Wideband circularly polarized antenna based on characteristic mode analysis

Abstract

Disclosed in the present invention is a wideband circularly polarized antenna based on characteristic mode analysis. An upper surface of the antenna is of an aperiodic regular hexagonal ring-shaped metasurface structure, and regular hexagonal structures can be arranged in three directions, such that a stronger coupling effect can be achieved, and the profile of the antenna can be reduced. The overall modal significance and current distribution of a metasurface can be controlled by means of adjusting the size of a regular hexagonal ring of each layer, so as to find an appropriate mode. After the overall size of the metasurface is determined, an appropriate feed position is found by means of the current distribution obtained by means of characteristic mode analysis, and the antenna uses the mode of coupled feeding with an L-shaped open slot to feed the antenna. The present invention applies characteristic mode analysis to an aperiodic regular hexagonal ring-shaped metasurface structure, regular hexagonal structures enhance coupling between units, such that the antenna profile is reduced, and aperiodicity can make the mode of the metasurface structure controllable, so as to find the most appropriate mode, thereby simplifying the metasurface design process.

Description

A broadband circularly polarized antenna based on eigenmode analysis Technical Field

[0001] The invention relates to a broadband circularly polarized antenna based on characteristic mode analysis, and belongs to the technical field of microwave antennas. Background Art

[0002] With the development of the times and the advancement of science and technology, the requirements for antennas in wireless communication systems are getting higher and higher. Linear polarization antennas can no longer meet the widely growing communication needs in many scenarios. Circular polarization antennas have many advantages that linear polarization antennas do not have, mainly including: (1) Anti-interference by clutter. Circular polarization waves can change their rotation direction during propagation, thus avoiding clutter interference; (2) Circular polarization waves have very little attenuation during propagation, thus avoiding multipath fading. (3) Circular polarization waves can avoid polarization mismatch during propagation. Therefore, circular polarization antennas can meet the widely growing needs of wireless communication systems, and the development of high-performance, widely used circular polarization antennas has become a research hotspot.

[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, offering new avenues for electromagnetic wave manipulation. Their exceptional electromagnetic wave manipulation properties offer numerous applications for improving antenna performance, broadening antenna design possibilities and effectively addressing many bottlenecks inherent in traditional antennas. Metasurfaces have several unique applications, such as using antennas as feed sources to excite metasurfaces, directly enhancing antenna performance, and even using metasurfaces as antenna radiating surfaces. Therefore, the rational use of metasurfaces is crucial for modern antenna design.

[0004] The design of traditional circularly polarized antennas relies heavily on the experience of engineers. With the advancement of technology, characteristic mode theory has been widely used to guide antenna design. Combining the advantages of both analytical and numerical methods, characteristic mode theory can perform an orthogonal expansion of the surface currents of conductors, and the characteristic electric fields generated by these characteristic currents are also orthogonal. In characteristic mode theory, characteristic modes refer to the current patterns corresponding to the characteristic vectors, thus enabling numerical analysis of conductors of arbitrary shapes. Characteristic modes are properties of the conductor itself that are solely related to the physical properties of the conductor itself. Characteristic mode theory can analyze the radiation of the antenna and select the appropriate characteristic mode, providing a theoretical basis for the selection of the feed position.

[0005] In order to design a high-performance circularly polarized antenna, metasurface and eigenmode analysis are applied to the non-periodic regular hexagonal metasurface low-profile broadband circularly polarized antenna.

[0006] Existing circularly polarized antennas have numerous shortcomings: 1) Existing circularly polarized antenna designs are relatively large, lacking flexibility and hindering integration. 2) Existing circularly polarized antennas have a relatively narrow axial bandwidth. 3) Existing circularly polarized antenna feeding methods are often complex, making complex feeding structures difficult to design, increasing costs and affecting antenna stability. Therefore, designing a circularly polarized antenna with a wide axial bandwidth, small size, and simple feeding method using the smallest possible dimensions has become a key focus in current circularly polarized antenna design. Summary of the Invention

[0007] The purpose of the present invention is to address the defects and shortcomings of the above-mentioned prior art and propose a broadband circularly polarized antenna based on characteristic mode analysis. The broadband circularly polarized antenna has a wide axial ratio bandwidth, a low profile, a simple feeding structure, etc., and is low-profile and easy to design and process. It simplifies the broadband circularly polarized antenna using characteristic mode analysis, combines the non-periodic regular hexagonal metasurface with the characteristic mode analysis, and uses the characteristic mode analysis to analyze the non-periodic regular hexagonal metasurface. By controlling the width of the non-periodic regular hexagonal metasurface, the appropriate mode and modal significance are found, and the appropriate feeding position is found by the current distribution of the mode to achieve broadband circular polarization.

