A radar calibration scatterer and a method of making the same

Abstract

This invention provides a radar calibration scattering source and its fabrication method. The scattering source comprises a transparent skin layer, a metal reflective layer, and a large-aperture lens. The transparent skin layer protects the metal reflective layer and the large-aperture lens. The metal reflective layer is spherical and attached to the bottom of the large-aperture lens, used to back-modulate incident radar waves focused thereon to generate radar echoes. The large-aperture lens comprises a solid layer, a spherical shell layer, a segmented layer, and a PMI outer layer, used to focus electromagnetic waves incident on its surface. This invention successfully overcomes the technical bottleneck of the difficulty in fabricating traditional large-aperture lenses. Furthermore, the resulting large-aperture lens can efficiently focus incident radar waves, maintaining passive operating characteristics while enabling the radar calibration scattering source to possess excellent performance characteristics such as wide bandwidth, multi-polarization, wide angle range, high angle, and high gain. This provides key technical support for the development of radar calibration scattering sources for satellite platform-based calibration applications.

Description

Technical Field

[0001] This invention relates to the field of passive radar calibration technology, and in particular to a radar calibration scattering source and its preparation method. Background Technology

[0002] As a core means of detecting targets and sensing the battlefield situation, radar has evolved into a complex system covering multiple frequency bands, multiple polarizations, multiple base stations, and multiple features. Before it can realize target detection, identification, and tracking functions, radar calibration is a key step.

[0003] In recent years, satellite-based calibration technology has become increasingly popular, placing higher demands on calibration sources.

[0004] A calibration source adapted to satellite platforms should possess at least the following characteristics: Wide bandwidth: adaptable to the operating frequency bands of different radars, broadening the application range; Multi-polarization: supports multiple polarization modes, matching diverse radar systems; Wide-angle domain: covers a wide effective angle domain, adapting to radars distributed across various sites within my country's vast territory; High precision: ensures its own accuracy to achieve effective calibration of radar measurement accuracy; High gain: compensates for signal attenuation caused by the distance between the satellite platform and the ground, preventing echoes from being submerged by noise; Passive operating mode: since the calibration source operates in space, maintenance is extremely difficult if a malfunction occurs. Therefore, a passive operating mode is preferred for this type of calibration source, as it offers high reliability and requires minimal maintenance once ground testing confirms its feasibility.

[0005] However, the design of calibration scattering sources for satellite-based calibration technologies is constrained by various factors, making it difficult to achieve a viable solution. Therefore, it is necessary to develop a passive calibration scattering source that meets the aforementioned requirements to support satellite-based radar passive calibration technology. Summary of the Invention

[0006] This invention provides a radar calibration scattering source and its preparation method, which can solve the problem that existing calibration scattering sources are difficult to achieve high gain.

[0007] This invention provides a radar calibration scattering source, comprising a wave-transparent skin layer, a metal reflective layer, and a large-aperture lens body; the wave-transparent skin layer is used to protect the metal reflective layer and the large-aperture lens body; the metal reflective layer is spherical and is attached to the bottom end of the large-aperture lens body, used to reverse-modulate the incident radar wave focused thereon to generate a radar echo; the large-aperture lens body comprises a solid layer, a spherical shell layer, a segmented layer, and a PMI outer layer, used to focus electromagnetic waves incident on its surface.

[0008] In one possible design, the radius of the large-aperture lens body is determined by the following formula: In the formula, R Let λ be the radius of the large-aperture lens body, and λ be the operating wavelength. G dB For gain requirements.

[0009] In one possible design, the solid layer consists of two hemispheres; the radius of the solid layer is 0.4 to 0.6 times the radius of the large-aperture lens body.

[0010] In one possible design, the dielectric constant of the solid layer is determined by the following formula: In the formula, ε0 is the dielectric constant of the solid layer, R is the radius of the large-aperture lens body, and r is the radius of the solid layer.

[0011] In one possible design, the spherical shell layer is formed by nesting at least two spherical shell layers from the inside out, and each of the spherical shell layers consists of two hemispherical shells.

