A method for pre-forming a complex curved FSS membrane and manufacturing a radome

Abstract

The application discloses a preparation method of a complex curved surface FSS film and a radome, and comprises the following steps: step one, preparing a forming die of a curved surface base material; step two, coating resin on the curved surface of the forming die; step three, obtaining a pre-formed frequency selective surface film and taking it off from the die for standby; step four, layer by layer laying a composite material skin and a sandwich structure; step five, laying a foaming adhesive film on a preset frequency selective surface film laying area; step six, making the pre-formed frequency selective surface film closely adhere to the adjacent laying layer through the foaming adhesive film by negative pressure; step seven, continuing to lay the remaining laying layers; and step eight, integrally curing the radome with all the laying layers. The self-supporting rigid base film with the curved surface shape independently maintained by the in-situ curing of the die can overcome the poor extensibility of the plane film, and can eliminate wrinkles, hollowing, damage and delamination during the laying of the complex variable-curvature curved surface.

Description

Technical Field

[0001] This invention belongs to the field of antenna technology, specifically a method for prefabricating a complex curved surface FSS film and preparing an antenna radome. Background Technology

[0002] Frequency selective surfaces (FSS), as periodic electromagnetic structures with precise frequency selection capabilities, have become core components in aerospace, stealth equipment, and communication equipment due to their ability to modulate the transmission, reflection, or absorption of electromagnetic signals in specific frequency bands. In aerospace, aircraft radar radomes must balance aerodynamic shape and electromagnetic compatibility, adapting to complex curved surfaces such as irregular arcs and variable curvature cavities. In stealth equipment, missile bodies and stealth drone surface protective layers need to integrate FSSs to achieve radar wave selection, adapting to asymmetric and multi-curvature combined surfaces. In communication equipment, 5G base station radomes and vehicle-mounted millimeter-wave radar protective covers also widely adopt arc-shaped and curved cavity designs to meet installation and signal requirements.

[0003] In the aforementioned scenarios, the FSS needs to be integrated with composite material skins such as carbon fiber reinforced epoxy resin skin and glass fiber prepreg skin used in the radome molding process, as well as sandwich structures such as honeycomb core and foam core. The curvature variations and irregular contours of complex surfaces place extremely high demands on the compatibility and bonding precision of the FSS with the substrate, ensuring no gaps or wrinkles, while guaranteeing stable interlayer bonding to withstand harsh environments and maintain electromagnetic performance and structural reliability.

[0004] Existing technologies have the following problems in the fabrication of FSS radomes adapted to complex curved surfaces:

[0005] Traditional prefabricated planar FSS membranes use polyimide and quartz film as substrates, with copper, gold, and aluminum plating on the surface to form frequency-selective patterns. The planar prefabricated membrane substrate itself has extremely poor ductility and cannot achieve stretching and adaptive bonding to complex curved surfaces. During skin laying, wrinkles, blistering, and delamination defects occur, which in turn lead to impedance mismatch, resonant point shift, and increased insertion loss, resulting in a significant reduction in overall electromagnetic wave transmission and stealth performance.

[0006] In existing technologies, while the FDM printing method using water-soluble substrates combined with 3D direct-write patterns can create frequency-selective patterns on curved surfaces, the water-soluble cleaning step can corrode the internal composite materials and sandwich structures, causing structural damage and deformation. This method requires expensive specialized equipment, resulting in a high cost barrier, and the complex process leads to a long molding cycle, making mass production difficult.

[0007] In terms of assembly process, the existing method directly lays the FSS film bare on the surface of the radome substrate without protection or limiting structure, which makes it impossible to accurately align with the subsequent frequency selective pattern. During assembly, laying and subsequent molding, the FSS metal pattern is subjected to external friction and extrusion, resulting in wear, deformation and even damage, causing electromagnetic parameter deviation and wave transmission performance fluctuation.

