Circularly polarized conformal antenna for curved carriers

Abstract

The application provides a circularly polarized conformal antenna for a curved carrier. 11 The antenna comprises a full-metal floor, a ring-shaped patch, a feed patch and four parasitic patches. The ring-shaped patch resonates in a TM The sequential 90° phase difference provided by the arc-shaped strips can realize circularly polarized radiation. Four parasitic patches surrounding the ring-shaped patch are introduced to excite another circularly polarized resonant mode, thereby widening the bandwidth and improving the gain. In order to verify the conformal performance of the antenna, the performances under different bending radii are compared and discussed. Finally, the final profile of the antenna of the application is 0.054λ0, λ0 is the free space wavelength of the antenna at the center frequency, and the antenna has the characteristics of low profile, wide bandwidth and high gain.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, specifically relating to a broadband high-gain circularly polarized conformal antenna applied to curved carriers. Background Technology

[0002] Conformal antennas typically have a low profile, which does not affect the aerodynamic performance of the carrier platform, and they are widely used in modern mobile communication platforms. Compared with 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 applicability of antennas to different curved carriers in wireless communication systems, antennas are required to have a sufficiently low profile and good circular polarization performance over a sufficiently wide frequency band. Currently, antennas that meet these requirements are rarely reported. Conformal antenna research mainly focuses on the wearable field, using flexible materials and conductive fabrics. Commonly used circularly polarized antenna types in wireless communication systems include metasurface antennas, microstrip antennas, and helical antennas.

[0003] Yang H et al. (Yang H, Liu X, Fan Y. Design of broadband circularlypolarized all-textile antenna and its conformal array for wearable devices[J]. IEEE Transactions on Antennas and Propagation, 2021, 70(1):209-220.) designed a flexible broadband circularly polarized all-textile antenna element with a wide-side radiation pattern for external human communication. To make the proposed antenna flexible, felt and conductive nylon fabric were used. Based on the proposed antenna element, a broadband circularly polarized wearable conformal antenna array was constructed, which radiates omnidirectionally in the azimuth plane, suitable for both in-body and out-of-body communication. Notably, a single-input stripline power divider was used in the feed network; due to its double ground plane, it can greatly reduce the antenna's radiation to the human body. However, due to insufficient material rigidity, this antenna is not suitable for applications such as aircraft.

[0004] Gao X et al. (Gao X, Tian G, Shou Z, et al. A low-profile broadband circularly polarized patch antenna based on characteristic mode analysis[J].IEEE Antennas and Wireless Propagation Letters,2020,20(2):214-218.) introduced a low-profile, high-gain, broadband circularly polarized metasurface antenna. The modal currents and radiation characteristics of the metasurface were studied using characteristic mode theory. Based on the characteristic mode analysis, two modes with orthogonal current directions and equal amplitudes were selected as the operating modes, realizing circularly polarized radiation. At the same time, a single-feed structure composed of a microstrip curved line and a cross slot was used to simultaneously excite two orthogonal modes with a phase difference of 90°. However, the disadvantage of this antenna is that the profile is still relatively high (λ0 is the free space wavelength of the antenna at the operating frequency).

[0005] Ding K et al. (Ding K, Guo YX, Gao C. CPW-fed wideband circularly polarized printed monopole antenna with open loop and asymmetric ground plane[J]. IEEE Antennas and Wireless Propagation Letters, 2016, 16: 833-836.) designed a simple rectangular monopole antenna with an asymmetric ground plane and an open loop to achieve wide impedance matching and wideband circular polarization operating bandwidth. Due to the asymmetric ground plane, a circular polarization mode is first introduced in the upper frequency band. To expand the impedance and circular polarization bandwidth, a square ring with a gap at the bottom is placed on the left side of the monopole. The antenna has a 3dB axial ratio bandwidth of 63.3% (1.9GHz, 2.05-3.95GHz), covering the WLAN (2.4GHz) and WiMAX (3.5GHz) bands. The disadvantage of this antenna is the incomplete ground plane, resulting in poor resistance to metallic environments and limiting its applicability to a wide variety of carrier platforms.

