Wideband circularly polarized antenna based on characteristic mode analysis.

Abstract

This invention discloses a wideband circularly polarized antenna based on characteristic mode analysis. The top surface of this antenna is a metasurface structure with aperiodic regular hexagonal rings. The regular hexagonal structure can be arranged in three directions, resulting in a stronger coupling effect and a reduced antenna profile. By adjusting the size of the regular hexagonal rings in each layer, it is possible to control the mode salience and current distribution throughout the metasurface and find the appropriate mode. After the overall dimensions of the metasurface are determined, the appropriate feed position is found based on the current distribution obtained through characteristic mode analysis. This antenna is fed using an L-shaped slot coupled feed method. This invention applies characteristic mode analysis to aperiodic regular hexagonal ring metasurface structures. The regular hexagonal structure strengthens inter-unit coupling and reduces the antenna profile. The aperiodicity allows for control of the modes in the metasurface structure, allowing for optimal mode finding, thereby simplifying the metasurface design process.

Description

[Technical Field]

[0001] The present invention relates to a wideband circularly polarized antenna based on characteristic mode analysis, which belongs to the field of microwave antenna technology. [Background technology]

[0002] With the development of the times and advances in science and technology, the requirements for antennas in wireless communication systems are increasing. Linearly polarized antennas are no longer able to meet the widespread and increasing communication demands in many scenarios. Circularly polarized antennas offer many advantages over linearly polarized antennas. These include: (1) Resistance to clutter interference: Circularly polarized waves can change direction during propagation, thereby avoiding clutter interference; (2) Avoidance of multipath fading: Circularly polarized waves have very little attenuation during propagation, thereby avoiding multipath fading; and (3) Avoidance of polarization mismatch: Circularly polarized waves can avoid the polarization mismatch phenomenon that occurs during propagation. Therefore, circularly polarized antennas can meet the widespread and increasing demands of wireless communication systems. Therefore, research into circularly polarized antennas, which offer high performance and wide applications, has become a hot topic of research.

[0003] Metasurfaces, composed of two-dimensional planar arrays of subwavelength metals, possess unique properties not found in nature, such as negative refractive index and negative magnetic permeability, providing new directions for electromagnetic wave control. The excellent electromagnetic wave control properties of metasurfaces have opened up numerous application scenarios for improving antenna performance, broadening the scope of antenna design and effectively resolving many traditional antenna bottlenecks. Metasurfaces have several special application directions, such as using an antenna as a power source to excite the metasurface, directly utilizing the metasurface to improve antenna performance, or using the metasurface as the radiating surface of an antenna. Therefore, rational utilization of metasurfaces is crucial for modern antenna design.

[0004] Traditional circularly polarized antenna design relied heavily on the experience of engineers. With the development of science and technology, characteristic mode theory has become widely used as a guide for antenna design. Characteristic mode theory combines the advantages of both analytical and numerical methods, allowing the surface currents of a conductor to be expanded orthogonally, and the characteristic electric fields generated by these characteristic currents are also orthogonal. In characteristic mode theory, characteristic modes refer to current modes corresponding to characteristic vectors, making it possible to numerically analyze conductors of any shape. Characteristic modes are attributes of the conductor itself and are related only to the physical properties of the conductor itself. Characteristic mode theory can analyze antenna radiation, select appropriate characteristic modes, and provide a theoretical basis for selecting the feed position.

[0005] To design high-performance circularly polarized antennas, both metasurface and characteristic mode analysis are applied to a low-profile, wideband circularly polarized antenna based on aperiodic regular hexagonal metasurfaces.

[0006] Existing circularly polarized antennas have many drawbacks. (1) Existing circularly polarized antennas are relatively large, lack flexibility, and are disadvantageous for integration. (2) Existing circularly polarized antennas have a relatively narrow axial bandwidth. (3) Existing circularly polarized antennas often have complex feed systems, which makes design difficult, increases costs, and also affects antenna stability. Therefore, the current focus of circularly polarized antenna design is to design a circularly polarized antenna with minimal size, a wide axial bandwidth, a small size, and a simple feed system. Summary of the Invention Problem to be solved

[0007] The present invention aims to overcome the drawbacks and deficiencies of the above-mentioned existing technologies and provide a wideband circularly polarized antenna based on characteristic mode analysis. This wideband circularly polarized antenna features a wide axial ratio bandwidth, a low profile, and a simple feed structure. Its low profile allows for easy design and fabrication. The present invention simplifies the wideband circularly polarized antenna using characteristic mode analysis. It combines an aperiodic regular hexagonal metasurface with characteristic mode analysis, analyzes the aperiodic regular hexagonal metasurface using characteristic mode analysis, and controls the width of the aperiodic regular hexagonal metasurface to find appropriate modes and mode salience. The appropriate feed position is then determined from the mode current distribution, thereby achieving wideband circular polarization. [Means for solving the problem]

