CN110098488B - A Mode Conversion Method for Low RCS Metasurfaces Based on Eigenmode Theory - Google Patents

Abstract

The invention belongs to the technical field of electromagnetism, relates to a low radar scattering cross section, and particularly relates to a mode conversion method of a low RCS (radar cross section) super surface based on a characteristic mode theory, which is characterized by comprising the following steps of: at least comprises the following steps: step 1: calculating a characteristic mode curve of the super-surface subunit (3) under the condition of fixed electromagnetic wave incidence according to a characteristic mode theory; step 2: carrying out array arrangement of 4 multiplied by 4 according to the super-surface subunits (3) obtained in the step 1; and 3, symmetrically arranging the super-surface sub-array (4) obtained in the step 2 and the rotary sub-array thereof by 2 x 2 to form a super-surface array (5) with RCS (radar cross section) reduction effect. The method for converting the low-RCS super-surface mode based on the characteristic model theory can realize the design of the low-RCS super-surface array according to the design flow without depending on the experience of designers, thereby greatly accelerating the design process, shortening the design period, and designing the low-RCS super-surface structure more intuitively, simply and efficiently.

Description

A Mode Conversion Method for Low RCS Metasurfaces Based on Eigenmode Theory

technical field

The invention belongs to the field of electromagnetic technology, relates to a low radar scattering cross section, and in particular relates to a mode conversion method of a low RCS metasurface based on characteristic mode theory.

Background technique

Radar Cross Section (RCS) is an important physical quantity to measure the scattering ability of scatterers. It can quantitatively characterize the ability of a target object to scatter electromagnetic energy in a fixed direction under the incident of electromagnetic waves. It is an important parameter to measure the scattering intensity of the target. The smaller the target, the better the concealment performance. At present, the technologies for reducing the target radar scattering cross section usually include three types: the technology of loading radar absorbing materials, the technology of shape optimization, and the technology of active or passive cancellation. Radar absorbers can convert electromagnetic energy into other forms of energy to achieve target RCS reduction. Shape optimization techniques optimize the shape of a target to steer its radar signal away from the threat or reduce radar echoes. Passive cancellation technology is to use passive stealth technology such as special shapes or materials to generate echoes that interfere with incoming waves to achieve mutual cancellation between incoming waves and echoes; while active cancellation technology is used in the target. Equipped with active cancellation electronics to generate electromagnetic waves suitable for cancellation, and to weaken or eliminate reflected waves through destructive interference.

An artificial electromagnetic metasurface refers to an artificial layered material with a thickness smaller than the wavelength. Generally speaking, it uses etching, printing, etc. to form an array with a certain arrangement on a layer of dielectric substrate. It can realize flexible and effective regulation of electromagnetic wave amplitude, phase, polarization, propagation mode and other characteristics. The current methods for low RCS metasurfaces are all based on the method of scattering cancellation, which belongs to passive cancellation technology. In 2007, M.Paquay et al. proposed an artificial electromagnetic metasurface structure in which the artificial magnetic conductor structure and the ideal conductor structure are arranged in a checkerboard. By using the phase difference between the artificial magnetic conductor structure and the ideal conductor structure by 180o, to achieve the goal. RCS reduction. However, the bandwidth of the in-phase reflection of the artificial magnetic conductor structure is very narrow, so the bandwidth of RCS reduction is limited. In order to widen the reduced bandwidth of RCS, A.Y.Modi et al. proposed a checkerboard structure based on two artificial magnetic conductors in 2016. By keeping the reflection phase difference of the two artificial magnetic conductor structures at 180°±37° in a wide frequency band, a wide-band low-RCS metasurface design is realized. However, the problem with this method is that it is difficult to intuitively associate the reflection phase with the metasurface structure in the design process of the metasurface subunit, and the working mechanism of the metasurface structure cannot be clearly reflected, so the design process is more dependent on Due to the experience of designers, it is necessary to continuously try to design metasurface subunits that meet the requirements, resulting in a substantial increase in the time and cost of the entire design process.

SUMMARY OF THE INVENTION

The purpose of the present invention is to aim at the above-mentioned deficiencies of the prior art, and propose a design of a metasurface array with low RCS that can be realized according to the design process without relying on the experience of designers, thereby greatly speeding up the design process and shortening the design cycle The mode conversion method of low RCS metasurface based on eigenmode theory can be more intuitive, concise and efficient to design low RCS metasurface structure.

