Gradient impedance surface structure for edge scattering suppression and design method

Abstract

The embodiment of the invention provides a gradient impedance surface structure for edge scattering suppression and a design method, the structure comprises a radar wave-absorbing coating material loaded at the edge position of a metal edge, and the surface impedance of the radar wave-absorbing coating material is gradually increased from the inner side of the metal to the outer side of the metal. According to the embodiment of the invention, the surface current is smoothly reduced by designing the gradually-changed surface impedance, so that the edge scattering is effectively suppressed, and the effectiveness and excellent performance of the broadband wide-angle edge scattering suppression effect are further verified through analogue simulation; moreover, the embodiment of the invention is simple, convenient and universal, the designed structure is simple and light, the RCS reduction effect is excellent, and the method has a wide application prospect in the electromagnetic scattering field control direction.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic structure functional materials technology, and in particular to a gradient impedance surface structure and design method for edge scattering suppression. Background Technology

[0002] To achieve low radar detectability, ship platforms are often designed with modified shapes, resulting in a large number of edge structures. When incident waves are perpendicular to the edges, strong edge-scattered echoes are generated, which makes it impossible to achieve good radar stealth performance.

[0003] Edge scattering is a typical non-spectral secondary scattering source. When electromagnetic waves strike a well-conducting target, they induce a current on the target surface, which then radiates a scattered field. Due to the impedance abrupt change from the well-conducting target to free space at the target edge, the induced current abruptly changes at this point, generating an edge scattering field. The edge scattering field is omnidirectional, and when the incident direction is perpendicular to the edge, it has a large component in the backward direction, thus producing a strong scattered echo. Existing research on edge scattering suppression mainly focuses on the propagation and excitation characteristics of edge scattering to reduce the backward edge scattering echo. One method is to modify the edge shape to avoid the incident wave direction being perpendicular to the edge, thus shifting the edge scattering to a non-backward direction. Another method is to suppress the surface current, attenuating the edge scattering field at its source.

[0004] Method 1 typically involves designing the edge in a sawtooth shape. The backscattering suppression effect of the edge is related to the number and shape of the sawtooth. The edge sawtooth shaping design is simple and easy to implement in engineering, but the suppression effect is limited. Furthermore, under perpendicular incidence, the outwardly extended sawtooth conductor will generate additional specular reflection, resulting in a significant increase in RCS.

[0005] Method 2 typically involves loading radar absorbing coating materials, which can reduce surface current and suppress edge scattering fields to some extent. However, this method has limited suppression effect under TE polarization, and the most commonly used magnetic coating materials are relatively heavy. Summary of the Invention

[0006] In view of the above-mentioned problems existing in the prior art, the present invention provides a gradient impedance surface structure and design method for edge scattering suppression, so as to solve the technical problem that the existing edge scattering suppression methods have limited effectiveness.

[0007] This invention provides a graded impedance surface structure for edge scattering suppression, comprising:

[0008] A radar-absorbing coating material is applied to the edge of a metal, wherein the surface impedance of the radar-absorbing coating material gradually increases from the inside to the outside of the metal.

[0009] In one embodiment, the radar absorbing coating material is a resistive thin film material mainly composed of carbon paste.

[0010] In one embodiment, the radar absorbing coating material is arranged in strips along the direction from the inside to the outside of the metal. The surface impedance of the radar absorbing coating material in the same strip is the same, while the surface impedance of the radar absorbing coating material in different strips is different.

[0011] In one embodiment, the surface current of the radar-absorbing coating material decreases linearly along the direction from the inside to the outside of the metal.

[0012] In one embodiment, the radar-absorbing coating material is fixed to the metal edge by physical connection, without the need for electrical connection.

[0013] In one embodiment, the radar absorbing coating material has a total width L along the direction from the inside of the metal to the outside of the metal, and its total width L is longer than half the wavelength of the lowest frequency point.

[0014] In one embodiment, the period width of the radar absorbing coating material at different strips is D, and the period width D is determined by the highest operating frequency and the maximum operating angle.

[0015] In addition, embodiments of the present invention also provide a method for designing a gradient impedance surface for edge scattering suppression, comprising the following steps:

[0016] Step S1, loading form design, applying strip-shaped radar absorbing coating material in a straight line along the metal edge;

[0017] Step S2, design the total width L. Determine the total loading width L based on the required lowest operating frequency, and ensure that the total width L is longer than half the wavelength of the lowest frequency.

[0018] Step S3, design the period width D. Determine the period width D based on the required highest operating frequency and maximum operating angle, and ensure that no grating lobes appear in the operating frequency band and angular domain.

