Asymmetric transmission double-sided image metamaterial dual-band stealth radome and its design method

Abstract

The present application discloses an asymmetric transmission double-sided image metamaterial dual-band stealth radome and its design method. The radome is composed of periodic extension of radome units. Each radome unit includes a phase regulation structure, a dual-band polarization conversion structure, and an absorbing structure. The phase regulation structure consists of two metal strips arranged along the y-axis, a dielectric plate, and a metal grating arranged along the y-axis. The dual-band polarization conversion structure is composed of the metal grating arranged along the y-axis in the phase regulation structure, three metal strips inclined at 45°, a metal grating arranged along the x-axis, and two dielectric plates sandwiched between them. The absorbing structure is composed of the metal grating arranged along the x-axis in the dual-band polarization conversion structure, two layers of ITO strip resistance films printed on PET thin plates, and two dielectric plates. This radome can achieve efficient transmission of x- and y-polarized waves at operating frequencies f1 and f2, and simultaneously realize the functions of RCS reduction stealth and absorbing stealth for y-polarized waves and x-polarized waves incident along the -z and +z axes.

Description

Technical Field

[0001] The present application relates to the technical field of radomes, and more particularly, to an asymmetric transmission double-sided image metamaterial dual-band stealth radome and a design method for the asymmetric transmission double-sided image metamaterial dual-band stealth radome. Background Art

[0002] Traditional radomes can be used to protect antennas from damage caused by some harsh natural environments such as rain, snow, and hail, provide a relatively safe working environment for antennas, improve the usage efficiency of equipment, and can also improve the working conditions of operators. However, as a special strong scattering source, when the antenna is detected by radar, it will generate a large scattering area, which will damage the stealth effect of the weapon equipment.

[0003] With the emergence of metamaterials and the development of stealth technology, it has been found that applying stealth metamaterials to the field of radomes can not only meet the protection function of traditional radomes, but also effectively reduce the radar cross section of the antenna by using stealth technology. So far, researchers in various countries have conducted certain explorations in this field and achieved certain results.

[0004] In the prior art, most of the metamaterial radomes work independently under the excitation of x-polarized or y-polarized electromagnetic waves, with a narrow application range. Moreover, these metamaterial radomes often only design functions on one side of the radome, greatly wasting the utilization rate of metamaterials. In addition, the metamaterial radomes often have problems such as strong angle sensitivity and narrow stealth frequency bands. Summary of the Invention

[0005] The purpose of the present application is to enhance the stealth effect of the radome so that the transmission from y-polarized waves to x-polarized waves and the transmission from x-polarized waves to y-polarized waves are not affected.

[0006] The technical solution of the first aspect of the present application is: providing an asymmetric transmission double-sided image metamaterial dual-band stealth radome, which includes: the radome is composed of a plurality of radome units arranged, and the radome unit includes: a phase regulation structure, a dual-band polarization conversion structure, and an absorbing structure; the phase regulation structure is arranged above the radome unit, and the phase regulation structure is used to control the phase of the reflected y-polarized wave; the dual-band polarization conversion structure is arranged below the phase regulation structure, and the dual-band polarization conversion structure includes a first metal grating, a first metal strip, and a second metal grating arranged in sequence. A first dielectric plate with the same thickness is arranged between the first metal grating and the first metal strip, and between the first metal strip and the second metal grating; the absorbing structure is arranged below the dual-band polarization conversion structure, and the absorbing structure is used to absorb the incident x-polarized wave and transmit the y-polarized wave.

[0007] In any of the above technical solutions, further, the first metal grating is a metal grating arranged along the y-axis, and the phase modulation structure includes: a second metal strip, a second dielectric plate, and the first metal grating; the second dielectric plate is arranged above the first metal grating, and two second metal strips are arranged on the second dielectric plate. Among them, the two second metal strips are arranged along the y-axis, and the distance between the two second metal strips is equal to the length of any one of the second metal strips.

[0008] In any of the above technical solutions, further, the second metal grating is a metal grating arranged along the x-axis, and the wave-absorbing structure includes a second metal grating, a third dielectric plate, a first ITO resistance film, a fourth dielectric plate, and a second ITO resistance film arranged in sequence. Among them, the first ITO resistance film has the same structure as the second ITO resistance film. The first ITO resistance film is composed of a PET thin layer and four I-shaped resistance thin films printed on the PET thin layer. The four I-shaped resistance thin films are grouped in pairs, and the length direction of the I-shaped resistance thin film is parallel to the x-axis.

[0009] In any of the above technical solutions, further, the first metal strip is arranged obliquely in the counterclockwise direction, and the inclination angle of the first metal strip is 45°.

[0010] In any of the above technical solutions, further, the number of the first metal strips is three. The length of the middle first metal strip is greater than the lengths of the first metal strips on both sides, and the lengths of the first metal strips on both sides are equal.

[0011] In any of the above technical solutions, further, the radome unit includes a first radome unit and a second radome unit. The length of the second metal strip in the first radome unit is not equal to the length of the second metal strip in the second radome unit. Multiple first radome units and multiple second radome units respectively form a first supercell and a second supercell according to the first arrangement period, and the first supercell and the second supercell alternately form a radome according to the second arrangement period.