To achieve the above object, the technical scheme of the present invention is: a mode conversion method of a low RCS metasurface based on the eigenmode theory, which is characterized in that: at least the following steps are included:

Step 1: Calculate the characteristic mode curve of a metasurface subunit 3 under the condition of fixed electromagnetic wave incidence according to the characteristic mode theory, so that the size and shape of the metasurface subunit 3 can realize mode conversion within the working frequency band;

Step 2: According to the metasurface subunits 3 obtained in step 1, perform a 4×4 array arrangement to form a metasurface subarray 4; calculate the characteristic mode curve of the metasurface subarray 4 under the condition of fixed electromagnetic wave incidence according to the characteristic mode theory , and optimize the structure size of the metasurface subarray 4 according to the characteristic mode analysis results in the working frequency band, and realize the mode conversion in the working frequency band;

In step 3, the metasurface sub-array 4 obtained in step 2 and its rotating sub-array are arranged symmetrically by 2×2 to form a meta-surface array 5 with RCS reduction effect.

Described step 1 includes the following specific steps:

1a) calculate the characteristic mode curve of a metasurface subunit 3 under fixed electromagnetic wave incident conditions, and determine the main excitation mode of the metasurface subunit 3 according to the amplitude curve of the mode expansion coefficient;

2a) extract the characteristic current of above-mentioned metasurface subunit 3, generate characteristic current vector distribution diagram;

3a) Combine the characteristic current vector distribution diagram of the main excitation mode and the phase curve of its mode expansion coefficient to obtain the composite mode current vector distribution of the main excitation mode, and adjust the structure size of the metasurface subunit 3 to achieve mode conversion in the working frequency band.

The fixed electromagnetic wave incident condition refers to the normal incidence of the electromagnetic field with known intensity, polarization, etc.

The main excitation mode is determined according to the size of the mode expansion coefficient. If the mode expansion coefficient corresponding to one mode is much larger than the mode expansion coefficient corresponding to other modes at the same operating frequency, the mode is the main excitation mode.

The composite mode current vector distribution is determined by the mode current distribution of the main excitation mode and the phase of the corresponding mode expansion coefficient. When the mode expansion coefficient phase of the main excitation mode is in the range of -90o to 90o, the corresponding mode current distribution remains unchanged. When the phase of the mode expansion coefficient of the main excitation mode is in the range of 90°~180° or -180°~-90°, the corresponding mode current direction is reversed, and all the main excitation modes after considering the phase are superimposed and synthesized, thus Obtain the composite mode current vector distribution.

The mode conversion refers to that the polarization direction of the scattered field generated by the combined mode current of the main excitation mode is orthogonal to the polarization direction of the incident electromagnetic field, that is, the scattering mode and the incident mode realize mode rotation.

The step 2 includes:

2a) performing an array arrangement on the metasurface subunits 3 obtained in step 1 to form a metasurface subarray 4, and performing characteristic pattern analysis on the metasurface subarray 4;

2b) According to the mode expansion coefficient amplitude curve obtained after the characteristic mode analysis in 2a), determine the main excitation mode in the working frequency band;

2c) Extract the characteristic current corresponding to the main excitation mode, and generate the characteristic current vector distribution map;

2d) Combining the characteristic current vector distribution diagram of the main excitation mode and the phase curve of its mode expansion coefficient, the synthesized mode current distribution of the main excitation mode is obtained, and the structure size of the metasurface subunit 3 is optimized to form a metasurface subarray 4, so that the metasurface subunit 3 is formed. The array 4 can realize mode conversion in the working frequency band.

The step 3 includes: rotating the metasurface subarray 4 clockwise with its center at angles of 90°, 180°, and 270°, and the obtained three metasurface subarrays after the rotation are together with the metasurface subarray 4 The metasurface array 5 with the RCS reduction effect is obtained by arranging it into a 2×2 array in a center-symmetric manner. The metasurface array 5 with the RCS reduction effect can achieve low RCS characteristics in the above-mentioned mode conversion frequency band.