[0019] Step S4: Design the specific impedance distribution. Calculate the impedance distribution based on the designed surface current distribution to ensure that the surface impedance increases smoothly along the metal edge from the inside to the outside of the metal, so that the electromagnetic boundary smoothly transitions from the metal to the air.

[0020] In one embodiment, it further includes:

[0021] Step S5: Based on the design schemes in steps S1 to S4, perform modeling and simulation to verify the effectiveness of the design schemes.

[0022] In one embodiment, the surface current of the radar-absorbing coating material decreases linearly along the direction from the inside to the outside of the metal.

[0023] Compared with the prior art, the beneficial effects of the graded impedance surface structure and design method for edge scattering suppression provided by the embodiments of the present invention are as follows:

[0024] 1. The embodiments of the present invention design a gradually changing surface impedance to smoothly reduce the surface current, thereby effectively suppressing edge scattering. Furthermore, the effectiveness and excellent performance of the wide-band and wide-angle edge scattering suppression effect are verified through simulation.

[0025] 2. The embodiments of the present invention are simple and universal, and the designed structure is simple, lightweight and has excellent RCS reduction effect, which has broad application prospects in the field of electromagnetic scattering control. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the scattering field of a metal plate;

[0027] Figure 2 A schematic diagram of the scattering field of a gradient impedance surface structure for edge scattering suppression provided in an embodiment of the present invention;

[0028] Figure 3 A model diagram of surface current and surface impedance of a metal plate;

[0029] Figure 4 This is a graph showing the relationship between surface current and surface impedance of a metal plate.

[0030] Figure 5 A schematic diagram of the periodic structure grating lobes corresponding to the strip-shaped radar absorbing coating material;

[0031] Figure 6 A schematic diagram of a radar absorbing coating material arranged in a wide-bandwidth, wide-angle strip pattern;

[0032] Figure 7 for Figure 6 Schematic diagram of surface current distribution of the corresponding material at different incident angles and x-axis directions under TE polarization at 2 GHz;

[0033] Figure 8 The single-station RCS reduction performance of the radar absorbing coating material with a wide-band and wide-angle strip arrangement: (a) TE polarization sweep results under 45° incident angle; (b) TM polarization sweep results under 45° incident angle; (c) TE polarization angle sweep results at 10 GHz; (d) TM polarization angle sweep results at 10 GHz. Detailed Implementation

[0034] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Various embodiments and features of this application are described herein with reference to the accompanying drawings.

[0036] These and other features of this application will become apparent from the following description of preferred forms of embodiments given as non-limiting examples, with reference to the accompanying drawings.

[0037] It should also be understood that although this application has been described with reference to some specific examples, those skilled in the art can certainly implement many other equivalent forms of this application, which have the features described in the claims and are therefore all within the scope of protection defined herein.

[0038] The above and other aspects, features and advantages of this application will become more apparent when taken in conjunction with the accompanying drawings and in view of the following detailed description.

[0039] Specific embodiments of this application are described below with reference to the accompanying drawings; however, it should be understood that the claimed embodiments are merely examples of this application, which can be implemented in various ways. Well-known and / or repeated functions and structures are not described in detail to ascertain the true intent based on the user's historical operations, and to avoid unnecessary or redundant details that would obscure this application. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as the basis and representative basis for the claims to teach those skilled in the art to use this application in various ways with substantially any suitable detailed structure.

[0040] This specification may use the phrases “in one embodiment,” “in another embodiment,” “in yet another embodiment,” or “in other embodiments,” all of which may refer to one or more of the same or different embodiments according to this application.

[0041] The principles and features of the present invention are described below with reference to the accompanying drawings. The embodiments described are for illustrative purposes only and are not intended to limit the scope of the invention. The following description, in conjunction with... Figure 1-8 The preferred embodiments of the present invention will be described in further detail below:

[0042] like Figure 2 As shown, an embodiment of the present invention provides a gradient impedance surface structure for edge scattering suppression, comprising:

[0043] A radar-absorbing coating material is applied to the edge of a metal, wherein the surface impedance of the radar-absorbing coating material gradually increases from the inside to the outside of the metal.

[0044] Resistive films based on carbon paste have a significant effect on surface current loss. Therefore, in one embodiment, the radar absorbing coating material is a resistive film material based on carbon paste. It is applied to the edge to attenuate the edge surface current to absorb radar waves, and a gradual surface impedance is designed to smoothly reduce the surface current, thereby effectively suppressing edge scattering.

