Broadband circularly polarized conformal antenna based on metasurface structure

Abstract

The broadband circular polarization conformal antenna adopts the combination of three layers of dielectric substrates and an air layer, and comprises an upper layer dielectric substrate, a middle layer dielectric substrate, a lower layer dielectric substrate, a central 2 * 2 corner cut square patch, a peripheral 16 corner cut square patch, a square feed patch with a rectangular groove formed along a diagonal line, a metal floor and a feed microstrip line, a metasurface structure is printed on the upper surface of the upper-layer dielectric substrate 1 and comprises a 2 * 2 corner cut square patch array 4 located in the center and 16 corner cut square patches 5 surrounding the center array; a square feed patch and a feed microstrip line are printed on the lower surface of the middle-layer dielectric substrate 2, the square feed patch is located at the dead center of the lower surface of the middle-layer dielectric substrate, and a rectangular groove is formed in the dead center of the square feed patch in the diagonal direction; and a complete metal floor is arranged on the lower surface of the lower dielectric substrate. The antenna has the characteristic of low profile, and the antenna can be conformal to a cylindrical surface carrier platform.

Description

Technical Field

[0001] This invention pertains to wireless communication technology, specifically relating to a broadband circularly polarized conformal antenna based on a metasurface structure. Background Technology

[0002] Conformal antennas fit perfectly against the carrier surface, without compromising the carrier's shape or aerodynamic characteristics, and are widely used in modern mobile communication platforms. Compared to linearly polarized antennas, circularly polarized antennas have many advantages, such as suppressing multipath distortion, being insensitive to changes in device orientation, and being unaffected by adverse weather conditions. To improve the flexibility and applicability of conformal antennas in wireless communication systems, the antenna is required to have high gain and good circular polarization performance over a sufficiently wide frequency band. Currently, antennas meeting these requirements are rarely reported. Research on conformal antennas can be broadly divided into two categories: one uses the human body as a carrier and flexible dielectric as a substrate, with applications in wearable devices; the other uses platforms such as aircraft and missiles as carriers, with applications primarily in the military field. Commonly used circularly polarized antenna types in wireless communication systems include metasurface antennas, microstrip antennas, and helical antennas.

[0003] Tian L et al. (T. Liu et al., "A broadband circularly polarized antenna based on transparent conformal metasurface", IEEE Antennas Wireless Propag. Lett., vol. 22, no. 12, pp. 3197-3201, Dec. 2023.) designed a circularly polarized antenna based on a transparent conformal polarization-conversion metasurface. The designed metasurface element is an ellipse with a rectangular slot rotated 45°. Three metasurface elements are arranged in a group and rotated 90° around the feed antenna. This metasurface is printed using a transparent and conformal PET film and also has low profile characteristics. Using this method, polarization-conversion of the antenna is achieved without destroying the original antenna structure, thereby extending the circular polarization bandwidth of the antenna. However, the antenna has the disadvantage of low gain of 5 dBi.

[0004] Zhengkun Y et al. (Zhengkun Y, Na K, Shixing Y, et al. A coplanar waveguide-fed broadband circularly polarized microstrip antenna for conformal applications[J]. International Journal of RF and Microwave Computer-Aided Engineering, 2021, 31(3).) proposed a broadband circularly polarized conformal microstrip antenna based on coplanar waveguide feeding. A pentagonal monopole and an asymmetric rectangular grounding ring constitute the CPW feeding structure. A pair of perturbation stubs are embedded on the grounding ring. In addition to generating a horizontal resonant current, the horizontal stub on the left side of the grounding ring also cooperates with the monopole to excite two orthogonal resonant modes. At the same time, a vertical branch is created at the top of the ring, which further improves the CP performance. Furthermore, the introduction of an asymmetric grounding plane greatly changes the surface current of the antenna, enabling the antenna to achieve broadband performance. This antenna has an axial ratio bandwidth of 67.7% (6.5GHz, 4.3-8.7GHz) and can be used for WLAN (5, 5.2, and 5.8GHz), WiMAX (5.5GHz), and other C-band (4GHz-8GHz) wireless communications. However, a drawback of this antenna is its incomplete ground plane, which results in poor resistance to metallic environments and limited applicability to a wide variety of carrier platforms.