The present invention has the following beneficial effects:

1. The present invention is a design method for realizing a low RCS metasurface array based on the characteristic mode theory. Through the analysis of the characteristic mode, the synthetic mode current distribution of the main excitation modes on the metasurface structure can be given, thereby clearly revealing the designed metasurface. The working mode and mechanism of the array.

2. Compared with the prior art, the present invention provides a general low-RCS metasurface array design process, without relying on the designer's experience, the design of the low-RCS metasurface array can be realized according to the design process, This greatly speeds up the design process and shortens the design cycle.

Description of drawings

1 is a flowchart of an embodiment of the present invention;

Fig. 2 is the mode expansion coefficient amplitude curve of metasurface subunit 3 in the present invention;

Fig. 3 is the mode expansion coefficient phase curve of metasurface subunit 3 in the present invention;

Fig. 4(a) is the mode current distribution of mode 1 of metasurface subunit 3 at 9 GHz;

Figure 4(b) is the mode current distribution of mode 2 of metasurface subunit 3 at 9 GHz;

Fig. 5(a) is the mode current distribution of mode 1 of metasurface subunit 3 at 11 GHz;

Fig. 5(b) is the mode current distribution of mode 2 of metasurface subunit 3 at 11 GHz;

Fig. 6(a) is the mode current distribution of mode 1 of metasurface subunit 3 at 17 GHz;

Fig. 6(b) is the mode current distribution of mode 2 of metasurface subunit 3 at 17 GHz;

Fig. 7(a) is the mode current distribution of mode 1 of metasurface subunit 3 at 21 GHz;

Fig. 7(b) is the mode current distribution of mode 2 of metasurface subunit 3 at 21 GHz;

Fig. 8(a) is the mode current distribution of mode 1 of metasurface subunit 3 at 23 GHz;

Fig. 8(b) is the mode current distribution of mode 2 of metasurface subunit 3 at 23 GHz;

Fig. 9 is the mode expansion coefficient amplitude curve of the metasurface subarray 4 in the present invention;

Fig. 10 is the mode expansion coefficient phase curve of the metasurface subarray 4 in the present invention;

Fig. 11(a) is the mode current distribution of mode 2 of metasurface subarray 4 at 7 GHz;

Fig. 11(b) is the mode current distribution of mode 6 of metasurface subarray 4 at 7 GHz;

Fig. 12(a) is the mode current distribution of mode 2 of metasurface subarray 4 at 9 GHz;

Fig. 12(b) is the mode current distribution of mode 6 of metasurface subarray 4 at 9 GHz;

Fig. 13(a) is the mode current distribution of mode 2 of metasurface subarray 4 at 13 GHz;

Fig. 13(b) is the mode current distribution of mode 6 of metasurface subarray 4 at 13 GHz;

Fig. 14(a) is the mode current distribution of mode 2 of metasurface subarray 4 at 21 GHz;

Fig. 14(b) is the mode current distribution of mode 6 of metasurface subarray 4 at 21 GHz;

Fig. 15(a) is the mode current distribution of mode 2 of metasurface subarray 4 at 23 GHz;

Fig. 15(b) is the mode current distribution of mode 6 of metasurface subarray 4 at 23 GHz;

Figure 16 (a) is a schematic top view of the layout structure of the metasurface subunit 3;

Figure 16(b) is a schematic side view of the layout structure of the metasurface subunit 3;

Figure 17 (a) is a top view of the layout structure of the metasurface sub-array 4;

Fig. 17(b) is a side view of the layout structure diagram of metasurface sub-array 4;

Figure 18 (a) is a top view of the layout structure of the mode conversion metasurface array 5;

FIG. 18(b) is a side view of the layout structure of the mode conversion metasurface array 5;

FIG. 19 is a schematic structural diagram of the reference metal floor 7;

FIG. 20 is a graph showing the comparison of the single-station RCS of the metasurface array 5 with the RCS reduction effect and the reference metal floor 7 as a function of frequency.

In the figure, 1. Metal patch unit; 2. Rogers5880 dielectric substrate; 3. Metasurface subunit; 4. Metasurface subarray; 5. Metasurface array with RCS reduction effect; 6. Metal floor; 7. Reference metal floor.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments:

In order to fully illustrate the idea of the present invention, it should be noted that the characteristic mode theory in the present invention can be found in the document 'Theory of Characteristic Modes for Conducting Bodies' introduced by Harrington in 1971.

