CN108470973B - Broadband RCS (radio control system) reduced super surface based on gap loading - Google Patents

Abstract

The invention discloses a gap loading-based broadband RCS (radio communication system) reduction super surface, which comprises a medium substrate, a metal patch loading gaps and a metal floor, wherein the metal patch loading a plurality of pairs of cross-shaped gaps is printed on the upper surface of the medium substrate, the metal floor is printed on the lower surface of the medium substrate, the resonance frequency of a designed artificial magnetic conductor unit is 12GHz, the in-phase reflection relative bandwidth is 50%, meanwhile, the broadband AMC super unit and another double-ring AMC super unit are arranged at intervals in a 3X 3 chessboard form, each AMC super unit consists of 3X 3 basic AMC units, and finally, the RCS reduction of more than 7.5dB in the frequency range of 8-19.2GHz is realized. The artificial magnetic conductor structure and the AMC-AMC checkerboard electromagnetic stealth surface have the advantages of good robustness, insensitivity to polarization and the like.

Description

Broadband RCS reduced metasurface based on gap loading

Technical field

The invention relates to the field of radar stealth technology, and in particular to a wideband RCS reduced metasurface based on gap loading.

Background technique

With the rapid development of detection technology and electromagnetic stealth technology, stealth characteristics have gradually become an important indicator to measure the performance of flying targets. Reducing the target's Radar Cross Section (RCS) has become a key factor in preemptive strikes in modern warfare. Traditional stealth technology mainly reduces RCS by changing the shape of flying targets and coating radar absorbing materials (RAM). For example, the B-2 bomber, in addition to achieving radar detection stealth through its flat shape design, is also coated on the surface of the aircraft body. 4-layer RAM to maximize RCS reduction. The F-22 Raptor fighter also achieves radar stealth in a similar way. However, due to the aerodynamic limitations of fast-flying targets, reducing the RCS through shape design will cause a sharp decrease in the target's maneuverability. At the same time, multi-layer coating RAM will increase the weight and thickness of the target. In addition, the comparison of high-absorption RAMs that can be applied to multiple bands Expensive, making it costly in targeted stealth applications. Relevant information shows that the B-2 and F-22 need to replace the RAM every time they fly, and each replacement takes 35 hours, which is very costly. In view of the many shortcomings of appearance and RAM stealth, researchers began to explore more cost-effective methods to achieve target stealth.

Artificial Magnetic Conductor (AMC) is a new type of artificial electromagnetic material composed of unit structures of specific shapes arranged periodically. Because of its ideal magnetic conductor properties, it is used to reduce antenna profiles, suppress surface waves, and improve antenna radiation performance. Various fields. Its phase control ability of reflected waves is expected to solve the shortcomings in the above-mentioned stealth solutions. At the same time, as a two-dimensional plane of metamaterials, it is easy to conform to some high-speed flying targets such as aircraft and missiles. It is widely used in military, aerospace, and communication systems. It has broad application prospects. Due to the excellent characteristics and powerful electromagnetic control capabilities of metasurfaces, their potential applications in target electromagnetic stealth have been gradually discovered and progress has been made in stages. In 2007, the artificial magnetic conductor (AMC) metasurface with a checkerboard structure was first used in the field of RCS reduction. Although the narrow frequency band of the AMC-PEC combination that meets the destructive requirements limits its practical application, this method has greatly inspired This has triggered an upsurge in research on new broadband, polarization-insensitive, and large-angle incidence devices based on the checkerboard pattern. It is hoped that one day this technology can be truly used in practice and become a new stealth material that replaces traditional RAM.

Contents of the invention

The technical problem to be solved by the present invention is to provide a broadband RCS reduced metasurface based on gap loading in view of the defects involved in the background technology.

The present invention adopts the following technical solutions to solve the above technical problems:

Broadband RCS reduced metasurface based on gap loading. Broadband RCS reduced metasurface is a two-dimensional finite size structure, which is composed of the first AMC super unit and the second AMC super unit in a staggered spaced array in the plane;

The first AMC super unit and the second AMC super unit are respectively square AMC super units arranged in a 3×3 checkerboard format by the first AMC unit and the second AMC unit;

The first AMC unit and the second AMC unit are squares of the same size, and both include an upper metal structure, a middle dielectric substrate and a lower metal floor;

