Metasurface circularly polarized antenna based on characteristic mode theory

Abstract

The invention provides a metasurface circularly polarized antenna based on a characteristic mode theory, and belongs to the technical field of antennae, the metasurface circularly polarized antenna comprises a metasurface, a first-layer dielectric substrate, a grounding plate, a second-layer dielectric substrate and an L-shaped microstrip line, and the grounding plate and the L-shaped microstrip line form a feed network; the method has the beneficial effects that the characteristic mode theory indicates that the characteristic mode of the passive conductor is only related to the structure of the passive conductor and is an inherent attribute, the potential modal behavior of the metasurface can be obtained through characteristic mode analysis, the radiation mode of the antenna can be predicted on the basis, and design and optimization of the antenna are guided; and the characteristic mode theory can guide how to reduce the mutual coupling effect between the array elements, and after the coupling generation mechanism is determined, mutual coupling between the array elements can be suppressed by increasing the inductive load, so that the antenna design based on the characteristic mode theory is clear and intuitive, and compared with a traditional method, a large amount of manpower and material resources can be saved, and the method has high practicability. And meanwhile, the design accuracy of the metasurface antenna can be ensured.

Description

Technical Field

[0001] The present invention relates to the field of antenna technology, and in particular to a metasurface circularly polarized antenna based on characteristic mode theory. Background Art

[0002] As an important component of wireless communication systems, antenna performance optimization and structural innovation have always been the key to antenna development. As wireless communication technology has developed to date, while spectrum resources are tight, massive data transmission has become an inevitable requirement for high-quality economic and social development.

[0003] In order to maintain the advantages of low profile, low cost and easy integration of microstrip antennas while broadening the working frequency band of the antenna, metasurface structures came into being. The metasurface structures can be used to convert linearly polarized waves into circularly polarized waves, thereby realizing the circular polarization of the antenna. The circularly polarized antenna loaded with a metasurface is simple to make, has a low profile and is inexpensive. It can not only improve the impedance bandwidth, axial ratio bandwidth and gain of the antenna, but also achieve the miniaturization of the antenna. However, compared with traditional microstrip patch antennas, the mathematical modeling of metasurface structures is more difficult and it is more difficult to obtain guidance on the direction of improving antenna performance. Therefore, in current satellite communications, in order to improve the reliability of signal transmission, the characteristic mode theory is introduced, and it is necessary to design a metasurface circularly polarized antenna; how to invent a metasurface circularly polarized antenna based on the characteristic mode theory to solve these problems has become an urgent problem to be solved by technicians in this field. Summary of the invention

[0004] In order to make up for the above shortcomings, the present invention provides a metasurface circularly polarized antenna based on characteristic mode theory, aiming to solve the problem that the mathematical modeling of the metasurface structure is more difficult than the traditional microstrip patch antenna and it is more difficult to obtain guidance on the direction of antenna performance improvement.

[0005] The present invention is achieved in that: The present invention provides a metasurface circularly polarized antenna based on characteristic mode theory, comprising a metasurface, a first dielectric substrate, a ground plane, a second dielectric substrate and an L-shaped microstrip line, wherein the metasurface comprises 16 4 4, the metasurface is printed on the upper surface of the first dielectric substrate, the ground plate is printed on the back of the first dielectric substrate, an H-shaped groove is opened on the side wall of the ground plate, the L-shaped microstrip line is printed on the lower surface of the second dielectric substrate, and the ground plate and the L-shaped microstrip line constitute a feeding network.

[0006] Preferably, the length and width of each I-shaped unit in the super surface structure are both 10 mm, the U-shaped groove in the I-shaped unit is 8 mm long and 3 mm wide, the super surface structure has a total of 16 units, and the distance between each unit is 0.4 mm.

[0007] Preferably, the L-shaped microstrip line is divided into two sections with lengths of 17 mm and 38 mm, widths of 3 mm and thicknesses of 1 mm.

[0008] Preferably, the grounding plate has a thickness of 0.813 mm, and the H-shaped groove is divided into three sections. The left and right vertical grooves have the same size, which is 20.4 mm long and 4 mm wide, and the middle horizontal groove has a length of 6 mm and a width of 4 mm.

[0009] Preferably, the relative dielectric constant of the first dielectric substrate is 3.38 and the thickness is 3.048 mm, and the relative dielectric constant of the second dielectric substrate is 3.38 and the thickness is 0.813 mm.