As shown in Figure 1, a mode conversion method for low RCS metasurfaces based on eigenmode theory, at least includes the following steps:

Step 1: Calculate the characteristic mode curve of a metasurface subunit under the condition of fixed electromagnetic wave incidence according to the characteristic mode theory, so that the size and shape of the metasurface subunit can realize mode conversion within the working frequency band;

The step 1 includes:

1a) calculate the characteristic mode curve of a metasurface subunit 3 under fixed electromagnetic wave incident conditions, and determine the main excitation mode of the metasurface subunit 3 according to the amplitude curve of the mode expansion coefficient;

2a) extract the characteristic current of above-mentioned metasurface subunit 3, generate characteristic current vector distribution diagram;

3a) Combine the characteristic current vector distribution diagram of the main excitation mode and the phase curve of its mode expansion coefficient to obtain the composite mode current vector distribution of the main excitation mode, and adjust the structure size of the metasurface subunit 3 to achieve mode conversion in the working frequency band.

The structure size of the metasurface subunit is finally determined. As shown in Figure 16, the long axis with an angle of 45° to the horizontal direction is 5.2mm, and the short axis is 1.4mm. The elliptical metal patch unit 1 is printed on 10mm × 10mm On the Rogers5880 dielectric substrate 2 with a size of ×3.2 mm, a metal floor 6 is located below the Rogers5880 dielectric substrate 2 .

The characteristic mode curve of the metasurface subunit under the condition of x-polarized electromagnetic wave incidence is calculated by the characteristic mode theory, and the main excitation mode in the working frequency band is determined according to the amplitude curve of the mode expansion coefficient. The mode expansion coefficient amplitude curve of metasurface subunit 3 is shown in Figure 2. In the operating frequency band of 7-23 GHz, the mode expansion coefficient amplitudes of mode 1 and mode 2 are much larger than other modes, so mode 1 and mode 2 are metasurfaces The main excitation mode of the subunit under x-polarized electromagnetic wave incidence. The characteristic currents of mode 1 and mode 2 extracted at five frequency points of 9GHz, 11GHz, 17GHz, 21GHz and 23GHz are shown in Fig. 4-Fig. 8. Mode current distribution; Fig. 4(b) Mode current distribution of metasurface subunit 3 at 9 GHz; Fig. 5(a) Mode current distribution of metasurface subunit 3 at 11 GHz; Fig. 5 (b) is the mode current distribution of the metasurface subunit 3 at 11 GHz; Fig. 6(a) is the mode current distribution of the metasurface subunit 3 at 17 GHz; Fig. 6(b) is the metasurface Mode current distribution of subunit 3 at 17 GHz; Fig. 7(a) is the mode current distribution of metasurface subunit 3 at 21 GHz; Fig. 7(b) is metasurface subunit 3 at 21 GHz Mode current distribution of mode 2; Fig. 8(a) is the mode current distribution of metasurface subunit 3 at 23 GHz in mode 1; Fig. 8(b) is the mode current distribution of metasurface subunit 3 at 23 GHz case.) and combined with the phase curve of the mode expansion coefficient as shown in Figure 3, the synthesized mode current distribution at these five frequency points is obtained. It can be seen that at the frequency point of 9 GHz, the phase of the mode expansion coefficient of mode 1 is in the range of -180° to -90°, and the corresponding mode current direction is reversed. The phase of the mode expansion coefficient of mode 2 is in the range of -90° to 90°, and the corresponding mode current direction remains unchanged. The composite mode current vector distribution is obtained by superimposing mode 1 and mode 2 after considering the phase. The current direction is along the x direction, which is consistent with the polarization direction of the incident wave, and no mode conversion occurs at this frequency. At the frequency of 11 GHz, the phase of the mode expansion coefficient of mode 1 is in the range of 90° to 180°, and the corresponding mode current direction is reversed. The phase of the mode expansion coefficient of mode 2 is in the range of -90° to 90°, and the corresponding mode current direction remains unchanged. The composite mode current vector distribution is obtained by superimposing the mode 1 and mode 2 after considering the phase. The current direction is along the y direction, which is orthogonal to the polarization direction of the incident wave, and the mode conversion occurs at this frequency point. At the frequency of 17GHz, the phase of the mode expansion coefficient of Mode 1 is in the range of 90° to 180°, and the corresponding mode current direction is reversed. The phase of the mode expansion coefficient of Mode 2 is in the range of -90° to 90°, and the corresponding mode current direction Unchanged, the composite mode current vector distribution is obtained by superimposing mode 1 and mode 2 after considering the phase. The current direction is along the y direction, which is orthogonal to the polarization direction of the incident wave, and mode conversion occurs at this frequency point. At the frequency of 21GHz, the phase of the mode expansion coefficient of Mode 1 is in the range of 90° to 180°, and the corresponding mode current direction is reversed. The phase of the mode expansion coefficient of Mode 2 is in the range of -180° to -90°, and the corresponding mode current If the direction is reversed, the composite mode current vector distribution is obtained by superposing Mode 1 and Mode 2 after considering the phase. The current direction is along the y direction, which is orthogonal to the polarization direction of the incident wave, and mode conversion occurs at this frequency. At the frequency of 23GHz, the phase of the mode expansion coefficient of Mode 1 is in the range of 90° to 180°, and the corresponding mode current direction is reversed. The phase of the mode expansion coefficient of Mode 2 is in the range of -90° to 90°, and the corresponding mode current direction Unchanged, the composite mode current vector distribution is obtained by superimposing mode 1 and mode 2 after considering the phase. The current direction is along the x direction, which is consistent with the polarization direction of the incident wave, and no mode conversion occurs at this frequency. In general, at the frequencies of 9GHz and 23GHz, the combined mode current direction is consistent with the incident wave, and no mode conversion occurs; at the frequencies of 11GHz, 17GHz, and 21GHz, the combined mode current direction is orthogonal to the incident wave, and mode conversion occurs. transform. It can be judged that the frequency range of metasurface subunit mode transformation is 11GHz-21GHz.