[0008] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0009] The wideband circularly polarized antenna based on characteristic mode analysis includes, from top to bottom, an upper aperiodic regular hexagonal annular metasurface metal layer, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer, and a lower feed network metal layer. The upper and lower dielectric layers are closely bonded to the metal layer, in order. The geometric centers of the patterns on the upper, intermediate, and lower dielectric layers are all collinear. The intermediate metal layer is a metal ground plane with an L-shaped slot in the middle, with the two slots of different lengths and the sides parallel to the antenna's outer shape. The L-shaped slotted ground plane is closely bonded to the upper and lower dielectric substrates. The bottom of the lower dielectric layer is a feed network metal layer, and the feed structure is a curved microstrip feed line.

[0010] Furthermore, each metasurface unit of the upper aperiodic regular hexagonal ring metasurface metal layer of the present invention is a regular hexagonal ring and is composed only of regular hexagonal rings, resulting in a hexagonal overall metasurface structure. The squares of the upper and lower dielectric layers have side lengths of 42 mm or more, and the plan views of the upper and lower dielectric layers are standard squares. The surface of the upper dielectric layer is an aperiodic regular hexagonal metasurface. The upper dielectric layer is composed of a dielectric and an aperiodic regular hexagonal metasurface on the upper surface of the dielectric layer. The metasurface on the surface of the upper dielectric layer is an aperiodic metasurface with a regular hexagonal outer contour, resulting in a three-layer structure containing 19 metasurface units. Each individual metasurface unit is also a regular hexagon, with equal spacing and the same side length. The metasurface units are all arranged in a regular hexagon, strengthening the coupling between each patch and thereby reducing the antenna profile.

[0011] Furthermore, the width of each layer of the aperiodic regular hexagonal ring metasurface metal layer of the upper dielectric layer of the present invention can be adjusted, and the metasurface structure can be analyzed using characteristic mode analysis to obtain the mode characteristic values ​​and current distribution of the metasurface structure. Adjusting the width of the regular hexagonal rings at different positions can change the mode characteristic values ​​and current distribution. Furthermore, characteristic mode analysis can be used to analyze the mode salience of the aperiodic regular hexagonal ring metasurface metal layer with different parameters to reduce the influence of higher-order modes on the employed degenerate modes and obtain the optimal current distribution to reduce the influence of higher-order mode currents on the employed degenerate modes. The regular hexagonal metasurfaces on the upper dielectric layer all have a ring structure, and the width of the regular hexagonal rings of the metasurface in each layer can be controlled. Since the modes and surface currents formed by combining different widths of the regular hexagonal metasurfaces are different, controlling the ring width of the metasurface units can find the optimal characteristic mode for achieving circular polarization.

[0012] The intermediate slotted ground plane is adhered to the upper dielectric layer and the lower dielectric layer in close contact with each other, and the upper metasurface metal layer and the lower feed network metal layer are not substantially in contact with each other. The distance between the upper dielectric layer and the intermediate slotted ground plane is the thickness of the upper dielectric layer, and the distance between the lower feed network layer and the intermediate slotted ground plane is the thickness of the lower dielectric layer.

[0013] Furthermore, the entire antenna of the present invention has a two-layer dielectric structure, with a metal ground plane with an L-shaped slot etched between the two dielectric layers, and the feed position is located at the bottom of the lower dielectric layer. The feed structure at the bottom of the lower dielectric layer is a bent microstrip feed line. To achieve circularly polarized radiation, the lower microstrip feed line couples with the L-shaped slot in the intermediate metal ground plane to form a 90° phase difference, exciting a pair of degenerate modes obtained by characteristic mode analysis. The slot in the intermediate slotted ground plane has an L-shaped structure, and its center is a regular hexagonal ring, which better excites the regular hexagonal metasurface ring at the center of the upper dielectric layer. The two walls of the L-shaped slot have different lengths but the same width, achieving a 90° phase difference and exciting the degenerate modes of the metasurface.

[0014] The upper and lower dielectric layers of the present invention are made of the same material but have different thicknesses and the same outline in plan view. The lower power supply network layer and the intermediate slotted ground plane are both adhered to the dielectric layer.

