Large-size frequency selective surface invisible antenna housing and preparation method thereof

Abstract

The invention discloses a large-size frequency selective surface invisible antenna housing and a preparation method thereof. The antenna housing comprises an outer skin layer, a frequency selective surface layer, a sandwich layer and an inner skin layer which are sequentially stacked from outside to inside. The preparation method comprises the following steps: splicing the frequency selective surface layer by adopting small-size diaphragms, filling butt joint gaps with conductive slurry, and curing to realize electric connection to form a complete surface. The method has the advantages that: 1, the production cost is less than 10% of that of a laser etching method; and 2, large-size products are manufactured by slicing and then splicing. And 3, the process is controllable. And 4, the stealth performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of aircraft radar radome design and manufacturing technology, specifically relating to a stealth radome structure with frequency selectivity and its manufacturing method, which is particularly suitable for the manufacturing of large-size, high-performance, and low-cost stealth radomes. Background Technology

[0002] With modern stealth aircraft reducing their radar cross-section through shape design, the radar radome (antenna radome) becomes crucial to their stealth performance, serving as a primary electromagnetic window and scattering source. Frequency-selective surface stealth radome technology integrates periodic metallic patterned units into the radome structure, achieving high transmittance in specific frequency bands (such as radar operating frequencies) and high reflection or absorption in other frequency bands (such as enemy detection frequencies), thereby significantly enhancing the platform's stealth capabilities.

[0003] To achieve high-performance frequency-selective stealth capabilities, the periodic metal structure on the radome must possess high element integrity and periodic continuity. Existing technologies primarily employ two manufacturing approaches, both of which have significant limitations: 1. Direct Laser Etching: This method involves first metallizing the entire surface of the radome composite material, and then directly etching out periodic patterns using a laser. Its advantages include high pattern precision and excellent continuity. However, its disadvantages are significant: for large radomes exceeding 3-4 meters in size, the investment in laser etching equipment is enormous, the processing cycle is extremely long, and the cost is exceptionally high. Furthermore, it is limited by the processing area of ​​the equipment, making it difficult to manufacture ultra-large components.

[0004] 2. Pre-fabricated thin-film splicing method: This method involves first preparing a flexible frequency-selective surface film with periodic units, then attaching it to the radome mold and co-curing it with the skin. This method significantly reduces costs. However, due to the industrial production width of the frequency-selective surface film (usually no more than 500 mm), multiple films must be spliced ​​when manufacturing large-size radomes. Existing simple physical overlapping or gap-filling methods cause metal unit breakage and periodic damage at the splicing seams, creating electromagnetic defects and severely degrading the radome's stealth performance, failing to meet the requirements of next-generation high-performance stealth equipment.

[0005] Therefore, there is an urgent need to develop a new radome manufacturing technology that can overcome size limitations, significantly reduce costs, and ensure the integrity of the frequency selectivity surface period and the continuity of electrical performance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the contradiction between "high cost" and "low performance" in the existing large-size frequency-selective stealth radome manufacturing technology, and to provide a large-size frequency-selective stealth radome that is low in cost, not limited by size, and can ensure the continuity of the electrical performance of the frequency-selective surface.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A large-size frequency selective surface stealth radome includes an outer skin layer, a frequency selective surface layer, a core layer, and an inner skin layer stacked sequentially from the outside to the inside. The frequency selective surface layer is composed of multiple independent frequency selective surface films spliced ​​together, with mating gaps between adjacent films. The mating gaps are filled with conductive paste and cured to achieve electrical connection between the frequency selective surface films, thereby forming a complete and periodically continuous frequency selective surface structure.

[0008] Furthermore, the width of the mating gap is less than or equal to 0.1 mm.

[0009] Furthermore, the conductive paste is silver paste, copper paste, or conductive epoxy resin coated by a screen printing process.

[0010] Furthermore, the frequency-selective surface film uses a flexible polymer film as a substrate, on which a metal periodic unit pattern is formed.

[0011] Furthermore, the flexible polymer film is a polyimide film, a polyester film, or a polyetheretherketone film; the metal layer of the metal periodic unit pattern is a copper layer or an aluminum layer.

[0012] Furthermore, both the outer skin layer and the inner skin layer are fiber-reinforced resin-based composite material layers, each with a thickness of 0.3 mm to 5 mm.

[0013] Furthermore, the reinforcing fibers in the fiber-reinforced resin matrix composite material are glass fibers, quartz fibers, or aramid fibers, and the resin matrix is ​​epoxy resin, bismaleimide resin, or phenolic resin.

[0014] Furthermore, the core layer is made of aramid paper honeycomb or polymethacrylamide foam, with a thickness of 1 mm to 50 mm.