Step 2: According to the metasurface subunits 3 obtained in step 1, a 4×4 array is arranged to form a metasurface subarray 4, and the characteristic mode curve of the metasurface subarray 4 under a fixed electromagnetic wave incidence condition is calculated according to the characteristic mode theory, And according to the characteristic mode analysis results in the working frequency band, the structure size of the metasurface subarray 4 is optimized, and a metasurface subarray that can realize mode conversion in the working frequency band is obtained.

Specifically include the following steps:

2a) performing a 4×4 array arrangement on the metasurface subunits 3 obtained in step 1 to form a metasurface subarray 4, and performing characteristic mode analysis on the first metasurface subarray 4;

2b) According to the mode expansion coefficient amplitude curve obtained after the characteristic mode analysis in 2a), determine the main excitation mode in the working frequency band;

2c) Extract the characteristic current corresponding to the main excitation mode, and generate the characteristic current vector distribution map;

2d) Combine the characteristic current vector distribution diagram of the main excitation mode and the phase curve of its mode expansion coefficient to obtain the composite mode current distribution of the main excitation mode, and optimize the structure size of the metasurface subarray 4, so that the metasurface subarray 4 is within the working frequency band. Mode conversion can be achieved.

Metasurface sub-units 3 are arranged in a 4×4 array to obtain meta-surface sub-array 4, and the structural size of meta-surface sub-array 4 is optimized, so that meta-surface sub-array 4 can realize mode conversion in the working frequency band. Finally, the optimized structure of the metasurface sub-array 4 is determined as shown in Figure 17. The elliptical metal patch unit 1 with a long axis of 5.2mm and a short axis of 1.2mm forming an angle of 45° with the horizontal direction is printed on 40mm×40mm × 3.2mm size Rogers5880 dielectric substrate 2.