The upper metal structure of the first AMC unit includes a first square patch and a first square frame patch, wherein the first square frame patch is placed outside the first square patch, and the centers of both are aligned with the first square patch. The centers of the middle dielectric substrates of an AMC unit coincide with each other; the two diagonal lines of the first square patch and the first square frame patch coincide with each other, and the first square patch and the first square frame patch are aligned along their two opposite sides. The corner lines are provided with slots to form cross-shaped slots; the centers of the four sides of the first square frame are provided with small cross-shaped slots, and one slot of the small cross-shaped slot is parallel to its corresponding side. The other slot is perpendicular to its corresponding side;

The upper metal structure of the second AMC unit includes a second square patch and a second square frame patch, wherein the second square frame patch is placed outside the second square patch, and the centers of both are aligned with the second square patch. The centers of the middle dielectric substrates of the two AMC units coincide; the two diagonals of the first square patch and the first square frame patch overlap accordingly;

The first AMC unit and the second AMC unit are both symmetrical reflective structures, and the rotation angles of the upper metal structures of the first AMC unit and the second AMC unit are the same. The thickness of the dielectric substrate of the first AMC unit and the second AMC unit is The range of H is 0.01λ-0.1λ, where λ is the free space wavelength.

As a further optimization solution for the broadband RCS reduction metasurface based on gap loading of the present invention, the dielectric constant er of the dielectric substrate of the first AMC unit and the second AMC unit ranges from 1 to 6, and the range of the electrical loss tangent tanσ is 0.0005-0.02.

As a further optimization solution for the broadband RCS reduction metasurface based on gap loading of the present invention, the dielectric plate thickness h of the first AMC unit and the second AMC unit is 2.4mm, and the relative dielectric constant er=4.4; the first AMC unit, The thickness of the upper metal structure of the second AMC unit is t=0.035mm.

As a further optimization solution of the wideband RCS reduction metasurface based on gap loading of the present invention, the length of the side in the first square frame patch is La=7mm, the width of the side Ws=1.5mm, and the length of the slot parallel to the side Ls =1mm; the length of the middle side of the first square patch Li=3mm; the length of the middle side of the second square frame patch a=5.6mm; the length of the middle side of the second square patch Lc=2.27mm; the second square frame patch The distance Wa between the sides of the patch and the second square patch is 0.4mm. At this time, the resonant frequency point of the first AMC unit is 12GHz; the second AMC unit is a dual-frequency ring-type artificial magnetic conductor unit, and the resonance points are respectively 8.5GHz and 17GHz.

Compared with the existing technology, the present invention adopts the above technical solution and has the following technical effects:

1. Simple structure and efficient use;

2. Solve the problem of narrow frequency band of the existing RCS based on artificial magnetic conductor checkerboard structure;

3. It has excellent properties such as polarization insensitivity and good reduction effect.

Description of the drawings

Figure 1 shows the electromagnetic reduction metasurface in the form of AMC-AMC checkerboard;

Figure 2(a), (b), and (c) are respectively a top view of the first AMC unit, a side view of the first AMC unit, and a top view of the second AMC unit;

Figure 3 is the equivalent circuit diagram of the first AMC unit under normal incidence of plane waves;

Figure 4(a), (b), (c), (d), and (e) are respectively the unit structure diagram when no gap is loaded, the gap structure diagram when only the square frame patch is loaded, and the unit structure diagram when there is no inner square patch. The structure diagram of the gap unit, the structure diagram of the unit without loading the gap on the internal square patch, and the structure diagram of the new unit with gaps loaded both inside and outside;

Figure 5 is a comparison chart of the reflection phase versus frequency curves of each unit corresponding to Figure 4(a), (b), (c), (d), and (e);

Figure 6 shows the effect of different gap widths n on the reflection phase of the unit;

Figure 7 is a schematic diagram of the AMC-PEC chessboard structure;

Figure 8(a) and (b) are respectively the unit reflection phase variation curve with frequency and the unit reflection phase difference variation curve with frequency;

Figure 9(a) and (b) are respectively the 3D RCS scattering diagram of the AMC-AMC electromagnetic reduced metasurface at 9GHz and the 3D RCS scattering diagram of the metal plate of equal size at 9GHz;

Figure 10(a) and (b) are respectively the 3D RCS scattering diagram of the AMC-AMC electromagnetic reduced metasurface at 12GHz and the 3D RCS scattering diagram of the metal plate of equal size at 12GHz;

Figure 11 shows the relative reduction in RCS of the AMC-AMC checkerboard metasurface under normal incidence of plane waves;

Figure 12 shows the relative reduction in RCS of plane waves incident on the AMC-AMC metasurface at different angles.