[0015] The technical solution of this invention adopts a "sandwich" composite structure, comprising, from the outside to the inside, an outer skin layer, a frequency selective surface layer, a core layer, and an inner skin layer. The core improvement of this invention lies in the frequency selective surface layer: it is not a single unit, but rather composed of multiple independently prefabricated frequency selective surface films with precise metal periodic unit patterns. During assembly, high-precision positioning controls the mating gaps between adjacent films to be extremely small. Most importantly, conductive paste is filled into these tiny mating gaps using methods such as screen printing. After curing, the conductive paste reliably connects the metal units on adjacent films electrically. Thus, from an electromagnetic perspective, the metal units, originally separated by physical gaps, are "bridged" back into a complete and continuous periodic structure, thereby ensuring the excellent electrical performance and stealth capabilities of the entire large-size frequency selective surface layer.

[0016] Another problem to be solved by the present invention is to provide a method for preparing a large-size frequency-selective surface stealth radome.

[0017] A method for fabricating a large-size frequency-selective surface stealth radome includes the following steps: S1. Structural Splitting and Frequency Selective Surface Film Prefabrication: The overall curved surface structure of the radome is divided into regions to obtain multiple unfolded planar diagrams; according to the shape and size of each unfolded planar diagram, frequency selective surface films with metal periodic unit patterns are prefabricated respectively. S2, Base layer forming of outer skin layer: Laying and pre-compacting the outer skin material on the mold; S3. Laying and splicing of frequency selective surface layers: On the outer skin base layer, laser projection positioning technology is used to sequentially lay each frequency selective surface film, controlling the width of the joint gap between adjacent films; then, conductive paste is applied to the joint gap and cured to achieve electrical connection between the films. S4. Outer skin layer forming and curing: The outer skin material is further laid on the spliced ​​frequency selective surface layer, and then the whole is cured to form an outer skin layer structure with the frequency selective surface layer. S5. Forming of the core layer and inner skin layer: The core layer and inner skin material are laid sequentially inside the cured outer skin layer structure and then cured. Optionally, the inner skin layer structure is pre-fabricated into a composite structure with a frequency-selective surface layer using the same method as in steps S2 to S4, and then assembled and cured with the core layer and outer skin layer structure.

[0018] An improvement to the above method, in step S3, is that the laser projection positioning technology is used to project the outline of the frequency-selective surface film and / or the pattern of the metal periodic unit onto the outer skin base layer to guide the precise placement of the film; the coating of the conductive paste is performed using a screen printing process.

[0019] The key steps of the process method of this invention include: 1. Segmented Design and Prefabrication: Based on the three-dimensional curved surface of the radome, a developable segmented design is performed to obtain the planar unfolded diagram of each segment. Based on this, the corresponding shape of the frequency-selective surface diaphragm is prefabricated. This breaks through the size limitation of a single diaphragm.

[0020] 2. High-precision installation and splicing: On the molding die, the outer skin base layer is first laid, and then precision positioning technology such as laser projection is used to accurately install the surface films of each frequency selection in the design position, and strictly control the splicing gap.

[0021] 3. Gap electrical bridging: High-precision screen printing technology is used to accurately print conductive paste on the micron-level splicing gaps, achieving seamless electrical connection of metal patterns between films.

[0022] 4. Composite material co-curing: On the spliced ​​and bridged frequency-selective surface film layer, the skin layup is completed, and together with the core layer, inner skin, etc., it is cured in an autoclave or by molding to form the final integral structure.

[0023] The beneficial effects of this invention are as follows: 1. Significantly reduced costs: By abandoning the expensive and inefficient direct laser etching process and adopting mature prefabricated frequency selective surface films and composite material molding processes, the manufacturing cost of large-size radomes can be reduced to one-tenth or even less of that of laser etching.

[0024] 2. Breaking size limitations: Through the "segmentation-splitting" strategy, radomes of any size can theoretically be manufactured, no longer limited by the size of a single processing equipment.

[0025] 3. Ensure high performance: The innovative "micro-slit conductive bridging" technology fundamentally solves the problem of unit discontinuity caused by traditional diaphragm splicing, making the spliced ​​frequency selective surface diaphragm layer equivalent to a complete whole in terms of electrical performance, thereby ensuring excellent frequency selectivity and stealth performance.

[0026] 4. Good process controllability: Laser projection positioning and screen printing are both mature and high-precision industrial technologies, which are easy to automate and control in terms of quality, ensuring product consistency and reliability. Attached Figure Description

[0027] Figure 1This is a schematic diagram (sectional view) of the overall structure of the large-size radome in an embodiment of the present invention.

[0028] Figure 2 A schematic diagram of the splicing structure for selecting the surface layer for frequency (the top image is before splicing, and the bottom image is after splicing).