[0012] The technical solution of the second aspect of this application is: to provide a design method for an asymmetric transmission double-sided image metamaterial dual-band stealth radome, which includes: Step 1, based on the Fabry-Perot resonator structure, determine a dual-band polarization conversion structure, where the dual-band polarization conversion structure includes a first metal grating, a first metal strip, a second metal grating, and a first dielectric plate; Step 2, set a second dielectric plate above the first metal grating, and set a second metal strip above the second dielectric plate to form a phase regulation structure; Step 3, sequentially set a third dielectric plate, a first ITO resistive film, a fourth dielectric plate, and a second ITO resistive film below the second metal grating to form an absorbing structure; Step 4, denote the dual-band polarization conversion structure, the phase regulation structure, and the absorbing structure as a radome unit, and perform periodic arrangement on the radome units according to a predetermined arrangement period to form a radome.

[0013] In any of the above technical solutions, further, the radome unit includes a first radome unit and a second radome unit, the length of the second metal strip in the first radome unit is not equal to the length of the second metal strip in the second radome unit, and the predetermined arrangement period includes a first arrangement period and a second arrangement period. Step 4 specifically includes: Step 41, according to the first arrangement period, periodically arrange multiple first radome units into a first super unit; Step 42, according to the first arrangement period, periodically arrange multiple second radome units into a second super unit; Step 43, according to the second arrangement period, alternately and periodically arrange the first super unit and the second super unit to form a radome.

[0014] In any of the above technical solutions, further, the first metal strip is inclined counterclockwise, and the inclination angle of the first metal strip is 45°.

[0015] In any of the above technical solutions, further, the number of the first metal strips is three, the length of the middle first metal strip is greater than the lengths of the first metal strips on both sides, and the lengths of the first metal strips on both sides are equal.

[0016] The beneficial effects of this application are:

[0017] In the technical solution of this application, by using the radome unit composed of a y-polarized wave phase regulation structure, a dual-band polarization conversion structure, and an x-polarized wave absorbing structure to perform periodic extension in the plane, a dual-band stealth radome is formed, which improves the stealth effect of the radome.

[0018] Compared with the prior art, the advantages of this application are:

[0019] (1) Apply the asymmetric transmission double-sided image metamaterial to the field of radomes, reduce the waste of radome space resources, and improve the space utilization rate of the radome.

[0020] (2) It can not only achieve dual channels near 10 and 11.9 GHz, but also achieve high-efficiency stealth for x (104.2%) polarized waves and y (49.4%) polarized waves within a relatively wide frequency band range.

[0021] (3) At the same time, it reduces the angular sensitivity of the radome when x-polarized waves and y-polarized waves are incident, enabling it to maintain good stealth performance within a range of 45°. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional advantages of the present application will become apparent and easily understood in the description of the embodiments in conjunction with the following drawings, where:

[0023] Figure 1 is a schematic diagram of the front of an asymmetric transmission double-sided image metamaterial dual-band stealth radome according to an embodiment of the present application;

[0024] Figure 2 is a schematic diagram of the back of an asymmetric transmission double-sided image metamaterial dual-band stealth radome according to an embodiment of the present application;

[0025] Figure 3 is a schematic diagram of a radome unit according to an embodiment of the present application;

[0026] Figure 4 is a functional schematic diagram of a radome according to an embodiment of the present application;

[0027] Figure 5 is a schematic diagram of a phase modulation structure according to an embodiment of the present application;

[0028] Figure 6 is a schematic diagram of a dual-band polarization conversion structure according to an embodiment of the present application;

[0029] Figure 7 is a schematic diagram of an ITO resistive film according to an embodiment of the present application;

[0030] Figure 8 is a curve of the reflection and transmission amplitudes of x-polarized waves when electromagnetic waves are incident vertically along the -z direction according to an embodiment of the present application;

[0031] Figure 9 is a schematic diagram of the electric field distribution and current distribution on different metal structures of a dual-band polarization conversion structure when x-polarized electromagnetic waves are incident vertically according to an embodiment of the present application;

[0032] Figure 10 is an electromagnetic characteristic diagram of a y-polarized wave phase modulation structure according to an embodiment of the present application;

[0033] Figure 11It is the equivalent circuit diagram of the wave-absorbing structure when the x-polarized wave is incident along the -z direction according to an embodiment of the present application;

[0034] Figure 12 It is a schematic diagram of the wave-absorbing situation of ITO resistive films with different resistances according to an embodiment of the present application;

[0035] Figure 13 It is a schematic diagram of the simulation result when the y-polarized wave is incident along the +z direction when R = 50Ω / sq according to an embodiment of the present application;

[0036] Figure 14 It is a schematic diagram of the angle sensitivity analysis of the radome when the x-polarized wave is incident along the +z direction according to an embodiment of the present application;

[0037] Figure 15 It is the RCS reduction curve of the radome when the y-polarized wave with different angles is incident along the -z direction according to an embodiment of the present application;

[0038] Figure 16 It is the wave-absorbing curve of the radome when the x-polarized wave with different angles is incident along the +z direction according to an embodiment of the present application;

[0039] Figure 17 It is the experimental environment and experimental results of the radome transmission when linearly polarized wave is incident according to an embodiment of the present application.

[0040] Figure 18 It is the experimental test environment and the measured wave-absorbing rate and RCS reduction curve of the radome when the x-polarized wave and y-polarized wave are incident at different angles according to an embodiment of the present application. Detailed implementation manners

[0041] In order to be able to more clearly understand the above objects, features and advantages of the present application, the present application will be further described in detail below in conjunction with the drawings and specific implementation manners. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0042] In the following description, many specific details are set forth in order to fully understand the present application. However, the present application can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present application is not limited by the specific embodiments disclosed below.