[0005] N. Supreeyatitikul et al. (N. Supreeyatitikul, A. Boonpoonga, and C. Phongcharoenpanich, “Z-shaped metasurface-based wideband circularly polarized Fabry-Perot antenna for C-band satellite technology,” IEEE Access, vol. 10, pp. 59428–59441, 2022.) proposed a broadband circularly polarized Fabry-Perot antenna based on a low-profile Z-shaped metasurface for C-band satellite communication. The proposed low-cost, low-complexity circularly polarized Fabry-Perot antenna is implemented using three substrate layers: upper, middle, and lower. The upper substrate contains 9 × 9 periodically arranged Z-shaped metasurface units, serving as a partial reflector and circular polarization converter. The middle substrate has a square patch with a truncated corner at its center. The lower substrate consists of a ground plane with an H-shaped slot in the center and a microstrip feed line. The lower and middle substrates function as the source antenna. Periodic Z-shaped metasurface elements are used to improve the operating bandwidth and gain of the source antenna and convert linear polarization into CP waves. However, the drawback of this antenna is that the profile is too high (0.51λ0, where λ0 is the free space wavelength of the antenna at the operating frequency).

[0006] Other broadband circularly polarized antennas that have been publicly disclosed so far have problems such as low gain or poor resistance to metallic environments. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a broadband circularly polarized conformal antenna for cylindrical carriers with low profile, high gain and good resistance to metallic environments.

[0008] The technical solution adopted by the present invention to solve the above-mentioned technical problems is a circularly polarized conformal antenna for a cylindrical carrier, comprising: an upper dielectric substrate 1, a middle dielectric substrate 2, a lower dielectric substrate 3, a 2×2 chamfered square patch 4 at the center, 16 chamfered square patches around the perimeter 5, a square feed patch with a rectangular slot along the diagonal 6, a metal ground plane 7, and a feed microstrip line 8.

[0009] It includes an upper dielectric substrate 1, a middle dielectric substrate 2 and a lower dielectric substrate 3 stacked from top to bottom, with air layers formed between the upper dielectric substrate 1 and the middle dielectric substrate 2, and between the middle dielectric substrate 2 and the lower dielectric substrate 3.

[0010] The upper surface of the upper dielectric substrate 1 is printed with a metasurface structure, which includes a 2×2 chamfered square patch array 4 located at the center and 16 chamfered square patches 5 surrounding the central array.

[0011] The lower surface of the middle layer dielectric substrate 2 is printed with a square power feed patch 6 and a power feed microstrip line 8. The square power feed patch 6 is located at the center of the lower surface of the middle layer dielectric substrate 2, and a rectangular groove is formed at its center along the diagonal direction.

[0012] The lower surface of the lower dielectric substrate 3 is provided with a complete metal floor 7.

[0013] The mechanism of this invention is as follows:

[0014] In this invention, the feed antenna is a square feed patch 6 located on the lower surface of the intermediate dielectric substrate 2. By cutting rectangular slots along the diagonal direction on the square feed patch 6, asymmetry is introduced to achieve circular polarization radiation. To further extend the axial ratio bandwidth of the circular polarization antenna, a metasurface structure is arranged on top of it.

[0015] This metasurface structure, located on the upper surface of the upper dielectric substrate 1, consists of two non-uniformly truncated square patches arranged in two different ways. The truncated corners introduce orthogonal currents with a 90-degree phase difference into the patches, achieving circularly polarized radiation. Simultaneously, due to the different arrangements of the central and surrounding patches, combining two differently arranged truncated square patches introduces two circularly polarized modes with different resonant frequencies. Therefore, two minimum axial ratio points are generated within the operating frequency band, extending the axial ratio bandwidth by 3dB.

[0016] In this invention, the antenna is bent along the direction of the feed microstrip line and the antenna center. It can be expected that the bending will not have a significant impact on antenna performance. Furthermore, the antenna uses microstrip line feeding, and the ends of the feed microstrip line 8 are widened to achieve better impedance matching.

[0017] Specifically, the thickness of the upper dielectric substrate 1, the middle dielectric substrate 2, and the lower dielectric substrate 3 is as thin as 0.254mm, which has a certain bending ability and is suitable for cylindrical carrier platforms; at the same time, the floor adopts an all-metal floor 7, which can be used in a metal environment and will not be affected by metal interference.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0019] 1. This invention provides a broadband high-gain circularly polarized conformal antenna for cylindrical carriers. The antenna is composed of a PCB board and metal conductors, and has a simple structure that is easy to process and assemble.

[0020] 2. This invention uses two different arrangements of chamfered square patches to excite two circularly polarized resonant modes, thereby expanding the bandwidth and improving the gain.

[0021] 3. Effectively expands bandwidth and improves antenna gain, with a 3dB axial ratio bandwidth of up to 23.3% and a peak gain of up to 9.84dBic.

[0022] 4. This invention uses a complete metal floor plane, which has good resistance to metal environment.

[0023] 5. This invention adopts a combination of a three-layer dielectric substrate and an air layer, which has a compact structure and simple design. It can effectively reduce the profile height of the antenna, and the final profile is 0.089λ0 (λ0 is the free space wavelength of the antenna at the center frequency). It has the characteristics of low profile. At the same time, the dielectric substrate adopts an ultra-thin thickness of 0.254mm, which is conducive to the conformal mounting of the antenna onto the cylindrical carrier platform. Attached Figure Description

[0024] Figure 1 This is a top view of the antenna structure;

[0025] Figure 2 Diagram of the antenna feeding structure;

[0026] Figure 3 This is a side view of the antenna structure;

[0027] Figure 4 The simulation results of antenna return loss are shown in the figure.