Detailed ways

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings:

The invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, components are exaggerated for clarity.

As shown in Figure 1, the broadband RCS reduced metasurface is a two-dimensional finite size structure, which is composed of the first AMC super unit and the second AMC super unit in a staggered spaced array in the plane;

The first AMC super unit and the second AMC super unit are respectively square AMC super units arranged in a 3×3 checkerboard format by the first AMC unit and the second AMC unit;

The first AMC unit and the second AMC unit are squares of the same size, and both include an upper metal structure, a middle dielectric substrate and a lower metal floor;

The upper metal structure of the first AMC unit includes a first square patch and a first square frame patch, wherein the first square frame patch is placed outside the first square patch, and the centers of both are aligned with the first square patch. The centers of the middle dielectric substrates of an AMC unit coincide with each other; the two diagonal lines of the first square patch and the first square frame patch coincide with each other, and the first square patch and the first square frame patch are aligned along their two opposite sides. The corner lines are provided with slots to form cross-shaped slots; the centers of the four sides of the first square frame are provided with small cross-shaped slots, and one slot of the small cross-shaped slot is parallel to its corresponding side. The other slot is perpendicular to its corresponding side;

The upper metal structure of the second AMC unit includes a second square patch and a second square frame patch, wherein the second square frame patch is placed outside the second square patch, and the centers of both are aligned with the second square patch. The centers of the middle dielectric substrates of the two AMC units coincide; the two diagonals of the first square patch and the first square frame patch overlap accordingly;

The first AMC unit and the second AMC unit are both symmetrical reflective structures, and the rotation angles of the upper metal structures of the first AMC unit and the second AMC unit are the same. The thickness of the dielectric substrate of the first AMC unit and the second AMC unit is The range of H is 0.01λ-0.1λ, where λ is the free space wavelength.

The reflection phase difference between the first AMC super unit and the second AMC super unit satisfies a range of 143°-217° in the range of 9-18 GHz.

The dielectric constant er of the dielectric substrate of the first AMC unit and the second AMC unit ranges from 1 to 6, and the electrical loss tangent tanσ ranges from 0.0005 to 0.02.

The thickness h of the dielectric plate of the first AMC unit and the second AMC unit is 2.4mm, and the relative dielectric constant er=4.4; the thickness t of the upper metal structure of the first AMC unit and the second AMC unit is 0.035mm. The length of the side in the first square frame patch is La=7mm, the width of the side is Ws=1.5mm, and the length of the slot parallel to the side is Ls=1mm; the length of the side in the first square patch is Li=3mm; the length of the side in the second square patch is Li=3mm. The length of the middle side of the frame patch a = 5.6mm; the length of the middle side of the second square patch Lc = 2.27mm; the distance between the sides of the second square frame patch and the second square patch Wa = 0.4mm, this At , the resonant frequency point of the first AMC unit is 12GHz; the second AMC unit is a dual-frequency ring-type artificial magnetic conductor unit, and the resonant points are 8.5GHz and 17GHz respectively.

For convenience of description, the first AMC unit is denoted as AMC 1 and the second AMC unit is denoted as AMC 2, and the width of each slot in the first square frame patch and the first square patch is denoted as n.

The design method steps of the present invention mainly include the following three-step design process:

Step one: Design of a new broadband, polarization-insensitive AMC unit based on gap loading:

Based on the broadband, polarization-insensitive RCS reduced metasurface design in the form of a checkerboard, the primary issue is to design an AMC unit with broadband operation and polarization-insensitive characteristics. The basic theoretical basis is to use the reflection destructive principle in array theory. The characteristic of the unit reflection phase changing with frequency makes the reflection phase difference between adjacent array elements satisfy 143°-217° in a wide frequency range, realizing the energy cancellation of the reflected wave and achieving backward RCS reduction. According to knowledge related to polarization conversion, in order to obtain polarization insensitivity, the unit must have four-week rotational symmetry. At the same time, in order to obtain broadband characteristics, the phase response has excellent characteristics such as good linearity and low quality factor in a wide frequency range.

