A wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna

Abstract

The invention discloses a wide-beam, low-profile, omnidirectional, circularly polarized metasurface antenna, comprising an upper dielectric substrate, a lower dielectric substrate, a circular metasurface located on the upper surface of the upper dielectric substrate, a one-to-four feeding network located between the upper dielectric substrate and the lower dielectric substrate, and a ground plane located on the lower surface of the lower dielectric substrate; a coaxial line feed passes through the ground plane and the lower dielectric substrate, contacts the one-to-four feeding network for feeding, and radiates upward to the circular metasurface after contacting the one-to-four feeding network; the circular metasurface comprises a star-shaped structure patch and a plurality of hexagonal patches evenly distributed in a circle around the star-shaped structure patch; each hexagonal patch is a non-uniform truncated patch.

Description

Technical Field

[0001] The present invention belongs to the technical field of antennas, and in particular relates to a wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna. Background Art

[0002] Search and rescue radar transponders are used in maritime distress and safety systems to indicate the location of distressed ships, lifeboats and survivors. In harsh maritime environments, using search and rescue radar transponders to locate distressed ships is an effective means of finding the target's location compared to low-precision positioning methods such as satellite positioning. Search and rescue radar transponders play an irreplaceable role in ensuring maritime navigation safety.

[0003] However, existing search and rescue radar transponders have defects such as lack of circular polarization, small radiation beam width, and susceptibility to harsh marine environments. Summary of the invention

[0004] Purpose of the invention: In order to solve the problems of existing search and rescue radar transponder antennas, such as lack of circular polarization, small radiation beam width, and susceptibility to harsh marine environment, the present invention discloses a wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna, which can be applied to search and rescue radar transponders. The antenna has the advantages of good omnidirectional circular polarization performance, wide radiation angle, and wide range. Parameters such as non-circularity and horizontal beam width are far better than the index requirements of search and rescue radar transponders, and have good application prospects.

[0005] Technical solution: A wide-beam, low-profile, omnidirectional, circularly polarized metasurface antenna, comprising an upper dielectric substrate, a lower dielectric substrate, a circular metasurface located on the upper surface of the upper dielectric substrate, a one-to-four feeding network located between the upper dielectric substrate and the lower dielectric substrate, and a ground plane located on the lower surface of the lower dielectric substrate; a coaxial line feed passes through the ground plane and the lower dielectric substrate, contacts the one-to-four feeding network for feeding, and radiates upward to the circular metasurface after contacting the one-to-four feeding network;

[0006] The circular super surface includes a star-shaped structure patch and a plurality of hexagonal patches evenly distributed in a circle around the star-shaped structure patch; each hexagonal patch is a non-uniform truncated patch.

[0007] Furthermore, the thickness of the circular metasurface, the thickness of the one-to-four feeding network and the thickness of the ground plane are all the same.

[0008] Furthermore, the upper dielectric substrate and the lower dielectric substrate are both circular dielectric substrates.

[0009] Furthermore, the one-to-four feeding network includes four T-type power dividers and a rectangular patch; the rectangular patch is arranged at the center of the one-to-four feeding network, and each T-type power divider is connected to the rectangular patch; the four T-type power dividers radiate a circle of hexagonal patches upwards.

[0010] Furthermore, the number of the hexagonal patches is 16.

[0011] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0012] (1) The antenna of the present invention adopts a circular metasurface structure, uses a coaxial line to feed from the bottom, and radiates upward to the circular metasurface after contacting the one-to-four feeding network; the present invention can effectively improve the working bandwidth and radiation efficiency of the antenna by using the metasurface, while making the cross-section of the antenna sufficiently low; the circular metasurface structure of the present invention is composed of two circular dielectric substrates, which are bonded to each other, and the absence of an air layer ensures the structural stability of the antenna, and the overall cross-section height is 31.054 mm;

[0013] (2) Compared with other search and rescue radar transponder antennas, the antenna of the present invention has good circular polarization characteristics; since circular polarization has orthogonal rotation, the electromagnetic waves reflected by the object present orthogonal polarization, which can effectively solve the communication problems caused by extremely harsh environments such as rain, fog and haze; the antenna of the present invention can greatly avoid the polarization mismatch between the transmitting antenna and the receiving antenna due to the lack of strict orientation, and the application of circular polarization has significant advantages in the search and rescue radar transponder system;