[0012] In one possible design, the thickness of each of the spherical shell layers is no greater than 0.25 times the operating wavelength.

[0013] In one possible design, the segmentation layer is formed by splicing together several small spherical shells of the same shape and size.

[0014] In one possible design, the small spherical shells are preferably spherical right-angled triangles, and the number is preferably 8.

[0015] In one possible design, the thickness of the segmentation layer is the difference between the outer diameter of the large-aperture lens body and the inner diameter of the PMI outer layer.

[0016] In one possible design, the dielectric constant of the outer layer of the PMI is 1.0 to 1.5.

[0017] In one possible design, the thickness of the PMI outer layer is determined by the following formula: In the formula, p The thickness of the outer layer of the PMI is [missing information]. p 0 represents the thickness of the PMI material, ε p is the dielectric constant of the outer layer of the PMI.

[0018] In one possible design, the solid layer, the spherical shell layer, and the segmented layer are all foamed from expandable medium particles.

[0019] In one possible design, the expandable medium particles are polystyrene particles.

[0020] In one possible design, the reflective layer is either aluminum foil or copper foil; the thickness of the reflective layer is no greater than 0.2 mm.

[0021] In one possible design, the height h of the reflective layer is determined by the following formula: In the formula, h The height of the reflective layer, R The radius of the large-diameter lens body is... θ For the angular domain response, θ ≥140°.

[0022] In one possible design, the thickness of the wave-transparent skin layer is 0.5~1.0 mm; the dielectric constant of the skin layer is 1.0~1.1 C. 2 / (N·M 2 ).

[0023] In a second aspect, the present invention also provides a method for preparing a radar calibration scattering source as described in any of the first aspects above, the method comprising: (1) Determine the radius of the large-aperture lens body based on the target gain and the working wavelength, and determine the size parameters of the solid layer, the spherical shell layer, the segmented layer and the PMI outer layer according to the radius of the large-aperture lens body; (2) Design several small spherical shell molds according to the size parameters of the segmentation layer, add expandable medium particles to each small spherical shell mold for foaming, obtain several small spherical shells, and splice the small spherical shells to form a segmentation layer; (3) Design several hemispherical shells according to the size parameters of the solid layer and the spherical shell layer PMI outer layer respectively, add the expandable medium particles into the corresponding hemispherical shell mold for foaming, and obtain the solid layer and the spherical shell layer PMI outer layer. (4) The solid layer, spherical shell layer, segmented layer and PMI outer layer are combined and nested to obtain a large-aperture lens body; (5) After covering the bottom of the large-aperture lens with a reflective layer, a transparent skin layer is used to encapsulate it to obtain the radar calibration scattering source.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects: This invention is based on the passive Luneburg lens reflector. It innovatively designs a large-aperture lens body as a layered structure combining a solid layer, a spherical shell layer, a segmented layer, and a PMI outer layer. It is fabricated using various dielectric materials and corresponding molding processes, successfully breaking through the technical bottleneck of traditional large-aperture lens fabrication. Furthermore, the large-aperture lens body produced in this way can efficiently focus incident radar waves. While maintaining passive operating characteristics, it enables the radar calibration scattering source to have excellent performance such as wide bandwidth, multi-polarization, wide angle range, high angle, and high gain. This provides key technical support for the development of radar calibration scattering sources for satellite platform calibration. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the composition of a radar calibration scattering source provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the design of a large-aperture lens in a radar calibration scattering source provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the design of a segmented layer in a radar calibration scattering source provided in an embodiment of the present invention; In the diagram: 1: Wave-transparent skin layer; 2: Metal reflective layer; 3: Large-aperture lens body; 301: Solid layer; 302: Spherical shell layer; 303: Segmentation layer; 304: PMI outer layer. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] In the field of passive calibration, commonly used scattering sources include metal spheres, dihedrals, cylinders, metal corner reflectors, and Luneburg lens reflectors. Among these, metal spheres, commonly used in microwave anechoic chambers, have an effective angular domain of 4π solid angle, but their gain is too small; to achieve a gain of -20dB, their diameter needs to exceed 1m. Dihedrals and cylinders have relatively high gain, but their effective range is too narrow. Metal corner reflectors have a slightly wider angular domain, but still cannot meet calibration requirements, and their accuracy is not high. In contrast, although Luneburg lens reflectors possess excellent characteristics such as wide bandwidth, multi-polarization, wide angular domain, and high angle, traditional large-aperture Luneburg lens reflectors are difficult to manufacture due to factors such as complex mold development, difficult demolding, low yield rate, high manufacturing process difficulty, and high requirements for supporting equipment, thus preventing the achievement of high gain.