[0028] Figure 5 The simulation results for the antenna axial ratio are shown in the figure.

[0029] Figure 6 The image shows the simulation results of the antenna gain. Detailed Implementation

[0030] To better understand the structure and principle of this invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] A broadband high-gain circularly polarized conformal antenna for cylindrical carriers is shown in the schematic diagram below. Figures 1-2 As shown, it specifically includes: an upper dielectric substrate 1, a middle dielectric substrate 2, a lower dielectric substrate 3, a 2×2 square patch with chamfered corners in the center 4, 16 square patches with chamfered corners around the perimeter 5, a square feed patch with rectangular slots along the diagonal 6, a metal ground plane 7, and a feed microstrip line 8.

[0032] Figure 1 This is a top view of the antenna structure of the present invention. Figure 2 This is a side view of the antenna structure of the present invention. Figure 1It can be seen that the metasurface structure can be considered as a combination of the outer 16 units 5 of the central 2×2 chamfered square patch array 4 and the 5×5 chamfered square patch array, distributed on the upper surface of the upper dielectric substrate 1. Each patch unit in the central 2×2 chamfered square patch array 4 is chamfered along the diagonal direction, and the spacing between units is the same. The outer 16 units 5 can be considered as the outer 16 units of the 5×5 chamfered square patch array, where the spacing between units is the same and each patch unit is chamfered along the diagonal direction. Figure 2 As can be seen, the square feed patch 6 and the feed microstrip line 8 are distributed on the lower surface of the intermediate dielectric substrate 2. The square feed patch 6 is located in the exact center of the intermediate dielectric substrate 2, and a rectangular slot is formed along its diagonal direction, with the slot located at the exact center of the square feed patch 6. The feed microstrip line 8 widens at its ends to achieve better impedance matching. From Figure 3 As can be seen, the metal ground plane 7 is disposed on the lower surface of the underlying dielectric substrate 3, adopting a full-ground structure, which can improve the antenna's resistance to metallic environments. This invention uses a microstrip line 8 for feeding. For antennas with different curvatures, the antenna bending direction follows... Figure 1 The line containing the x-axis is shown.

[0033] Example

[0034] In this embodiment, the total size of the circularly polarized conformal antenna is 73mm × 73mm, and the overall height is 4.822mm. The air layer height between the upper and middle dielectric substrates is h2 = 1.56mm, and the air layer height between the middle and lower dielectric substrates is h1 = 1.5mm. The upper, middle, and lower dielectric substrates are all the same size, 73mm × 73mm, and the thickness is h3 = 0.254mm. An F4BM with a dielectric constant of 2.2 and a loss tangent of 0.001 can be selected. The central 2×2 chamfered square patch array 4 is composed of four identical metasurface units. Each unit is a square patch with a side length of W1 = 16.22 mm, and two isosceles right triangles with a right angle side length of d1 = 4.8 mm are cut off along opposite directions. Adjacent units are evenly distributed at the center of the upper dielectric substrate 1 with the same interval q1 = 1.17 mm. The outer 16 cells are formed by removing the inner patches from the 5×5 chamfered square patch array evenly distributed on the dielectric substrate 1, taking only the outer 16 units. Each unit of the 5×5 chamfered square patch array is a square patch with a side length of W2 = 13 mm, and two isosceles right triangles with a right angle side length of d2 = 3.5 mm are cut off along opposite directions. The interval between adjacent units is the same, q2 = 1 mm. The square feed patch 6 is located at the center of the lower surface of the middle dielectric substrate 2, and the rectangular slot with a length of s along the diagonal direction is s. l =11.73mm, width is s w=2.5mm. The feed microstrip line 8 is also located on the lower surface of the middle dielectric substrate 2, with a length of l = 26.94mm. The microstrip line with a length of l1 = 4.17mm at its end has a width of w1 = 8.33mm, and the remaining length has a width of w2 = 4.67mm. The ground plane is a solid metal ground plane. In this example, the antenna operates at a frequency of 5.5GHz.

[0035] In addition, in order to bend the antenna to a fixed curvature, this invention proposes to use 3D printing technology to print resin hollow brackets with different curvatures, so that the antenna can be bent to different radii without affecting the antenna performance, thereby meeting the requirements of the invention.

[0036] The dimensions mentioned above are specific dimensions that have been calculated and optimized. If the dimensions change, the performance of the embodiment will deteriorate.