[0008] Therefore, there is an urgent need for a frequency-selective film preforming process and an integrated fabrication and assembly method for radomes that can adapt to complex and variable curvature surfaces, in order to solve the problems existing in the above-mentioned technologies. Summary of the Invention

[0009] The technical solution adopted in this invention is as follows: A method for preforming a complex curved surface FSS film and preparing an antenna radome, comprising the following steps:

[0010] Step 1: Select the curved surface shape structure of the surface layer according to the frequency in the radome, and prepare the molding mold for the curved substrate.

[0011] Step 2: Coat the curved surface of the molding die with resin and cure it in situ to form a curved substrate layer with self-supporting rigidity, so that the curved substrate layer can independently maintain the curved shape and has no springback deformation.

[0012] Step 3: Using the curved surface of the molding mold as a reference, a frequency-selective periodic pattern is etched on the surface of the cured curved substrate layer using 3D laser etching technology to obtain a pre-formed frequency-selective surface film, which is then removed from the mold for later use.

[0013] Step 4: Following the radome design layering sequence, lay down the composite material skin and sandwich structure layer by layer until the pre-fabricated frequency selection surface film is embedded in the layup position.

[0014] Step 5: Select the surface film laying area at the preset frequency, lay a layer of foam film, and then precisely align and lay the prepared pre-formed frequency-selective surface film on the surface of the foam film.

[0015] Step 6: Implement a vacuum bag pressing process on the current layup structure. By applying negative pressure, the pre-formed frequency selection surface film is tightly bonded to the adjacent layup through the foamed adhesive film, achieving pre-fixation without wrinkles or voids.

[0016] Step 7: Continue laying the remaining layers to complete the overall layering of the radome.

[0017] Step 8: Curing and shaping the antenna radome after all layers have been laid up, so that the foam film, pre-formed frequency selective surface film, composite material skin and sandwich structure are cured into an integrated whole.

[0018] Furthermore, the curved substrate forming mold in step one is a male or female mold that matches the shape of the target curved surface. The mold material is metal or composite material, and the mold surface is polished.

[0019] Furthermore, the resin coated in step two is a spray-applied polyimide resin or a modified cyanate ester resin.

[0020] Furthermore, in step three, 3D laser etching is performed by non-contact etching on a curved substrate layer to form a periodic pattern with selected frequency, according to the designed periodic units and arrangement parameters. After etching is completed, surface residue is cleaned.

[0021] Furthermore, the composite material skin and sandwich structure sequentially laid in step four includes one or more of the following: quartz cyanate prepreg, carbon fiber prepreg, honeycomb core, PMI foam, and stealth material.

[0022] Furthermore, the foamed film in step five is a modified epoxy foamed film or a modified cyanate ester foamed film.

[0023] Furthermore, the vacuum bag pressing process in step six applies negative pressure uniformly to eliminate interfacial gaps and prevent layup slippage and misalignment.

[0024] Furthermore, the laying of the remaining layers in step seven is a cyclic execution of the laying process described in steps four and five, with the number of cycles being 2 to 5, selecting the surface film at the frequency of laying multiple preforms.

[0025] Furthermore, in step eight, the overall curing and molding process adopts a composite material molding process or an autoclave curing process, and the heating, heat preservation and pressure curing are completed according to the predetermined curing curve of the composite material.

[0026] Furthermore, the complex curved surface frequency selective radome prepared by the above method has no wrinkles or voids between the preformed frequency selective surface film and the adjacent layers, and the frequency selective pattern is free from wear and deformation.

[0027] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0028] (1) The present invention pre-forms a curved substrate layer with self-supporting rigidity through in-situ curing process, so that it independently maintains a shape that is completely in contact with the complex variable curvature surface of the radome without springback deformation. This serves as the bearing base for the frequency selective pattern, completely avoiding the stretching, bending and laying of the planar film with poor extensibility. It solves the problems of wrinkling, hollowing, damage and delamination that are very easy to occur in the laying of complex curved surfaces from the root, and ensures high-precision gapless bonding between the frequency selective surface film and the radome substrate.