[0029] Figure 3 This is a process flow diagram of frequency selective surface film splicing and conductive bridging in one embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram of frequency-selective surface film positioning and placement using laser projection.

[0031] Figure 5 This is a schematic diagram of printing conductive paste into the seams of the joints using a screen printing method.

[0032] Numbers in the diagram: 1-Outer skin layer, 2-Frequency selective surface layer, 21-Frequency selective surface film, 22-Butt joint gap, 23-Conductive paste bridge after curing, 3-Core layer, 4-Inner skin layer, 5-Mold, 6-Laser projector, 7-Screen printing template, 8-Conductive paste scraper. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0034] Example 1: Typical large-size airborne radome like Figures 1 to 5 As shown, this embodiment provides an elliptical parabolic airborne radome with dimensions of approximately 5m × 3m and its preparation method.

[0035] Step 1: Structural Decomposition and Frequency Selection, Surface Film Prefabrication 1. The radome surface was divided into 12 approximate expandable regions using 3D CAD software.

[0036] 2. Unfold the curved surface of each region into a plane to obtain 12 planar drawings of different shapes.

[0037] 3. A 0.05mm thick polyimide film is selected as the substrate, upon which an 18μm thick copper layer is deposited. Using photolithography and etching processes, a "cross-shaped" metal periodic unit pattern with a period of 5mm and a linewidth of 0.2mm is formed on each diaphragm (frequency-selective surface diaphragm 21). The maximum width of each diaphragm (frequency-selective surface diaphragm 21) is 480mm, conforming to industrial standard width, enabling the prefabrication of large-size radomes in sections.

[0038] Step 2: Forming the base layer of outer skin layer 1 1. Manufacture a composite material female mold (mold 5) that conforms to the outer surface of the radome.

[0039] 2. After applying a release agent to the surface of mold 5, lay two layers of 0.2mm thick glass fiber fabric prepreg as the base layer of the outer skin layer 1, and gently compact it.

[0040] Step 3: Frequency Selection, Surface Layer 2 Laying and Splicing 1. Using laser projector 6, project the outline and unit pattern of the first frequency-selective surface film 21 onto the corresponding position of the mold.

[0041] 2. Select the surface film 21 according to the precise frequency of the projection, and then lay the surface film 21 of the adjacent frequency. Control the width of the joint gap 22 to 0.08±0.02mm through precision tooling.

[0042] 3. Lay all 12 frequency selection surface films 21 in sequence.

[0043] 4. Cover all the joint gaps 22 with screen printing template 7, and use conductive paste scraper 8 to scrape conductive silver paste into the joint gaps 22.

[0044] 5. Bake at 80℃ for 30 minutes to cure the silver paste and form the cured conductive paste bridge 23 structure.

[0045] Step 4: Outer layer forming and curing of outer skin layer 1 Three layers of glass fiber prepreg are then laid on the spliced ​​and bridged frequency selective surface layer 2 to form a complete outer skin layer. The mold 5 is then placed in an autoclave and cured according to the standard curing process (125℃ / 0.6MPa, heat and pressure holding for 2 hours) to obtain the outer layer structure of the outer skin layer 1 with the frequency selective surface layer 2.

[0046] Step 5: Forming of the core layer 3 and the inner skin layer 4 1. A 10mm thick aramid paper honeycomb core material is laid on the inner side of the outer skin layer 1 obtained in step four.

[0047] 2. Three layers of glass fiber prepreg are laid on the inside of the honeycomb core as the inner skin layer 4.

[0048] 3. Perform autoclave co-curing again to bond the layers into a whole structure.

[0049] 4. After demolding, trim and paint to obtain the final radome.

[0050] Test results: The radome has a transmittance of >85% in the X-band (8-12GHz) and a reflectance of >15dB in the Ku-band (16-18GHz). The RCS imaging performance is uniform and there are no electromagnetic defects caused by splicing seams, which verifies the effectiveness of the conductive bridging technology.

[0051] Example 2: Low-cost simplified solution like Figures 1 to 5 As shown, this embodiment demonstrates a cost optimization solution achieved through material and process substitution.

[0052] 1. Frequency selective surface film 21: A polyester film (PET) substrate is sputtered onto which a 0.1 μm thick aluminum layer is etched to form a square ring unit.

[0053] 2. Conductive paste: Copper-based conductive epoxy resin is used.

[0054] 3. Skin layer: Hand lay-up process is used, with fiberglass cloth and room temperature curing epoxy resin.

[0055] 4. Positioning method: The positioning lines are engraved on the mold 5 and the positioning pin holes are used to align the diaphragm (frequency selection surface diaphragm 21). The width of the mating gap 22 is ≤0.2mm (although slightly wider, it is still feasible, reflecting the flexibility of the process).

