CN115831689A

CN115831689A - Gradual change grid width type staggered double-grid slow wave structure based on exponential function

Info

Publication number: CN115831689A
Application number: CN202211582953.4A
Authority: CN
Inventors: 赵晨; 许航
Original assignee: Nanjing University of Information Science and Technology
Current assignee: Nanjing University of Information Science and Technology
Priority date: 2022-12-09
Filing date: 2022-12-09
Publication date: 2023-03-21

Abstract

The invention discloses a gradual-change grid width type staggered double-grid slow-wave structure based on an exponential function, which is formed by periodically arranging a plurality of single grid bodies in a rectangular waveguide; the single gate body is of a double-gate structure with upper gate units and lower gate units which are arranged in a staggered manner, and a band-shaped electron beam channel is arranged between the upper gate units and the lower gate units at a certain interval; the upper gate unit and the lower gate unit have the same structure, and the cross section of the upper/lower gate unit has the following shape: the two ends are rectangles, and the section profile curve of the middle part is an exponential function. On the premise of similar phase speed, the longitudinal electric field has high amplitude, so that the coupling impedance is high, and higher output power, gain and electronic efficiency are provided for the traveling wave tube.

Description

Gradual change grid width type staggered double-grid slow wave structure based on exponential function

Technical Field

The invention relates to a slow wave structure, in particular to a gradual-change gate width type staggered double-gate slow wave structure based on an exponential function.

Background

The traveling wave tube is widely applied to the fields of communication satellites, radars, electronic countermeasure and the like due to the characteristic of high power and wide frequency band, and has an irreplaceable position in a plurality of microwave vacuum electronic devices. The traveling wave tube mainly comprises five parts: the electron gun emits electrons with a certain speed, the slow wave structure is a place where the electrons and electromagnetic waves interact, after the phase speed of the transmitted electromagnetic waves is reduced to the synchronous speed, the electromagnetic field modulates the electrons, the modulated electrons exchange energy to amplify the power of the electromagnetic waves, the slow wave structure is also the working principle of a traveling wave tube, the input coupling structure couples high-frequency signals to a slow wave line, the output coupling structure couples the amplified high-frequency signals to an output circuit, the collector is used for collecting the electrons after the energy conversion with the electromagnetic field is completed, and the focusing system is used for restraining the traveling direction of the electrons and ensuring that the electrons smoothly pass through the slow wave structure without being intercepted. The slow wave structure is a key component of the traveling wave tube, and the performance of the slow wave structure determines the working performance of the traveling wave tube.

In recent years, with the development of vacuum electronic devices to millimeter wave and terahertz frequency bands, slow wave structures are also changed from spiral line type and coupling cavity type suitable for low frequency bands to folded waveguide type and staggered double-gate type, wherein the staggered double-gate slow wave structures are widely applied to the terahertz frequency bands due to the characteristics of high power capacity, natural electron beam channels and easiness in processing, the traditional rectangular staggered double-gate slow wave structures are high in dispersion and low in coupling impedance, the working bandwidth of the devices can be influenced by the intensity of dispersion according to the pierce small signal theory and the microwave tube large signal theory, the key indexes of the devices, such as gain, electronic efficiency and the like, can be directly influenced by the intensity of coupling impedance, and therefore a novel staggered double-gate slow wave structure with low dispersion and high coupling impedance needs to be explored.

Disclosure of Invention

The invention aims to: the invention aims to provide an exponential function-based gradually-variable-grating-width staggered double-grating slow-wave structure which can improve coupling impedance and dispersion characteristics.

The technical scheme is as follows: the gradually-changed grid width type staggered double-grid slow-wave structure is formed by periodically arranging a plurality of single grid bodies in a rectangular waveguide; the single grid body is of a double-grid structure with upper grid units and lower grid units which are arranged in a staggered mode, and a strip-shaped electron beam channel is arranged between the upper grid units and the lower grid units at a certain interval; the upper gate unit and the lower gate unit have the same structure, and the cross section of the upper/lower gate unit has the following shape: the two ends are rectangles, and the section profile curve of the middle part is an exponential function.

Further, the cross-sectional shape of the upper/lower gate unit satisfies x-axial symmetry and y-axial symmetry, and the expression of the exponential function is as follows:

wherein x is more than or equal to c and is less than or equal to c, and c is the transverse half length of the gradual change part; a is the coefficient of the exponential function; d is the distance of the profile curve in the direction of the positive half axis of the y-axis.

Furthermore, the distance between the upper grid unit (2) and the lower grid unit (3) arranged in the horizontal direction is p/2, the distance between the upper grid unit (2) of the first single grid body and the end face of the rectangular waveguide (1) is p/4, and p is the period length of a single period.