[0043] Embodiment 1:

[0044] Such as Figures 1 to 3As shown in the figure, this embodiment provides an asymmetric transmission double-sided image metamaterial dual-band stealth radome, which is composed of a plurality of radome units arranged. Each radome unit includes: a phase regulation structure, a dual-band polarization conversion structure, and an absorbing structure.

[0045] Specifically, the phase regulation structure completely reflects the incident y-polarized wave and regulates the phase, and completely transmits the incident x-polarized wave. The dual-band polarization conversion structure constructed by the vertical grating structure greatly improves the polarization conversion efficiency. The absorbing structure completely absorbs the incident x-polarized wave and transmits the y-polarized wave.

[0046] As Figure 4 shown in the figure, when the x-polarized waves with frequencies f1 and f2 are incident along the +z direction, the radome can convert them into y-polarized waves with corresponding frequencies and transmit them smoothly. When the y-polarized wave is incident along the +z direction, the radome can scatter the incident electromagnetic wave in all directions of space, effectively reducing the backscattering. When the electromagnetic wave is incident from the -z direction, the radome can convert the incident y-polarized waves with frequencies f1 and f2 into x-polarized waves and transmit them out, and can absorb the incident x-polarized wave to achieve the stealth function.

[0047] In this embodiment, as Figure 5 shown in the figure, the phase regulation structure is arranged above the radome unit, and the phase regulation structure is used to control the phase of the reflected y-polarized wave; the phase regulation structure includes: a second metal strip, a second dielectric plate, and a first metal grating; the second dielectric plate is arranged above the first metal grating, and two second metal strips are arranged on the second dielectric plate. Among them, the two second metal strips are arranged along the y-axis, and the distance between the two second metal strips is equal to the length of any one of the second metal strips.

[0048] Specifically, the phase regulation structure is composed of two second metal strips along the y-axis, a second dielectric plate, and a first metal grating along the y-axis. The first metal grating along the y-axis can completely reflect the incident y-polarized wave and completely transmit the x-polarized wave. By changing the length of the second metal strip along the y-axis, the phase of the reflected y-polarized wave can be effectively controlled. The length of the second metal strip along the y-axis is i, the width is c, the distance between the two second metal strips is i, which is the same as the length of the second metal strip. The width of the metal sheet in the first metal grating is a, the length is P, and the distance is b. The thickness of the second dielectric plate is h1.

[0049] In this embodiment, as Figure 6As shown in the figure, the dual-band polarization conversion structure is disposed below the phase modulation structure. The dual-band polarization conversion structure includes a first metal grating, a first metal strip, and a second metal grating arranged in sequence. A first dielectric plate with the same thickness is provided between the first metal grating and the first metal strip, and between the first metal strip and the second metal grating. Among them, the dual-band polarization conversion structure shares the first metal grating with the phase modulation structure. The first metal grating is a metal grating arranged along the y-axis, and the second metal grating is a metal grating arranged along the x-axis.

[0050] Further, the first metal strip is inclined counterclockwise, and the inclination angle of the first metal strip is 45°.

[0051] Further, the number of the first metal strips is three. The length of the middle first metal strip is greater than the lengths of the first metal strips on both sides, and the lengths of the first metal strips on both sides are equal.

[0052] Specifically, the dual-band polarization conversion structure is composed of a metal grating along the y-axis in the phase modulation structure, three first metal strips inclined at 45°, a second metal grating along the x-axis, and two layers of the first dielectric plate. The dual-band polarization conversion structure and the y-polarized wave phase modulation structure share the first metal grating arranged along the y-axis. The inclined first metal strips can ensure the realization of polarization conversion of the linearly polarized wave. The second metal grating along the x-axis can completely reflect the incident x-polarized wave and completely transmit the y-polarized wave. The mutually perpendicular metal grating structure and the inclined first metal strips form a structure similar to a Fabry-Perot resonant cavity, greatly improving the polarization conversion efficiency. The widths of the inclined first metal strips are all c, the spacing is e, and the lengths are d and j respectively. The thicknesses of the two layers of F4B first dielectric plates are both h.

[0053] In this embodiment, as Figure 7 shown in the figure, the wave-absorbing structure is disposed below the dual-band polarization conversion structure. The wave-absorbing structure is used to absorb the incident x-polarized wave and transmit the y-polarized wave.

[0054] Further, the second metal grating is a metal grating arranged along the x-axis. The wave-absorbing structure includes a second metal grating, a third dielectric plate, a first ITO resistive film, a fourth dielectric plate, and a second ITO resistive film arranged in sequence.

[0055] Among them, the first ITO resistive film and the second ITO resistive film have the same structure. The first ITO resistive film is composed of a PET thin layer and four I-shaped resistive thin films printed on the PET thin layer. The four I-shaped resistive thin films are grouped in pairs, and the length direction of the I-shaped resistive thin films is parallel to the x-axis.

