular interleaved double-grid slow-wave structures have strong dispersion and low coupling impedance. According to Peirce's small-signal theory and microwave tube large-signal theory, the strength of dispersion affects the operating bandwidth of the device, and the magnitude of coupling impedance directly affects the device's gain, electronic efficiency and other key indicators. Therefore, it is necessary to explore a new type of interleaved double-grid slow-wave structure with weak dispersion and high coupling impedance. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a gradient grating width type interleaved dual-grating slow-wave structure based on an exponential function that can improve coupling impedance and dispersion characteristics.

[0005] Technical solution: The gradient grating width type staggered double grating slow wave structure of the present invention is composed of multiple individual gratings arranged periodically in a rectangular waveguide; the individual grating is a double grating structure in which upper grating units and lower grating units are arranged in an alternating manner, and a certain spacing is provided between the upper grating units and the lower grating units, which is a strip-shaped electron beam channel; the upper grating units and the lower grating units have the same structure, and the cross-sectional shape of the upper / lower grating units is as follows: the two ends are rectangular, and the cross-sectional profile curve of the middle part is an exponential function.

[0006] Furthermore, the cross-sectional shape of the upper / lower gate unit satisfies x-axis symmetry and y-axis symmetry, and its exponential function expression is:

[0007]

[0008] Where -c≤x≤c, c is the horizontal half-length of the gradient part; a is the coefficient of the exponential function; and d is the distance of the contour curve in the positive half-axis direction of the y-axis.

[0009] Furthermore, the horizontal spacing between the upper grating unit (2) and the lower grating unit (3) is p / 2, and the distance between the upper grating unit (2) of the first single grating body and the end face of the rectangular waveguide (1) is p / 4, where p is the period length of a single period.

[0010] Furthermore, the total cross-sectional length of the upper / lower gate unit is the width of the rectangular waveguide.

[0011] Furthermore, both the rectangular waveguide and the individual gratings are made of conductive metal.

[0012] Compared with the prior art, the significant advantages of this invention are as follows:

[0013] 1. The cross-sectional shape of the upper / lower gate unit in this invention adopts a structure with rectangular ends and an exponential function profile curve in the middle section. Under the premise of similar phase velocity, the longitudinal electric field amplitude is high, resulting in high coupling impedance, which provides higher output power, gain and electronic efficiency for the traveling wave tube.

[0014] 2. In the cross-section of the upper / lower gate unit of the present invention, the transverse half-length of the gradient portion can improve the dispersion characteristics and coupling impedance in the operating frequency band of the slow wave structure; the structure of the present invention has low dispersion and can operate in a wider frequency band. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0016] Figure 2 This is an isometric view of a single periodic structure of the present invention;

[0017] Figure 3 This is a front view of a single periodic structure of the present invention;

[0018] Figure 4 for Figure 3 The right view;

[0019] Figure 5(a) is an axonometric view of the gate unit structure of the present invention.

[0020] Figure 5(b) is a schematic cross-sectional view of the gate unit of the present invention;

[0021] Figure 6This is a comparison diagram of the longitudinal electric field at 195 GHz between the present invention and the traditional rectangular staggered dual-grid slow-wave structure;

[0022] Figure 7 This is a comparison diagram of the normalized phase velocity of the present invention and the traditional rectangular interlaced dual-grid slow-wave structure;

[0023] Figure 8 This is a comparison diagram of the coupling impedance of the present invention and the traditional rectangular staggered dual-grid slow-wave structure;

[0024] Figure 9 The figure shows the effect of changes in the key structural parameter 'a' of the grating on the performance of the slow-wave structure.

[0025] Figure 10 The figure shows the effect of changes in the key structural parameter c of the grating on the performance of the slow-wave structure. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] (I) Structural Design

[0028] like Figure 1 The diagram shown illustrates the slow-wave structure of this invention; the slow-wave structure is constructed by periodically arranging multiple individual gratings within a rectangular waveguide 1. Figure 2 As shown, a single grating is a double-grating structure with upper grating unit 2 and lower grating unit 3 arranged alternately. Between the upper grating unit 2 and lower grating unit 3 is a strip-shaped electron beam channel with a height of b. Both the rectangular waveguide and the grating units are made of conductive metals, such as copper, aluminum, gold, and silver. The more periods, the higher the gain of the traveling wave tube; this embodiment uses 80 periods.

[0029] like Figure 3 , Figure 4 As shown, p is the period length of a single period, l is the thickness of the support plate, w is the width of the rectangular waveguide, b is the electron beam channel height, and h is the grating height. The upper grating unit 2 and the lower grating unit 3 are semi-periodically staggered: the distance between the longitudinal axis of the upper grating unit 2 and the longitudinal axis of the lower grating unit 3 is p / 2. The dimensions of each part are: a = 1.25, w = 0.8 mm, b = 0.2 mm, h = 0.3 mm, l = 0.05 mm, c = 0.18 mm, d = 0.08 mm, p = 0.5 mm. This embodiment is designed based on a working center frequency of 200 GHz. The structural dimensions in other application frequency bands can be obtained by scaling the structural dimensions of this invention according to the ratio of the width of the standard rectangular waveguide in the application frequency band to the width of the rectangular waveguide w in this structure. This invention is not limited to specific embodiments.