[0029] Based on this, embodiments of the present invention provide a radar calibration scattering source, such as... Figure 1 and Figure 2 As shown, it includes a wave-transparent skin layer 1, a metal reflective layer 2, and a large-aperture lens body 3. The wave-transparent skin layer 1 is used to protect the metal reflective layer 2 and the large-aperture lens body 3, so that the radar calibration scattering source in this embodiment of the invention has basic mechanical strength during use, transportation, and storage. The metal reflective layer 2 is spherical and is attached to the bottom of the large-aperture lens body 3. It is used to reverse-modulate the incident radar wave focused at this point to generate a radar echo and make the echo propagate in the opposite direction of incident, so that the scattering source in this embodiment of the invention has a wide-angle domain characteristic. The large-aperture lens body 3 adopts a layered design, specifically including a solid layer 301, a spherical shell layer 302, a segmented layer 303, and a PMI outer layer 304, which is used to focus the electromagnetic waves incident on its surface.

[0030] In this embodiment of the invention, based on the passive working mechanism of the Luneburg lens reflector, the large-aperture lens body is innovatively designed as a layered structure combining a solid layer, a spherical shell layer, a segmented layer, and a PMI outer layer. It is fabricated using various dielectric materials and corresponding molding processes, successfully breaking through the technical bottleneck of traditional large-aperture lenses being difficult to mold. Furthermore, the large-aperture lens body thus fabricated can efficiently focus incident radar waves. While maintaining passive working characteristics, it enables the radar calibration scattering source to have excellent performance such as wide bandwidth, multi-polarization, wide angle range, high angle, and high gain. This provides key technical support for the development of radar calibration scattering sources for satellite platform calibration.

[0031] In some embodiments, the radius of the large-aperture lens body is determined by the following formula: In the formula, R Let λ be the radius of the large-aperture lens body, and λ be the operating wavelength. G dB For gain requirements.

[0032] In this embodiment of the invention, the radius of the large-aperture lens in the calibration scattering source is determined by the target gain and the operating wavelength. Generally speaking, the larger the radius, the higher the gain. However, in practical engineering applications, the final performance of the lens layer is not solely determined by the radius, but is also influenced by a combination of factors such as dielectric loss, shell concentricity, interlayer spacing, and shell parameters. Therefore, the above theoretical formula is only for design reference. In engineering implementation, it must be modified according to the actual performance of the large-aperture lens. For example, a prototype of the large-aperture lens can be prepared first, and its actual performance parameters can be obtained through testing, which can then serve as the basis for the design of the calibration scattering source in this embodiment of the invention.

[0033] In some embodiments, the solid layer is composed of two hemispheres; the radius of the solid layer is 0.4 to 0.6 times the radius of the large-aperture lens body; The dielectric constant of the solid layer is determined by the following formula: In the formula, ε0 is the dielectric constant of the solid layer, R is the radius of the large-aperture lens body, and r is the radius of the solid layer.

[0034] In the embodiments of the invention, the core parameters of the solid layer include its radius and dielectric constant. The radius must be appropriately selected, as its value directly affects the performance and ease of manufacturing of the large-aperture lens. If its value is too large, it will lead to an increase in the aperture phase difference, thereby degrading the performance of the large-aperture lens; if its value is too small, it will increase the difficulty of the manufacturing process. Therefore, the radius of the solid layer is preferably 0.4 to 0.6 times the radius of the large-aperture lens layer; the dielectric constant of the solid layer is determined jointly based on its radius and the radius of the large-aperture lens.