[0056] Specifically, the absorbing structure for x-polarized waves consists of a second metal grating along the x-axis, two layers of ITO resistive films along the x-axis and printed on a PET thin layer, and two dielectric plates (the third and fourth dielectric plates). Among them, the two layers of ITO resistive films printed on the PET thin layer are respectively denoted as the first ITO resistive film and the second ITO resistive film. The absorbing structure for x-polarized waves and the dual-band polarization conversion structure share the second metal grating arranged along the x-axis. The two layers of ITO resistive films are exactly the same, and each layer is composed of four "I"-shaped ITO resistive thin films with the same resistance value, which can completely absorb the incident x-polarized waves and transmit the y-polarized waves. The width of each "I"-shaped ITO resistive thin film is k, the length is l, the spacing in the y-axis direction is n, and the spacing in the x-axis direction is m. The thicknesses of the third and fourth dielectric plates are h2 and h3.

[0057] Furthermore, the radome unit includes a first radome unit and a second radome unit. The length of the second metal strip in the first radome unit is not equal to the length of the second metal strip in the second radome unit. Multiple first radome units and multiple second radome units respectively form a first supercell and a second supercell according to a first arrangement period, and the first supercell and the second supercell alternately form a radome according to a second arrangement period.

[0058] To verify the stealth performance of the above radome, the performance of each structure is simulated and tested respectively. The structural parameters of the radome unit are set as follows:

[0059] P = 12 mm, a = 2 mm, b = 1 mm, c = 0.5 mm, d = 8 mm, e = 0.5 mm, j = 7 mm, k = 1 mm, l = 5.8 mm, m = 0.2 mm, n = 5 mm, h = 1 mm, h1 = 3 mm, h2 = 2 mm, h3 = 1 mm; the metal material is copper, the thickness is 0.017 mm, and the conductivity is 5.8×10 7 S / m; the ITO surface resistance is 50 Ω / sq.

[0060] Through simulation verification, when the antenna operates with x-polarized waves (x-polarized radiation), the antenna is placed on the back side (-z axis) of the radome, and the x-polarized detection electromagnetic wave can be effectively received by the antenna itself, so that no large scattering will occur. When the y-polarized detection electromagnetic wave is incident, the front side (+z axis) of the stealth metamaterial radome can effectively reduce the backscattering cross-sectional area of the y-polarized wave, realizing the stealth effect of the antenna;

[0061] When the antenna operates in the y - polarized wave (y - polarized radiation), the radome is flipped, and the antenna is placed on the front side of the radome (+z - axis). The y - polarized detection electromagnetic wave can be effectively received by the antenna itself, thus not generating a large scattering. When the x - polarized detection electromagnetic wave is incident, the ITO absorbing structure on the back side is used to reduce the back - scattering cross - section area of the x - polarized wave, achieving the stealth effect of the antenna.

[0062] In both cases, the transmission from the y - polarized wave to the x - polarized wave and the transmission from the x - polarized wave to the y - polarized wave of the radome are not affected.

[0063] Embodiment 2:

[0064] This embodiment provides a design method for an asymmetric - transmission double - sided image metamaterial dual - band stealth radome, including:

[0065] Step 1: Based on the Fabry - Perot resonant cavity structure, determine the dual - band polarization - conversion structure. The dual - band polarization - conversion structure includes a first metal grating, a first metal strip, a second metal grating, and a first dielectric plate. Among them, the first metal strip is inclined counter - clockwise, and the inclination angle of the first metal strip is 45°. The number of the first metal strips is three. The length of the middle first metal strip is greater than the lengths of the first metal strips on both sides, and the lengths of the first metal strips on both sides are equal.

[0066] Specifically, in order to achieve the stealth function of the radome, it should be able to achieve dual - band polarization - conversion transmission, and have a high cross - polarization transmittance for a certain polarized linear - polarized wave, while having a high co - polarization reflectivity for its orthogonal linear - polarized wave. For a symmetric structure, cross - polarization modes cannot be generated when excited by x - polarized waves and y - polarized waves. Therefore, the reflection and transmission Jones matrices can be expressed by the following formula:

[0067]

[0068] In the formula, r xx and t xx are respectively the co - polarization reflection coefficient and the co - polarization transmission coefficient under the incidence of x - polarized waves, and other symbols are similar to the above two. If the structure is rotated by α degrees around the center, the rotated reflection Jones matrix can be expressed as:

[0069] R(α) = S( - α)·R·S(α) (2)

[0070] Among them, S(α) represents the rotation matrix, which can be expressed by the following formula:

[0071]

[0072] It can be seen from (2) and (3) that the cross - polarization reflection coefficient after rotating by α degrees is:

[0073] r yx r(α) = r xy r(α) = 0.5(r xx -r yy )sin2α (4)

[0074] For a given structure, r xx and r yy are both constant values. Therefore, from (4), it can be seen that the cross-polarization reflection coefficient of the structure is proportional to sin2α, that is:

[0075] r yx r(α) = r xy r(α) ∝ sin2α (5)

[0076] Similarly, it can be obtained that the cross-polarization transmission coefficient of the structure is also proportional to sin2α, that is:

[0077] t yx t(α) = t xy t(α) ∝ sin2α (6)

[0078] Although the absorption of the polarization conversion wave can be achieved through the sin2α component, the polarization conversion efficiency is relatively low, and the maximum can only reach 25%.