Based on the above analysis, we invented a new broadband artificial magnetic conductor unit structure based on multiple pairs of cross-shaped gap loading. Figure 2(a), (b), and (c) are the top view of the first AMC unit and the second AMC unit respectively. Top view of the unit, side view of the first AMC unit. AMC 1 is composed of an upper metal structure, a middle dielectric board and a bottom metal floor. Since the upper metal structure is loaded with multiple gaps, its equivalent inductance and capacitance characteristics are excited, so it becomes a strong resonance structure, using the equivalent circuit principle. It can be seen that The linearity of the unit phase is crucially related to the loaded gap. By loading the gap on the outer ring, the current flow excited by the incident electromagnetic wave increases and the inductance L is increased. Loading two long gaps on the inner ring increases the series capacitance. This reduces C, thereby ultimately achieving the purpose of expanding the operating bandwidth of the unit. Figure 3 is the equivalent circuit diagram of AMC1 under vertical incidence of plane waves.

In order to clearly show the impact of the gap loaded on the unit on the in-phase reflection frequency band, Figure 4(a) shows the structure diagram of the unit without loading the gap, (b) shows the structure diagram of the unit loading the slot on the square frame patch, (c) (d) is the structure diagram of the unit loaded with gaps when there is no inner square patch, (d) is the structure diagram of the unit without loading gaps on the inner square patch, (e) is the structural diagram of the new unit with gaps loaded both inside and outside, Figure 5 shows the structure diagram of loading the outside The effect on the reflection phase of the unit after loading gaps, loading internal gaps, and loading gaps both inside and outside. It can be seen that loading the slots in the outer ring has a greater impact on the bandwidth of the unit. Loading multiple pairs of slots at the same time effectively improves the in-phase reflection frequency band of the unit.

In order to further explain the reasons for the broadband characteristics of this structure, Figure 6 shows the impact of the reflection phase under different sizes of a pair of cross-shaped gap widths n loaded in the middle. It can be seen that when n is increased, the resonance point of AMC1 shifts to high frequency. At the same time, the in-phase reflection frequency band of the unit is expanded.

At the same time, due to the rotational symmetry of the unit, similar resonance effects will occur when electromagnetic waves of different polarizations are irradiated to the AMC unit. The electromagnetic scattering response of the unit is polarization insensitive to x- and y-line polarization waves, which is a good way to build a polarization-insensitive Low RCS electromagnetic surface provides suitable structure.

In order to maximize the unit phase characteristics, commercial simulation software CST is used to optimize the unit structure parameters. The final unit period is p=10mm, the dielectric plate is polytetrafluoroethylene with a thickness of 2.4mm, a relative dielectric constant of 4.4, and an electrical loss tangent of 0.02. The thickness of the underlying metal copper plate can be 0.035mm. The desired phase distribution is obtained by changing the overall metal structure dimension a while keeping other parameters unchanged. The final size of AMC unit 1 is t=0.035mm, La=7mm, Ls=1mm, Ws=1.5mm, Li=3mm in AMC1.

Step 2: Design of dual-frequency ring-type AMC unit based on array theory:

The AMC-AMC checkerboard form structure is improved from the AMC-PEC form, but the analysis principles of the two forms are the same, and array theory is usually used for analysis. The following is an analysis of the AMC-PEC checkerboard form reduced backward RCS principle, as shown in Figure 4. According to the array theory, when electromagnetic waves are vertically incident, since both the AMC structure and the PEC structure are total reflection structures, the The reflection amplitude is consistent, and the total reflected electric field can be expressed by the following formula:

E＝E _AMC ·AF _AMC +E _PEC ·AF _PEC (1)

The electric field components reflected by the AMC and PEC blocks can be expressed as:

Among them, Φ1 and Φ2 represent the reflection phases of AMC and PEC respectively, AFAMC and AFPEC are the array factors of the AMC structure and PEC structure respectively, and since the reflection amplitudes of the two structures are the same, we can get

The array factor is expressed as

In the formula, d is the center distance between the AMC structure and the PEC structure, and

It can be seen that when the electromagnetic wave is vertically incident, that is, when the incident angle is 0, it can be obtained, so the total radiation field can be obtained as

When the reflected wave energy in the normal direction is more than 10dB smaller than the incident wave energy, that is

|E| ² /|E ₀ | ² ≤-10dB (7)

Further calculation can be obtained

The above equation reveals the relationship between the phases of PEC and AMC and the amount of RCS reduction. Because the reflection phase of PEC is fixed at 180 degrees, the phase condition of AMC can be obtained.