[0035] In some embodiments, the spherical shell layer is formed by nesting at least two spherical shell layers from the inside out, and each spherical shell layer consists of two hemispherical shells; the thickness of each spherical shell layer is not greater than 0.25 times the working wavelength.

[0036] In the embodiments of the invention, a spherical shell layer surrounds the solid layer. The spherical shell layer has a multi-layered structure that encloses the solid layer at the center. The spherical shell layer is made of foamed polystyrene material, and each layer consists of two hemispherical shells, nested from the inside out according to diameter. Simultaneously, to minimize phenomena such as defocusing, beam tilting, or pattern distortion, the design of the spherical shell layer requires strict control of the interlayer gaps. The gap between the solid layer and the innermost spherical shell layer, as well as the gap between adjacent spherical shell layers, must not exceed 0.5 mm. The maximum radius of the spherical shell layer is determined by the mold size, while the selection of the number of layers N and the thickness d of each layer directly affects the performance of the lens and the ease of engineering implementation. In a preferred embodiment, the thickness d of each layer is not greater than 0.25λ, and the specific number of layers is determined by dividing the difference between the thickness of the large-diameter lens and the solid layer (i.e., the total thickness of the spherical shell layer) by the thickness d of each layer.

[0037] In some embodiments, the dielectric constant of the outer layer of the PMI is 1.0 to 1.5; The thickness of the outer layer of the PMI is determined by the following formula: In the formula, p The thickness of the outer layer of the PMI is [missing information]. p 0 represents the thickness of the PMI material, ε p is the dielectric constant of the outer layer of the PMI.

[0038] In this embodiment, the PMI outer layer is made of polymethacrylamide material with a dielectric constant between 1.0 and 1.5 and extremely low density, making it ideal for use as the outermost layer of a large-aperture lens. Furthermore, this material can be directly purchased from the market and then machined to meet the required PMI outer layer specifications. The thickness p of the PMI outer layer is determined by the thickness p0 of the commercially available PMI material and its dielectric constant ε. p This joint decision allows for flexible design adjustments based on existing material specifications, simplifies the manufacturing process, and ensures the stability of lens performance.

[0039] In some embodiments, the solid layer, the spherical shell layer, and the segmented layer are all foamed from expandable medium particles; the expandable medium particles are polystyrene particles.

[0040] In the embodiments of the invention, the solid layer, the spherical shell layer, and the segmented layer are all foamed from expandable medium particles. This not only facilitates the molding of large-diameter lenses, but also significantly reduces the complexity of process control and equipment investment costs. At the same time, it facilitates the precise control of the dimensional parameters of each layer, thereby effectively ensuring the concentricity and dimensional consistency between the layers of the spherical shell layer, and ensuring that the interlayer gap meets the design requirements.

[0041] In some embodiments, the segmentation layer is formed by splicing together several small spherical shells of the same shape and size; the small spherical shells are preferably spherical right-angled triangles, and the number is preferably 8; the thickness of the segmentation layer is the difference between the outer diameter of the large-aperture lens body and the inner diameter of the PMI outer layer.

[0042] In the embodiments of the invention, to reduce the molding difficulty of the segmented layer, it is designed to be composed of several small spherical shells of the same shape and size spliced ​​together. Specifically, each hemisphere of the spherical shell layer is spherically divided to obtain several identical small spherical shells; then, a mold is designed according to the shape and thickness of the small spherical shells, and expandable medium particles are filled in for foaming molding. The design of the small spherical shells is particularly critical; on the one hand, it must ensure that multiple identical small spherical shells can be accurately spliced ​​to form a complete hemisphere; on the other hand, it must fully adapt to the molding process requirements of mold foaming. In a preferred embodiment, as... Figure 3 As shown, the small spherical shells are designed as spherical right-angled triangles, and each hemispherical shell is composed of four small spherical shells of the same size and dimensions.