[0008] The technical solution adopted by the present invention to solve its technical problems is: a broadband circularly polarized antenna based on characteristic mode analysis, which includes, from top to bottom, an upper non-periodic regular hexagonal ring-shaped metasurface metal layer, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer, and a lower feed network metal layer. The upper dielectric layer and the lower dielectric layer are tightly fitted with the metal layer in sequence. 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 straight line. The intermediate metal layer is a metal ground plate with an L-shaped slot in the middle. The two slots of the L-shaped slot are of different lengths, and the side lengths are parallel to the outer contour of the antenna. The L-shaped slotted grounded metal layer is tightly attached to the upper and lower dielectric substrates. The bottom of the lower dielectric layer is the feed network metal layer, and the feeding structure is a curved microstrip feeder.

[0009] Furthermore, each supersurface unit of the upper non-periodic regular hexagonal ring-type supersurface metal layer of the present invention is a regular hexagonal ring, and is composed only of regular hexagonal rings, and the entire supersurface structure is also hexagonal. The square side length of the upper dielectric layer and the lower dielectric layer is not less than 42 mm, the top view of the upper dielectric layer and the lower dielectric layer is a standard square, and the surface of the upper dielectric layer is a non-periodic regular hexagonal supersurface. The upper dielectric layer is composed of a dielectric and a non-periodic regular hexagonal supersurface on the upper surface of the dielectric layer. The supersurface on the surface of the upper dielectric layer is a non-periodic supersurface with an outer contour of a regular hexagon. The overall structure is a three-layer structure containing 19 supersurface units. Each individual supersurface unit is also a regular hexagon, with equal spacing and the same side length. The supersurface units are all arranged in a regular hexagon, which enhances the coupling between the patches, and the enhanced coupling reduces the cross-section of the antenna.

[0010] Furthermore, the width of each layer of the non-periodic regular hexagonal ring-type metasurface metal layer of the upper dielectric layer of the present invention can be adjusted. The mode characteristic value and current distribution of the metasurface structure can be obtained by analyzing the metasurface structure using characteristic mode analysis. By adjusting the width of the regular hexagonal rings at different positions, the mode characteristic value and current distribution can be changed. In addition, the mode significance of the non-periodic regular hexagonal ring-type metasurface metal layer with different parameters is analyzed using characteristic mode analysis to reduce the influence of high-order modes on the adopted merged mode, and at the same time, the most suitable current distribution is obtained to reduce the influence of high-order mode current on the adopted merged mode. The regular hexagonal metasurface on the upper surface of the upper dielectric layer is a ring structure. The width of the regular hexagonal ring of each layer of the metasurface can be controlled. The regular hexagonal metasurface modes formed by different width combinations are different, and the surface currents are different. Therefore, by controlling the width of the metasurface unit ring, the most suitable characteristic mode for achieving circular polarization can be found.

[0011] The middle slotted grounding metal layer is tightly fitted with the upper dielectric layer and the lower dielectric layer. The upper super-surface metal layer has no substantial contact with the lower feed network metal layer. The distance between the upper dielectric layer and the middle slotted grounding metal layer is the thickness of the upper dielectric layer, and the distance between the lower feed network layer and the middle slotted grounding metal layer is the thickness of the lower dielectric layer.

[0012] Furthermore, the entire antenna of the present invention has a dual-dielectric layer structure. A metal grounding layer etched with an L-shaped gap is located between the two dielectric layers, and the feeding position is at the bottom of the antenna dielectric layer. The feeding structure at the bottom of the antenna dielectric layer is a zigzag microstrip feeder. In order to obtain circularly polarized radiation, the bottom microstrip feeder is coupled with the L-shaped slot of the middle metal grounding layer to form a 90° phase difference to excite a pair of merged modes obtained by characteristic mode analysis. The slot of the middle slotted grounding metal layer is an L-shaped structure, and the center of the slot is a regular hexagonal ring to better excite the regular hexagonal metasurface ring at the center of the upper surface of the upper dielectric layer. The two walls of the L-shaped slot are of different lengths but the same width, so as to achieve a 90° phase difference to excite the merged mode of the metasurface.

[0013] The upper dielectric layer and the lower dielectric layer of the present invention are made of the same material but different thicknesses and have the same outer contours in top view. The lower feed network layer and the middle slotted grounding metal layer are both tightly fitted to the dielectric layer.