When the above conditions are met, the backward RCS reduction of the AMC-PEC checkerboard structure can reach 10dB. It can be seen that for general units, the bandwidth of the phase of the unit structure between the above conditions is narrow, which limits the bandwidth of RCS reduction. The researchers used another AMC structure to replace the PEC structure, so that both structures are in an adjustable state. When the phase difference condition is met, RCS reduction is achieved, which greatly improves the reduction bandwidth. The phase difference condition calculated by the formula is

When the above conditions are met, since the reflection amplitude of the two parts of the AMC-AMC checkerboard structure is equal and the phase difference is 180 degrees, the energy in the reflection direction is scattered to other directions, that is, the reflected wave in the reflection direction is transformed from a main beam to Multi-beam form, which can achieve RCS reduction in this direction. If the broadband AMC unit can be combined with an AMC unit with dual resonance points, so that the resonance point of the broadband AMC unit is located between the two resonance points of the dual-frequency AMC unit, the reflection phase difference can be maximized to meet the 10dB RCS reduction condition. Based on this, a dual-band ring-type resonant AMC unit 2 is designed. By reasonably adjusting the internal and external dimensions of the double-ring AMC2, AMC2 resonates at 8.5GHz and 17GHz respectively. The reflection phase characteristics and phase difference of the two different units vary with the The frequency change curves are shown in Figure 8(a) and (b). The final dimensions of AMC2 are a=5.6mm, Lc=2.27mm, Wa=0.4mm, and the AMC1 unit and The reflection phase difference between AMC2 units is maintained between 150° and 210°, that is, ideally, the RCS reduction in this frequency band can reach more than 10dB.

The third step: Based on the design of a new broadband AMC unit in the first step and the design of two AMC units that meet the phase difference requirements in the second step, the third step is how to rationally utilize the two AMC units to construct an RCS reduced metasurface. First, we need to determine the size of the metasurface, that is, the number of superunits. To facilitate design here, the metasurface adopts a square layout, that is, the number L and M of AMC units in the x and y directions are the same. To comprehensively measure the impact of calculation time, sample production cost and the limited size of the metasurface on the RCS reduction characteristics, the number of AMC units in the metasurface is L×M=9×9, and the size is 90×90mm2;

Next, determine the arrangement of the two AMC units. In order to disperse the incident electromagnetic waves to the greatest extent, reduce the scattering intensity of the target at various angles, and thus reduce the probability of radar discovery under single-station RCS detection, the unit arrangement in the metasurface includes traditional square and spaced arrangements, and spaced The arrangement forms are divided into two situations: AMC block 1 and block 2 are arranged at intervals, and AMC unit 1 and unit 2 are arranged at intervals. Due to the limitations of the actual electromagnetic surface, it needs to be specifically optimized through electromagnetic simulation software. Finally, the present invention designed an electromagnetic stealth surface in the form of a 3×3 checkerboard. The specific arrangement sequence is 222-111-, "-" Indicates the turning point of the AMC unit, and the numbers represent the corresponding different AMC units, which correspond to the numerical sequence in Figure 1. The final AMC-AMC distribution is shown in Figure 1. The metasurface designed through this arrangement ensures the phase difference distribution of any adjacent AMC unit while ensuring the inheritance of an infinite arrangement, thereby maximizing the destruction of the metasurface. Uniform scattering of equal-phase planes achieves the purpose of maximizing the scattering of electromagnetic waves.

Finally, according to the cyclic arrangement of AMC unit 1 and AMC unit 2 with a local unit interval of 3×3, a checkerboard-shaped metasurface structure is established in CST.

The following takes a checkerboard-shaped metasurface composed of 3×3 AMC units arranged at intervals as an example to introduce the design process, design results, and analyze the results. In order to reveal the superiority of the method of the present invention, the results are compared with the scattering characteristics of an ideal metal plate of equal size. For fair comparison, the surface dimensions, dielectric plate specifications, incident angle and other conditions are exactly the same in the two cases.

In the simulation design, the dielectric board uses polytetrafluoroethylene, its dielectric constant εr = 4.4, the electrical tangent loss tanσ = 0.02, the metal copper foil thickness is 0.035mm, the dielectric board thickness is h = 2.4mm, and the two AMC unit periods are p=10mm, the geometric structure parameters of the two AMC units that form a checkerboard are: La=7mm, Ls=1mm, Ws=1.5mm, Li=3mm in AMC1; a=5.6mm, Lc=2.27mm in AMC2, Wa=0.4mm.

