An optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz

Abstract

This invention discloses an optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz, belonging to the fields of microwave antenna design and transparent optoelectronic technology. The antenna includes a transparent laminated composite dielectric substrate, a transparent metal mesh radiating layer disposed on its upper surface, and a coplanar waveguide feeding structure. The transparent laminated composite dielectric substrate consists of a PMMA substrate and a PET film from bottom to top. The transparent metal mesh radiating layer constitutes a ring-based iteratively stacked fractal monopole radiator, which is generated through a three-order iterative fractal process: the first order is an outer ring, the second order is eight intersecting stacked inner rings formed by scaling and rotation, and the third order is a petal-shaped continuous radiating surface formed by filling the overlapping region and connecting the central hollow region. This invention achieves continuous broadband coverage of the core frequency bands of Bluetooth ISM and 5G Sub-6GHz within a compact size, possessing both excellent optical transparency and stable radiation performance.

Description

Technical Field

[0001] This invention relates to the fields of microwave antenna design and transparent optoelectronic technology, and in particular to an optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz. Background Technology

[0002] With the rapid development of wireless communication, smart wearable devices, and new building and transportation electronics, "functional stealth integration" and "high form transparency" have become the core evolutionary directions of terminal design. Traditional metal antennas and conventional conductive thin-film devices are gradually revealing their technical limitations in adapting to new carriers.

[0003] In the field of building smart IoT, curtain walls and windows need to integrate communication modules to enable data interaction and remote control of indoor and outdoor environments. In the field of automotive electronics and smart cockpits, windshields, side windows, and panoramic sunroofs need to embed radio frequency (RF) front-ends to support V2X vehicle networking, high-precision positioning, and short-range communication. In the field of next-generation consumer electronics, transparent OLED display panels, AR / VR optical lenses, and smart wearable devices also need to be seamlessly integrated with wireless transmission units. These application scenarios all place stringent requirements on the optical transmittance of antennas, ensuring that the embedded RF functions do not obstruct the user's view, weaken the carrier's light-gathering performance, or damage the visual integrity of the displayed image.

[0004] Current wireless communication protocols have evolved from single discrete frequency bands to multi-band collaboration and continuous wideband: short-range low-power IoT, medium-to-high-speed local transmission, and 5G mobile communication require spectrum sharing and seamless switching within a compact space. Traditional narrowband patch antennas or dipole antennas often require multiple antennas arranged in parallel or complex switching networks to cover the above multi-band applications. This not only drastically reduces the internal space of the equipment and increases the system integration cost, but also easily causes signal crosstalk and pattern distortion due to strong coupling between antennas.

[0005] Despite some progress in existing transparent antenna technology, significant performance bottlenecks and structural defects remain, making it difficult to meet the synergistic requirements of "high optical transmittance," "continuous wideband coverage," and "stable radiation efficiency." Specifically: First, continuous transparent conductive films based on indium tin oxide (ITO) or gallium-doped zinc oxide (ZNO) typically have a sheet resistance higher than 10 Ω / sq, resulting in low radiation efficiency for antennas constructed from them. Measured peak gains are often below 0 dBi, and the operating bandwidth is severely limited, failing to effectively cover the cross-band range of 2.4 GHz to 5.6 GHz. Second, while transparent antennas based on metal mesh offer improved conductivity, their designs often follow traditional narrowband radiating structures (such as single-loop or simple patch structures), resulting in narrow impedance bandwidth and a relative bandwidth generally below 30%, making it difficult to simultaneously accommodate discontinuous spectrum resources such as Bluetooth / ISM and 5G Sub-6 GHz. Third, a few transparent antennas that can achieve broadband operation either rely on auxiliary means such as multi-layer parasitic structures and frequency selective surfaces, resulting in increased profile and large size; or they sacrifice low-frequency coverage capabilities, making it impossible to achieve a balance between continuous broadband, high transparency and good radiation efficiency within an ultra-compact size. Summary of the Invention

[0006] The purpose of this invention is to provide an optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz, resolving the contradiction between "narrow-band transparent antennas" and "opaque broadband antennas" in existing technologies. Through innovative laminated transparent substrate composite, coplanar waveguide impedance modulation, and circular iterative fractal topology optimization, the surface current distribution path is reconstructed, achieving a deep integration of high light transmittance, wideband impedance matching, and robust far-field radiation characteristics. Ultimately, this provides a radio frequency integrated solution with both engineering practicality and industrial value for smart building glass, automotive transparent displays, and next-generation wireless terminals.

