Broadband circularly polarized antenna based on feature 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 broadband circularly polarized antenna based on characteristic mode analysis and belongs to the field of microwave antenna technology.

Background Art

[0002] With the development of the era and the progress of science and technology, the requirements for antennas in wireless communication systems are increasing. In the case of linearly polarized antennas, it becomes impossible to meet the widely increasing communication demands in many scenarios, and circularly polarized antennas have many advantages that linearly polarized antennas do not have. The main advantages are as follows. (1) Resistance to clutter interference: Since circular polarization can change the rotation direction during propagation, clutter interference can be avoided. (2) Avoidance of multipath fading: Circular polarization has very little attenuation during propagation and can avoid multipath fading. (3) Avoidance of polarization mismatch: Circular polarization can avoid the polarization mismatch phenomenon that occurs during propagation. Therefore, circularly polarized antennas can meet the wide range of demands of wireless communication systems, and the research on high-performance and widely applicable circularly polarized antennas has become a research hotspot.

[0003] Metasurface is composed of a two-dimensional planar array of sub-wavelength metals and has unique properties that do not exist in nature, such as negative refractive index and negative permeability, providing a new direction for the control of electromagnetic waves. The excellent electromagnetic wave control characteristics of metasurface bring many application scenarios in the improvement of antenna performance, broaden the direction of antenna design, and effectively solve the bottleneck problems of many conventional antennas. There are several special application directions for metasurface. For example, exciting the metasurface with an antenna as a power supply, directly using the metasurface to improve the performance of the antenna, or using the metasurface as the radiation surface of the antenna, etc. Therefore, the reasonable use of metasurface is important for modern antenna design.

[0004] Traditional circularly polarized antenna design relied heavily on the engineer's experience. With advancements in science and technology, feature mode theory has become widely used as a guideline for antenna design. Feature mode theory combines the advantages of both analytical and numerical methods, allowing for the orthogonal expansion of surface currents in conductors, and the feature electric fields generated by these feature currents are also orthogonal. In feature mode theory, a feature mode refers to a current mode corresponding to a feature vector, allowing for the numerical analysis of conductors of any shape. Feature modes are attributes of the conductor itself and relate only to the physical properties of the conductor. Feature mode theory can analyze antenna radiation, select appropriate feature modes, and provide a theoretical basis for selecting the feed point.

[0005] To design high-performance circularly polarized antennas, both metasurface and feature mode analysis are being applied to low-profile, broadband circularly polarized antennas using aperiodic hexagonal metasurfaces.

[0006] Existing circularly polarized antennas have many drawbacks: (1) Existing circularly polarized antennas are relatively large, lack flexibility, and are unsuitable for integration. (2) Existing circularly polarized antennas have a relatively narrow axial ratio bandwidth. (3) The feeding methods of existing circularly polarized antennas are often complex, and complex feeding structures make design difficult, increase costs, and simultaneously affect antenna stability. Therefore, the current focus of circularly polarized antenna design is to design a circularly polarized antenna that is small, has a wide axial ratio bandwidth, and uses a simple feeding method. [Overview of the project] The problem to be solved

[0007] The objective of the present invention is to solve the shortcomings and deficiencies of the above-mentioned existing technologies and to provide a broadband circularly polarized antenna based on feature mode analysis. This broadband circularly polarized antenna features a wide axial ratio bandwidth, a low profile, and a simple feeding structure. It is easy to design and manufacture due to its low profile, and it simplifies broadband circularly polarized antennas using feature mode analysis. By combining a non-periodic regular hexagonal metasurface with feature mode analysis, analyzing the non-periodic regular hexagonal metasurface using feature mode analysis, and controlling the width of the non-periodic regular hexagonal metasurface, appropriate modes and mode strife are found, and an appropriate feeding position is found from the current distribution of the modes, thereby realizing broadband circular polarization. [Means for solving the problem]

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

[0009] The broadband circularly polarized antenna, based on characteristic mode analysis, includes, from top to bottom, an upper non-periodic regular hexagonal annular metasurface metal layer, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer, and a lower feeding network metal layer. The upper and lower dielectric layers are bonded in close contact with the metal layers in that order. The geometric centers of the patterns of the upper dielectric layer, intermediate metal layer, and lower dielectric layer are all collinear. The intermediate metal layer is a metal grounding plate with an L-shaped slot in the middle, where the two slots of the L-shaped slot have different lengths and their side lengths are parallel to the outer shape of the antenna. The L-shaped slotted grounding plate is bonded in close contact with the upper and lower dielectric substrates. The bottom of the lower dielectric layer is a feeding network metal layer, and the feeding structure is a curved microstrip feed line.