[0030] As shown in Figure 5(a), the height of the grid element is h; the cross-section of the grid element is shown in Figure 5(b), and its profile curve satisfies an exponential function. The function expression of the curve is:

[0031]

[0032] In the formula, a is the coefficient of the exponential function, d is the distance of the contour curve in the positive half-axis direction of the y-axis, and c is the horizontal half-length of the gradient part.

[0033] (II) Simulation Experiment

[0034] The invention was simulated at different locations within one cycle at 195 GHz using three-dimensional electromagnetic simulation software. Figure 6 This is a comparison diagram of the longitudinal electric field of the present invention and the traditional rectangular staggered double-grid structure. It can be seen that the longitudinal electric field amplitude of the staggered double-grid slow-wave structure proposed in this invention is 2.5 × 10⁻⁶. 10 V / m, while the longitudinal electric field amplitude of the traditional rectangular staggered double-grid structure is 2.1×10 10 V / m; The longitudinal electric field of the staggered double-grid structure proposed in this invention is 19% higher than that of the traditional rectangular staggered double-grid slow-wave structure at 195 GHz. According to the theory of traveling wave tube slow-wave structure, the improvement of the longitudinal electric field can improve the coupling impedance, increase the interaction strength between the electron beam and the electromagnetic field, and thus improve the performance indicators such as gain and output power.

[0035] Figure 7 The dispersion curves of this invention and the traditional rectangular interlaced dual-grid slow-wave structure show that, within the operating frequency band of 190 GHz-230 GHz, the phase velocity of this invention exhibits a small change with frequency, with a difference of only 0.003. In contrast, the phase velocity difference of the traditional rectangular interlaced dual-grid slow-wave structure is 0.005. This clearly demonstrates that, compared to the traditional rectangular interlaced dual-grid slow-wave structure, the interlaced dual-grid slow-wave structure of this invention possesses significantly lower dispersion characteristics. This low dispersion characteristic ensures strong synchronization conditions for the interaction between the electron beam and the electromagnetic field over a wide frequency band, providing a very wide operating bandwidth for the traveling wave tube. Therefore, compared to the existing rectangular structure, the longitudinal electric field of this invention is more concentrated in the middle of the electron beam channel. According to the coupling impedance formula, when the phase velocities are similar, a stronger longitudinal electric field results in a higher coupling impedance, which is beneficial for the interaction between the electromagnetic field and the electron beam.

[0036] Figure 8 The figure shows a comparison of the coupling impedance of the present invention with that of the traditional rectangular interleaved dual-grid slow-wave structure. In the operating range of 190GHz–230GHz, the coupling impedance of the present invention is improved by 42%–67% compared with the traditional rectangular interleaved dual-grid slow-wave structure. According to the working principle of traveling wave tubes, traveling wave tubes based on the interleaved dual-grid slow-wave structure of the present invention can obtain higher output power, gain and electronic efficiency.

[0037] Figure 9 The key structural parameter 'a' of this invention affects the performance of the slow-wave structure. Structurally, parameter 'a' influences the smoothness of the gradient section; the smaller 'a' is, the smoother the gradient section. It can be observed that parameter 'a' has a negligible effect on the phase velocity of the slow-wave structure, but a significant effect on the coupling impedance. A moderate gradient can increase the magnitude of the coupling impedance, thereby increasing the intensity of the interaction between the electron beam and the electromagnetic wave.

[0038] Figure 10 The key structural parameter c of this invention affects the performance of the slow-wave structure. In terms of structure, parameter c is the lateral half-length of the gradient section. It can be found that parameter c has a significant impact on the phase velocity and coupling impedance of the slow-wave structure. The larger c is, the smaller the phase velocity and the greater the dispersion of the slow-wave structure. The coupling impedance is smaller at low frequencies and larger at high frequencies. An appropriate lateral length of the gradient section can improve the dispersion characteristics and coupling impedance of the slow-wave structure in the operating frequency band.

Claims

1. A gradient-width staggered double-gate slow-wave structure based on an exponential function, comprising multiple individual gratings periodically arranged within a rectangular waveguide (1); wherein each individual grating is a double-gate structure with upper grating unit (2) and lower grating unit (3) staggered, and a certain spacing is provided between the upper grating unit (2) and the lower grating unit (3) to form a strip-shaped electron beam channel; the upper grating unit (2) and the lower grating unit (3) have the same structure, characterized in that, The cross-sectional shape of the upper / lower gate unit is as follows: both ends are rectangular, and the contour curve of the middle section is an exponential function; The cross-sectional shape of the upper / lower gate unit satisfies x-axis symmetry and y-axis symmetry, and its exponential function expression is: Where -c≤x≤c, c is the horizontal half-length of the gradient part; a is the coefficient of the exponential function; d is the distance of the contour curve in the positive half-axis direction of the y-axis; The horizontal spacing between the upper grating unit (2) and the lower grating unit (3) is p / 2, and the distance between the upper grating unit (2) of the first single grating body and the end face of the rectangular waveguide (1) is p / 4, where p is the period length of a single period.

2. The gradient grating width interlaced double-grating slow-wave structure based on an exponential function according to claim 1, characterized in that, The total cross-sectional length of the upper / lower gate unit is the width of the rectangular waveguide.

3. The gradient grating width interlaced double-grating slow-wave structure based on an exponential function according to claim 1, characterized in that, Both the rectangular waveguide and the individual grating are made of conductive metal.

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