[0006] Other publicly available broadband circularly polarized antennas have problems such as excessively high profile 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 high-gain circularly polarized conformal antenna for curved carriers with low profile 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 curved carriers, comprising: an upper dielectric substrate 1, a lower dielectric substrate 2, an annular patch 3, a parasitic patch 4, a feed patch 5, a metal ground plane 6, and a coaxial feed line 7.

[0009] The upper dielectric substrate 1 and the lower dielectric substrate 2 are identical, thin, and have an air layer in between. Annular patches 3 and parasitic patches 4 are printed on the upper surface of the upper dielectric substrate 1. The square ring surrounding the annular patch 3 is obtained by subtracting the smaller square patch from the larger one and then chamfering the corners. The arc-shaped strip at the center of the annular patch 3 is a three-quarter circle, with rectangular strips connecting its ends to the outer square ring. The four parasitic patches 4 are identical, all being rectangular patches with rectangular slots. Taking patch number "4" as an example, the distance from the slot to both the right and bottom edges is half the length of the longer side. On the lower surface of the upper dielectric substrate 1, a circular feed patch 5 is printed. The outer conductor of the coaxial feed wire 7 is connected to the lower dielectric substrate 2, and the inner conductor passes through the lower dielectric substrate 2, connecting to the feed patch 5 on the lower surface of the upper dielectric substrate 1.

[0010] The mechanism of this invention is as follows:

[0011] Since the outer perimeter of the annular patch 3 is approximately equal to one operating wavelength, the annular patch 3 operates in TM. 11 The arc-shaped strip introduces a 90° phase difference to the square ring, which, when fed by a coaxial line at an appropriate location, enables circularly polarized radiation. The induced currents on the four slotted parasitic patches 4 contribute to the coupling energy, thus enhancing the gain. Furthermore, since the currents on each side of the annular patch 3 have a sequential 90° phase difference, orthogonal currents with a 90° phase difference can be induced on the parasitic patch 4, thereby exciting new circularly polarized modes. Therefore, two minimum axial ratio points are generated within the operating frequency band, extending the axial ratio bandwidth by 3dB.

[0012] In this invention, the antenna is bent along the direction of the feed point and the antenna center. This bending causes the horizontal current on the left and right parasitic patches to become more concentrated. It can be expected that the bending will not have a serious impact on the antenna performance. Furthermore, the antenna uses a coaxial probe for feeding, but its input impedance exhibits extremely high inductive reactance, resulting in a large reflection coefficient within the bandwidth, which does not meet the operational requirements. Therefore, a feed patch 5 is introduced on the lower surface of the upper dielectric substrate 1, forming a capacitive coupling with the annular patch 3 on the upper surface to offset the high inductive reactance of the feed probe and improve matching.

[0013] Finally, the upper dielectric substrate 1 and the lower dielectric substrate 2 used are very thin, both 0.254mm, and have a certain bending ability, making them suitable for curved carrier platforms; the floor uses an all-metal floor 6, which can be used in metal environments and will not be affected by metal interference.

[0014] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0015] 1. This invention provides a broadband high-gain circularly polarized conformal antenna for curved carriers. The antenna is composed of a PCB board and a metal conductor, which has a simple structure and is easy to process and assemble.

[0016] 2. This invention broadens the bandwidth and improves the gain by employing a sequentially rotating feed structure and four parasitic patches surrounding the annular patch to excite a circularly polarized resonant mode.

[0017] 3. Effectively widens antenna bandwidth and improves antenna gain, with a 3dB axial ratio bandwidth of up to 20% and a peak gain of up to 11.2dBic.

[0018] 4. This invention uses a complete metal floor plane, which has good resistance to metal environment.