[0010] Furthermore, each metasurface unit of the upper non-periodic hexagonal annular metasurface metal layer of the present invention is a hexagonal ring and is composed solely of hexagonal rings, and the overall metasurface structure also exhibits a hexagonal shape. The side length of the square of the upper and lower dielectric layers is 42 mm or more, the plan view of the upper and lower dielectric layers is a standard square, and the surface of the upper dielectric layer is a non-periodic hexagonal metasurface. The upper dielectric layer consists of a dielectric and a non-periodic hexagonal metasurface on the upper surface of the dielectric layer. The metasurface on the surface of the upper dielectric layer is a non-periodic metasurface with a hexagonal outer contour and has a three-layer structure containing 19 metasurface units in total. Each individual metasurface unit is also a hexagon, with equal spacing and the same side length. All metasurface units are arranged in a hexagonal pattern, which strengthens the coupling between each patch, and this strengthening of coupling reduces the antenna profile.

[0011] Furthermore, the width of each layer of the aperiodic hexagonal annular metasurface metal layer of the upper dielectric layer of the present invention is adjustable, and the mode characteristics 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 hexagonal rings at different positions, the mode characteristics and current distribution can be changed. In addition, by analyzing the mode saturation of the aperiodic hexagonal annular metasurface metal layer with different parameters using characteristic mode analysis, the influence of higher-order modes on the adopted degenerate mode can be reduced, and an optimal current distribution can be obtained to reduce the influence of higher-order mode currents on the adopted degenerate mode. All of the hexagonal metasurfaces on the upper surface of the upper dielectric layer are annular structures, and the width of the hexagonal rings of the metasurfaces of each layer can be controlled. Since the modes and surface currents of the hexagonal metasurfaces formed by combinations of different widths are different, the optimal characteristic mode for realizing circular polarization can be found by controlling the width of the rings of the metasurface unit.

[0012] The aforementioned grounding plate with intermediate slots is bonded in close contact with the upper dielectric layer and the lower dielectric layer, and the upper metasurface metal layer and the lower power supply network metal layer are not in substantial contact. The distance between the upper dielectric layer and the grounding plate with intermediate slots is the thickness of the upper dielectric layer, and the distance between the lower power supply network layer and the grounding plate with intermediate slots is the thickness of the lower dielectric layer.

[0013] Furthermore, the entire antenna of the present invention has a two-layer dielectric structure, with an L-shaped slot etched into a metal ground plate in close contact between the two dielectric layers, and the feed point is 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, and in order to obtain circularly polarized radiation, the lower microstrip feed line is coupled with the L-shaped slot of the intermediate metal ground plate to form a 90° phase difference, exciting a pair of degenerate modes obtained by characteristic mode analysis. The slot of the intermediate slotted ground plate has an L-shaped structure, and the center of the slot is a regular hexagonal ring, which better excites the regular hexagonal metasurface ring at the center of the upper surface of the upper dielectric layer. The lengths of the two walls of the L-shaped slot are different, but the width is the same, which realizes a 90° phase difference and excites the degenerate modes of the metasurface.

[0014] The materials of the upper and lower dielectric layers of this invention are the same, but their thicknesses differ, and their outer contours in the plan view are the same. The lower power supply network layer and the grounding plate with intermediate slots are both bonded in close contact with the dielectric layers.