[0015] The feeding structure of the low-profile, wideband, circularly polarized antenna of the present invention is located on the lower surface of the lower dielectric layer, and the antenna employs a microstrip-coupled feeding scheme. The microstrip line has a curved structure, and the radiated energy penetrates the slotted ground plane to excite the aperiodic metasurface on the upper surface of the upper dielectric layer. [Effects of the Invention]

[0016] This invention proposes a method for realizing a low-profile, wideband circularly polarized antenna using a non-periodic regular hexagonal metasurface with characteristic mode analysis, thereby filling the gap in wideband circular polarization achieved by non-periodic metasurfaces. Compared to conventional circularly polarized antennas, this low-profile, wideband circularly polarized antenna with a non-periodic regular hexagonal metasurface innovatively designs the metasurface with a regular hexagonal structure. Characteristic mode analysis is used to analyze the overall structure of the metasurface and find the optimal mode and current distribution for achieving wideband circular polarization. The width of the regular hexagonal rings in each layer is adjustable, allowing for control of the overall mode and current distribution of the metasurface. At the same time, the regular hexagonal arrangement enhances coupling between surfaces and reduces the antenna profile. This circularly polarized antenna employs a microstrip coupled feed scheme. Characteristic mode analysis is used to analyze the current distribution of the metasurface and find the optimal feed scheme and feed location for achieving circular polarization, simplifying the feed design of the circularly polarized antenna. The antenna's feed structure is simple, easy to fabricate, and significantly reduces costs. With smaller size, wider circular polarization bandwidth and simpler feeding scheme, the present invention has a larger application space in communication systems.

[0017] 1. The top surface of the antenna of the present invention is an aperiodic regular hexagonal ring metasurface structure, and the regular hexagonal structure can be arranged in three directions, which has a stronger coupling effect and can reduce the antenna profile.

[0018] 2. This invention uses characteristic mode analysis to analyze the top-surface aperiodic regular hexagonal ring metasurface to find the appropriate degenerate modes and then analyze the surface current distribution to find the appropriate feed position. Because the top-surface regular hexagonal ring metasurface structure is aperiodic, adjusting the size of the regular hexagonal rings in each layer allows us to control the mode salience and current distribution throughout the metasurface and find the appropriate modes. After determining the overall size of the metasurface, we find the appropriate feed position based on the current distribution obtained through characteristic mode analysis. This antenna is fed using an L-shaped aperture slot coupling feed method to achieve circular polarization. The L-shaped aperture slots are of different lengths, creating a 90° phase difference to excite the two orthogonal modes of the metasurface.

[0019] 3. This invention applies characteristic mode analysis to a non-periodic regular hexagonal annular metasurface structure. The regular hexagonal structure enhances the coupling between units and reduces the antenna profile. The non-periodicity allows for control of the modes in the metasurface structure, making it possible to find the optimal mode and simplifying the metasurface design process. Due to the low profile and circular polarization, this invention is expected to have important applications in the field of wireless communications. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 10 is a structural decomposition schematic of a low-profile, wideband, circularly polarized antenna based on a non-periodic regular hexagonal metasurface using the characteristic mode analysis of the present invention. [Figure 2] 1A and 1B are top and bottom views of a low-profile, wideband, circularly polarized antenna based on a non-periodic regular hexagonal metasurface using the characteristic mode analysis of the present invention. [Figure 3] FIG. 10 is a side view of a low-profile, wideband, circularly polarized antenna based on a non-periodic regular hexagonal metasurface using the characteristic mode analysis of the present invention. [Figure 4] We present the mode prominence of metasurfaces for low-profile, wideband, circularly polarized antennas based on non-periodic regular hexagonal metasurfaces using characteristic mode analysis. [Figure 5]The S11 parameters of a low-profile, wideband, circularly polarized antenna based on aperiodic regular hexagonal metasurfaces are presented using characteristic mode analysis. [Figure 6] Gain diagram of a low-profile, wideband, circularly polarized antenna based on aperiodic regular hexagonal metasurfaces using characteristic mode analysis. [Figure 7] Axial ratio bandwidth of low-profile wideband circularly polarized antenna based on non-periodic regular hexagonal metasurface using characteristic mode analysis. [Figure 8] This figure shows a comparison of the directivity patterns of left-handed and right-handed circular polarization at 3.5 GHz for a low-profile, wideband circularly polarized antenna based on a non-periodic regular hexagonal metasurface using characteristic mode analysis. [Figure 9] Comparison of the directivity patterns of 4GHz left-handed and right-handed circular polarization of a low-profile, wideband circularly polarized antenna based on a non-periodic regular hexagonal metasurface using characteristic mode analysis. [Figure 10] This figure shows a comparison of the directivity patterns of left-handed and right-handed circular polarization at 4.5 GHz for a low-profile, wideband circularly polarized antenna based on a non-periodic regular hexagonal metasurface using characteristic mode analysis. DETAILED DESCRIPTION OF THE INVENTION

[0021] In order to more specifically describe the objectives, technical solutions, etc. of the present invention, the technical solutions of the present invention will be further described below in conjunction with the drawings.