[0019] 5. The present invention adopts a combination of two dielectric substrates 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 0.054λ0 (λ0 is the free space wavelength of the antenna at the center frequency). It has the characteristics of low profile, which is conducive to the conformal adaptation of the antenna to the curved carrier platform. Attached Figure Description

[0020] Figure 1 This is a top view of the antenna structure;

[0021] Figure 2 This is a side view of the antenna structure;

[0022] Figure 3 This is a simulation result of the antenna return loss;

[0023] Figure 4 Simulation results of antenna return loss under different r3 values;

[0024] Figure 5 This is a simulation result of the antenna axial ratio;

[0025] Figure 6 This is a graph showing the simulation results of the antenna gain. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0027] A broadband high-gain circularly polarized conformal antenna for curved carriers is shown in the schematic diagram below. Figures 1-2 As shown, it specifically includes: an upper dielectric substrate 1, a lower dielectric substrate 2, a ring patch 3, a parasitic patch 4, a power supply patch 5, a metal ground plane 6, and a coaxial power supply line 7.

[0028] 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. As can be seen from the figure, the annular patch 3 and parasitic patches 4 are disposed on the upper surface of the upper dielectric substrate 1. The annular patch 3 has a square-cut corner on its outer perimeter and an arc-shaped strip with a circumference of three-quarters of a complete circle at its center. The outer and central portions are connected by a rectangular strip. The four parasitic patches 4 are identical, all rectangular patches, arranged at equal intervals around the annular patch 3, with rectangular slots formed. The rectangular slots form a 45° angle with the axis of symmetry of the rectangular patches. When the parasitic patch is square, the center of the rectangular slot coincides with the center of the square; when the parasitic patch is not square, the longer side of the parasitic patch is the side closest to the annular patch, and the distance from the center of the rectangular slot to the side closest to the annular patch and the two sides perpendicular to that side are both half the length of the longer side. Taking the patch labeled "4" as an example, the distance from the slot position to the right edge and the bottom edge is half the length of the longer side; the remaining parasitic patches are obtained by rotating the patch 90° each time. To generate a sequentially rotating 90° phase difference in the currents on the four sides of the annular patch 3, the feed point is located on a rectangular strip at a distance from the center of the structure. The feed patch 5 is disposed on the lower layer of the upper dielectric substrate 1, forming capacitive coupling with the annular patch 3. The metal ground plane 6 is disposed on the lower layer of the lower dielectric substrate 2, adopting a full-ground structure, which can improve the antenna's resistance to metallic environments. This invention uses a coaxial feed cable 7 for feeding, with the outer conductor connected to the metal ground plane 6 and the inner conductor connected to the feed patch 5 on the lower surface of the upper dielectric substrate 1. The annular patch 3 is fed through the feed patch 5. For antennas with different curvatures, the antenna bending direction is along... Figure 1 The line containing the x-axis is shown.

[0029] Example

[0030] In this embodiment, the circularly polarized conformal antenna is cubic with a total size of 80mm × 80mm and a total height of 3.008mm. The air gap height between the upper and lower dielectric substrates is h2 = 2.5mm, and the thickness of the upper and lower dielectric substrates is h1 = 0.254mm. An F4BM with a dielectric constant of 2.2 and a loss tangent of 0.001 can be selected. The outer periphery of the annular patch is obtained by subtracting a square patch with a side length of l1 = 12.2mm from a square patch with a side length of l2 = 17mm, and then cutting an isosceles right triangle with a right angle of side length d1 = 2.9mm. The central arc-shaped strip comprises two parts: one part is a three-quarter circle with an inner radius of r1 = 1.1mm and an outer radius of r2 = 3.5mm; the other part consists of two rectangular strips connecting the arc and the outer periphery of the annular patch, with a width of w. f =1.25mm. The parasitic patch is a slotted rectangular patch with a patch length of l. s =19mm, width is w s =18.62mm, the length of the rectangular groove is s l =5mm, width is s w =1mm. The distance d2 from the center of the antenna structure to the feed position is 5mm. The circular feed patch is located on the lower surface of the upper dielectric substrate, also at a distance of d2 = 5mm from the center of the patch, and its radius r3 = 1.7mm. A complete metal ground plane is used. In this example, the antenna operates at a frequency of 5.5GHz.