[0014] (3) The antenna of the present invention has good omnidirectional characteristics. In order to further compare the advantages and disadvantages of the antenna omnidirectionality, the out-of-roundness index parameter is introduced. The out-of-roundness is the deviation between the maximum or minimum value and the average value in the H-plane radiation pattern. The smaller the out-of-roundness, the better the omnidirectionality. The antenna of the present invention is less than 0.5 dB at 9.2-9.8 GHz. The search and rescue radar transponder requires that the out-of-roundness of the antenna at 9.2-9.5 GHz is less than 2 dB. The antenna of the present invention far exceeds its requirements and has good omnidirectional radiation characteristics.

[0015] (4) The present invention effectively regulates the main lobe radiation angle of the antenna, covering the horizontal plane and above. On the basis of maintaining omnidirectional radiation, the half-power beam width of the antenna is relatively wide, and the radiation angle tends to be horizontal. The half-power beam width (HPBW) of the main lobe is 82.8° (°33.2-116°), and the main lobe axis is at 55°. This is the effect produced by a circle of hexagonal patches on the metasurface. A circle of hexagonal patches is radiated through four T-type power dividers, and the radiation in the horizontal direction is stronger. In the harsh marine environment, it is necessary to transmit and receive signals in the horizontal direction over a large range. The search and rescue radar transponder is installed on a lifeboat or a ship. When it is tilted due to the influence of wind and waves, the antenna of the present invention has great advantages.

[0016] (5) The antenna of the present invention focuses on wide beam and utilizes the characteristics of metasurface antennas that are easy to integrate and easy to realize circular polarization. At the same time, the antenna has radiation characteristics such as circular polarization, low profile and high gain. It has good omnidirectional performance and is suitable for maritime search and rescue radar transponder systems. Parameters such as non-circularity and horizontal beam width are far better than the index requirements of search and rescue radar transponders, which can greatly increase the probability of rescue of people in distress at sea. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the overall structure of a wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna proposed by the present invention;

[0018] Figure 2 The result diagram of antenna simulation and test return loss (S11), where the horizontal axis represents frequency (GHz) and the vertical axis represents return loss intensity (dB);

[0019] Figure 3 This is the result diagram of antenna simulation and test axial ratio;

[0020] Figure 4 This is the antenna simulation and test gain result diagram;

[0021] Figure 5 The E-plane radiation pattern simulated for the antenna at 9.35GHz, including the main lobe half-power beamwidth range and the main lobe axis position;

[0022] Figure 6 The E-plane radiation pattern of the antenna simulated and tested at 9.35GHz;

[0023] Figure 7 This is the H-plane radiation pattern of the antenna simulated and tested at 9.35GHz. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is now further described in conjunction with the accompanying drawings and embodiments.

[0025] Embodiment 1:

[0026] This embodiment proposes a wide beam, low profile, omnidirectional, circularly polarized metasurface antenna, which can be applied to, but not limited to, search and rescue radar transponders. Figure 1As shown, the antenna includes: an upper dielectric substrate 1, a lower dielectric substrate 4, a circular metasurface located on the upper surface of the upper dielectric substrate 1, a one-to-four feeding network located between the upper dielectric substrate 1 and the lower dielectric substrate 4, and a ground plane 7 located on the lower surface of the lower dielectric substrate 4. The coaxial line feed passes through the ground plane 7 and the lower dielectric substrate 4, and contacts the one-to-four feeding network for feeding. The SMA interface 8 is used for coaxial feeding, and radiates upward to the circular metasurface after contacting the one-to-four feeding network. In this embodiment, the thickness of the circular metasurface, the thickness of the one-to-four feeding network, and the thickness of the ground plane are all the same, and can all be 0.018mm. The use of the circular metasurface can effectively improve the working bandwidth and radiation efficiency of the antenna, while making the cross-section of the antenna sufficiently low. The antenna in this embodiment is composed of two circular dielectric substrates, which are bonded to each other. The absence of an air layer ensures the structural stability of the antenna, and the overall cross-section height is 31.054mm.