[0007] To achieve the above objectives, the present invention provides an optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz, comprising a transparent laminated composite dielectric substrate, wherein the transparent laminated composite dielectric substrate comprises, from bottom to top, a bottom transparent PMMA substrate, a middle transparent PET film, and a top transparent metal mesh radiating layer; the antenna is fed by a coplanar waveguide; the top transparent metal mesh radiating layer includes a ring-based iterative fractal radiator body, the ring-based iterative fractal radiator body is a centrally symmetrical flower-shaped structure, and its outermost side includes a circular ring boundary.

[0008] Preferably, the main body of the ring-based iterative fractal radiator starts from a first-order single ring, and generates a second-order cross-stacked ring structure through scaling and multi-angle rotation iteration. Then, a solid conductive area is formed by selectively filling the overlapping and intersecting areas between all adjacent cross-stacked rings, while the hollow area at the center of the second-order pattern is integrated and expanded into a continuous radiating surface.

[0009] Preferably, the ring-based iterative fractal radiator body is generated through the following third-order iterative fractal process: The first-order structure is an outer ring with an outer radius R1 and an inner radius R2; The second-order structure is formed by scaling the outer ring by a scaling factor α=0.5 to form an inner ring. The outer radius of the inner ring is R3, the inner radius is R4, and R1=2×R3 is satisfied. The inner ring is translated downward so that the lower edge of the inner ring is tangent to the lower edge of the outer ring. Then, it is rotated around the center of the outer ring by 0°, 45°, 90°, 135°, 180°, 225°, 270° and 315° in sequence to form eight centrally symmetrically stacked inner rings. The third-order structure is based on the second-order structure. The overlapping areas between all adjacent and stacked inner rings are solidified and filled. The central hollow area enclosed by the eight inner rings is connected and expanded into a continuous radiating surface, forming a continuous monopole radiator with a petal-shaped outline.

[0010] Preferably, the thickness of the bottom transparent PMMA substrate is 0.5 mm, the relative permittivity is 3.7, and the loss tangent is 0.01; the thickness of the middle transparent PET film is 0.1 mm, the relative permittivity is 3.2, and the loss tangent is 0.005; the overall length of the antenna is 35 mm, the width is 25 mm, and the thickness is 0.6 mm.

[0011] Preferably, the sheet resistance of the top transparent metal mesh radiation layer is 0.5Ω / sq; the metal mesh pattern is formed on the surface of the intermediate transparent PET film and laminated onto the bottom transparent PMMA substrate.

[0012] Preferably, the coplanar waveguide feeding structure includes a central feeding strip and coplanar grounds symmetrically arranged on both sides of the central feeding strip; the central feeding strip is electrically connected to the main body of the ring-based iterative fractal radiator, and a coupling gap is formed between the coplanar grounds and the central feeding strip.

[0013] Preferably, the edges of the coplanar surfaces are rounded, and the radius of the rounded corner is a fifth radius R5.

[0014] Therefore, the present invention employs the aforementioned optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz, which has the following beneficial effects: 1) It pioneered a three-order iterative fractal topology of "circular scaling-cross stacking-overlapping area filling", which effectively extended the low-frequency current path on the surface of the radiator and introduced multiple high-frequency resonant modes at the same time. This enabled a single, ultra-compact antenna structure to achieve a measured continuous -10dB impedance bandwidth of 2.4-5.6GHz, while covering Bluetooth ISM (2.4-2.484GHz) and my country's mainstream 5G Sub-6GHz frequency band, solving the problem of narrow bandwidth and inability to continuously cover across frequency bands of existing transparent antennas; 2) By using a low sheet resistance metal mesh and an optimized laminated PMMA-PET transparent substrate, combined with CPW feeding and fractal structure for synergistic impedance matching, stable radiation performance is achieved while maintaining high visible light transmittance. 3) Broadbanding is achieved through the space-filling characteristics and topology optimization of fractal geometry itself, without the need to introduce additional parasitic layers, frequency-selective surfaces, multi-layer stacking, or multi-port decoupling networks. Its overall structure is a simple sandwich configuration of "one layer of metal mesh + two layers of transparent dielectric film", which has the advantages of extremely low profile, manufacturing process compatibility with standard PCB / laser etching process, and easy mass production. It provides a highly practical and low-cost ideal RF solution for application scenarios with stringent requirements for aesthetic integration and RF performance, such as smart windows, automotive laminated glass, and transparent OLED display terminals.