[0029] (2) The present invention uses 3D laser curved surface non-contact etching process to accurately form frequency selection periodic patterns on pre-cured rigid curved surface substrate, which completely replaces the traditional copper-clad film pattern transfer and contact-type laying process. It eliminates the wear, deformation and damage caused by external force friction, extrusion and stretching to the metal pattern during assembly and laying, and ensures the integrity and dimensional accuracy of the frequency selection pattern, thereby significantly improving the consistency and working stability of the electromagnetic performance of the finished antenna radome.

[0030] (3) In this invention, a foamed film with suitable wave transmission performance is integrally laid between the pre-formed frequency selective surface film and adjacent layers, and vacuum bag compression is performed for pre-compacting and shaping. The negative pressure is used to uniformly press the frequency selective surface film to tightly adhere to the surrounding structure through the foamed film, which not only effectively eliminates interface gaps and prevents slippage and misalignment, but also provides reliable pre-fixation for subsequent lay-ups and overall curing. Finally, the foamed film, the pre-formed frequency selective surface film, the composite skin and the sandwich structure are cross-linked and cured to form a strong integrated whole through composite molding or autoclave co-curing, which greatly improves the interlayer bonding strength and structural reliability and can withstand harsh operating environments.

[0031] (4) The entire preparation method of the present invention has a tight connection between processes. It uses dry molding and laser etching to replace the water-soluble substrate cleaning scheme, which in principle eliminates the erosion and damage of water to the internal composite material and sandwich structure. Furthermore, it does not require expensive special equipment, effectively reducing manufacturing costs and process thresholds, and has good mass production adaptability. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Example 1

[0035] This embodiment provides a method for preforming a complex curved surface FSS film and for fabricating an antenna radome, referring to... Figure 1 The specific steps are as follows:

[0036] Step 1: Preparation of Curved FSS Substrate Molding Mold: Based on the complex variable curvature surface structure of each FSS layer in the radome, a matching male or female single-sided molding mold is fabricated. The mold is made of metal or composite material. The mold surface is polished to ensure the accuracy of the curved surface contour and demolding performance. This step precisely fabricates a matching male or female single-sided molding mold based on the complex variable curvature surface shape of each FSS layer. The mold is made of metal or composite material and has a polished surface, providing a high-precision molding benchmark for the subsequent molding of the self-supporting rigid curved substrate layer. Its advantages are: the mold surface contour is completely consistent with the target curved surface of the radome, ensuring precise adaptation between the substrate layer and the complex curved surface from the source, completely avoiding gaps and wrinkles caused by contour deviation. The mold made of metal or composite material has good rigidity and thermal stability, and does not deform during the curing process, ensuring the consistency of the base film shape in batch production. Polishing the mold surface not only ensures the accuracy of the curved surface contour, but also enables smooth demolding after the base film is cured, preventing adhesion damage to the base film and allowing the entire base film to be removed intact. This lays a reliable process foundation for subsequent 3D laser etching of frequency-selective patterns and defect-free integrated assembly of the entire radome.

[0037] Step Two: Curing and Molding of Rigid FSS Substrate for Curved Surfaces: On the prepared curved surface of the mold, spray-applied polyimide (PI) or modified cyanate ester resin is applied and cured in situ at a constant temperature. This results in a rigid, integral substrate layer that perfectly conforms to the curved surface of the radome, independently maintaining its curved shape without springback deformation. This step directly molds an integral substrate layer that perfectly conforms to the complex, variable curvature surface of the radome by coating the mold surface with spray-applied polyimide or modified cyanate ester resin and curing it in situ at a constant temperature. Its core advantage lies in the self-sustaining rigidity of the substrate layer after curing, enabling it to independently maintain its curved shape without springback deformation, fundamentally replacing traditional planar films with poor ductility. This rigid curved substrate provides a stable curved carrier for subsequent 3D laser etching of frequency-selective patterns. Furthermore, it eliminates the need for any stretching or bending of the film material during installation and assembly, completely eliminating defects such as wrinkling, hollowing, damage, and delamination caused by insufficient substrate elongation. This ensures a gapless and precise fit between the frequency-selective surface layer and the radome substrate, laying the foundation for the structural reliability and electromagnetic performance stability of the final integrated radome.

