Frequency-adjustable high-power microwave pulse compression system

Abstract

The invention provides a frequency-adjustable SLED pulse compression system, and belongs to the technical field of high-power microwave pulse compression. The system comprises a 3dB coupler, two double-hole coupling structures, two resonant cavities and two choke piston type tuning structures, wherein the double-hole coupling structure enables the power in the 3dB coupler to be coupled into the resonant cavity, a choke piston type tuning structure is arranged in the resonant cavity, and the resonant frequency is adjusted by moving the position of the choke piston type tuning structure. According to the tuning structure, high-power microwaves in the resonant cavity can be prevented from leaking, the sparking phenomenon in a high-power state caused by friction between the short-circuit piston and the inner surface of the cavity can be prevented, and high-power application can be achieved; meanwhile, the piston is adopted for tuning, the movable range is large, wide frequency adjustment can be achieved, and the pulse compression system can be applied to a broadband high-power microwave system.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-power microwave pulse compression, and particularly relates to an SLED pulse compression system with a choke piston type tuning structure, which can achieve pulse compression with wide bandwidth, continuous frequency modulation, and low-loss tuning. Background Art

[0002] In a high-power microwave (HPM) system, a pulse compressor compresses a microwave long pulse generated by an HPM source into a narrow pulse signal with a pulse width of several hundred or even dozens of nanoseconds and a peak power increased by several times or even dozens of times, so as to generate a pulse signal with a higher peak power.

[0003] As the earliest developed pulse compressor, the SLED pulse compressor is widely used in the fields of accelerators and HPM. It mainly consists of a 3dB coupler and two high-Q resonators. The high-Q resonator stores microwave energy and instantaneously releases the energy when the signal pulse is inverted, achieving the purpose of compression. Since the Q value of the resonator is very high, generally on the order of 10 5 magnitude, the pulse compression system belongs to a point-frequency system. When the input signal frequency deviates from the resonance frequency of the resonator, the performance of the compression system drops significantly; and the design and processing errors of the resonator often result in a deviation between the frequency of the processed resonator and the theoretical design. Therefore, a tuning structure is generally designed in the design of the resonator to adjust the resonance frequency of the resonator to match the frequency of the signal source in actual applications.

[0004] Generally, the tuning structure adopts a forced deformation structure. For example, a mechanical structure is designed at the bottom end of a cylindrical resonator to force a small deformation at the bottom end of the resonator, thereby achieving the purpose of tuning. However, the frequency range that such a tuning structure can adjust is very small because the forced deformation amount is almost only on the order of micrometers, which makes the pulse compression system still a point-frequency system and unable to achieve broadband applications. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a frequency-tunable SLED pulse compression system. The present invention uses a choke piston as the tuning structure, which can prevent the leakage of high-power microwave in the resonator and prevent the occurrence of arcing under high-power conditions due to the friction between the short-circuit piston and the inner surface of the cavity, and can achieve high-power applications; at the same time, the piston is used for tuning, and the movable range is large, and a relatively wide frequency adjustment can be achieved, so that the pulse compression system can be applied to a broadband high-power microwave system, further enhancing the application potential of the pulse compressor in the field of high-power microwave.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A frequency-tunable SLED pulse compression system, comprising: a 3dB coupler, two double-hole coupling structures, two resonant cavities, and two choke piston tuning structures.

[0008] The 3dB coupler includes an input end, an output end, a coupling end, and a through end, and is used to isolate the input signal and the output signal.

[0009] The double-hole coupling structure has a rectangular waveguide as the main body. One end thereof is connected to the coupling end or the through end of the 3dB coupler, and the other end is closed. The narrow side wall of the rectangular waveguide is connected to the resonant cavity through two cylindrical through holes, so that energy is coupled into the cylindrical resonant cavity.

[0010] The resonant cavity is a cylindrical resonant cavity, and the coupled energy excites the TE 01p mode inside the resonant cavity; where p is the number of half-waves in the axial direction of the resonant cavity.

[0011] The choke piston tuning structure uses a "mountain"-shaped choke piston. By adjusting the position of the choke piston tuning structure in the resonant cavity, the resonant frequency is changed, so as to realize linear continuous adjustment of the working frequency of the pulse compression system.

[0012] Further, the "mountain"-shaped choke piston includes a front end part and a rear end part; wherein, there is a gap between the front end part and the inner wall of the resonant cavity, and the rear end part is in contact with the inner wall of the resonant cavity and can move back and forth; the length of the gap between the front end part and the inner wall of the resonant cavity and the depth of the choke groove inside the front end part both satisfy the quarter-wavelength impedance transformation property, so that the end face of the front end part forms a short circuit surface with the inner wall of the resonant cavity to achieve good electrical contact and prevent microwave leakage.

[0013] Further, the distance between the cylindrical coupling holes is half a wavelength; the distance from the center of the cylindrical coupling hole near the short circuit surface of the rectangular waveguide to this short circuit surface is a quarter wavelength.

[0014] Further, the four ports of the 3dB coupler all adopt standard rectangular waveguides, and TE 10 mode is transmitted inside.