[0027] Specifically, the upper dielectric substrate 1 used in this embodiment is a FR-4 dielectric substrate with a relative dielectric constant of 4.4 and a thickness of 1.5 mm, and the lower dielectric substrate 4 is a F4BM-2 dielectric substrate with a relative dielectric constant of 2.65 and a thickness of 1.6 mm; both the FR-4 dielectric substrate and the F4BM-2 dielectric substrate are circular with a radius of 27.13 mm.

[0028] Specifically, Figure 1 As shown, the circular metasurface of this embodiment is composed of a star-shaped structure patch 3 in the middle and 16 hexagonal patches 2 evenly distributed in a circle around the star-shaped structure patch 3. Each hexagonal patch 2 is a non-uniform truncated patch. The diagonal length of each hexagonal patch 2 is 12.6 mm, and the gap between two adjacent hexagonal patches 2 is 2 mm.

[0029] Specifically, the one-to-four feed network of this embodiment is composed of four T-type power dividers 5, each T-type power divider 5 is connected to the middle rectangular patch 6, and the size of the rectangular patch 6 is 5.65mm×5.65mm. The size of the feeder line connecting the rectangular patch 6 and the T-type power divider 5 is 8.35mm×0.4mm, the vertical rectangle size in the T-type power divider 5 is 3mm×2mm, and the horizontal rectangle size is 1.10mm×2mm. The four T-type power dividers 5 radiate a circle of hexagonal patches 2 upwards, so that the radiation in the horizontal direction is more concentrated.

[0030] The cavity model is now used to analyze the electric field and current distribution of the wide beam low profile omnidirectional circularly polarized metasurface antenna proposed in this embodiment. The wide beam low profile omnidirectional circularly polarized metasurface antenna can establish a cylindrical wall model with the top and ground as electric fields and the edges as magnetic fields. Therefore, the electric field and magnetic field distribution in the dielectric substrate of the wide beam low profile omnidirectional circularly polarized metasurface antenna can be analyzed by solving the wave equation to obtain the corresponding TM nm mold.

[0031] The solution of the wave equation for the electric field in a cylindrical cavity can be expressed in cylindrical coordinates as:

[0032] E z =E0J n (kρ)cosnφ

[0033] Among them, J n (kρ) is an nth-order Bessel function. Because its electric field component E has only a component in the z direction, and is 0. According to the conversion relationship between electric field and magnetic field, the magnetic field component of the wide beam low profile omnidirectional circularly polarized metasurface antenna is expressed as:

[0034]

[0035] The magnetic field in the cylindrical cavity will generate an induced current, so the surface current of the wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna is expressed as:

[0036]

[0037] in, and are unit vectors respectively.

[0038] The proposed antenna is fed through a coaxial probe to the rectangular patch 6 in the center of the one-to-four feeding network. The rectangular patch 6 conducts current to the star-shaped patch 3 in the middle of the circular metasurface to form capacitive feeding, so that TM 01 The mode resonates with the monopole mode of the top load, and the 90° equal-amplitude phase difference generated by the star-shaped patch 3 achieves omnidirectional circular polarization. Similarly, the currents conducted by the four T-type power dividers 5 resonate with the currents around the circular metasurface, further widening the beam width.

[0039] Figure 2 The simulation and test return loss (S11) result diagrams of the wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna proposed in this embodiment are given. The simulation results show that the -10dB impedance bandwidth is 7.9% (9.08-9.8GHz), and the test results show that the -10dB impedance bandwidth is 7.54% (9.02-9.7GHz).

[0040] Figure 3 The simulation and test axial ratio result diagrams of the wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna proposed in this embodiment are given. The simulation results show that the 3dB axial ratio bandwidth is 14.5% (8.54-9.78GHz), and the test results show that the 3dB axial ratio bandwidth is 12.14% (8.65-9.7GHz).

[0041] Figure 4The simulation and test gain result diagrams of the wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna proposed in this embodiment are given. The maximum gain is 3.11 dBic at 9.78 GHz.

[0042] Figure 5 The E-plane radiation pattern of the wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna proposed in this embodiment is given, with a main lobe half-power beamwidth (HPBW) of 82.8° (°33.2-116°), and a main lobe axis at 55°.

[0043] Figure 6 The left E-plane radiation pattern of the simulation and test of the wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna proposed in this embodiment is given.

[0044] Figure 7 The H-plane radiation pattern of the simulation and test of the wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna proposed in this embodiment is given.