[0031] Furthermore, in order to bend the antenna to a fixed curvature, this invention proposes to use 3D printing technology to print hollow brackets with different curvatures. Without affecting the antenna performance, the antenna can be bent to different radii to meet the requirements of the invention.

[0032] The dimensions mentioned above are specific dimensions that have been calculated and optimized. If the dimensions change, the performance of the embodiment will deteriorate.

[0033] Simulation tests were conducted on it, and the results showed that: Figure 3 The figure shows the simulation results of the return loss of the antenna structure in the embodiment of the present invention. As can be seen from the figure, the impedance bandwidth of the antenna with a return loss of less than -10dB in the embodiment of the present invention is 4.93GHz to 6.61GHz, reaching 30.5%. Bending the antenna in the present invention to different radii reveals that bending the antenna causes a slight decrease in impedance bandwidth, with the impedance bandwidth in the bent state being about 28%. However, different bending radii have almost no effect on the impedance bandwidth. Figure 4The graph shows the simulation results of antenna return loss under different r3 values. It can be observed that when r3 = 1.3 mm, the antenna resonates at a higher frequency; when r3 = 2.1 mm, the antenna resonates at a lower frequency; and when r3 = 1.7 mm, the antenna resonates near the operating frequency of this example design, and at this point, the antenna has the widest impedance bandwidth. Therefore, the value of r3 should be set to r3 = 1.7 mm. 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 4.95GHz to 6.05GHz, reaching 20%. Bending the antenna of this invention to different radii reveals that the bending of the antenna has almost no effect on the axial ratio bandwidth. 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 11.2 dBic, and the in-band gain variation range is 9.9 dBic-11.2 dBic. Bending will affect the peak gain of the antenna, with a variation range within 1 dBic.

[0034] 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 circularly polarized conformal antenna for a curved carrier, characterized in that, include: Upper dielectric substrate, lower dielectric substrate, ring patch, parasitic patch, power supply patch, metal ground plane and coaxial power supply line; The upper and lower dielectric substrates are made of the same material and have the same shape, with an air layer between them; The annular patch and parasitic patch are printed on the upper surface of the upper dielectric substrate. The annular patch is surrounded by an externally cleaved square ring, and the center of the annular patch is a three-quarter circular strip. The two ends of the three-quarter circular strip are connected to the externally cleaved square ring through rectangular strips. Four identical rectangular patches with rectangular slots are set as parasitic patches on the outer sides of the four outer edges of the externally cleaved square ring. The rectangular slots and the axis of symmetry of the rectangular patches form a 45° angle. A circular power feed patch is printed on the lower surface of the upper dielectric substrate; the outer conductor of the coaxial power feed line is connected to the lower dielectric substrate, and the inner conductor passes through the lower dielectric substrate and connects to the power feed patch on the lower surface of the upper dielectric substrate. The circumference of the square ring of the ring patch is approximately equal to the operating wavelength of the antenna, allowing the ring patch to operate in TM. 11 The three-quarter circular strips bring a 90° phase difference to the square ring, and circular polarization radiation is achieved by coaxial feeding. The induced current on the four open rectangular slot parasitic patches couples the energy to enhance the gain of circular polarization radiation.

2. The antenna as described in claim 1, characterized in that, When the parasitic patch is square, the center of the rectangular groove coincides with the center of the square.

3. The antenna as described in claim 1, characterized in that, When the parasitic patch is not square, the longer side of the parasitic patch is the side closest to the annular patch, and the distance from the center of the rectangular groove to the side closest to the annular patch and the two sides perpendicular to that side are both half the length of the longer side.

4. The antenna as described in claim 1, characterized in that, The thickness of both the upper and lower dielectric substrates is 0.254 mm.

5. The antenna as described in claim 1, characterized in that, When making the circumscribed square ring, use the square patch with the larger side length to center the square patch and subtract the square patch with the smaller side length to get the square ring. Then cut off an isosceles right triangle angle from each of the four vertices of the square ring.

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