[0010] The beneficial effects of the present invention are: The present invention application points out through the characteristic mode theory that the characteristic mode of a passive conductor is only related to its own structure and is an inherent property. The potential modal behavior of the metasurface can be obtained through characteristic mode analysis, and on this basis, the radiation pattern of the antenna can be predicted and the design and optimization of the antenna can be guided. In addition, the characteristic mode theory can provide guidance on how to reduce the mutual coupling effect between array elements. After determining the mechanism of coupling, the mutual coupling between array elements can be suppressed by increasing the inductive load. Therefore, the antenna design based on the characteristic mode theory is clear and intuitive. Compared with the traditional method of blindly optimizing antenna parameters, it can save a lot of manpower and material resources, and at the same time ensure the accuracy of the metasurface antenna design. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 It is a front structural schematic diagram of a metasurface circularly polarized antenna based on characteristic mode theory provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of an exploded structure of a metasurface circularly polarized antenna based on characteristic mode theory provided in an embodiment of the present invention; Figure 3 is a MS curve diagram of a metasurface circularly polarized antenna based on characteristic mode theory provided in an embodiment of the present invention; Figure 4 It is a characteristic far-field diagram of a metasurface circularly polarized antenna based on characteristic mode theory provided by an embodiment of the present invention; Figure 5It is a characteristic current diagram of a metasurface circularly polarized antenna based on characteristic mode theory provided by an embodiment of the present invention; Figure 6 It is a characteristic angle curve diagram of a metasurface circularly polarized antenna based on characteristic mode theory provided by an embodiment of the present invention; Figure 7 A metasurface circularly polarized antenna based on characteristic mode theory provided by an embodiment of the present invention S 11 picture; Figure 8 It is an AR diagram of a metasurface circularly polarized antenna based on characteristic mode theory provided by an embodiment of the present invention; Fig. 9 It is a separate characteristic far-field pattern diagram of a metasurface circularly polarized antenna based on characteristic mode theory provided in an embodiment of the present invention.

[0013] In the figure: 1. metasurface; 2. first dielectric substrate; 3. ground plane; 4. second dielectric substrate; 5. L-shaped microstrip line; 6. H-shaped slot. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] Example, see Figure 1-Figure 8 A metasurface circularly polarized antenna based on characteristic mode theory includes a metasurface 1, a first dielectric substrate 2, a ground plane 3, a second dielectric substrate 4 and an L-shaped microstrip line 5. The metasurface 1 includes 16 4 4, the metasurface 1 is printed on the upper surface of the first dielectric substrate 2, the ground plate 3 is printed on the back of the first dielectric substrate 2, an H-shaped groove 6 is opened on the side wall of the ground plate 3, and an L-shaped microstrip line 5 is printed on the lower surface of the second dielectric substrate 4, and the ground plate 3 and the L-shaped microstrip line 5 constitute a feeding network.

[0016] Furthermore; the length and width of each I-shaped unit in the metasurface 1 structure are both 10 mm, the U-shaped groove in the I-shaped unit is 8 mm long and 3 mm wide, the metasurface 1 structure has a total of 16 units, and the distance between each unit is 0.4 mm; the L-shaped microstrip line 5 is divided into two sections with lengths of 17 mm and 38 mm, widths of 3 mm and thicknesses of 1 mm; the ground plate 3 is 0.813 mm thick, the H-shaped groove 6 is divided into three sections, the left and right vertical grooves have the same size, length of 20.4 mm, width of 4 mm, and the length of the middle horizontal groove is 6 mm and width of 4 mm; the relative dielectric constant of the first layer of dielectric substrate 2 is 3.38 and the thickness is 3.048 mm, and the relative dielectric constant of the second layer of dielectric substrate 4 is 3.38 and the thickness is 0.813 mm.

[0017] It should be noted that the feeding network includes a ground plate 3 with an H-shaped groove 6 and an L-shaped microstrip line 5 attached to the back of the second dielectric plate 4. The metasurface structure is analyzed by the characteristic mode theory, and the mode importance, characteristic current, characteristic angle and far-field diagram of this structure are calculated to determine whether the conditions for realizing circular polarization are met, and the optimal feeding position is determined according to the distributed current of the desired mode. The feeding network is designed. The realization of circular polarization based on the characteristic mode theory must correspond to four requirements: (1) The radiation far-field directivity is the same; (2) The mode current is orthogonally distributed; (3) The MS values ​​of the patterns are equal; (4) The characteristic angle difference is around 90 degrees; After finding the mode that meets the circular polarization antenna design, the antenna only needs to be fed appropriately to excite the desired mode without exciting the unwanted mode. In addition, in order to have high gain in the corresponding direction, the feed should provide good impedance matching for the symmetric mode without exciting the antisymmetric mode. For this device, symmetrical currents need to be excited to prevent exciting unwanted modes. In addition, it should be kept as consistent as possible with the model of characteristic analysis to keep the characteristic results less disturbed. Considering these factors, aperture feeding is a good choice for the antenna.