[0014] The feeding structure of the low-profile broadband circularly polarized antenna of the present invention is on the lower surface of the lower dielectric layer. The antenna adopts a microstrip coupling feeding method. The microstrip line has a curved structure. The radiated energy passes through the slotted grounded metal layer to excite the non-periodic metasurface on the upper surface of the upper dielectric layer. Beneficial effects:

[0015] The present invention uses a method for realizing a low-profile broadband circularly polarized antenna using a non-periodic regular hexagonal metasurface based on characteristic mode analysis, filling the gap in the realization of broadband circular polarization using non-periodic metasurfaces. Compared with traditional circularly polarized antennas, this non-periodic regular hexagonal metasurface low-profile broadband circularly polarized antenna innovatively designs the metasurface into a regular hexagonal structure. The characteristic mode analysis method is used to analyze the overall structure of the metasurface to find the mode and current distribution that are most suitable for achieving broadband circular polarization. The width of each layer of regular hexagonal rings can be adjusted to control the overall mode and current distribution of the metasurface. At the same time, the regular hexagonal arrangement enhances the coupling between the surfaces and reduces the cross-section of the antenna. This circularly polarized antenna adopts a microstrip coupling feeding method. The characteristic mode analysis is used to analyze the current distribution of the metasurface to find the feeding method and feeding position suitable for achieving circular polarization, simplifying the feeding design of the circularly polarized antenna. This antenna feeding structure is simple and easy to manufacture, which greatly reduces the cost. The smaller size, wider circular polarization bandwidth, and simpler feeding method make the present invention have greater application space in communication systems.

[0016] Beneficial effects:

[0017] 1. The upper surface of the antenna of the present invention is a non-periodic regular hexagonal ring-shaped metasurface structure. Since the regular hexagonal structure can be arranged in three directions, it has a stronger coupling effect and can reduce the cross-section of the antenna.

[0018] 2. The present invention uses the characteristic mode analysis method to analyze the non-periodic regular hexagonal ring-type metasurface on the upper surface to find a suitable merged mode, and analyzes its surface current distribution to find a suitable feeding position. Since the regular hexagonal ring-type metasurface structure on the upper surface is non-periodic, the modal significance and current distribution of the metasurface as a whole can be controlled by adjusting the size of the regular hexagonal rings of each layer to find a suitable mode. After determining the overall size of the metasurface, the current distribution obtained by the characteristic mode analysis is used to find a suitable feeding position. This antenna uses L-shaped open slot coupling feeding to feed the antenna, realizing circular polarization of the antenna. The slot lengths of the L-shaped open slots are different to achieve a 90° phase difference to excite the two orthogonal modes of the metasurface.

[0019] 3. This invention applies eigenmode analysis to a non-periodic, regular hexagonal ring-shaped metasurface structure. The regular hexagonal structure enhances coupling between elements and reduces the antenna profile. The non-periodic nature allows for controllable metasurface modes to find the most optimal mode, simplifying the metasurface design process. The low profile and circular polarization make this invention promising for applications in wireless communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a schematic diagram of the structural decomposition of a low-profile broadband circularly polarized antenna implemented in the present invention using a non-periodic regular hexagonal metasurface based on characteristic mode analysis.

[0021] FIG2 shows the top view and bottom view of the low-profile broadband circularly polarized antenna implemented by the present invention using a non-periodic regular hexagonal metasurface based on characteristic mode analysis.

[0022] FIG3 is a side view of a low-profile broadband circularly polarized antenna implemented using a non-periodic regular hexagonal metasurface analyzed by characteristic modes in the present invention.

[0023] Figure 4. Mode saliency of a non-periodic regular hexagonal metasurface for realizing a low-profile broadband circularly polarized antenna using eigenmode analysis.

[0024] Figure 5 S11 parameters of a low-profile broadband circularly polarized antenna achieved using a non-periodic regular hexagonal metasurface analyzed using characteristic modes.

[0025] Figure 6 shows the gain diagram of a low-profile broadband circularly polarized antenna achieved using a non-periodic regular hexagonal metasurface analyzed using eigenmodes.

[0026] Figure 7 Axial ratio bandwidth of a low-profile broadband circularly polarized antenna achieved using a non-periodic regular hexagonal metasurface analyzed using characteristic modes.

[0027] Figure 8 compares the 3.5 GHz left-hand circular polarization and right-hand circular polarization radiation patterns of the low-profile broadband circularly polarized antenna realized using a non-periodic regular hexagonal metasurface with characteristic mode analysis.