[0022] As shown in Figure 1, the low-profile, wideband circularly polarized antenna based on the nonperiodic regular hexagonal metasurface constructed using characteristic mode analysis of the present invention mainly consists of an aperiodic metasurface on the upper dielectric layer, two dielectric layers, a metal ground plane with L-shaped slots, and a microstrip feeder. Specifically, it is divided into an aperiodic metasurface on the upper dielectric layer, an upper dielectric layer, a metal ground plane with L-shaped slots, a lower dielectric layer, and a microstrip feeder on the lower dielectric layer. The upper dielectric layer is made of f4b dielectric material with a dielectric constant of 3.5 and a dielectric loss angle of 0.0027. The lower dielectric layer is made of FR-4 dielectric material with a dielectric constant of 4.3 and a dielectric loss angle of 0.025. The metal metasurface, metal ground plane with L-shaped slots, and microstrip feeder are all bonded tightly to the dielectric layer. Both the upper and lower dielectric layers have a square structure with a side length of 42 mm and no slots or notches.

[0023] As shown in Figure 2, the top surface of the upper dielectric layer of the present invention is an aperiodic metasurface with a three-layer regular hexagonal arrangement. The gap between each metasurface unit is 0.3 mm, and the outer edge lengths of the three metasurface units are all 4 mm. From the center to the outside, the side lengths of the internal regular hexagonal cutouts are 3.5 mm, 3.2 mm, and 3.5 mm, respectively. The metal ground plane is a square with a side length of 42 mm, and the side lengths of the central regular hexagonal slot are 3.75 mm and 3.5 mm, respectively. The rectangular slot is 13.75 mm long and 3 mm wide. The short rectangular slot is 9 mm long and 3 mm wide. The two slots extend outward from the inner diameter of the central regular hexagonal ring.

[0024] As shown in Figure 2, the microstrip feeder on the lower surface of the lower dielectric layer of the present invention has a bent structure and is composed of two sections. The first section is a straight microstrip line with a length of 18 mm and a width of 6 mm. The second section is a curved section with a length of 8.8 mm and a width of 6 mm, a bent angle of 45°, a notch angle of 22.5°, and a width of 3 mm.

[0025] As shown in Figure 3, the height of the upper dielectric layer of the present invention is 5.5 mm, and the height of the lower dielectric layer is 2.67 mm. The aperiodic metasurface on the top surface of the upper dielectric layer, the upper dielectric layer, the slotted metal ground plane, the lower dielectric layer, and the microstrip feed line are all bonded together in close contact.

[0026] As shown in Figure 4, the present invention shows the first four modes of the metasurface structure obtained by characteristic mode analysis of the nonperiodic regular hexagonal metasurface. As can be seen from the figure, Modes 1 and 2 are completely identical and form a pair of degenerate modes. The mode salience of the entire metasurface can be controlled by adjusting the structural parameters of the nonperiodic metasurface. To avoid the influence of Modes 3 and 4 on the degenerate modes, the non-overlap bandwidth of Modes 3 and 4 should be increased and the overlap bandwidth of Modes 3 and 4 should be reduced. By controlling the structural parameters of the metasurface, the final mode salience of Modes 1 and 2 and the non-overlap bandwidth of Modes 3 and 4 are 1 GHz. After determining the metasurface parameters and mode salience, the microstrip feed line at the bottom excites Modes 1 and 2 of the nonperiodic metasurface on the top surface through the L-shaped slot. The different slot lengths allow for a 90° phase difference, thereby achieving circular polarization.

[0027] The present invention presents the S11 parameters of a low-profile, wideband, circularly polarized antenna based on aperiodic regular hexagonal metasurfaces using characteristic mode analysis, as shown in Figure 5. As can be seen from the figure, the -10 dB bandwidth of this antenna is 50% (3.2 GHz to 5.5 GHz), and the minimum return loss within the operating bandwidth is -26 dB.

[0028] As shown in Figure 6, the present invention provides a gain schematic diagram of a low-profile, wideband circularly polarized antenna based on a non-periodic regular hexagonal metasurface using characteristic mode analysis. As can be seen from the figure, the maximum gain in the circular polarization range is 6 dBi, and the maximum gain in the linear polarization range is 5.75 dBi.