The amplitude curve of the mode expansion coefficient of metasurface subarray 4 is shown in Fig. 9. In the operating frequency band of 7-23 GHz, the mode expansion coefficient amplitudes of mode 2 and mode 6 are much larger than those of other modes. The main excitation mode under the condition of electromagnetic wave incidence. After that, extract the characteristic currents of mode 2 and mode 6 at five frequency points of 7GHz, 9GHz, 13GHz, 21GHz and 23GHz to obtain the characteristic current vector distribution as shown in Fig. 11-15 (Fig. 11(a) is the metasurface subarray 4 The mode current distribution of mode 2 at 7 GHz; Fig. 11(b) is the mode current distribution of metasurface subarray 4 at 7 GHz in mode 6; Fig. 12(a) is the mode 2 distribution of metasurface subarray 4 at 9 GHz Mode current distribution; Fig. 12(b) is the mode current distribution of metasurface subarray 4 at 9 GHz in mode 6; Fig. 13(a) is the mode current distribution in metasurface subarray 4 at 13 GHz in mode 2; Fig. 13(b) is the mode current distribution of the metasurface subarray 4 at 13 GHz in mode 6; Fig. 14(a) is the mode current distribution of the metasurface subarray 4 at 21 GHz in mode 2; Fig. 14(b) is the metasurface subarray 4 mode 2 distribution Mode current distribution of surface sub-array 4 at 21 GHz; Fig. 15(a) is the mode current distribution of meta-surface sub-array 4 at 23 GHz; Fig. 15 (b) is meta-surface sub-array 4 at 23 GHz mode current distribution in mode 2); and combined with the phase curve of the mode expansion coefficient as shown in Figure 10, the combined mode current distribution is obtained. It can be seen that at the frequency of 7GHz, the phase of the mode expansion coefficient of Mode 2 is in the range of 90° to 180°, the corresponding mode current direction is reversed, and the phase of the mode expansion coefficient of Mode 6 is in the range of 90° to 180°. The corresponding The mode current direction is reversed. The composite mode current vector distribution is obtained by superimposing mode 2 and mode 6 after considering the phase. The current direction is along the x direction, which is consistent with the polarization direction of the incident wave. No mode conversion occurs at this frequency. At the frequency of 9GHz, the phase of the mode expansion coefficient of Mode 2 is in the range of 90° to 180°, and the corresponding mode current direction is reversed. The phase of the mode expansion coefficient of Mode 6 is in the range of -90° to 90°, and the corresponding mode current direction Unchanged, the composite mode current vector distribution is obtained by superimposing mode 2 and mode 6 after considering the phase. The current direction is along the y direction, which is orthogonal to the polarization direction of the incident wave, and mode conversion occurs at this frequency point. At the frequency of 13 GHz, the phase of the mode expansion coefficient of Mode 2 is in the range of -90° to 90°, and the corresponding mode current direction remains unchanged. The phase of the mode expansion coefficient of Mode 6 is in the range of -90° to 90°, and the corresponding mode current When the direction remains unchanged, the composite mode current vector distribution is obtained by superimposing Mode 2 and Mode 6 after considering the phase. At the frequency of 21GHz, the phase of the mode expansion coefficient of Mode 2 is in the range of 90° to 180°, and the corresponding mode current direction is reversed. The phase of the mode expansion coefficient of Mode 6 is in the range of -180° to -90°, and the corresponding mode current If the direction is reversed, the combined mode current vector distribution is obtained by superposing Mode 2 and Mode 6 after considering the phase. The current direction is along the y direction, which is orthogonal to the polarization direction of the incident wave, and mode conversion occurs at this frequency. At the frequency of 23GHz, the phase of the mode expansion coefficient of Mode 2 is in the range of -90° to 90°, and the corresponding mode current direction is unchanged. The phase of the mode expansion coefficient of Mode 6 is in the range of -90° to 90°, and the corresponding mode current With the direction unchanged, the composite mode current vector distribution is obtained by superimposing Mode 2 and Mode 6 after considering the phase. In general, at the frequencies of 7GHz and 23GHz, the direction of the combined mode current is consistent with the incident wave, and no mode conversion occurs; at the frequencies of 9GHz, 13GHz, and 21GHz, the direction of the combined mode current is orthogonal to the incident wave, and a mode occurs. transform. Therefore, it can be determined that the frequency range in which the metasurface sub-array 4 realizes mode conversion is 9 GHz-21 GHz.

In step 3, the metasurface sub-array 4 obtained in step 2 and its rotating sub-array are arranged symmetrically by 2×2 to form a meta-surface array 5 with an RCS reduction effect.