[0038] Step 3: 3D Laser Curved Surface Etching for Pre-formed FSS Film: Using the mold surface as a reference, a 3D laser etching process is employed to precisely etch the FSS periodic frequency selection pattern onto the cured curved substrate surface according to the designed periodic units and layout parameters. After etching, surface residue is cleaned, and the entire pre-formed FSS film is removed from the mold for separate use. This step uses the mold surface as a positioning reference and employs a 3D laser curved surface non-contact etching process to directly form a frequency selection periodic pattern on the cured rigid curved substrate surface. Its core advantage lies in completely avoiding the wear, deformation, and damage to the metal pattern caused by external friction, extrusion, and stretching in traditional planar film copper plating, transfer, and laying processes, ensuring the geometric integrity and high precision of the frequency selection pattern. Laser etching is precisely executed according to the designed periodic units and layout parameters, resulting in excellent pattern consistency and fundamentally guaranteeing the accuracy and operational stability of the radome's electromagnetic performance. Etching with the mold as a reference ensures synchronous matching between the pattern and the curved surface shape, eliminating positioning deviations. After etching, the residue can be cleaned and the entire pre-formed FSS film can be completely removed for later use. The process is simple, and the obtained curved FSS film has independent structural integrity and can be directly used for subsequent lay-up assembly, laying a key technological foundation for the non-destructive and high-precision manufacturing of the final integrated radome.

[0039] Step Four: Layered Laying of the Radome Substrate: Following the designed layering sequence of the radome, one or more structural materials, such as quartz cyanate prepreg, carbon fiber prepreg, honeycomb or PMI foam, and stealth materials, are laid layer by layer until the prefabricated FSS is embedded. This step strictly adheres to the designed layering sequence, sequentially laying one or more of the following structural materials until the prefabricated FSS film is embedded. Its advantage lies in the orderly layered construction, precisely establishing the load-bearing structure, wave-transmitting functional layer, and interlayer support system of the radome, providing accurate layup positions and a flat substrate for the embedding of the frequency selective surface. The combined use of multiple functional materials allows the radome to simultaneously achieve multi-functional integration such as wave transmission, stealth, and weight reduction while meeting structural load-bearing requirements. The method of laying the FSS film layer by layer to the predetermined embedding position ensures that the subsequent prefabricated FSS film is laid out cleanly and flatly, and the laying sequence is accurate. This lays a reliable foundation for the seamless bonding of the FSS film and the integration of the overall structure, ensuring that the functional layers of the final radome work together and have stable performance.

[0040] Step 5: Laying and Positioning of the Foamed Film and Pre-formed FSS Membrane: In the pre-designed FSS laying area, first lay a layer of modified epoxy or modified cyanate ester foamed film with suitable wave transmission properties; then precisely align the prepared curved pre-formed FSS membrane and lay it smoothly on the surface of the foamed film. This step involves first laying a layer of modified epoxy or modified cyanate ester foamed film with suitable wave transmission properties in the pre-designed FSS laying area, and then precisely aligning and smoothly laying the curved pre-formed FSS membrane on top. Its advantage lies in the fact that the foamed film, as a transitional adhesive layer, can fully fill the tiny gaps between the FSS membrane and adjacent layers during subsequent vacuum compaction and curing, achieving a tight, gapless bond and eliminating interface defects. The whole-layer laying method of the foamed film provides uniform and continuous support and protection for the FSS membrane, preventing the metal pattern from directly contacting the underlying rigid substrate and being subjected to compression and wear. Meanwhile, the pre-formed FSS film, based on its self-supporting rigidity, can be precisely aligned and laid smoothly without stretching or slippage. From an operational perspective, this ensures the precise positional relationship between the frequency selection pattern and the overall structure of the radome, providing a guarantee for strong interlayer bonding and stable electromagnetic performance after final integrated curing.