[0079] To ensure that the radome has a high cross-polarization transmittance for one linearly polarized wave and a high co-polarization reflectivity for its orthogonal polarized wave, we utilize the polarization filtering characteristics of the metal grating (i.e., fully transmitting one linearly polarized wave and reflecting its orthogonal linearly polarized wave), and by constructing a high-transmission structure similar to the F-P resonant cavity, while maintaining a high co-polarization reflectivity, the cross-polarization transmittance of the radome is improved.

[0080] The dual-band polarization conversion structure is composed of three layers of metal structures and two layers of dielectric plates, with a period of P. The first layer of metal structure is the first metal grating in the y direction, with a metal thickness of 0.017 mm, a width of a, and a grating pitch of b. The second layer consists of three adjacent first metal strips inclined at 45°. The width of the middle metal strip is c, and the length is d. The sizes of the two side metal strips are the same, with a width of c and a length of j. The spacing between the three metal strips is all e. The third layer of metal structure is a grating structure identical to and perpendicular to the first layer of metal structure, the second metal grating. These three layers of metal structures are separated by two layers of F4B dielectric plates (the first dielectric plate). The thickness of the F4B dielectric plate is h, the dielectric constant is 2.65, and the dielectric tangent loss is 0.001. The three-layer cascaded metal constructs a high-transmission structure similar to the F-P resonant cavity, which can effectively improve the cross-polarization transmittance of the dual-band polarization conversion structure.

[0081] As Figure 8As shown, when an x-polarized wave is incident, the structure can achieve an efficient transmission polarization conversion function near two frequency bands of f1 = 10 GHz and f2 = 11.9 GHz, and the transmission coefficients can both reach above 0.96. Since the upper layer of this dual-band polarization conversion structure is the first metal grating in the y direction, the structure can achieve total reflection of the y-polarized wave.

[0082] As can be seen from Figure 9 (a) and (b), when an x-polarized wave is incident, the electric fields at these two frequency points are mainly concentrated on three adjacent metal strips in the middle layer. Through Figure 9 the current distribution diagrams at 10 GHz and 11.9 GHz shown in (c) and (d), it can be seen more clearly that at these two frequency points, the vertically incident x-polarized wave can pass through the structure. At the same time, it can also be clearly understood that the vertically incident y-polarized wave will be reflected back. In addition, based on the optical path reversibility theorem, it can be known that the y-polarized wave incident along the +z direction can also be converted into an x-polarized wave and pass through the structure at 10 GHz and 11.9 GHz, while the incident x-polarized wave will be completely reflected back.

[0083] Increasing the number of parallel and obliquely placed metal strips with different lengths can increase the number of frequency bands of polarization conversion. However, for the convenience of calculation, only a dual-band asymmetric transmission structure is designed in this embodiment.

[0084] Step 2: Set a second dielectric plate above the first metal grating, and set a second metal strip above the second dielectric plate to form a phase modulation structure;

[0085] Specifically, the structure designed above can achieve efficient dual-band asymmetric transmission. However, when a y-polarized wave is incident along the -z direction, the structure will generate strong backscattering. To effectively achieve the stealth function when a y-polarized wave is incident, a stealth structure that can achieve phase modulation for the y-polarized wave is designed on the original basis. This structure is composed of loading a layer of F4B dielectric plate (the second dielectric plate) and a layer of metal structure (the second metal strip) above the original structure. The thickness of the second dielectric plate is h1. The metal structure is the second metal strip composed of two metal strips symmetric about the y-axis, with a width of c and a length of i, and the distance between the two metal strips is also i.

[0086] As shown in Figure 10 (a), it can be clearly seen from the electromagnetic response when an x-polarized wave is vertically incident that the coincidence degree between the two is extremely high, which indicates that loading the phase modulation structure of the y-polarized wave on the original structure will not affect its original working characteristics.

[0087] Due to the polarization filtering characteristics of the metal grating (i.e., fully transmitting one linearly polarized wave and reflecting its orthogonal linearly polarized wave), the reflection phase can be effectively regulated by adjusting the metal strips along the y-axis. From Figure 10 (b), it can be seen that in the frequency band of 8 - 16 GHz, when the structural parameter i changes from 3 mm to 11 mm, the reflection amplitude of the y-polarized wave is close to 1, and the reflection phase remains relatively parallel. Therefore, this structure is very suitable for realizing the phase regulation of the y-polarized wave. From Figure 10 (c), it can be seen that when i = 5 mm and i = 9 mm, these two metamaterial units can have a phase difference of 180° ± 37° in the range of 10 - 16 GHz when the y-polarized wave is incident. Therefore, after arranging these two structures in a checkerboard pattern, the backscattering RCS can be effectively reduced.

[0088] Step 3: A third dielectric plate, a first ITO resistive film, a fourth dielectric plate, and a second ITO resistive film are sequentially arranged below the second metal grating to form an absorbing structure;

[0089] The above-designed radome can better achieve double-passband cross-polarization transmission for the x-polarized wave incident along the -z direction and RCS reduction for the y-polarized wave incident in the same direction. To further expand the application range of the radome, another absorbing structure for the x-polarized wave is integrated on the back of the radome, which can well absorb the x-polarized wave incident along the +z direction and transmit the y-polarized wave.

[0090] This structure is composed of adding two layers of F4B dielectric plates and two layers of ITO resistive films with the same PET thin layers each with four ITO resistive films on the back of the structure designed in the previous step, which are sequentially denoted as the third dielectric plate, the first ITO resistive film, the fourth dielectric plate, and the second ITO resistive film. The thicknesses of the F4B dielectric plates are h2 and h3 respectively, the dielectric constant of PET is 3, the electrical tangent loss is 0.003, the thickness is 0.1 mm, the surface resistance value of the ITO resistive film is RΩ / sq, the length is l, the width is k, and the distances between the four resistive films are m and n.