[0018] The working principle of the metasurface circularly polarized antenna based on the characteristic mode theory: the metasurface 1 antenna in the present application has two dielectric layers and three metal layers. The relative dielectric constant of the first dielectric substrate 2 is 3.38, the thickness is 3.048 mm, the loss tangent is set to 0, and a 4×4 unit I-shaped patch is printed on the upper surface; the relative dielectric constant of the second dielectric substrate 4 is 3.38, the thickness is 0.813, the loss tangent is set to 0, and an L-shaped microstrip line 5 is attached to the lower surface; the ground plate 3 is in the middle of the two dielectric substrates, and the ground plate 3 is a metal floor with a height of 0.813. An H-shaped groove 6 is dug in the middle, and the total thickness of the antenna is 4.674 mm; like Figure 2 The 4×4 I-shaped patch metasurface 1 array shown is printed on the first dielectric substrate 2. The relative dielectric constant of the first dielectric substrate 2 is 3.38 and the thickness is 3.048 mm. The period of the unit is 10 mm in both the x and y directions. The gap between each unit is 0.4 mm in both the x and y directions. The design starts with the I-shaped unit because the quasi-rectangular unit has better circular polarization properties than the rectangular unit. In the fundamental mode, the current flows over the entire antenna, which helps the radiation at lower frequencies. In the higher mode, the mode current mainly flows through part of the antenna (such as the internal 2×2 unit), which helps the radiation at higher frequencies. Unlike ordinary patch antennas, radiation occurs not only at the edges, but also at the gaps between the units, so there are more radiation modes and the choice of far-field electric field phase is more flexible. Since the modes existing in the metal material unit in these x and y directions are different from each other, it is able to excite two modes with a 90-degree difference in direction within a certain frequency range. Through the slots between the units, more than one mode can be excited. In order to better understand the modes existing in the antenna, the characteristic mode theory is used to analyze the unfed metasurface antenna. It is worth noting that the substrate and the ground plane are considered to be infinite. The modal importance of the first 10 modes is obtained as follows Figure 3 As shown in the figure, the resonance state and radiation capability of each mode can be seen through the mode significance (MS) curve. When the MS value of the mode (MS value refers to Metasurface) is greater than 0.707, it is considered to have the potential for resonance. The closer it is to 1, the easier it is to resonate, that is, the easier it is to radiate. When the MS value of the mode is less than 0.707, the energy is stored and it has no radiation capability. Figure 3 At medium and lower frequencies (such as 4GHz), only the modal significance of mode 1 is greater than 0.707, so only mode 1 is dominant in the antenna. As the frequency increases, the number of modes with relatively large modal significance will increase. In the 3-7GHz frequency band, only mode 10 has no resonance point, so mode 10 is no longer analyzed. The resonance points of mode 1, mode 2, mode 3, mode 4, mode 5, mode 6, mode 7, mode 8, and mode 9 are recorded as 4.17 GHz, 4.30 GHz, 4.77 GHz, 4.89 GHz, 5.01GHz, 6.99 GHz, 5.66 GHz, 4.48 GHz, and 5.60 GHz, respectively. To determine whether the conditions for circular polarization are met, observe the far-field pattern at each resonance point. Figure 4 , it can be found that only mode 1, mode 6, mode 8, and mode 9 radiate along the positive direction of the z-axis. These four modes ensure that the propagation direction of the electromagnetic field is consistent, so the characteristic currents of these four modes are as follows Figure 5 , Figure 5 Mode 1, mode 6 and mode 8 are orthogonal, and the currents of the three modes are symmetrical; the current of mode 9 is antisymmetric, which will lead to the cancellation of the electric field in the far field area in the positive direction of the z-axis, causing the antenna to have side lobes at higher frequencies, which well explains the reason for the appearance of side lobes in mode 9; The electromagnetic fields of the metasurface 1 antennas can be inferred to be orthogonal to each other through the orthogonal mode currents, so circular polarization can be achieved with only a 90-degree phase difference. The characteristic angle curve is as follows: Figure 6 The results show that the phase difference between mode 1 and mode 8 is close to 90 degrees in the frequency range of 4.46 GHz-4.50 GHz; the phase difference between mode 6 and mode 8 is close to 90 degrees in the frequency range of 6.5 GHz-6.9 There is a phase difference of nearly 90 degrees in the GHz frequency range; Mode 6 is in the high frequency band, and its modal importance at low frequencies is very low, so it is not easy to excite at low frequencies. Modes 1 and 8 are in the low frequency band and their potential bandwidth does not cover the frequency band of Mode 6. Their modal importance at high frequencies is extremely low, so they are not easy to excite at high frequencies. Modes 1 and 8 are selected as the desired modes, and only a suitable feeding structure is needed to excite these two modes; in order to have high gain in the corresponding direction, the feed should provide good impedance matching for the symmetric mode without exciting the antisymmetric mode. If there is only one mode with high modal importance, there can be more than one type of feed suitable for the antenna. For example, probe feeding, microstrip feeding, and aperture feeding can all be used for rectangular patch antennas. When there are multiple modes at the operating frequency, the feed needs to excite the required mode without exciting other modes. This requirement brings more restrictions to the feed design. For the antenna proposed in this article, it is necessary to excite symmetrical currents and keep the characteristic results as little perturbated as possible. Considering these factors, aperture feeding is a good choice for the antenna. In order to excite the desired mode, according to Figure 5 Characteristic current distribution of the desired mode Knowing that the current is mainly distributed in the four middle patches and the gap, a coupled feeding method is adopted, and a ground plate 3 with an H-shaped groove 6 is attached under the dielectric layer, and the point with the maximum current is taken as the best feeding point, and an L-shaped microstrip line 5 is used as the feed source, and the L-shaped microstrip line 5 is printed on the lower surface of the second dielectric substrate 4; In addition, the S11 of a metasurface circularly polarized antenna based on characteristic mode theory of the present invention is as follows: Figure 7 As shown, the vertical value dB represents decibel, AR is as follows Figure 8 As shown in the figure, the operating bandwidth is 4.3 GHz-4.65 GHz, the relative bandwidth is 7.82%, it has broadband properties, and circular polarization is achieved in the 4.48 GHz-4.52 GHz frequency band. Fig. 9It is a separate pattern diagram, where Phi (φ) represents the azimuth, which is an angle parameter used to describe the angle from the reference direction (usually north or the positive direction of the x-axis) to the target point in the horizontal plane in a clockwise direction, and Theta (θ) is a crucial parameter, which represents the angle of the incident plane wave relative to the antenna surface, that is, the incident angle of the incident plane wave, and Prop.Dir represents the propagation direction. Prop.Dir is usually used to describe the direction of the antenna main lobe, that is, the direction of the strongest radiation area of ​​the antenna.