[0015] Further, after the required radius of the resonant cavity and the resonant mode p are selected, the initial position of the choke piston tuning structure under the working condition of the TE 01p mode is calculated according to formula (1);

[0016]

[0017] where L is the length of the resonant cavity, D is the diameter of the resonant cavity, f is the resonant frequency, μ' is the root of the derivative function of the first-order Bessel function, and c is the speed of light.

[0018] Further, in TE 01p Under the single-mode condition, the movable range of the choke piston type tuning structure is determined by modeling and simulation.

[0019] Further, in TE 01p Under the single-mode working condition, the corresponding relationship between the position of the choke piston type tuning structure and the resonance frequency is calculated according to formula (1), and then the moving distance of the choke piston type tuning structure is controlled by the motor system, so as to realize the linear continuous adjustment of the working frequency of the pulse compression system.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) In the present invention, a piston is used as the tuning structure of the resonant cavity. Compared with the mechanically tuned structure with forced deformation, the movable range of the piston is wider, the tuning range of the resonant cavity is increased, and thus the working bandwidth of the entire pulse compression system is improved.

[0022] (2) In the present invention, the tuning piston adopts a "mountain" shaped choke structure, which can prevent the piston from directly contacting the inner wall of the resonant cavity, resulting in the sparking phenomenon caused by the friction between the piston and the inner wall during the movement of the piston. At the same time, the tuning piston can well suppress the energy leakage in the resonant cavity and withstand the high power inside the resonant cavity.

[0023] (3) The present invention can realize the linear continuous adjustment of the working frequency of the pulse compression system by programming the moving distance of the piston through the motor system. Description of the Drawings

[0024] Figure 1 . is a schematic diagram of the SLED pulse compression system of the present invention

[0025] Figure 2 . is a schematic diagram of the coupling structure of the present invention

[0026] Figure 3 . is a schematic diagram of the choke piston type tuning structure of the present invention

[0027] Figure 4 . is a simulation structure of the S-band SLED pulse compression system according to an embodiment of the present invention

[0028] Figure 5 . is the range of the resonance frequency change after the piston movement calculated according to an embodiment of the present invention

[0029] Figure 6 . is a comparison of the compression curves corresponding to three different frequency points within the working frequency band according to an embodiment of the present invention

[0030] Wherein: 1. 3dB coupler; 2. Double-hole coupling structure; 3. Cylindrical resonant cavity; 4. Choke piston type tuning structure. Detailed Embodiments

[0031] In order to more clearly illustrate the objectives, features, and advantages of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0032] This embodiment designs an SLED pulse compression system operating in the S band, and the overall structure is as Figure 1 shown, and the simulation model is as Figure 4 shown.

[0033] This system includes: a 3dB coupler, two double-hole coupling structures, two cylindrical resonators, and two choke piston tuning structures.

[0034] The 3dB coupler includes an input end, an output end, a coupling end, and a through end, and is used to isolate the input signal and the output signal.

[0035] The double-hole coupling structure has a main body of a standard rectangular waveguide, one end of which is connected to the coupling end or the through end of the 3dB coupler, and the other end is closed; the narrow side wall of the rectangular waveguide is connected to the resonator through two cylindrical through holes, so that energy is coupled into the cylindrical resonator.

[0036] The resonator is a cylindrical resonator, and the coupled energy excites a TE 01p mode inside the resonator; where p is the number of half-waves in the axial direction of the resonator and is related to the length of the resonator.

[0037] The choke piston tuning structure uses a "mountain"-shaped choke piston. By adjusting the position of the choke piston tuning structure in the resonator, the resonant frequency is changed, so as to realize linear continuous adjustment of the operating frequency of the pulse compression system.

[0038] As Figure 3 shown, the "mountain"-shaped choke piston includes a front end part and a rear end part. Among them, the rear end part is in contact with the inner wall of the resonator and can move back and forth. In the front end part, fg is a short-circuit plane, and the length from the fg plane to the end point c satisfies the quarter-wavelength impedance transformation property. Therefore, the impedance between c and d tends to infinity, which is an open-circuit plane. The distance between point a and point c also satisfies the quarter-wavelength impedance transformation property. Therefore, the ab plane is a short-circuit plane, that is, there is good electrical contact between point a and point b, which can prevent microwave leakage.

[0039] In this system, in order to ensure that the Q0 value of the resonator is close to the order of 10 5 magnitude, the diameter D of the resonator is selected to be 190 mm, and the resonant mode is TE 015 mode, that is, p = 5.

[0040] According to the relationship between the length of the resonant cavity and the resonant frequency of the TE 01p mode, as shown in Equation (1):

[0041]

[0042] Among them, μ' is the root of the derivative function of the first-order Bessel function, and its value is approximately 3.832, and c is the speed of light. When the operating frequency is calculated to be 2.458 GHz, the cavity length L is 488.92 mm.

[0043] When the final cavity length is optimized to be 489 mm through simulation, the resonant frequency of the resonant cavity is 2.4579 GHz, and under this size condition, the Q0 of the resonant cavity is calculated to be 8.9e+4.