The working principle of the AMC unit: When the electromagnetic wave is vertically incident, the y and x polarized electric fields will generate an induced current on the thin metal patch parallel to the polarization direction, and the upper metal structure is loaded with multiple pairs of gaps. Equivalent capacitance is introduced between adjacent metals, and the unit itself undergoes strong resonance, so the degree of coupling between adjacent units becomes weak, better simulating the situation of infinite units. Since the unit has rotational symmetry and the inherent symmetry of the checkerboard form, it has exactly the same electromagnetic response under both y and x polarizations. At the same time, in order to reduce the distance between the units and make the structure more compact, both units are centered around the center. Rotate 45°.

AMC-AMC checkerboard form metasurface RCS reduction principle: On the one hand, the reflection phases of the two types of AMC units are different. When the plane wave is vertically irradiated onto the metasurface composed of the two designed AMC units, according to the array theory, it can be seen that the reflected wave will be scattered by these AMC units with different reflection phases, thus achieving electromagnetic stealth in the original direction.

By optimally adjusting the metal structure parameters of the unit and the loaded gap size, the resonance point and in-phase reflection bandwidth of the AMC unit can be controlled to tune the reflection phase of the entire unit to obtain the best linearity and broadband phase response.

In order to verify the broadband scattering characteristics of the AMC-AMC chessboard-shaped metasurface of the present invention, the commercial simulation software CST Microwave Studio was used to conduct electromagnetic simulation of the scattering spectrum of the metasurface, in which the six boundaries along the x, y, and z directions were all open boundaries. Conditions, plane waves are vertically incident along the -z direction, and plane linearly polarized waves are used for vertical illumination.

Example: Broadband RCS reduction results of an AMC-AMC checkerboard metasurface with dimensions of 90 mm × 90 mm × 2.4 mm.

The metasurface RCS reduction results of the above-mentioned design are explained and verified below. Due to the checkerboard form and the inherent symmetry of the two AMCs, it can be seen that the electromagnetic stealth surface has polarization insensitivity characteristics. Both checkerboard form metasurfaces can reduce the backward RCS well and have almost identical scattering spectrum responses, which is verified. Polarization-insensitive properties of the metasurface of the present invention. At the same time, the RCS reduction spectrum results show that the checkerboard-shaped metasurface has excellent RCS reduction characteristics in the range of 8-20GHz, in which the RCS reduction values exceed 7.5dB and the effective bandwidth is 9-19GHz.

In order to verify the two-station RCS reduction characteristics of the metasurface, the far-area scattering field was simulated to obtain the 3D scattering pattern of the metasurface. Figure 9(a) and Figure 9(b) respectively show the far-zone 3D scattering pattern of an ideal metal plate of equal size at 9GHz and 12GHz. Figure 10(a) and Figure 10(b) respectively show the dual frequency band Far-zone 3D scattering pattern of AMC-AMC metasurface at 9GHz and 12GHz. It can be seen that compared with the strong mirror scattering of the metal plate, the AMC-AMC checkerboard-shaped metasurface can perfectly disperse the reflected electromagnetic waves evenly in four directions. The scattering energy in the original direction is dispersed in the four directions, thus reducing the The incoming wave vertically illuminates the RCS on the lower surface.

In order to further verify the ability of the method of the present invention to disperse electromagnetic waves and achieve ultra-wideband RCS reduction, changing the incident angle of electromagnetic waves shows that the simulation results under the incident situations of 15°, 30° and 45° show that when the incident angle of electromagnetic waves is less than 45°, In all cases, the metasurface can achieve an RCS reduction effect of more than 7.5dB within 12.5-17.5GHz. When the incident angle is 0°, the 7.5dB RCS reduced simulation bandwidth of the AMC-AMC checkerboard metasurface is 8-19.2GHz; when the incident angle is 15°, the 7.5dB RCS reduced simulation bandwidth is 8-18.5GHz; the incident angle is At 30°, the 7.5dB RCS reduction simulation bandwidth is 11-17.8GHz; when the incident angle is 45°, the RCS reduction performance decreases, but both meet the RCS reduction effect of more than 7.5dB and the R simulation bandwidth reaches 12.5-17.5GHz. To sum up, the checkerboard-shaped AMC-AMC metasurface still has good RCS reduction characteristics in the range of 9-18GHz under the condition of large angle (up to 45°) incidence.