[0019] It should be noted that the specific model and specifications of the motor need to be selected and determined based on the actual specifications of the device, and the specific selection calculation method adopts the existing technology in this field, so it will not be described in detail.

[0020] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A metasurface circularly polarized antenna based on characteristic mode theory, characterized in that: The invention comprises a metasurface (1), a first dielectric substrate (2), a ground plane (3), a second dielectric substrate (4) and an L-shaped microstrip line (5), wherein the metasurface (1) comprises 16 4 4, the metasurface (1) is printed on the upper surface of a first dielectric substrate (2), the grounding plate (3) is printed on the back of the first dielectric substrate (2), an H-shaped groove (6) is provided on the side wall of the grounding plate (3), the L-shaped microstrip line (5) is printed on the lower surface of a second dielectric substrate (4), and the grounding plate (3) and the L-shaped microstrip line (5) form a feeding network.

2. The metasurface circularly polarized antenna based on characteristic mode theory according to claim 1, characterized in that: The length and width of each I-shaped unit in the metasurface (1) structure are both 10 mm, the length of the U-shaped groove in the I-shaped unit is 8 mm and the width is 3 mm. The metasurface (1) structure has a total of 16 units, and the distance between each unit is 0.4 mm.

3. The metasurface circularly polarized antenna based on characteristic mode theory according to claim 1, characterized in that: The L-shaped microstrip line (5) is divided into two sections, with lengths of 17 mm and 38 mm, widths of 3 mm and thicknesses of 1 mm.

4. The metasurface circularly polarized antenna based on characteristic mode theory according to claim 1, characterized in that: The grounding plate (3) has a thickness of 0.813 mm. The H-shaped groove (6) is divided into three sections. The left and right vertical grooves have the same size, with a length of 20.4 mm and a width of 4 mm. The middle horizontal groove has a length of 6 mm and a width of 4 mm.

5. The metasurface circularly polarized antenna based on characteristic mode theory according to claim 1, characterized in that: The relative dielectric constant of the first dielectric substrate (2) is 3.38 and the thickness is 3.048 mm; the relative dielectric constant of the second dielectric substrate (4) is 3.38 and the thickness is 0.813 mm.

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