[0045] In one embodiment, considering the operability of laying the resistive thin film material mainly composed of carbon paste, the radar absorbing coating material is arranged in strips along the direction from the inside of the metal to the outside of the metal. The surface impedance of the radar absorbing coating material in the same strip is the same, and the surface impedance of the radar absorbing coating material in different strips is different. Furthermore, the surface impedance of the radar absorbing coating material in different strips is set in a way that makes the surface current decrease linearly along the direction from the inside of the metal to the outside of the metal.

[0046] In addition, embodiments of the present invention also provide a method for designing a gradient impedance surface for edge scattering suppression, comprising the following steps:

[0047] Step S1, loading form design: a strip of radar absorbing coating material is loaded in a straight line along the metal edge. The radar absorbing coating material is fixed to the metal edge by physical connection, without the need for electrical connection.

[0048] Step S2, design the total width L. Determine the total loading width L based on the required lowest operating frequency, and ensure that the total width L is longer than half the wavelength of the lowest frequency.

[0049] Step S3, design the period width D. Determine the period width D based on the required highest operating frequency and maximum operating angle, and ensure that no grating lobes appear in the operating frequency band and angular domain.

[0050] Step S4, specific impedance distribution design, calculate the impedance distribution based on the designed surface current distribution, and ensure that the surface impedance increases smoothly along the metal edge position from the inside of the metal to the outside of the metal, so that the electromagnetic boundary smoothly transitions from the metal to the air;

[0051] Step S5: Based on the design schemes in steps S1 to S4, perform modeling and simulation to verify the effectiveness of the design schemes.

[0052] According to the high-frequency approximation theory, when radar waves are incident perpendicularly to an edge, they will produce a strong edge-scattered echo in the rearward direction, as shown in the attached figure. Figure 1 As shown. To effectively suppress edge scattering, tapered resistive sheets (TRS) need to be applied linearly along the leading and trailing edges. The TRS is the radar-absorbing coating material arranged in a strip pattern as described above, as shown in the attached figure. Figure 2 As shown.

[0053] From the perspective of surface current, when an incident wave strikes the surface, there is a sudden impedance change at the edge from metal to air, leading to a sudden change in surface current and thus exciting an edge scattering field. To suppress edge scattering, the surface current at the edge needs to be smoothly reduced, i.e., the surface impedance at the edge needs to be smoothly increased, allowing the electromagnetic boundary to smoothly transition from metal to air. The relationship between surface impedance and surface current is shown in the attached figure. Figure 3-4 As shown, the general calculation formula is given:

[0054]

[0055] Where η is the surface impedance (equivalent sheet resistance, in units of...). ), J z (x) represents the surface current density of the metal in the z-direction.

[0056] The general design steps for TRS are as follows:

[0057] ① Loading method: When the incident wave is perpendicular to a certain edge, a TRS is applied in a straight line along the metal edge. The TRS can be physically connected to the metal edge without electrical connection.

[0058] ② Total length L of TRS: Determined based on the required lowest operating frequency. Generally, the total length L needs to be longer than half the wavelength of the lowest frequency. Note that TRS will slightly increase the normal incidence monostatic RCS, and the longer the total length, the greater the increase. This needs to be carefully considered.

[0059] ③ TRS Period D: Determined by formula (2) based on the required highest operating frequency and maximum operating angle, avoiding grating lobes within the operating frequency band and angular domain. Periodic structures will exhibit special directional echoes outside the mirror direction, i.e., grating lobes, as shown in the attached figure. Figure 5 As shown, the formula for calculating the frequency of the backward grating lobe is as follows:

[0060]

[0061] Where n is an integer, D is the period length, φ is the incident angle, and c is the speed of light. Once the highest effective frequency and the maximum effective angle are determined, the upper limit of the period D can be calculated. Generally, a smaller period D is better, as a smaller period D indicates a more continuous impedance gradient.

[0062] ④Specific impedance distribution of TRS: The impedance distribution is calculated based on the surface current distribution of the design and formula (1). Generally, the surface current is designed to decrease linearly from the metal edge to the air.

[0063] ⑤ Modeling and simulation verification to ensure the effectiveness of the design scheme.

[0064] Example 1

[0065] With attachment Figure 6The structure shown is used as an example to illustrate the specific design method. The simulation software used in this example is the commercial software CSTDESIGN STUDIO.

[0066] Step S1: The radar wave is incident perpendicularly to the edge of the metal plate. The target operating frequency is set to 2GHz to 18GHz, and the target operating angle is set to 90°.

[0067] Step S2: The total length L of the TRS must be greater than the half wavelength of the lowest operating frequency of 2GHz (75mm). In this example, it is 96mm.