[0091] As Figure 11 shown, Z0 represents the vacuum wave impedance, and Z d represents the equivalent impedance of the dielectric layer. The two-layer ITO resistive film structure is equivalent to two series branches connected in parallel in the circuit, where R1 and R2 respectively represent the equivalent resistances of the two-layer ITO resistive film structure, L1 and L2 respectively represent the equivalent impedances of the two-layer ITO resistive film structure, C1 represents the sum of the equivalent capacitance between the first ITO resistive film structure and the second ITO resistive film structure and the equivalent capacitance between the first ITO resistive film structure and the metal grating, and C2 represents the equivalent capacitance between the second ITO resistive film structure and the metal grating.

[0092] The input impedance Z of this structure (metamaterial unit) in can be expressed as:

[0093]

[0094] where Z p represents the surface impedance of the resistive film structure. The equivalent impedance Z of the dielectric layer d can be expressed as:

[0095]

[0096] where ε0 and μ0 are the vacuum permittivity and permeability respectively, ω is the resonance frequency, d is the thickness of the dielectric, and ε r is the relative permittivity of the dielectric layer.

[0097] The surface impedance Z of the ITO resistive film p can be approximately calculated by the following formula:

[0098]

[0099] where R represents the equivalent resistance, which is related to the sheet resistance R s of the ITO resistive film. R can be approximately calculated as:

[0100]

[0101] where S unitcell is the area of the unit structure, and S patch is the area of the ITO resistive film.

[0102] To achieve an efficient wave absorption effect, the Z of this metamaterial unit in must be matched with the free space impedance Z0 to ensure that electromagnetic waves can fully enter the metamaterial structure. Through the above theoretical introduction, it can be found that the Z of the dielectric d is mainly affected by its permittivity and thickness, while the Z of the resistive film p is mainly affected by its sheet resistance and relative area, and both deeply affect the Z in of the metamaterial unit. Since the free space impedance Z0 is usually a fixed value, therefore, by analyzing the permittivity and thickness of the dielectric and the sheet resistance and shape of the resistive film, the metamaterial unit can obtain good wave absorption function.

[0103] Such as Figure 12As shown, as the surface resistance R of the ITO resistive film increases from 20 Ω / sq to 70 Ω / sq, the reflection amplitude of the x-polarized wave gradually decreases because the incident electromagnetic wave is converted into heat energy by the ohmic loss generated by the ITO resistive film. It can also be seen from the simulation results shown in the figure that when R = 50 Ω / sq, this metamaterial unit can reduce the reflection amplitude below -10 dBsm in the frequency band of 7.5 - 23.8 GHz (absorption rate greater than 90%), so as to achieve broadband absorption of the x-polarized wave, and the relative bandwidth is 104.2%.

[0104] As Figure 13 shown, this structure can still maintain the transmission polarization conversion of the double passband near the two frequency bands of f1 = 10 GHz and f2 = 11.8 GHz, and compared with the previous structure, the amplitude remains basically unchanged. This shows that the added double-layer ITO resistive film structure only absorbs the x-polarized wave and has little impact on the transmission of the y-polarized wave.

[0105] In the real environment, electromagnetic waves often do not enter the radome surface vertically. To fully simulate the real environment, the angle sensitivity analysis of the radome is carried out, as Figure 14 shown. During the simulation, the surface resistance of the ITO resistive film is taken as R = 50 Ω / sq, and the x-polarized wave is incident on the radome surface from different angular directions in steps of 15°. It can be seen from Figure 14 that as the incident angle increases continuously, the wave absorption ability of the radome also gradually increases, but the wave absorption frequency band gradually moves to the high frequency. And when the incident angle reaches 45°, this radome can still achieve a wave absorption effect of more than -10 dBsm in the frequency range of 8.4 - 26.6 GHz, and the relative bandwidth reaches 104%. Therefore, this radome has a certain angle insensitivity to the incident x-polarized wave.

[0106] Step 4, denote the double passband polarization conversion structure, the phase regulation structure, and the wave absorption structure as the radome unit, and perform periodic arrangement on the radome units according to the predetermined arrangement period to form a radome.

[0107] Furthermore, the radome unit includes a first radome unit and a second radome unit. The length of the second metal strip in the first radome unit is not equal to the length of the second metal strip in the second radome unit. The predetermined arrangement period includes a first arrangement period and a second arrangement period. Step 4 specifically includes:

[0108] Step 41, arrange multiple first radome units periodically according to the first arrangement period to form a first super unit;

[0109] Step 42, arrange multiple second radome units periodically according to the first arrangement period to form a second super unit;

[0110] Step 43: According to the second arrangement period, the first super unit and the second super unit are alternately arranged periodically to form an antenna radome.

[0111] For the x-polarized wave, only the periodic repetition arrangement of the antenna radome units is needed to construct an absorbing array. For the y-polarized wave, first, two kinds of 5×5 antenna radome units with i = 5mm and i = 9mm are constructed, and then these two kinds of antenna radome units are arranged in a 3×3 layout to construct a 0-π checkerboard structure.