[0056] 5. Slurry coating: Apply conductive slurry along the butt joint 22 using a precision dispensing machine.

[0057] Performance results: The radome has a reflectivity of >10dB in the Ku band, which meets the basic stealth requirements and is suitable for cost-sensitive scenarios, proving that the invention has strong adaptability and scalability in terms of materials and processes.

[0058] Example 3: Double-sided frequency selective surface layer structure This embodiment demonstrates an implementation where the inner skin layer 4 can also integrate the frequency-selective surface layer 2: 1. Prepare the outer skin layer 1 and inner skin layer 4 with frequency selective surface layer 2 respectively (the method is the same as steps S2-S4 in Example 1).

[0059] 2. Lay aramid paper honeycomb core material on the inner side of the outer skin layer 1.

[0060] 3. Cover the other side of the honeycomb core with the pre-fabricated inner skin layer 4 (with frequency-selective surface layer 2) and co-cur the whole structure.

[0061] This structure can achieve dual-band or wideband stealth, further expanding the scope of application of this invention.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Those skilled in the art should understand that any equivalent substitutions, combinations, or modifications to the technical features, materials, and process parameters without departing from the principles and spirit of the present invention should be included within the protection scope of the present invention.

Claims

1. A large-size frequency-selective surface stealth radome, comprising an outer skin layer, a frequency-selective surface layer, a core layer, and an inner skin layer stacked sequentially from the outside to the inside, characterized in that: The frequency selective surface layer is composed of multiple independent frequency selective surface films spliced ​​together, with mating gaps between adjacent films; the mating gaps are filled and cured with conductive paste to achieve electrical connection between the frequency selective surface films, thereby forming a complete and periodically continuous frequency selective surface structure.

2. The large-size frequency-selective surface stealth radome according to claim 1, characterized in that: The width of the joint gap is less than or equal to 0.1 mm.

3. The large-size frequency-selective surface stealth radome according to claim 1, characterized in that: The conductive paste is silver paste, copper paste, or conductive epoxy resin coated by screen printing process.

4. The large-size frequency-selective surface stealth radome according to claim 1, characterized in that: The frequency selective surface film uses a flexible polymer film as a substrate, on which a metal periodic unit pattern is formed.

5. The large-size frequency-selective surface stealth radome according to claim 4, characterized in that: The flexible polymer film is a polyimide film, a polyester film, or a polyetheretherketone film; the metal layer of the metal periodic unit pattern is a copper layer or an aluminum layer.

6. The large-size frequency-selective surface stealth radome according to claim 1, characterized in that: Both the outer skin layer and the inner skin layer are fiber-reinforced resin-based composite material layers, and their thicknesses are independently 0.3 mm to 5 mm.

7. The large-size frequency-selective surface stealth radome according to claim 6, characterized in that: The reinforcing fibers in the fiber-reinforced resin matrix composite material are glass fibers, quartz fibers, or aramid fibers, and the resin matrix is ​​epoxy resin, bismaleimide resin, or phenolic resin.

8. The large-size frequency-selective surface stealth radome according to claim 1, characterized in that: The core layer is made of aramid paper honeycomb or polymethacrylamide foam, with a thickness of 1 mm to 50 mm.

9. A method for preparing a large-size frequency-selective surface stealth radome as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Structural Splitting and Frequency Selective Surface Film Prefabrication: The overall curved surface structure of the radome is divided into regions to obtain multiple unfolded planar diagrams; according to the shape and size of each unfolded planar diagram, frequency selective surface films with metal periodic unit patterns are prefabricated respectively. S2, Base layer forming of outer skin layer: Laying and pre-compacting the outer skin material on the mold; S3. Laying and splicing of frequency selective surface layers: On the outer skin base layer, laser projection positioning technology is used to sequentially lay each frequency selective surface film, controlling the width of the joint gap between adjacent films; then, conductive paste is applied to the joint gap and cured to achieve electrical connection between the films. S4. Outer skin layer forming and curing: The outer skin material is further laid on the spliced ​​frequency selective surface layer, and then the whole is cured to form an outer skin layer structure with the frequency selective surface layer. S5. Forming of the core layer and inner skin layer: The core layer and inner skin material are laid sequentially inside the cured outer skin layer structure and then cured. Optionally, the inner skin layer structure is pre-fabricated into a composite structure with a frequency-selective surface layer using the same method as in steps S2 to S4, and then assembled and cured with the core layer and outer skin layer structure.

10. The method according to claim 9, characterized in that: In step S3, the laser projection positioning technology is used to project the outline of the frequency selective surface film and / or the pattern of the metal periodic unit onto the base layer of the outer skin layer to guide the precise placement of the film; the coating of the conductive paste is performed using a screen printing process.

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