Further, the total length of the cross sections of the upper/lower gate units is the length of the wide side of the rectangular waveguide.

Further, the rectangular waveguide and the single gate body are made of conductive metal.

Compared with the prior art, the invention has the following remarkable effects:

1. according to the invention, the cross section shape of the upper/lower grid unit adopts a structure that two ends are rectangular and the profile curve of the middle cross section is an exponential function, and the amplitude of a longitudinal electric field is high on the premise of similar phase speed, so that the coupling impedance is high, and higher output power, gain and electronic efficiency are provided for a traveling wave tube;

2. in the cross section of the upper/lower gate unit, the transverse half length of the gradual change part can improve the dispersion characteristic and the coupling impedance in the working frequency band of the slow wave structure; the structure of the invention has low dispersion and can work in a wider frequency band range.

Drawings

FIG. 1 is a schematic diagram of the general structure of the present invention;

FIG. 2 is an isometric view of a single periodic structure of the present invention;

FIG. 3 is a front view of a single periodic structure of the present invention;

FIG. 4 is a right side view of FIG. 3;

figure 5 (a) is an isometric view of a gate cell structure of the present invention,

FIG. 5 (b) is a schematic cross-sectional view of a gate cell of the present invention;

FIG. 6 is a comparison graph of longitudinal electric field at 195GHz of the present invention and a conventional rectangular staggered double-gate slow-wave structure;

FIG. 7 is a graph comparing the normalized phase velocity of the present invention with that of a conventional rectangular staggered dual gate slow wave structure;

FIG. 8 is a graph comparing the coupling impedance of the present invention with that of a conventional rectangular staggered dual gate slow wave structure;

FIG. 9 is a graph showing the effect of the variation of the critical structure parameter a of the gate on the performance of the slow-wave structure;

FIG. 10 is a graph showing the effect of the variation of the critical structure parameter c of the grid body on the performance of the slow wave structure.

Detailed Description

The invention is described in further detail below with reference to the drawings and the detailed description.

Structural design

FIG. 1 is a schematic diagram of a slow wave structure according to the present invention; the slow wave structure of the present invention is constituted by a plurality of individual grating bodies periodically arranged in the rectangular waveguide 1. As shown in fig. 2, a single gate body is a dual-gate structure in which upper gate cells 2 and lower gate cells 3 are arranged in a staggered manner, a strip-shaped electron beam channel is arranged between the upper gate cells 2 and the lower gate cells 3, and the height of the electron beam channel is b. The rectangular waveguide and the grid unit are made of conductive metal, such as: copper, aluminum, gold, silver, and the like. The larger the number of cycles, the higher the gain of the traveling wave tube, and 80 cycles are adopted in this embodiment.

As shown in fig. 3 and 4, p is the period length of a single period, l is the thickness of the supporting plate, w is the width length of the rectangular waveguide, b is the height of the electron beam channel, and h is the height of the gate; the upper gate cell 2 and the lower gate cell 3 are half-cycle interleaved: the longitudinal axis of the upper gate unit 2 is at a distance p/2 from the longitudinal axis of the lower gate unit 3. The sizes of all parts are as follows: a =1.25, w =0.8mm, b =0.2mm, h =0.3mm, l =0.05mm, c =0.18mm, d =0.08mm, p =0.5mm. The present embodiment is designed on the basis that the working center frequency is 200GHz, and the structural dimension under other application frequency bands can be obtained by scaling the structural dimension according to the ratio of the length of the broadside of the rectangular waveguide of the application frequency band standard to the length w of the broadside of the rectangular waveguide of the present embodiment. The invention is not limited to the specific embodiments.

As shown in fig. 5 (a), the gate cell height is h; the cross section of the gate unit is shown in fig. 5 (b), and the contour curve of the gate unit satisfies an exponential function, and the function expression of the curve is as follows:

in the formula, a is a coefficient of an exponential function, d is a distance of the profile curve in the direction of a positive half axis of a y axis, and c is a transverse half length of the gradual change part.

(II) simulation experiment

The invention is simulated by three-dimensional electromagnetic simulation software at different positions in one period at 195GHz, and FIG. 6 is a comparison graph of longitudinal electric fields of the invention and a traditional rectangular staggered double-gate structure. It can be found that the longitudinal electric field amplitude value of the staggered double-gate slow wave structure provided by the invention is 2.5 multiplied by 10 ¹⁰ V/m, and the amplitude of the longitudinal electric field of the conventional rectangular staggered double-gate structure is 2.1 multiplied by 10 ¹⁰ V/m; compared with the traditional rectangular staggered double-gate slow-wave structure, the longitudinal electric field of the staggered double-gate structure provided by the invention is improved by 19% at 195GHz, and the improvement of the longitudinal electric field can improve the coupling impedance and increase the interaction strength of electron beams and an electromagnetic field, so that the performance indexes such as gain, output power and the like are improved.