[0043] In some embodiments, the reflective layer is either aluminum foil or copper foil; the thickness of the reflective layer is no greater than 0.2 mm.

[0044] In the embodiments of the invention, the reflective layer can be made of ultra-thin aluminum foil, copper foil, or other metal foil. In specific implementations, the reflective layer can be cut from a single sheet of metal foil or formed by splicing multiple sheets of metal foil. It should be noted that if multiple sheets of foil are spliced, it should be ensured that there are no gaps at the splice points. In a preferred embodiment, the thickness of the reflective layer is no greater than 0.2 mm. This configuration effectively avoids strong electromagnetic scattering at the edges of the reflective layer due to its excessive thickness, thus preventing adverse effects on the overall reflection performance of the radar calibration scattering source.

[0045] In some embodiments, the height h of the reflective layer is determined by the following formula: In the formula, h The height of the reflective layer, R The radius of the large-diameter lens body is... θ For the angular domain response, θ ≥140°.

[0046] In the embodiments of the invention, the height of the reflective layer is determined based on the radius of the large-aperture lens and the angular response requirements. To achieve a wide angular response, the value of θ is not less than 140°.

[0047] In some embodiments, the thickness of the wave-transparent skin layer is 0.5~1.0 mm; the dielectric constant of the skin layer is 1.0~1.1 C. 2 / (N·M 2).

[0048] In the embodiments of the invention, by controlling the thickness and dielectric constant of the wave-transparent skin layer within the above-mentioned range, the wave-transparent skin layer can not only have a certain mechanical strength, but also minimize the transmission loss of electromagnetic waves, thus giving it good wave-transparent performance. In specific implementation, the wave-transparent skin layer can be formed by curing epoxy resin, alkali-free fiberglass cloth, polyamide resin and tetraethylenepentamine.

[0049] The present invention also provides a method for preparing the radar calibration scattering source according to any one of the above claims, the method comprising: (1) Determine the radius of the large-aperture lens body based on the target gain and the working wavelength, and determine the size parameters of the solid layer, the spherical shell layer, the segmented layer and the PMI outer layer according to the radius of the large-aperture lens body; (2) Design several small spherical shell molds according to the size parameters of the segmentation layer, add expandable medium particles to each small spherical shell mold for foaming, obtain several small spherical shells, and splice the small spherical shells to form a segmentation layer; (3) Design several hemispherical shells according to the size parameters of the solid layer and the spherical shell layer PMI outer layer respectively, add the expandable medium particles into the corresponding hemispherical shell mold for foaming, and obtain the solid layer and the spherical shell layer PMI outer layer. (4) The solid layer, spherical shell layer, segmented layer and PMI outer layer are combined and nested to obtain a large-aperture lens body; (5) After covering the bottom of the large-aperture lens with a reflective layer, a transparent skin layer is used to encapsulate it to obtain the radar calibration scattering source.

[0050] In the embodiments of the invention, after fabricating the solid layer, spherical shell layer, segmented layer, and PMI outer layer using the above-described molding method, the solid layer, spherical shell layer, segmented layer, PMI outer layer, metal reflective layer, and wave-transparent skin layer are sequentially assembled into a whole, thus forming a complete calibration scattering source. This calibration scattering source is placed in a microwave anechoic chamber, and measurements can be performed at different frequencies in the P-Ka band, with linear or circular polarization modes, and at attitudes including azimuth, pitch, and roll, to comprehensively verify its various performance characteristics and provide a basis for subsequent applications and optimization. This scattering source, based on a passive operating mechanism, possesses excellent characteristics such as wide bandwidth, multi-polarization, wide-angle domain, high angle, and high gain, providing key technical support for the development of radar calibration scattering sources for satellite platform-mounted calibration applications.