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a three-dimensional structural diagram of an optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz provided in an embodiment of the present invention, which includes a layered cross-sectional structure; Figure 2 This is a schematic diagram showing the planar dimensions of an optically transparent fractal monopole antenna provided in an embodiment of the present invention, wherein... Figure 2 (a) is a partially enlarged schematic diagram of the fractal radiator; Figure 3 This is a schematic diagram of the third-order structural evolution of the ring-based iterative fractal radiator provided in an embodiment of the present invention; wherein, Figure 3 (a) is a first-order initial structure. Figure 3 (b) is a second-order iterative structure. Figure 3 (c) represents the third-order final iterative structure; Figure 4 This is a schematic diagram showing the comparison between simulation and actual measurement results of the return loss (S11) of the optically transparent fractal monopole antenna provided in the embodiment of the present invention; Figure 5This is a schematic diagram of the voltage standing wave ratio (VSWR) of the optically transparent fractal monopole antenna provided in the embodiment of the present invention within the operating frequency band; Figure 6 This is a schematic diagram of the peak gain of the optically transparent fractal monopole antenna provided in the embodiment of the present invention within the operating frequency band; Figure 7 This is a schematic diagram showing the radiation efficiency of the optically transparent fractal monopole antenna provided in the embodiment of the present invention within the operating frequency band; Figure 8 This is a two-dimensional radiation direction diagram of the optically transparent fractal monopole antenna provided in an embodiment of the present invention at a typical frequency point in the target operating frequency band; wherein Figure 8 (a) is the 2.9 GHz frequency point. Figure 8 (b) refers to the 4.2 GHz frequency point; Figure 9 This is a schematic diagram of the transmittance test results of the optically transparent fractal monopole antenna provided in the embodiment of the present invention in the visible light band; Figure 10 These are photographs of the optically transparent fractal monopole antenna and magnified microscopic diagrams of the transparent metal mesh structure provided in the embodiments of the present invention.

[0017] Figure Labels 1. Ring-based iterative fractal radiator body; 2. Central feed line; 3. Coplanar ground; 4. Intermediate layer transparent PET film; 5. Bottom layer transparent PMMA substrate; 6. Transparent laminated composite dielectric substrate. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0020] Example 1 like Figure 1As shown, this embodiment provides an optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz bands. It has an overall rectangular sheet structure with planar dimensions of 35mm × 25mm and an overall thickness of 0.6mm. The antenna core includes a transparent laminated composite dielectric substrate 6, which, from bottom to top, comprises a bottom transparent PMMA substrate 5, an intermediate transparent PET film 4, and a top transparent metal mesh radiating layer disposed on the upper surface of the intermediate transparent PET film 4. The antenna uses a coplanar waveguide (CPW) feeding method.

[0021] The bottom transparent PMMA substrate 5 has a thickness of 0.5 mm, a relative permittivity of 3.7, and a loss tangent of 0.01. The intermediate transparent PET film 4 has a thickness of 0.1 mm, a relative permittivity of 3.2, and a loss tangent of 0.005. A transparent metal mesh radiating structure is printed on the upper surface of the intermediate transparent PET film 4 and is tightly bonded to the bottom transparent PMMA substrate 5 through a lamination process. The sheet resistance of the transparent metal mesh radiating layer is 0.5 Ω / sq, exhibiting both excellent conductivity and optical transparency.

[0022] like Figure 2 , Figure 3 As shown, the top transparent metal mesh radiating layer contains a ring-based iterative fractal radiator body 1. This ring-based iterative fractal radiator body 1 is a centrally symmetric flower-like structure, and its outermost edge includes a circular ring boundary. The ring-based iterative fractal radiator body 1 starts from a first-order single ring, and through scaling and multi-angle rotation iterations, generates a second-order cross-stacked ring structure. Then, by selectively filling the overlapping and intersecting areas between all adjacent cross-stacked rings, a solid conductive area is formed. At the same time, the hollow area at the center of the second-order pattern is integrated and expanded into a continuous radiating surface. The third-order iterative fractal generation process of the ring-based iterative fractal radiator body 1 is as follows: Figure 3 As shown: First-order initial structure ( Figure 3 (a)): Given an outer ring with an outer radius R1=11mm and an inner radius R2=10mm, determine the core dimension boundary of the radiator; Second-order iterative structure ( Figure 3 (b) : The outer ring is scaled by a scaling factor α=0.5 to form an inner ring. The outer radius of the inner ring is R3=5.5mm and the inner radius is R4=5mm, and R1=2×R3 and R2=2×R4 are satisfied. The inner ring is translated downward by a distance R1 / 2=5.5mm so that the lower edge of the inner ring is tangent to the lower edge of the outer ring. Then, the inner ring is rotated around the center of the outer ring by 0°, 45°, 90°, 135°, 180°, 225°, 270° and 315° in sequence to form eight centrally symmetrically stacked inner rings, which constitute a second-order hollow iterative structure.