[0041] Step Six: Vacuum Bag Pressing Pre-compacting and Shaping: A vacuum bag pressing process is applied to the current layup structure. Using uniform negative pressure, the FSS membrane is tightly bonded to the underlying quartz cyanate prepreg, carbon fiber prepreg, honeycomb or PMI foam, etc., through the foamed adhesive film. This eliminates interfacial gaps, prevents slippage and misalignment, and achieves wrinkle-free and void-free pre-fixation. The core advantage lies in utilizing the uniform force characteristics of vacuum negative pressure to synchronously press the entire FSS membrane onto the curved layup surface, effectively eliminating interfacial gaps and preventing localized void defects. Simultaneously, uniform pressure compacts and fixes the FSS membrane to adjacent layups, preventing slippage and misalignment during subsequent layup operations and ensuring the precise positional relationship between the frequency selection pattern and the radome structure remains unchanged. This pre-compaction and shaping achieves wrinkle-free and void-free pre-fixation, providing a stable operating surface for subsequent layer laying and laying a reliable foundation for full cross-linking and firm integration between layers during final overall curing.

[0042] Step Seven: Subsequent Layer Laying: After vacuum compaction and shaping, continue laying one or more of the remaining structural materials such as quartz cyanate prepreg, carbon fiber prepreg, honeycomb or PMI foam, stealth materials, and prefabricated FSS film, repeating this process 2-5 times to complete the overall radome structure. This step, following vacuum compaction and shaping, involves laying the remaining structural materials such as quartz cyanate prepreg, carbon fiber prepreg, honeycomb or PMI foam, stealth materials, and prefabricated FSS film, completing the overall radome structure through 2-5 cycles. Its advantage lies in the ability to achieve the orderly embedding of multiple frequency-selective surfaces through multi-cycle layering, meeting the complex requirements of the radome for broadband, multi-band electromagnetic control. Each FSS film layer is laid on a stable pre-compacted foundation, ensuring that the already laid structures do not experience disturbance or misalignment during the layer-by-layer stacking process, guaranteeing precise alignment of the frequency-selective patterns in each layer. Meanwhile, the alternating layering of functional and structural materials deeply integrates multiple functions such as wave transmission, stealth, and load-bearing, enabling the overall radome structure to meet the requirements of aerodynamic shape and structural strength while achieving the optimal design of electromagnetic performance, laying a complete layered foundation for the final overall co-curing molding.