[0029] As shown in Figure 7, the present invention provides a schematic diagram of the axial ratio of a low-profile, wideband, circularly polarized antenna based on a non-periodic regular hexagonal metasurface using characteristic mode analysis. As can be seen from the figure, the axial ratio bandwidth of this antenna is 24.5% (3.6 GHz to 4.55 GHz).

[0030] As shown in Figures 8, 9, and 10, the present invention demonstrates the radiation patterns of a low-profile, wideband circularly polarized antenna based on a non-periodic regular hexagonal metasurface using characteristic mode analysis at 3.5 GHz, 4 GHz, and 4.5 GHz. These include left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). As can be seen from the figures, the primary polarization of the antenna is left-hand circular polarization.

[0031] The top surface of the antenna of this invention has an aperiodic regular hexagonal annular metasurface structure. The regular hexagonal structure can be arranged in three directions, resulting in a stronger coupling effect and a smaller antenna profile. Using characteristic mode analysis, the aperiodic regular hexagonal annular metasurface on the top surface is analyzed to find the appropriate degenerate modes, and its surface current distribution is analyzed to find the appropriate feed position. Because the regular hexagonal annular metasurface structure on the top surface is aperiodic, adjusting the size of the regular hexagonal annular rings in each layer allows for control of the mode salience and current distribution throughout the metasurface and for finding the appropriate modes. After determining the overall size of the metasurface, the appropriate feed position is found from the current distribution obtained by characteristic mode analysis. This antenna is fed using an L-shaped aperture slot coupling feed method. This achieves circular polarization of the antenna, and by varying the lengths of the L-shaped aperture slots, two orthogonal modes of the metasurface are excited with a 90° phase difference. This invention applies characteristic mode analysis to an aperiodic regular hexagonal annular metasurface structure. The regular hexagonal structure enhances the coupling between the units and reduces the antenna profile. The aperiodicity also allows for control of the modes in the metasurface structure, simplifying the design process by finding the optimal mode. The low profile and circular polarization make this invention potentially useful for wireless communications.

[0032] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention, and it should be understood that the above-described embodiments are merely specific embodiments of the present invention and do not limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall all be included in the scope of protection of the present invention.

Claims

1. A wideband circularly polarized antenna based on characteristic mode analysis, comprising: From top to bottom, it includes an upper aperiodic regular hexagonal ring metasurface metal layer, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer, and a lower power supply network metal layer. the upper dielectric layer and the lower dielectric layer are adhered to a metal layer in that order, the geometric centers of the patterns of the upper dielectric layer, the intermediate metal layer, and the lower dielectric layer are all on the same line; the intermediate metal layer is a metal ground plane with an L-shaped slot in the middle; The two slots of the L-shaped slot have different lengths, and the side lengths are parallel to the outer shape of the antenna. The ground plate with the L-shaped slot is bonded to the upper and lower dielectric substrates in close contact with each other. the bottom of the lower dielectric layer is a feed network metal layer; The feed structure is a curved microstrip feed line, the upper surface of the upper dielectric layer is a three-layer aperiodic metasurface with a regular hexagonal arrangement; A wideband circularly polarized antenna characterized in that the gap between each metasurface unit is 0.3 mm, the outer side lengths of the three-layer metasurface units are all 4 mm, and the side lengths of the internal regular hexagonal cutouts from the center to the outside are 3.5 mm, 3.2 mm, and 3.5 mm, respectively.

2. The wideband circularly polarized antenna described in claim 1, characterized in that each metasurface unit of the upper-layer non-periodic regular hexagonal ring metasurface metal layer is a regular hexagonal ring and is composed only of regular hexagonal rings, and the overall metasurface structure is also hexagonal.

3. 2. The wideband circularly polarized antenna according to claim 1, wherein the entire antenna has a two-layer dielectric structure, a metal ground layer with an L-shaped slot etched therein is closely placed between the two dielectric layers, and the feed position is at the bottom of the lower dielectric layer.

4. The wideband circularly polarized antenna described in claim 2, characterized in that the metasurface units are all arranged in a regular hexagon, strengthening the coupling between each patch and reducing the antenna profile through enhanced coupling.

5. 4. The wideband circularly polarized antenna according to claim 3, wherein the feed structure at the bottom of the lower dielectric layer is a meandering microstrip feed line, and the lower microstrip feed line is coupled with the L-shaped slot in the intermediate metal ground layer to form a 90° phase difference, which excites a pair of degenerate modes obtained by characteristic mode analysis.

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