[0015] The feeding structure of the low-profile broadband circularly polarized antenna of the present invention is located on the underside of the lower dielectric layer, and the antenna employs a microstrip coupled feeding method. The microstrip wire has a curved structure, and the radiated energy passes through a slotted grounding plate to excite a non-periodic metasurface on the upper surface of the upper dielectric layer. [Effects of the Invention]

[0016] This invention provides a method for realizing a low-profile, broadband circularly polarized antenna using a non-periodic hexagonal metasurface with feature mode analysis, filling a gap in broadband circular polarization using non-periodic metasurfaces. Compared to conventional circularly polarized antennas, this low-profile, broadband circularly polarized antenna using a non-periodic hexagonal metasurface innovatively designs the metasurface into a hexagonal structure, analyzes the overall structure of the metasurface using feature mode analysis, finds the optimal mode and current distribution for realizing broadband circular polarization, and allows adjustment of the width of each layer's hexagonal ring to control the overall mode and current distribution of the metasurface. At the same time, the hexagonal arrangement strengthens the coupling between surfaces and reduces the antenna profile. This circularly polarized antenna employs a microstrip coupled feeding method, and analyzes the current distribution of the metasurface using feature mode analysis to find a suitable feeding method and feeding position for realizing circular polarization, simplifying the feeding design of the circularly polarized antenna. The feeding structure of this antenna is simple and easy to manufacture, significantly reducing costs. With its smaller size, wider circular polarization bandwidth, and simpler power supply method, the present invention offers a greater range of applications in communication systems.

[0017] 1. The antenna surface of the present invention is a non-periodic regular hexagonal annular metasurface structure, and since the regular hexagonal structure can be arranged in three directions, it has a stronger coupling effect and can reduce the antenna profile.

[0018] 2. The present invention analyzes the aperiodic regular hexagonal annular metasurface on the upper surface using a characteristic mode analysis method to find an appropriate degenerate mode and to find an appropriate feeding position by analyzing its surface current distribution. Since the regular hexagonal annular metasurface structure on the upper surface is aperiodic, the mode saturation and current distribution of the entire metasurface can be controlled by adjusting the size of the regular hexagonal rings in each layer, and an appropriate mode can be found. After determining the size of the entire metasurface, an appropriate feeding position is found from the current distribution obtained by characteristic mode analysis, and this antenna is fed using an L-shaped aperture slot coupled feeding method to achieve circular polarization of the antenna. The lengths of the L-shaped aperture slots are different, achieving a 90° phase difference to excite two orthogonal modes of the metasurface.

[0019] 3. This invention applies feature mode analysis to a non-periodic regular hexagonal annular metasurface structure. The regular hexagonal structure enhances coupling between units and reduces the antenna profile. The non-periodic nature allows for controllable modes of the metasurface structure, enabling the discovery of optimal modes and simplifying the metasurface design process. Due to its low profile and circular polarization, this invention is expected to have significant applications in the field of wireless communication. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic diagram of the structural decomposition of a low-profile broadband circularly polarized antenna using a non-periodic hexagonal metasurface based on the characteristic mode analysis of the present invention. [Figure 2] This invention provides a plan view and a bottom view of a low-profile broadband circularly polarized antenna using a non-periodic hexagonal metasurface based on characteristic mode analysis. [Figure 3] This is a side view of a low-profile broadband circularly polarized antenna using a non-periodic hexagonal metasurface based on the characteristic mode analysis of the present invention. [Figure 4] This paper demonstrates the mode splendor of a low-profile, broadband, circularly polarized antenna metasurface using a non-periodic hexagonal metasurface based on feature mode analysis. [Figure 5]Shows the S11 parameter of a low-profile broadband circularly polarized antenna using an aperiodic regular hexagonal metasurface with characteristic mode analysis. [Figure 6] It is the gain diagram of a low-profile broadband circularly polarized antenna using an aperiodic regular hexagonal metasurface with characteristic mode analysis. [Figure 7] It is the axial ratio bandwidth of a low-profile broadband circularly polarized antenna using an aperiodic regular hexagonal metasurface with characteristic mode analysis. [Figure 8] It is a comparison diagram of the radiation patterns of the left-handed circular polarization and right-handed circular polarization of a low-profile broadband circularly polarized antenna using an aperiodic regular hexagonal metasurface with characteristic mode analysis at 3.5 GHz. [Figure 9] It is a comparison diagram of the radiation patterns of the left-handed circular polarization and right-handed circular polarization of a low-profile broadband circularly polarized antenna using an aperiodic regular hexagonal metasurface with characteristic mode analysis at 4 GHz. [Figure 10] It is a comparison diagram of the radiation patterns of the left-handed circular polarization and right-handed circular polarization of a low-profile broadband circularly polarized antenna using an aperiodic regular hexagonal metasurface with characteristic mode analysis at 4.5 GHz.