[0043] Step 8: Overall Curing and Molding: After all layers are laid up, composite material molding or autoclave curing processes are used to complete the heating, heat preservation, and pressure curing according to the established curing curve of the composite material. This allows the foam film, FSS film, prepreg, sandwich structure, and absorbing structure to form a solid integrated whole, ultimately producing a complex curved integrated FSS radome. The core advantage lies in the uniform application of temperature and pressure fields, which allows the foam film to fully foam and cure, resulting in a thorough cross-linking reaction with the pre-formed FSS film, quartz cyanate prepreg, carbon fiber prepreg, honeycomb or PMI foam sandwich, and absorbing structure. The interfaces of each layer fuse into a continuous whole, completely eliminating microscopic gaps between layers and forming a solid integrated structure. During the curing process, the foamed film expands and fills, compensating for minor shape deviations between layers. This ensures that there are no voids or delamination between the FSS film and adjacent layers, significantly improving interlayer bonding strength and enabling it to withstand aerodynamic loads and vibration impacts during high-speed flight. Simultaneously, overall co-curing avoids the accumulation of thermal stress and interface weakening caused by step-curving, guaranteeing the long-term structural reliability and electromagnetic wave transmission performance of the radome under complex variable curvature shapes.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preforming a complex curved surface FSS film and fabricating an antenna radome, characterized in that, Includes the following steps: Step 1: Select the curved surface shape structure of the surface layer according to the frequency in the radome, and prepare the molding mold for the curved substrate; Step 2: Coat the curved surface of the molding die with resin and cure it in situ to form a curved substrate layer with self-supporting rigidity, so that the curved substrate layer can independently maintain the curved shape and has no springback deformation. Step 3: Using the curved surface of the forming mold as a reference, a frequency-selective periodic pattern is etched on the surface of the cured curved substrate layer using 3D laser etching technology to obtain a pre-formed frequency-selective surface film, which is then removed from the mold for later use. Step 4: Following the radome design layering sequence, lay down the composite material skin and sandwich structure layer by layer until the pre-fabricated frequency selection surface film is embedded in the layup position. Step 5: Select the surface film laying area at the preset frequency, lay a layer of foam film, and then precisely align and lay the prepared pre-formed frequency-selected surface film on the surface of the foam film. Step 6: Implement vacuum bag pressing process on the current layup structure. Apply negative pressure to make the pre-formed frequency selection surface film tightly bonded to the adjacent layup through the foamed film, so as to achieve pre-fixation without wrinkles or voids. Step 7: Continue laying the remaining layers to complete the overall layering of the radome; Step 8: Curing and shaping the antenna radome after all layers have been laid up, so that the foam film, pre-formed frequency selective surface film, composite material skin and sandwich structure are cured into an integrated whole.

2. The method for preforming a complex curved surface FSS film and preparing an antenna radome according to claim 1, characterized in that, The curved substrate forming mold in step one is a male or female mold that matches the shape of the target curved surface. The mold is made of metal or composite material and the mold surface is polished.

3. The method for preforming a complex curved surface FSS film and preparing an antenna radome according to claim 1, characterized in that, The resin applied in step two is a spray-applied polyimide resin or a modified cyanate ester resin.

4. The method for prefabrication of a complex curved surface FSS film and preparation of an antenna radome according to claim 1, characterized in that, In step three, 3D laser etching is performed by non-contact etching on a curved substrate layer to form a periodic pattern with selected frequency, according to the designed periodic units and arrangement parameters. After etching is completed, surface residue is cleaned.

5. The method for preforming a complex curved surface FSS film and preparing an antenna radome according to claim 1, characterized in that, The composite material skin and sandwich structure laid sequentially in step four includes one or more of the following: quartz cyanate prepreg, carbon fiber prepreg, honeycomb core, PMI foam, and stealth material.

6. The method for preforming a complex curved surface FSS film and preparing an antenna radome according to claim 1, characterized in that, The foamed film mentioned in step five is a modified epoxy foamed film or a modified cyanate ester foamed film.

7. The method for preforming a complex curved surface FSS film and preparing an antenna radome according to claim 1, characterized in that, The vacuum bag pressing process in step six uses negative pressure to apply pressure evenly, which is used to eliminate interfacial gaps and prevent layup slippage and misalignment.

8. The method for preforming a complex curved surface FSS film and preparing an antenna radome according to claim 1, characterized in that, The laying of the remaining layers in step seven is a cyclic execution of the laying process described in steps four and five, with the number of cycles being 2 to 5, and the surface film is selected according to the frequency of laying multiple preforms.

9. The method for preforming a complex curved surface FSS film and preparing an antenna radome according to claim 1, characterized in that, In step eight, the overall curing and molding process adopts a composite material molding process or an autoclave curing process, and completes the heating, heat preservation and pressure curing according to the established curing curve of the composite material.

10. The method for preforming a complex curved surface FSS film and preparing an antenna radome according to claim 1, characterized in that, The complex curved surface frequency selective radome prepared by the above method has no wrinkles or voids between the preformed frequency selective surface film and the adjacent layers, and the frequency selective pattern is free from wear and deformation.

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