[0028] Figure 9 compares the 4 GHz left-hand circular polarization and right-hand circular polarization radiation patterns of a low-profile broadband circularly polarized antenna realized using a non-periodic regular hexagonal metasurface with characteristic mode analysis.

[0029] Figure 10 shows a comparison of the 4.5 GHz left-hand circular polarization and right-hand circular polarization radiation patterns of a low-profile broadband circularly polarized antenna realized using a non-periodic regular hexagonal metasurface with characteristic mode analysis. DETAILED DESCRIPTION

[0030] In order to more specifically explain the purpose, technical solutions, etc. of the present invention, the technical solutions of the present invention are further described below with reference to the accompanying drawings.

[0031] As shown in Figure 1, the present invention uses a non-periodic regular hexagonal metasurface of characteristic mode analysis to realize a low-profile broadband circularly polarized antenna, which is mainly composed of a non-periodic metasurface on the upper surface of the upper dielectric layer, two dielectric layers, an L-shaped slotted metal ground backplane and a microstrip feeder. It is divided into: a non-periodic metasurface on the upper surface of the upper dielectric layer, an upper dielectric layer, an L-shaped slotted metal ground backplane, a lower dielectric layer, and a microstrip feeder on the lower surface of the lower dielectric layer. The upper dielectric layer adopts f4b dielectric material with a dielectric constant of 3.5 and a dielectric loss angle of 0.0027. The lower dielectric layer adopts FR-4 dielectric material with a dielectric constant of 4.3 and a dielectric loss angle of 0.025. The metal metasurface, the L-shaped slotted metal ground backplane and the microstrip feeder are all tightly attached to the dielectric layer. The upper and lower dielectric layers are both square structures with a side length of 42 mm and do not have any slots or cut corners.

[0032] As shown in Figure 2, the upper surface of the upper dielectric layer of the present invention is a non-periodic metasurface with three layers of regular hexagonal arrangement. The gap between each metasurface unit is 0.3mm. The outer side lengths of the three layers of metasurface units are the same, all 4mm. From the center outward, the side lengths of the inner regular hexagonal grooves are 3.5mm, 3.2mm, and 3.5mm, respectively. The metal grounding backplane is a square with a side length of 42mm. The side lengths of the central regular hexagonal grooves are 3.75mm and 3.5mm, respectively. The long rectangular groove is 13.75mm long and 3mm wide. The short rectangular groove is 9mm long and 3mm wide. Both grooves extend outward from the inner diameter of the central regular hexagonal ring.

[0033] As shown in FIG2 , the microstrip feed line on the lower surface of the lower dielectric layer of the present invention has a zigzag structure consisting of two parts. The length of the straight line of the first microstrip is 18 mm and the width is 6 mm. The length of the curved part of the second part is 8.8 mm and the width is 6 mm. The angle of the curved part is 45°, the angle of the cut angle is 22.5°, and the width is 3 mm.

[0034] 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 non-periodic metasurface on the upper surface of the upper dielectric layer, the upper dielectric layer, the slotted metal ground backplane, the lower dielectric layer, and the microstrip feeder are all tightly fitted.

[0035] As shown in Figure 4, the present invention is the first four modes of the metasurface structure obtained by analyzing the characteristic modes of the non-periodic regular hexagonal metasurface. It can be seen from the figure that mode one and mode two are exactly the same as a pair of merged modes. By adjusting the structural parameters of the non-periodic metasurface, the modal significance of the metasurface as a whole can be controlled. In order to avoid the influence of mode three and mode four on the merged mode, the non-overlapping bandwidth of mode three and mode four should be expanded, and the overlapping bandwidth of mode three and mode four should be reduced. By controlling the structural parameters of the metasurface, the mode significance of mode one and mode two and the non-overlapping bandwidth of mode three and mode four are finally obtained to be 1GHz. After determining the metasurface parameters and modal significance, the bottom microstrip feed line excites mode one and mode two of the non-periodic metasurface on the upper surface through the L-shaped slot. Due to the different slot lengths, a phase difference of 90° can be achieved, thereby realizing circular polarization.

[0036] As shown in Figure 5, the present invention uses a non-periodic regular hexagonal metasurface based on characteristic mode analysis to achieve the S11 parameters of a low-profile broadband circularly polarized antenna. It can be seen from the figure that the -10dB bandwidth of this antenna is 50% (3.2GHz-5.5GHz), and the minimum return loss within the working bandwidth is -26dB.

[0037] As shown in Figure 6, the present invention is a schematic diagram of the gain of a low-profile broadband circularly polarized antenna achieved by using a non-periodic regular hexagonal metasurface analyzed by characteristic mode. The figure shows that the maximum gain is 6dBi in the circular polarization range and 5.75dBi in the linear polarization range.