[0037] Simulation tests were conducted on it, and the results showed that: Figure 4 The figure shows the simulation results of the return loss of the antenna structure in this embodiment of the invention. As can be seen from the figure, the impedance bandwidth of the antenna with a return loss of less than -10dB in this embodiment of the invention is 4.83GHz~6.21GHz, reaching 25.1%. By bending the antenna of this invention to different radii, it can be found that the bending of the antenna has little effect on the impedance bandwidth. The impedance bandwidth in the bent state is about 25.6%, and different bending radii have almost no effect on the impedance bandwidth. Figure 5 The figure shows the simulation results of the antenna axial ratio. As can be seen from the figure, the axial ratio bandwidth of the antenna in this embodiment of the invention, which is less than 3dB, is 4.89GHz~6.17GHz, reaching 23.3%. Bending the antenna of this invention to different radii reveals that bending the antenna causes a slight decrease in the axial ratio bandwidth, with the axial ratio bandwidth in the bent state being approximately 20.2%. Figure 6 The figure shows the simulation results of the antenna gain. As can be seen from the figure, the peak gain of the antenna in this embodiment of the invention can reach 9.84 dBic, and the in-band gain varies from 6.9 dBic to 9.84 dBic. Bending will affect the peak gain of the antenna, with a variation range within 1 dBic.

[0038] Therefore, it can be seen that the antenna of the present invention can effectively reduce the antenna profile height, and the antenna achieves broadband circular polarization, low profile, and high gain performance.

Claims

1. A broadband circularly polarized conformal antenna based on a metasurface structure, characterized in that, It includes an upper dielectric substrate (1), a middle dielectric substrate (2) and a lower dielectric substrate (3) stacked from top to bottom, with air layers formed between the upper dielectric substrate (1) and the middle dielectric substrate (2) and between the middle dielectric substrate (2) and the lower dielectric substrate (3); The upper surface of the upper dielectric substrate (1) is printed with a metasurface structure, which includes a 2×2 chamfered square patch array (4) located in the center and 16 chamfered square patches (5) surrounding the central array. The lower surface of the middle layer dielectric substrate (2) is printed with a square power feed patch (6) and a power feed microstrip line (8). The square power feed patch (6) is located at the center of the lower surface of the middle layer dielectric substrate (2), and a rectangular groove is formed at its center along the diagonal direction. The lower surface of the lower dielectric substrate (3) is provided with a complete metal floor (7).

2. The broadband circularly polarized conformal antenna according to claim 1, characterized in that, Each patch unit in the central 2×2 chamfered square patch array (4) is a square patch with a side length of W1, and two right-angled triangles with a right angle side length of d1 are cut off along opposite sides; each patch unit in the 16 chamfered square patches around the perimeter (5) is a square patch with a side length of W2, and two right-angled triangles with a right angle side length of d2 are cut off along opposite sides; W1>W2.

3. The broadband circularly polarized conformal antenna according to claim 2, characterized in that, In the central 2×2 chamfered square patch array (4), the interval between each adjacent patch unit is q1; in the 16 chamfered square patches (5) around the perimeter, the interval between each adjacent patch unit is q2. W1=16.22mm, d1=4.8mm, W2=13mm, d2=3.5mm.

4. The broadband circularly polarized conformal antenna according to claim 1, characterized in that, The rectangular slot on the square power supply patch (6) has a length of s1 = 11.73 mm and a width of s. w =2.5mm.

5. The broadband circularly polarized conformal antenna according to claim 4, characterized in that, The width of the end portion of the feed microstrip line (8) is greater than the width of the rest portion in order to achieve impedance matching.

6. The broadband circularly polarized conformal antenna according to claim 5, characterized in that, The total length of the feed microstrip line (8) is l=26.94mm, of which the width of the part with a length of l1=4.17mm at the end is w1=8.33mm, and the width of the remaining part of the microstrip line is w2=4.67mm.

7. The broadband circularly polarized conformal antenna according to claim 6, characterized in that, The upper dielectric substrate (1), the middle dielectric substrate (2), and the lower dielectric substrate (3) have the same dimensions and a thickness of h3=0.254mm.

8. The broadband circularly polarized conformal antenna according to claim 7, characterized in that, The air layer height h2 between the upper dielectric substrate (1) and the middle dielectric substrate (2) is 1.56 mm, and the air layer height h1 between the middle dielectric substrate (2) and the lower dielectric substrate (3) is 1.5 mm.

9. The broadband circularly polarized conformal antenna according to claim 7, characterized in that, The profile of the broadband circularly polarized conformal antenna is 0.089λ0, where λ0 is the free-space wavelength of the antenna at the center frequency.

10. The broadband circularly polarized conformal antenna according to any one of claims 1 to 9, characterized in that, The antenna can be bent along the direction of the feed microstrip line (8) and the antenna center to conform to the cylindrical carrier.

Images