Figures 11 and 12 show the RCS reduction results when electromagnetic waves are incident vertically and at different angles.

In summary, the near-field distribution, far-field scattering pattern and RCS reduction spectrum all show the ultra-wideband, polarization-insensitive RCS reduction characteristics and ability to uniformly disperse electromagnetic waves based on the AMC-AMC checkerboard metasurface. The above characteristics and capabilities are in It still maintains very good performance under the incident angle range of 45°. The metasurface is simple in design, has obvious effects, is very robust to polarization and incident angle, does not require optimization, and has the inherent ability to disperse electromagnetic waves. At the same time, the proposed broadband artificial magnetic conductor structure based on gap loading has in-phase reflection frequency. The band is wider and the coupling effect between units is small. The electromagnetic stealth surface and new artificial magnetic conductor structure designed in the present invention have important potential application value in the future electromagnetic stealth field and antenna miniaturization design.

It can be understood by one of ordinary skill in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms such as those defined in general dictionaries are to be understood to have meanings consistent with their meaning in the context of the prior art, and are not to be taken in an idealized or overly formal sense unless defined as herein. explain.

The above-mentioned specific embodiments further describe the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (4)

1. The broadband RCS reduction super surface based on gap loading is characterized in that the broadband RCS reduction super surface is of a two-dimensional limited-size structure and is formed by staggered interval arrays of a first AMC super unit and a second AMC super unit in a plane;

the first AMC superunit and the second AMC superunit are square AMC superunits formed by arranging the first AMC unit and the second AMC unit in a 3 multiplied by 3 chessboard mode respectively;

the first AMC units and the second AMC units are square with the same size and each comprise an upper metal structure, a middle dielectric substrate and a lower metal floor;

the upper metal structure of the first AMC unit comprises a first square patch and a first square frame patch, wherein the first square frame patch is sleeved outside the first square patch, and the centers of the first square frame patch and the first square frame patch are overlapped with the center of the middle layer dielectric substrate of the first AMC unit; the two diagonal lines of the first square patch and the first square frame patch are correspondingly overlapped, and grooves are formed in the first square patch and the first square frame patch along the two diagonal lines of the first square patch and the first square frame patch respectively to form cross grooves; the centers of the four sides of the first positive square frame are respectively provided with a small cross slot, one slot of the small cross slot is parallel to the corresponding side of the small cross slot, and the other slot is perpendicular to the corresponding side of the small cross slot;

the upper metal structure of the second AMC unit comprises a second square patch and a second square frame patch, wherein the second square frame patch is sleeved outside the second square patch, and the centers of the second square frame patch and the second square frame patch are overlapped with the center of the middle layer dielectric substrate of the second AMC unit; the two diagonal lines of the first square patch and the first square frame patch are correspondingly overlapped;

the first AMC unit and the second AMC unit are both symmetrical reflection structures, the rotation angles of the upper metal structures of the first AMC unit and the second AMC unit are the same, the thickness h of the dielectric substrates of the first AMC unit and the second AMC unit ranges from 0.01λ to 0.1λ, and λ is the free space wavelength.

2. The gap-loading based broadband RCS reduced super surface according to claim 1, wherein the dielectric substrates of the first and second AMC units have a dielectric constant er ranging from 1 to 6 and an electric loss tangent tan σ ranging from 0.0005 to 0.02.

3. The slot loading based broadband RCS reduced super surface according to claim 2, wherein the dielectric plate thickness h of the first AMC unit, the second AMC unit is 2.4mm, the relative dielectric constant er = 4.4; the thickness t=0.035 mm of the upper metal structure of the first AMC unit and the second AMC unit.

4. A slot-loading based broadband RCS reduced super surface according to claim 3, wherein the length La = 7mm of the sides, the width Ws = 1.5mm of the sides, and the length Ls = 1mm of the slots parallel to the sides in the first square frame patch; the length li=3 mm of the sides in the first square patch; the length of the side in the second square frame patch is a=5.6mm; the length lc=2.27 mm of the side in the second square patch; the spacing Wa=0.4 mm between the edges of the second square frame patch and the second square patch, and at this time, the resonance frequency point of the first AMC unit is at 12GHz; the second AMC unit is a double-frequency annular artificial magnetic conductor unit, and resonance points are 8.5GHz and 17GHz respectively.