[0023] Third-order final structure ( Figure 3 (c)): Based on the second-order structure, the overlapping areas between all adjacent stacked inner rings are solidified and filled, and the central hollow area enclosed by the eight inner rings is connected and expanded into a continuous radiating surface, ultimately forming a continuous monopole radiator with a petal-shaped outline.

[0024] The coplanar waveguide feeding structure includes a central feed strip 2 and coplanar ground planes 3 symmetrically arranged on both sides of the central feed strip 2. The central feed strip 2 is electrically connected to the main body 1 of the ring-based iterative fractal radiator. A coupling gap is formed between the coplanar ground planes 3 and the central feed strip 2, and the width of the coupling gap is G = 0.35 mm. In this embodiment, as shown... Figure 2 As shown, the width of the center feed line 2 is W1=2.9mm and the length is L1=12mm; the length of the coplanar ground 3 is L2=11.5mm, and its edge is set as a rounded corner with a radius of R5=7.5mm.

[0025] The above-mentioned dimensional parameters were determined through electromagnetic simulation optimization, which enables the antenna to achieve good impedance matching with a return loss of less than -10dB in the Bluetooth ISM band and the 5G Sub-6GHz band.

[0026] The optically transparent fractal monopole antenna provided in this embodiment was simulated and debugged using electromagnetic simulation software, and then verified by actual testing. The test results are as follows: (1) Return loss and voltage standing wave ratio: such as Figure 4 As shown, the antenna meets the impedance matching requirement of S11≤-10dB in the 2.4-5.6GHz frequency band, fully covering the 2.4GHz Bluetooth ISM band and the 5G Sub-6GHz core operating frequency band. Voltage Standing Wave Ratio (VSWR) test results are as follows... Figure 5 As shown, the antenna's VSWR is consistently less than 2 across the entire operating frequency band, fully meeting the impedance matching requirements for antenna engineering applications; this is highly consistent with the return loss test results, verifying that the antenna possesses stable and reliable impedance matching performance.

[0027] (2) Peak gain and radiation efficiency: The peak gain test results are as follows Figure 6 As shown, the peak gain of the antenna in the 2.4-5.6 GHz frequency band is increased from a negative value at 2.4 GHz to about 2.6 dBi at 5.6 GHz. This invention utilizes the synergistic design of metal mesh and fractal structure to significantly enhance the surface current radiation capability, achieving a balance between high transparency and high gain performance.

[0028] Radiation efficiency test results are as follows Figure 7As shown, the antenna's radiation efficiency increases rapidly with frequency across the entire operating frequency band of 2.4-5.6 GHz, and remains stable at over 70% within the core operating frequency band of 3-5.6 GHz, with a peak efficiency reaching 80%. These results demonstrate that the present invention effectively reduces conductor loss and radiation loss through the synergistic design of a ring-based iterative fractal structure and a low-sheet-resistance metal mesh.

[0029] (3) Radiation pattern: Typical frequencies of 2.9 GHz and 4.2 GHz were selected, and the two-dimensional radiation patterns of the antenna in the E-plane and H-plane were obtained as follows. Figure 8 As shown, where Figure 8 (a) is the 2.9 GHz frequency point. Figure 8 (b) is at the 4.2 GHz frequency point. The test results show that the antenna exhibits near-omnidirectional radiation characteristics in the H-plane at both typical frequency points, and a typical figure-eight radiation characteristic in the E-plane, which conforms to the radiation law of a monopole antenna. It can achieve stable omnidirectional signal transmission and reception within the target operating frequency band.

[0030] (4) Optical Transparency Test: The visible light transmittance of the antenna in this embodiment was measured using a Linshang LS101 transmittance meter. The results are as follows: Figure 9 As shown, the antenna has an average transmittance of 80.3% in the visible light band (380nm~780nm), exhibiting excellent optical transparency.