[0051] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. In this application, the term "multiple" refers to two or more, unless otherwise expressly defined. In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; "linking" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0052] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A radar calibration scattering source, characterized in that, It includes a wave-transparent skin layer, a metal reflective layer, and a large-aperture lens body; the wave-transparent skin layer is used to protect the metal reflective layer and the large-aperture lens body; the metal reflective layer is spherical and is attached to the bottom end of the large-aperture lens body, used to reverse-modulate the incident radar wave focused at that point to generate a radar echo; the large-aperture lens body includes a solid layer, a spherical shell layer, a segmented layer, and a PMI outer layer, used to focus electromagnetic waves incident on its surface.

2. The radar calibration scattering source according to claim 1, characterized in that, The radius of the large-aperture lens body is determined by the following formula: In the formula, R Let λ be the radius of the large-aperture lens body, and λ be the operating wavelength. G dB For gain requirements.

3. The radar calibration scattering source according to claim 2, characterized in that, The solid layer consists of two hemispheres; The radius of the solid layer is 0.4 to 0.6 times the radius of the large-aperture lens body; and / or The dielectric constant of the solid layer is determined by the following formula: In the formula, ε0 is the dielectric constant of the solid layer, R is the radius of the large-aperture lens body, and r is the radius of the solid layer.

4. The radar calibration scattering source according to claim 1, characterized in that, The spherical shell layer is formed by nesting at least two spherical shell layers from the inside out, and each of the spherical shell layers consists of two hemispherical shells; and / or The thickness of each of the spherical shell layers is no greater than 0.25 times the operating wavelength.

5. The radar calibration scattering source according to claim 1, characterized in that, The segmentation layer is formed by splicing together several small spherical shells of the same shape and size; The small spherical shells are preferably spherical right-angled triangles, and the number is preferably 8; and / or The thickness of the segmentation layer is the difference between the outer diameter of the large-diameter lens body and the inner diameter of the PMI outer layer.

6. The radar calibration scattering source according to claim 1, characterized in that, The dielectric constant of the outer layer of the PMI is 1.0~1.5; and / or The thickness of the outer layer of the PMI is determined by the following formula: In the formula, p The thickness of the outer layer of the PMI is [missing information]. p 0 represents the thickness of the PMI material, ε p is the dielectric constant of the outer layer of the PMI.

7. The radar calibration scattering source according to any one of claims 1 to 6, characterized in that, The solid layer, spherical shell layer, and segmented layer are all foamed from expandable medium particles. Preferably, the expandable medium particles are polystyrene particles.

8. The radar calibration scattering source according to claim 1, characterized in that, The reflective layer is either aluminum foil or copper foil; the thickness of the reflective layer is no greater than 0.2 mm; and / or The height h of the reflective layer is determined by the following formula: In the formula, h The height of the reflective layer, R The radius of the large-diameter lens body is... θ For the angular domain response, θ ≥140°.

9. The radar calibration scattering source according to claim 1, characterized in that, The thickness of the wave-transparent skin layer is 0.5~1.0 mm; the dielectric constant of the skin layer is 1.0~1.1 C. 2 / (N·M 2 ).

10. A method for preparing a radar calibration scattering source according to any one of claims 1 to 9, characterized in that, The preparation method includes: (1) Determine the radius of the large-aperture lens body based on the target gain and the working wavelength, and determine the size parameters of the solid layer, the spherical shell layer, the segmented layer and the PMI outer layer according to the radius of the large-aperture lens body; (2) Design several small spherical shell molds according to the size parameters of the segmentation layer, add expandable medium particles to each small spherical shell mold for foaming, obtain several small spherical shells, and splice the small spherical shells to form a segmentation layer; (3) Design several hemispherical shells according to the size parameters of the solid layer and the spherical shell layer PMI outer layer respectively, add the expandable medium particles into the corresponding hemispherical shell mold for foaming, and obtain the solid layer and the spherical shell layer PMI outer layer. (4) The solid layer, spherical shell layer, segmented layer and PMI outer layer are combined and nested to obtain a large-aperture lens body; (5) After covering the bottom of the large-aperture lens with a reflective layer, a transparent skin layer is used to encapsulate it to obtain the radar calibration scattering source.

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