[0044] The diameter of the designed cylindrical through-hole is 32 mm. According to the waveguide wavelength calculation formula of the circular waveguide TE 01 mode, the calculated waveguide wavelength corresponding to the frequency of 2.4579 GHz is approximately 196.3 mm. Therefore, the distance between the centers of the two coupling holes is half of the waveguide wavelength, and the distance from the center of the coupling hole near the short circuit surface of the rectangular waveguide to this short circuit surface is one-fourth of the waveguide wavelength. The distance between points ac of the choke piston is approximately one-fourth of the waveguide wavelength, and through simulation optimization, it is 43 mm, and the distance between points cd is 3 mm.

[0045] Through simulation, when the piston moves in the range of -50 mm to +40 mm at the initial position of 489 mm, the resonant frequency corresponding to the TE 015 mode of the resonant cavity changes from 2.3723 - 2.5448 GHz, and the simulation results are as Figure 5 shown. The mode interval between the TE 015 mode corresponding to each frequency point in this 172 MHz frequency band and the adjacent mode is greater than 20 MHz, that is, it can be considered that there is only one resonant mode TE 015 mode inside the cavity at the frequency corresponding to each size.

[0046] Select any three resonant frequency points in this frequency band, which are 2.404 GHz / 2.4579 GHz / 2.5212 GHz respectively, and the corresponding piston movement distances d L are -30 mm / 0 mm / 30 mm respectively. The compression curves corresponding to each frequency point are obtained through time-domain simulation as Figure 6 shown. Since the input signal frequency changes and the cavity length also changes, the time constant of this compression system changes, manifested as the translation of the lowest point of the compression curve. However, this curve translation does not affect the compression gain, because as Figure 6 can be seen, the compression gains corresponding to the three frequency points of this system are close, which are: 8.336 / 8.376 / 8.417 respectively. That is, when the frequency offset is 117.2 MHz, the compression gain only changes by 0.88%, verifying the broadband characteristic of the compression system in this invention.

Claims

1. A frequency-tunable SLED pulse compression system, characterized in that, Including: A 3dB coupler, two double-hole coupling structures, two resonant cavities, and two choke piston tuning structures; The 3dB coupler includes an input end, an output end, a coupling end, and a through end, and is used to isolate the input signal and the output signal; The double-hole coupling structure has a rectangular waveguide as the main body. One end of the rectangular waveguide is connected to the coupling end or the through end of the 3dB coupler, and the other end is closed. The narrow side wall of the rectangular waveguide is connected to the resonant cavity through two cylindrical through holes to couple energy into the cylindrical resonant cavity; The resonant cavity is a cylindrical resonant cavity, and the coupled energy excites the TE 01p mode inside the resonant cavity, where p is the number of half-waves in the axial direction of the resonant cavity; The choke piston tuning structure uses a "mountain"-shaped choke piston. By adjusting the position of the choke piston tuning structure in the resonant cavity, the resonant frequency is changed, so as to realize linear continuous adjustment of the operating frequency of the pulse compression system.

2. The frequency - tunable SLED pulse compression system according to claim 1, characterized in that, The "mountain"-shaped choke piston includes a front part and a rear part; among them, there is a gap between the front part and the inner wall of the resonant cavity, and the rear part is in contact with the inner wall of the resonant cavity and can move back and forth; the length of the gap between the front part and the inner wall of the resonant cavity and the depth of the choke groove inside the front part both satisfy the quarter-wavelength impedance transformation property, so that the end face of the front part forms a short circuit surface with the inner wall of the resonant cavity to achieve good electrical contact and prevent microwave leakage.

3. A frequency-tunable SLED pulse compression system according to claim 2, wherein The distance between the cylindrical coupling holes is a half wavelength; the distance from the center of the cylindrical coupling hole close to the short circuit surface of the rectangular waveguide to the short circuit surface is a quarter wavelength.

4. The frequency-tunable SLED pulse compression system according to claim 3, characterized in that, All four ports of the 3dB coupler use standard rectangular waveguides and internally transmit TE 10 mode.

5. A frequency-tunable SLED pulse compression system according to claim 4, characterized in that, After selecting the required resonator radius and the resonance mode p, the initial position of the choke piston tuning structure under the operating conditions of the TE 01p mode is calculated according to formula (1); Wherein, L is the length of the resonant cavity, D is the diameter of the resonant cavity, f is the resonant frequency, μ' is the root of the derivative function of the first-order Bessel function, and c is the speed of light.

6. A frequency-tunable SLED pulse compression system according to claim 5, characterized in that, At TE 01p Under the single-mode condition, the movable range of the choke piston type tuning structure is determined by modeling and simulation.

7. The frequency tunable SLED pulse compression system according to claim 6, characterized in that, Under TE 01p Under the single-mode working condition, the corresponding relationship between the position of the choke piston tuning structure and the resonance frequency is calculated according to formula (1), and then the moving distance of the choke piston tuning structure is controlled by the motor system, so as to realize the linearly continuous adjustment of the working frequency of the pulse compression system.

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