[0112] Use the commercial CST software to perform numerical simulation on it. During the simulation, open boundary conditions are set in the x, y, and z directions, and the x-polarized wave is incident along the +z direction, and the y-polarized wave is incident along the -z direction. From Figure 15 it can be seen that when the y-polarized wave is vertically incident on the antenna radome along the -z direction, the antenna radome can achieve an RCS reduction of more than -10dBsm in the range of 9.3 - 15.4GHz (49.4%). From Figure 16 it can be seen that when the x-polarized wave is vertically incident on the antenna radome along the +z direction, the antenna radome can achieve an absorption efficiency of more than 0.9 in the range of 7.5 - 23.8GHz (104.2%).

[0113] From Figure 15 it can be seen that as the incident angle increases, the stealth performance of the antenna radome decreases. Specifically, in the range of 0° - 30°, the RCS reduction of the antenna radome at the high-frequency band increases as the incident angle increases; the opposite is true at the low-frequency band. At 45°, there is an obvious change in the RCS reduction curve, with an obvious depression near 9GHz, and in the range of 10 - 12GHz, the curve has an obvious upward shift, and the maximum value can reach -7dBsm.

[0114] From Figure 16 it can be seen that as the incident angle increases, the absorbing frequency band of the antenna radome will gradually shift to the high frequency. When the electromagnetic wave is incident at a 45° angle, the antenna radome can still maintain an absorption rate of more than 0.9 in the range of 8.4 - 26.6GHz, which fully verifies the excellent absorption performance of the designed double-layer ITO structure for the x-polarized wave.

[0115] As Figure 17 (a) shows, two linearly polarized feed horns operating in the range of 2 - 18GHz are used as transmitters and receivers. To ensure the accuracy of the experiment, the sample is placed in the middle of the two horns, and the center is always kept at the same height as the two horns. The distance between the horns and the sample is set to 2m to ensure plane wave incidence. Before the experiment starts, the network analyzer is calibrated through the supporting calibration component and a time-domain gate is added to the network analyzer to reduce the influence of the surrounding environment and the system error existing in the network analyzer itself on the experimental results.

[0116] like Figure 17 As shown in (b), it can be clearly seen that the experimentally measured t yx The transmission wave has two obvious transmission peaks. Compared with the simulation results, the frequencies of these two transmission peaks are offset to a certain extent, and the amplitude has decreased, but it can still be maintained above 0.9. The main reason for the error is that the processing accuracy of the physical sample is not enough, there may be deviations, resulting in the offset of the working frequency; the layers of the structure are bonded with adhesives, and there may be air bubbles between the layers, which will lead to a decrease in the transmission amplitude of the electromagnetic wave. Secondly, compared with the ideal environment in the simulation software, although the environmental impact has been reduced by calibration and adding time domain gates, it is still impossible to completely eliminate the errors caused by the surrounding environment to the experimental test.

[0117] like Figure 18 (a) and Figure 18 As shown in (b), two co-polarized linearly polarized horns are used to receive and transmit y- and x-polarized electromagnetic waves, respectively. The simulation platform is controlled by a computer, and the angle of incidence of the electromagnetic wave can be precisely controlled by controlling the angle of the two arms. Figure 18 (c) and (d) show the RCS reduction test results of the front side (incident along -z axis) and the absorption test results of the back side (incident along +z axis) of the radome when y-polarized waves and x-polarized waves are incident at different angles. Due to the limitation of experimental equipment, only the response of the radome sample to electromagnetic waves below 18GHz was tested. Compared with the simulation results, it can be clearly seen that when the y-polarized wave is incident, although the resonance point has a certain degree of offset, the offset is maintained within 0.5GHz. The scattering values ​​of the test are generally smaller than those of the simulation, which is caused by the large space loss during the test. When the x-polarized wave is incident, the absorption frequency band moves slightly to the high frequency, but the overall effect is in good agreement with the simulation results. In general, the radome can maintain a good stealth effect for x-polarized waves and y-polarized waves incident on different sides within a range of 45°. There are some errors in the figure, which are mainly caused by machining accuracy errors and incomplete elimination of the influence of the surrounding environment.

[0118] The technical solution of the present application has been described in detail with reference to the accompanying drawings. The present application proposes an asymmetric transmission double-sided image metamaterial double-band stealth radome and its design method. Among them, the radome is composed of periodic extension of radome units in the plane. The radome unit is composed of a y-polarized wave phase regulation structure, a double-band polarization conversion structure, and an x-polarized wave absorbing structure. The y-polarized wave phase regulation structure is composed of two metal strips arranged along the y-axis on the upper layer, an intermediate dielectric plate, and a metal grating arranged along the y-axis at the bottom. The double-band polarization conversion structure is composed of the metal grating arranged along the y-axis in the phase regulation structure, three metal strips inclined at 45°, the metal grating arranged along the x-axis in the absorbing structure, and two dielectric plates sandwiched between them. The double-band polarization conversion structure and the y-polarized wave phase regulation structure share the metal grating arranged along the y-axis. The x-polarized wave absorbing structure is composed of a metal grating arranged along the x-axis, two ITO strip resistive films printed on a PET thin layer along the x-axis, and two dielectric plates. The x-polarized wave absorbing structure and the double-band polarization conversion structure share the metal grating arranged along the x-axis. Through the technical solution in the above embodiments, the double-band stealth radome can achieve efficient transmission of x- and y-polarized waves at the working frequencies f1 and f2, and at the same time, achieve the functions of RCS reduction stealth and absorbing stealth for y-polarized waves and x-polarized waves incident along the +z and -z axes, making full use of the double-sided regulation function and working characteristics of the radome.