[0045] The wide-beam, low-profile, omnidirectional, circularly polarized metasurface antenna proposed in this embodiment has good omnidirectional characteristics. In order to further compare the advantages and disadvantages of the antenna omnidirectionality, the out-of-roundness index parameter is introduced. The out-of-roundness is the deviation of the maximum or minimum value from the average value in the H-plane radiation pattern. The smaller the out-of-roundness, the better the omnidirectionality. The wide-beam, low-profile, omnidirectional, circularly polarized metasurface antenna proposed in this embodiment is less than 0.5dB at 9.2-9.8GHz. The search and rescue radar transponder requires that the antenna has an out-of-roundness of less than 2dB at 9.2-9.5GHz. This antenna far exceeds its requirements and has good omnidirectional radiation characteristics.

[0046] In summary, the wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna proposed in this embodiment effectively controls the main lobe radiation angle of the antenna, covering above and below the horizontal plane. On the basis of maintaining omnidirectional radiation, the half-power beam width of the antenna is relatively wide, and the radiation angle tends to be horizontal. Ultimately, the main lobe half-power beam width (HPBW) of 82.8° (33.2°-116°) is achieved, and the main lobe axis is at 55°. This is the effect produced by a circle of hexagonal patches on the metasurface. A circle of hexagonal patches is radiated through four T-type power dividers, and the radiation in the horizontal direction is stronger. In harsh marine environments, it is necessary to send and receive signals in the horizontal direction over a large range. The search and rescue radar transponder is installed on a lifeboat or ship. When it is tilted due to the influence of wind and waves, this antenna has great advantages. And the wide-beam low-profile omnidirectional circularly polarized metasurface antenna proposed in this embodiment achieves a -10dB impedance bandwidth of 7.9% (9.08-9.8GHz), a 3dB axial ratio bandwidth of 14.5% (8.54-9.78GHz), and a maximum gain of 3.11dBic at 9.78GHz. The wide-beam low-profile omnidirectional circularly polarized metasurface antenna has good omnidirectional performance on the basis of achieving omnidirectional circular polarization. Since circular polarization has orthogonal rotation, the electromagnetic waves reflected by the object show orthogonal polarization, which can effectively solve the communication problems caused by extremely harsh environments such as rain, fog and haze. It can avoid polarization mismatch between the transmitting antenna and the receiving antenna due to the lax orientation. The application of circular polarization has significant advantages in search and rescue radar transponder systems. The national standard GB 15216-2021 requires that the vertical beam width of the transceiver antenna on the search and rescue radar transponder is at least ±12.5° relative to the horizontal plane of the radar transponder, and the horizontal beam width of the antenna is within ±2dB in all directions. When the wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna proposed in this embodiment is used in the maritime search and rescue radar transponder system, the parameters such as non-circularity and horizontal beam width are far better than the index requirements of the search and rescue radar transponder, and it has good application prospects.

Claims

1. A wide-beam, low-profile, omnidirectional, circularly polarized metasurface antenna, characterized in that: It includes an upper dielectric substrate, a lower dielectric substrate, a circular super surface located on the upper surface of the upper dielectric substrate, a one-to-four feeding network located between the upper dielectric substrate and the lower dielectric substrate, and a ground plane located on the lower surface of the lower dielectric substrate; The coaxial line feed passes through the ground plane and the lower dielectric substrate, contacts the one-to-four feeding network for feeding, and radiates upward to the circular metasurface after contacting the one-to-four feeding network; The upper dielectric substrate and the lower dielectric substrate are both circular dielectric substrates; The circular metasurface includes a star-shaped structure patch and a plurality of hexagonal patches uniformly distributed around the star-shaped structure patch; each hexagonal patch is a non-uniform truncated patch; The one-to-four feeding network includes four T-type power dividers and a rectangular patch; the rectangular patch is arranged at the center of the one-to-four feeding network, and each T-type power divider is connected to the rectangular patch; the four T-type power dividers radiate a circle of hexagonal patches upwards.

2. The wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna according to claim 1, characterized in that: The thickness of the circular metasurface, the thickness of the one-to-four feeding network and the thickness of the ground plane are all the same.

3. The wide-beam, low-profile, omnidirectional circularly polarized metasurface antenna according to claim 1, characterized in that: The number of the hexagonal patches is 16.

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