Embodiments for Carrying Out the Invention

[0021] To more specifically explain the object, technical solution, etc. of the present invention, the technical solution of the present invention will be further described below in conjunction with the drawings.

[0022] As shown in Figure 1, the low-profile broadband circularly polarized antenna using a non-periodic hexagonal metasurface based on the characteristic mode analysis of the present invention mainly consists of a non-periodic metasurface on the upper surface of the upper dielectric layer, two dielectric layers, a metal grounding plate with an L-shaped slot, and a microstrip feed line. Specifically, it can be divided into a non-periodic metasurface on the upper surface of the upper dielectric layer, the upper dielectric layer, the metal grounding plate with an L-shaped slot, the lower dielectric layer, and the microstrip feed line on the underside of the lower dielectric layer. The upper dielectric layer uses an f4b dielectric material with a dielectric constant of 3.5 and a dielectric loss angle of 0.0027. The lower dielectric layer uses an FR-4 dielectric material with a dielectric constant of 4.3 and a dielectric loss angle of 0.025. The metal metasurface, the metal grounding plate with an L-shaped slot, and the microstrip feed line are all bonded in close contact with the dielectric layers. Both the upper and lower dielectric layers have a square structure with a side length of 42 mm, and there are no slots or notches.

[0023] As shown in Figure 2, the upper surface of the upper dielectric layer of the present invention is a non-periodic metasurface arranged in a three-layer regular hexagonal configuration, with a gap of 0.3 mm between each metasurface unit, and the outer side length of all three metasurface units being 4 mm. From the center outward, the side lengths of the internal regular hexagonal cutouts are 3.5 mm, 3.2 mm, and 3.5 mm, respectively. The metal grounding plate is a square with a side length of 42 mm, and the side lengths of the central regular hexagonal slots are 3.75 mm and 3.5 mm, respectively. The rectangular slot has a length of 13.75 mm and a width of 3 mm. The rectangular slot has a length of 9 mm and a width of 3 mm. The two slots extend outward from the inner diameter of the central regular hexagonal ring.

[0024] As shown in Figure 2, the microstrip power supply line on the underside of the lower dielectric layer of the present invention has a bent structure and is composed of two parts. The first part is a straight microstrip with a length of 18 mm and a width of 6 mm. The second part is a curved section with a length of 8.8 mm and a width of 6 mm, with a curved section 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 upper surface of the upper dielectric layer, the upper dielectric layer, the slotted metal grounding plate, the lower dielectric layer, and the microstrip power supply line are all tightly bonded together.

[0026] As shown in Figure 4, the present invention illustrates the first four modes of a metasurface structure obtained by characteristic modal analysis of a nonperiodic hexagonal metasurface. As can be seen from the drawing, modes 1 and 2 are completely identical and constitute a pair of degenerate modes. The mode stellarity 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-overlapping bandwidth of modes 3 and 4 should be increased, and the overlapping bandwidth of modes 3 and 4 should be decreased. By controlling the structural parameters of the metasurface, the final obtained mode stellarity of modes 1 and 2, and the non-overlapping bandwidth of modes 3 and 4, is 1 GHz. After determining the parameters and mode stellarity of the metasurface, the microstrip feed lines at the bottom excite modes 1 and 2 of the upper nonperiodic metasurface via L-shaped slots. The different lengths of the slots allow for a 90° phase difference, thereby achieving circular polarization.

[0027] As shown in Figure 5, the present invention presents the S11 parameters of a low-profile broadband circularly polarized antenna using a non-periodic hexagonal metasurface with feature mode analysis. As can be seen from the drawing, the -10dB bandwidth of this antenna is 50% (3.2GHz to 5.5GHz), and the minimum return loss within the operating bandwidth is -26dB.