Rotate the center of the metasurface subarray 4 clockwise at an angle of 90°, 180°, and 270°, and the obtained three rotated metasurface subarrays are arranged together with the metasurface subarray 4 in a centrosymmetric manner. A 2×2 array is used to obtain a metasurface array 5 with RCS reduction effect, as shown in Figure 18. Comparing the RCS curves of the designed metasurface subarray 5 and the reference metal floor 7 shown in Fig. 19, as shown in Fig. 20, it can be seen that an RCS exceeding 10 dB is achieved in the 7-21 GHz frequency band (mode conversion frequency band). reduction effect.

Claims (4)

1. a mode conversion method based on the low RCS metasurface of eigenmode theory, is characterized in that: comprise the following steps at least: Step 1: Calculate the characteristic mode curve of a metasurface subunit (3) under the condition of fixed electromagnetic wave incidence according to the characteristic mode theory, so that the size and shape of the metasurface subunit (3) can realize mode conversion within the working frequency band; The mode conversion refers to that the polarization direction of the scattered field generated by the combined mode current of the main excitation mode is orthogonal to the polarization direction of the incident electromagnetic field, that is, the scattering mode and the incident mode realize mode rotation; Step 2: According to the metasurface subunits (3) obtained in step 1, a 4×4 array is arranged to form a metasurface subarray (4); The characteristic mode curve under the condition, and according to the characteristic mode analysis results in the working frequency band, the structure size of the metasurface subarray (4) is optimized, and the mode conversion is realized in the working frequency band; Step 3: Rotate the metasurface subarray (4) obtained in step 2 clockwise with its center at angles of 90°, 180°, and 270° to obtain a rotation subarray, and combine the metasurface subarray (4) with the rotation subarray. A 2×2 symmetrical arrangement is performed to form a metasurface array with RCS reduction effect (5); Described step 1 includes the following specific steps: 1a) Calculate the characteristic mode curve of a metasurface subunit (3) under a fixed electromagnetic wave incident condition, and determine the main excitation mode of the metasurface subunit (3) according to the amplitude curve of the mode expansion coefficient; 2a) extracting the characteristic current of the above-mentioned metasurface subunit (3), and generating a characteristic current vector distribution diagram; 3a) Combine the characteristic current vector distribution diagram of the main excitation mode and the phase curve of its mode expansion coefficient to obtain the composite mode current vector distribution of the main excitation mode, and adjust the structure size of the metasurface subunit (3) to realize the mode in the working frequency band transform; The step 2 includes: 2a) performing an array arrangement on the metasurface subunit (3) obtained in step 1 to form a metasurface subarray (4), and performing characteristic mode analysis on the metasurface subarray (4); 2b) According to the mode expansion coefficient amplitude curve obtained after the characteristic mode analysis in 2a), determine the main excitation mode in the working frequency band; 2c) Extract the characteristic current corresponding to the main excitation mode, and generate the characteristic current vector distribution map; 2d) Combine the characteristic current vector distribution diagram of the main excitation mode and the phase curve of its mode expansion coefficient to obtain the composite mode current distribution of the main excitation mode, and optimize the structure size of the metasurface subunit (3) to form a metasurface subarray (4), The metasurface sub-array (4) can realize mode conversion in the working frequency band. 2 . The mode conversion method of a low RCS metasurface based on the eigenmode theory according to claim 1 , wherein the fixed electromagnetic wave incident condition refers to the vertical incidence of the electromagnetic field with known intensity and polarization. 3 . 3. a kind of mode conversion method based on the low RCS metasurface of eigenmode theory according to claim 1, it is characterized in that: described main excitation mode is to judge according to the size of mode expansion coefficient, at the same operating frequency point If the mode expansion coefficient corresponding to one mode is much larger than the mode expansion coefficient corresponding to other modes, the mode is the main excitation mode. 4. The mode conversion method of a low RCS metasurface based on eigenmode theory according to claim 1, wherein the composite mode current vector distribution is composed of the mode current distribution of the main excitation mode and the corresponding mode The phase of the expansion coefficient is determined. When the phase of the mode expansion coefficient of the main excitation mode is in the range of -90° to 90°, the corresponding mode current distribution remains unchanged, and when the mode expansion coefficient phase of the main excitation mode is between 90° and 180° or In the range of -180°～-90°, the corresponding mode current direction is reversed, and all the main excitation modes after considering the phase are superimposed and synthesized to obtain the composite mode current vector distribution.

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