[0031] The physical sample of the optically transparent fractal monopole antenna, fabricated according to the above structural design and manufacturing process, is shown below. Figure 10 As shown. The metal mesh structure of the antenna radiator was magnified and observed using a microscope, resulting in the following microscopic image. Figure 10 As shown in the inset diagram, the metal mesh structure is uniform and complete, and its parameters are perfectly matched with the low sheet resistance transparent conductive structure designed above, verifying the feasibility and engineering applicability of the design scheme of this invention.

[0032] Therefore, the present invention adopts the above-mentioned optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz. Through the synergistic design of ring-based iterative fractal topology and laminated transparent substrate, continuous broadband coverage of the core frequency bands of Bluetooth ISM and 5G Sub-6GHz is achieved in a compact size. The antenna has both excellent optical transparency and stable radiation performance, requires no additional parasitic elements, has a simple overall structure, and can be seamlessly integrated into various transparent carriers such as smart displays and automotive glass.

[0033] 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An optically transparent fractal monopole antenna for Bluetooth ISM and 5G Sub-6GHz, characterized in that, The antenna includes a transparent laminated composite dielectric substrate (6), which, from bottom to top, comprises a bottom transparent PMMA substrate (5), a middle transparent PET film (4), and a top transparent metal mesh radiating layer; the antenna is fed by a coplanar waveguide; the top transparent metal mesh radiating layer includes a ring-based iterative fractal radiator body (1), which is a centrally symmetrical flower-shaped structure, and its outermost side includes a circular ring boundary.

2. The optically transparent fractal monopole antenna according to claim 1, characterized in that, The main body (1) of the ring-based iterative fractal radiator starts from a first-order single ring, and generates a second-order cross-stacked ring structure through scaling and multi-angle rotation iteration. Then, a solid conductive area is formed by selectively filling the overlapping and intersecting areas between all adjacent cross-stacked rings. At the same time, the hollow area at the center of the second-order pattern is integrated and expanded into a continuous radiating surface.

3. The optically transparent fractal monopole antenna according to claim 2, characterized in that, The ring-based iterative fractal radiator body (1) is generated through the following third-order iterative fractal process: The first-order structure is an outer ring with an outer radius R1 and an inner radius R2; The second-order structure is formed by scaling the outer ring by a scaling factor α=0.5 to form an inner ring. The outer radius of the inner ring is R3, the inner radius is R4, and R1=2×R3 is satisfied. The inner ring is translated downward so that the lower edge of the inner ring is tangent to the lower edge of the outer ring. Then, it is rotated around the center of the outer ring by 0°, 45°, 90°, 135°, 180°, 225°, 270° and 315° in sequence to form eight centrally symmetrically stacked inner rings. The third-order structure is based on the second-order structure. The overlapping areas between all adjacent and stacked inner rings are solidified and filled. The central hollow area enclosed by the eight inner rings is connected and expanded into a continuous radiating surface, forming a continuous monopole radiator with a petal-shaped outline.

4. The optically transparent fractal monopole antenna according to claim 1, characterized in that, The bottom transparent PMMA substrate (5) has a thickness of 0.5 mm, a relative permittivity of 3.7, and a loss tangent of 0.01; the middle transparent PET film (4) has a thickness of 0.1 mm, a relative permittivity of 3.2, and a loss tangent of 0.005; the antenna has an overall length of 35 mm, a width of 25 mm, and a thickness of 0.6 mm.

5. The optically transparent fractal monopole antenna according to claim 1, characterized in that, The sheet resistance of the top transparent metal mesh radiation layer is 0.5Ω / sq; the metal mesh pattern is formed on the surface of the intermediate transparent PET film (4) and laminated onto the bottom transparent PMMA substrate (5).

6. The optically transparent fractal monopole antenna according to claim 1, characterized in that, The coplanar waveguide feeding structure includes a central feeding strip (2) and coplanar grounds (3) symmetrically arranged on both sides of the central feeding strip (2); the central feeding strip (2) is electrically connected to the main body (1) of the ring-based iterative fractal radiator, and a coupling gap is formed between the coplanar grounds (3) and the central feeding strip (2).

7. The optically transparent fractal monopole antenna according to claim 6, characterized in that, The edges of the coplanar surface (3) are rounded, and the radius of the rounded corner is the fifth radius R5.

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