[0028] As shown in Figure 6, the present invention is a schematic diagram of the gain of a low-profile broadband circularly polarized antenna using a non-periodic hexagonal metasurface with feature 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 is a schematic diagram of the axial ratio of a low-profile broadband circularly polarized antenna using a non-periodic regular hexagonal metasurface based on feature mode analysis. As can be seen from the drawing, 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 at 3.5 GHz, 4 GHz, and 4.5 GHz for a low-profile broadband circularly polarized antenna using a non-periodic regular hexagonal metasurface with feature mode analysis. Both left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) are included, and as can be seen from the figures, the primary polarization scheme of the antenna is left-handed circular polarization.

[0031] The antenna surface of this invention is a non-periodic regular hexagonal annular metasurface structure. Since the regular hexagonal structure can be arranged in three directions, it has a stronger coupling effect and can reduce the antenna profile. Using a feature mode analysis method, the non-periodic regular hexagonal annular metasurface of the surface is analyzed to find an appropriate degenerate mode, and its surface current distribution is analyzed to find an appropriate feeding position. Since the regular hexagonal annular metasurface structure of the surface is non-periodic, the mode saturation and current distribution of the entire metasurface can be controlled by adjusting the size of the regular hexagonal rings in each layer, and an appropriate mode can be found. After determining the size of the entire metasurface, an appropriate feeding position is found from the current distribution obtained by feature mode analysis. This antenna is fed using an L-shaped aperture slot coupled feeding method. This realizes circular polarization of the antenna, and by making the lengths of the L-shaped aperture slots different, two orthogonal modes of the metasurface are excited with a 90° phase difference. This invention applies feature 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. Furthermore, the aperiodicity allows for controllable modes of the metasurface structure, enabling the discovery of the optimal mode and thus simplifying the metasurface design process. Due to its low profile and circular polarization, this invention is expected to have significant applications in the field of wireless communication.

[0032] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that these are merely specific embodiments of the present invention and do not limit the scope of protection of the present invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should all be included within the scope of protection of the present invention.

Claims

1. A broadband circularly polarized antenna based on characteristic mode analysis, From top to bottom, it includes an upper non-periodic regular hexagonal annular 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 bonded to the metal layer in close contact in that order. The geometric centers of the upper dielectric layer, the intermediate metal layer, and the lower dielectric layer all lie on the same line. The aforementioned intermediate metal layer is a metal grounding plate with an L-shaped slot in the middle. The rectangular slots and short rectangular slots constituting the L-shaped slots are of different lengths, the sides of the rectangular slots and short rectangular slots are parallel to the straight outer edges of the upper dielectric layer, the intermediate metal layer, and the lower dielectric layer, and the L-shaped slotted grounding plate is bonded in close contact with the upper and lower dielectric substrates. The bottom of the aforementioned lower dielectric layer is a power supply network metal layer. The power supply structure is a curved microstrip power supply line. The upper surface of the aforementioned upper dielectric layer is a non-periodic metasurface arranged in a three-layer regular hexagonal configuration. A broadband circularly polarized antenna characterized by a gap of 0.3 mm between each metasurface unit, an outer side length of 4 mm for each of the three layers of metasurface units, and side lengths of the internal regular hexagonal notches from the center outward being 3.5 mm, 3.2 mm, and 3.5 mm respectively.

2. The broadband circularly polarized antenna according to claim 1, characterized in that each metasurface unit of the upper non-periodic regular hexagonal ring-shaped metasurface metal layer is a regular hexagonal ring and is composed solely of regular hexagonal rings.

3. The broadband circular polarization antenna according to claim 1, characterized in that the entire antenna of the broadband circular polarization antenna has a two-layer dielectric structure, a metal ground layer with an L-shaped slot is placed in close contact between the two dielectric layers, and the feed point is at the bottom of the lower dielectric layer.

4. The broadband circular polarization antenna according to claim 2, characterized in that the metasurface units are all arranged in a regular hexagon, strengthening the coupling between each metasurface unit and reducing the antenna profile by strengthening the coupling.

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

Images