[0038] As shown in FIG7 , the present invention is a schematic diagram of the axial ratio of a low-profile broadband circularly polarized antenna achieved by using a non-periodic regular hexagonal metasurface analyzed by characteristic mode. The figure shows that the axial ratio bandwidth of this antenna is 24.5% (3.6 GHz-4.55 GHz).

[0039] As shown in Figures 8, 9, and 10, the present invention uses a non-periodic regular hexagonal metasurface based on characteristic mode analysis to achieve the 3.5GHz, 4GHz, and 4.5GHz radiation patterns of a low-profile broadband circularly polarized antenna, including left-hand circular polarization (LFCP) and right-hand circular polarization (RFCP). It can be seen from the figure that the main polarization mode of the antenna is left-hand circular polarization.

[0040] The upper surface of the antenna of the present invention is a non-periodic regular hexagonal ring-type metasurface structure. Since the regular hexagonal structure can be arranged in three directions, it has a stronger coupling effect and can reduce the cross-section of the antenna. The non-periodic regular hexagonal ring-type metasurface on the upper surface is analyzed using the characteristic mode analysis method to find a suitable merged mode, and its surface current distribution is analyzed to find a suitable feeding position. Since the regular hexagonal ring-type metasurface structure on the upper surface is non-periodic, the modal significance and current distribution of the entire metasurface can be controlled by adjusting the size of the regular hexagonal rings of each layer to find a suitable mode. After determining the overall size of the metasurface, the current distribution obtained by the characteristic mode analysis is used to find a suitable feeding position. This antenna is fed by L-shaped open slot coupling feeding. Circular polarization of the antenna is achieved, and the slot lengths of the L-shaped open slots are different to achieve a 90° phase difference to excite two orthogonal modes of the metasurface. This invention applies eigenmode analysis to a non-periodic, regular hexagonal ring-shaped metasurface structure. The regular hexagonal structure enhances coupling between elements and reduces the antenna's profile. The non-periodic nature allows for controllable modes in the metasurface structure to find the most suitable mode, simplifying the metasurface design process. The low profile and circular polarization make this invention promising for applications in wireless communications.

[0041] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A broadband circularly polarized antenna based on characteristic mode analysis, characterized in that: from top to bottom, it includes an upper non-periodic regular hexagonal ring-shaped metasurface metal layer, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer, and a lower feed network metal layer, wherein the upper dielectric layer and the lower dielectric layer are closely attached to the metal layer in sequence, and 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 straight line, and the intermediate metal layer is a metal ground plate with an L-shaped slot in the middle, and the two slots of the L-shaped slot are 1 / 40mm long. The lengths of the L-shaped slotted grounded metal layers are different, and the side lengths are parallel to the outer contour of the antenna. The L-shaped slotted grounded metal layer is close to the upper and lower dielectric substrates. The bottom of the lower dielectric layer is the feed network metal layer, and the feeding structure is a curved microstrip feeder. The upper surface of the upper dielectric layer is a non-periodic metasurface with three layers of regular hexagonal arrangement. The gap between each metasurface unit is 0.3mm, and the outer side lengths of the three-layer metasurface units are the same, all 4mm. The side lengths of the inner regular hexagonal grooves from the center to the outside are 3.5mm, 3.2mm, and 3.5mm respectively.

2. The broadband circularly polarized antenna based on characteristic mode analysis according to claim 1, characterized in that: Each supersurface unit of the upper non-periodic regular hexagonal ring-type supersurface metal layer is a regular hexagonal ring and is only composed of regular hexagonal rings, and the entire supersurface structure is also hexagonal.

3. The broadband circularly polarized antenna based on characteristic mode analysis according to claim 1, characterized in that: The entire broadband circularly polarized antenna is a double dielectric layer structure, a metal grounding layer etched with an L-shaped gap is closely attached to the middle of the two dielectric layers, and the feeding position is at the bottom of the antenna dielectric layer.

4. The broadband circularly polarized antenna based on characteristic mode analysis according to claim 2, characterized in that: The metasurface units are arranged in regular hexagons to enhance the coupling between patches. The enhanced coupling reduces the cross-section of the antenna.

5. The broadband circularly polarized antenna based on characteristic mode analysis according to claim 3, characterized in that: The feeding structure at the bottom of the antenna dielectric layer is a zigzag microstrip feed line. The bottom microstrip feed line is coupled with the L-shaped slot of the middle metal ground layer to form a 90° phase difference to excite a pair of merged modes obtained by characteristic mode analysis.

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