FIG. 7 is a dispersion curve of the present invention and a conventional rectangular staggered dual-gate slow-wave structure, and it can be found that the variation of the phase velocity with frequency is small and the variation difference is 0.003 in the working frequency range of 190GHz-230 GHz; the phase speed variation difference of the traditional rectangular staggered double-gate slow-wave structure is 0.005, which fully shows that compared with the traditional rectangular staggered double-gate slow-wave structure, the staggered double-gate slow-wave structure has lower dispersion characteristic, the low dispersion characteristic can ensure stronger interaction synchronization condition of electron beams and electromagnetic fields in a very wide frequency band, and very wide working bandwidth can be provided for the traveling wave tube. Therefore, compared with the existing rectangular structure, the longitudinal electric field is more concentrated in the middle of the electron beam channel, and according to the formula of the coupling impedance, when the phase speeds are close, the stronger the longitudinal electric field is, the higher the coupling impedance is, and the interaction between the electromagnetic field and the electron beam is facilitated.

Fig. 8 is a comparison graph of coupling impedance of the staggered dual-gate slow-wave structure of the invention and a conventional rectangular staggered dual-gate slow-wave structure, and compared with the conventional rectangular staggered dual-gate slow-wave structure, the coupling impedance of the invention is improved by 42% -67% in 190GHz-230GHz work, and according to the working principle of a traveling-wave tube, the traveling-wave tube based on the staggered dual-gate slow-wave structure of the invention can obtain higher output power, gain and electronic efficiency.

Fig. 9 shows the influence of the key structural parameter a on the performance of the slow wave structure, in terms of structure, the parameter a influences the smoothness of the gradual change part, and the smaller a is, the smoother the gradual change part is. It can be found that the parameter a has a small influence on the phase velocity of the slow wave structure and a large influence on the coupling impedance, and the moderate gradual change can increase the magnitude of the coupling impedance so as to improve the strength of the interaction between the electron beam and the electromagnetic wave.

Fig. 10 shows the influence of the key structural parameter c on the performance of the slow wave structure, in terms of structure, the parameter c is the transverse half length of the gradual change portion, and it can be found that the parameter c has a large influence on the phase speed and the coupling impedance of the slow wave structure, the larger the parameter c is, the smaller the phase speed and the larger the dispersion of the slow wave structure are, the smaller the coupling impedance at the low frequency is, the larger the coupling impedance at the high frequency is, and the appropriate transverse length of the gradual change portion can improve the dispersion characteristic and the coupling impedance in the operating frequency band of the slow wave structure.

Claims

1. A gradual-change grid width type staggered double-grid slow-wave structure based on an exponential function is formed by periodically arranging a plurality of single grid bodies in a rectangular waveguide (1); the single grid body is of a double-grid structure with upper grid units (2) and lower grid units (3) which are arranged in a staggered mode, and a strip-shaped electron beam channel is arranged between the upper grid units (2) and the lower grid units (3) at a certain interval; the upper grid unit (2) and the lower grid unit (3) have the same structure, and are characterized in that the cross-sectional shapes of the upper/lower grid units are as follows: the two ends are rectangles, and the profile curve of the section of the middle part is an exponential function.

2. The structure of claim 1, wherein the cross-sectional shape of the upper/lower gate units satisfies x-axis symmetry and y-axis symmetry, and the expression of the exponential function is:

wherein x is more than or equal to c and c is the transverse half length of the gradual change part; a is the coefficient of the exponential function; d is the distance of the profile curve in the direction of the positive half axis of the y-axis.

3. The structure of claim 1, wherein the upper gate unit (2) and the lower gate unit (3) are horizontally arranged at a pitch of p/2, and the upper gate unit (2) of the first single gate body is spaced from the end face of the rectangular waveguide (1) at a distance of p/4, where p is the period length of a single period.

4. The exponential-function-based graded-gate-width-type staggered double-gate slow-wave structure according to claim 1, wherein the total length of the cross-section of the upper/lower gate units is the length of the wide side of the rectangular waveguide.

5. The exponential-function-based graded-gate-width-type staggered double-gate slow-wave structure according to claim 1, wherein the rectangular waveguide and the single gate body are both made of conductive metal.