[0068] Step S3: Based on the highest operating frequency of 18GHz, the maximum operating angle of 90°, and formula (2), the TRS period D is calculated to be less than 8.3mm. In this example, it is taken as 8mm.

[0069] Step S4: The surface current distribution is selected to decrease linearly from the metal edge to the air. The TRS impedance distribution is calculated according to formula (1), as shown in the table below.

[0070] Table 1 Impedance Distribution of Wideband Wide-Angle TRS Loading Structure

[0071]

[0072] Step S5: Modeling and Simulation Verification. The specific structure of the model and its surface current structure are shown in the attached figure. Figure 6-7 As shown. (Attached) Figure 7 Simulations of the surface current distribution show that before the TRS is applied, the surface current is concentrated at the front and rear edges of the metal. After the TRS is applied, the surface current does indeed decrease linearly on the TRS as designed.

[0073] The results show that the simulation results of single-station frequency sweep and angle sweep RCS are as follows: Figure 8 As shown, for metal flat plates, the designed structure has a single-station RCS reduction effect of about 20dB at an incident angle of 30° to 90° and within the range of 2GHz to 18GHz.

[0074] The embodiments of the present invention have the following beneficial effects:

[0075] 1) A general relationship between surface current and surface impedance is given, which can be used to freely control the surface current to achieve effects such as RCS reduction and scattered beam modulation.

[0076] 2) The idea of ​​suppressing edge scattering by controlling the surface current to reduce smoothly through gradual impedance is proposed, and a general method for designing gradual impedance surfaces is given.

[0077] 3) The design method and performance of wideband and wide-angle gradient impedance surface are illustrated through examples. The simulation realizes the RCS reduction effect of metal plate monostation of about 20dB at the incident angle of 30°~90° from 2GHz to 18GHz.

[0078] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A gradient impedance surface structure for edge scattering suppression, characterized in that, include: A radar-absorbing coating material is applied to the edge of a metal, wherein the surface impedance of the radar-absorbing coating material gradually increases from the inside to the outside of the metal.

2. The graded impedance surface structure for edge scattering suppression according to claim 1, characterized in that: The radar absorbing coating material is a resistive thin film material mainly composed of carbon paste.

3. The graded impedance surface structure for edge scattering suppression according to claim 1, characterized in that: Along the direction from the inside to the outside of the metal, the radar absorbing coating material is arranged in strips. The surface impedance of the radar absorbing coating material in the same strip is the same, while the surface impedance of the radar absorbing coating material in different strips is different.

4. The graded impedance surface structure for edge scattering suppression according to claim 3, characterized in that: Along the direction from the inside to the outside of the metal, the surface current of the radar absorbing coating material decreases linearly at different strips.

5. A graded impedance surface structure for edge scattering suppression according to claim 1, characterized in that: The radar-absorbing coating material is fixed to the metal edge by physical connection, without the need for electrical connection.

6. The graded impedance surface structure for edge scattering suppression according to claim 1, characterized in that: The radar absorbing coating material has a total width L along the direction from the inside of the metal to the outside of the metal, and its total width L is longer than half the wavelength of the lowest frequency point.

7. A gradient impedance surface structure for edge scattering suppression according to claim 3, characterized in that: The period width of the radar absorbing coating material at different strips is D, and the period width D is determined by the highest operating frequency and the maximum operating angle.

8. A method for designing a gradient impedance surface for edge scattering suppression, characterized in that, Includes the following steps: Step S1, loading form design, applying strip-shaped radar absorbing coating material in a straight line along the metal edge; Step S2, design the total width L. Determine the total loading width L based on the required lowest operating frequency, and ensure that the total width L is longer than half the wavelength of the lowest frequency. Step S3, design the period width D. Determine the period width D based on the required highest operating frequency and maximum operating angle, and ensure that no grating lobes appear in the operating frequency band and angular domain. Step S4: Design the specific impedance distribution. Calculate the impedance distribution based on the designed surface current distribution to ensure that the surface impedance increases smoothly along the metal edge from the inside to the outside of the metal, so that the electromagnetic boundary smoothly transitions from the metal to the air.

9. A method for designing a gradient impedance surface for edge scattering suppression according to claim 8, characterized in that, Also includes: Step S5: Based on the design schemes in steps S1 to S4, perform modeling and simulation to verify the effectiveness of the design schemes.

10. A method for designing a gradient impedance surface for edge scattering suppression according to claim 8, characterized in that: Along the direction from the inside to the outside of the metal, the surface current of the radar absorbing coating material decreases linearly at different strips.

Images