[0119] The steps in the present application can be adjusted, combined, and deleted according to actual needs.

[0120] The units in the device of the present application can be combined, divided, and deleted according to actual needs.

[0121] Although the present application has been disclosed in detail with reference to the accompanying drawings, it should be understood that these descriptions are merely exemplary and are not intended to limit the application of the present application. The protection scope of the present application is defined by the appended claims and may include various modifications, improvements, and equivalent solutions made to the invention without departing from the protection scope and spirit of the present application.

Claims

1. Asymmetric transmission double-sided image metamaterial double-band stealth radome, characterized in that The radome is composed of a plurality of radome units arranged, and the radome unit includes: a phase regulation structure, a dual-band polarization conversion structure, and an absorbing structure; The phase regulation structure is arranged above the radome unit, and the phase regulation structure is used to control the phase of the reflected y-polarized wave; The dual-band polarization conversion structure is arranged below the phase regulation structure. The dual-band polarization conversion structure includes a first metal grating, a first metal strip, and a second metal grating arranged in sequence. A first dielectric plate with the same thickness is arranged between the first metal grating and the first metal strip, and between the first metal strip and the second metal grating; The absorbing structure is arranged below the dual-band polarization conversion structure, and the absorbing structure is used to absorb the incident x-polarized wave and transmit the y-polarized wave; The first metal grating is a metal grating arranged along the y-axis. The phase regulation structure includes: a second metal strip, a second dielectric plate, and the first metal grating; The second dielectric plate is arranged above the first metal grating, and two second metal strips are arranged on the second dielectric plate; Wherein, the two second metal strips are arranged along the y-axis, and the distance between the two second metal strips is equal to the length of any one of the second metal strips; The second metal grating is a metal grating arranged along the x-axis. The absorbing structure includes the second metal grating, a third dielectric plate, a first ITO resistive film, a fourth dielectric plate, and a second ITO resistive film arranged in sequence; Wherein, the first ITO resistive film and the second ITO resistive film have the same structure. The first ITO resistive film is composed of a PET thin layer and four I-shaped resistive films printed on the PET thin layer. The four I-shaped resistive films are grouped in pairs, and the length direction of the I-shaped resistive film is parallel to the x-axis; 2. The asymmetric transmission double-sided image metamaterial double-band stealth radome according to claim 1, characterized in that The first metal strip is arranged obliquely in the counterclockwise direction, and the inclination angle of the first metal strip is 45°; 3. The asymmetric transmission double-sided image metamaterial double-band stealth radome according to claim 2, wherein The number of the first metal strips is three. The length of the middle first metal strip is greater than the lengths of the first metal strips on both sides, and the lengths of the first metal strips on both sides are equal; 4. The asymmetric transmission double-sided image metamaterial double-band stealth radome according to claim 1, characterized in that, The radome unit includes a first radome unit and a second radome unit, and the length of the second metal strip in the first radome unit is not equal to the length of the second metal strip in the second radome unit; A plurality of the first radome units and a plurality of the second radome units respectively form a first super unit and a second super unit according to a first arrangement period, and the first super unit and the second super unit alternately form the radome according to a second arrangement period; 5. Design method of an asymmetric transmission double-sided image metamaterial double-band stealth radome, characterized in that, This method includes: Step 1, based on the Fabry-Perot resonator structure, determine the dual-band polarization conversion structure, wherein the dual-band polarization conversion structure includes a first metal grating, a first metal strip, a second metal grating, and a first dielectric plate; Step 2, arrange a second dielectric plate above the first metal grating and arrange a second metal strip above the second dielectric plate to form a phase regulation structure; Step 3, a third dielectric plate, a first ITO resistive film, a fourth dielectric plate, and a second ITO resistive film are sequentially disposed under the second metal grating to form an absorbing structure; Step 4, the dual-band polarization conversion structure, the phase regulation structure, and the absorbing structure are denoted as radome units, and the radome units are periodically arranged according to a predetermined arrangement period to form the radome.

6. The design method of the asymmetric transmission double-sided image metamaterial double-band stealth radome according to claim 5, characterized in that The radome unit includes a first radome unit and a second radome unit. The length of the second metal strip in the first radome unit is not equal to the length of the second metal strip in the second radome unit. The predetermined arrangement period includes a first arrangement period and a second arrangement period. Step 4 specifically includes: Step 41, according to the first arrangement period, a plurality of the first radome units are periodically arranged into a first super unit; Step 42, according to the first arrangement period, a plurality of the second radome units are periodically arranged into a second super unit; Step 43, according to the second arrangement period, the first super unit and the second super unit are alternately and periodically arranged to form the radome.

7. The design method of the asymmetric transmission double-sided image metamaterial double-band stealth radome according to claim 5, characterized in that The first metal strip is inclined counterclockwise, and the inclination angle of the first metal strip is 45°.

8. The design method of the asymmetric transmission double-sided image metamaterial double-band stealth radome according to claim 5, characterized in that, The number of the first metal strips is three. The length of the middle first metal strip is greater than the lengths of the first metal strips on both sides, and the lengths of the first metal strips on both sides are equal.

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