Single Dirac cone directional antenna based on gyromagnetic photonic crystal

Abstract

The invention relates to the field of directional antennas, in particular to a single Dirac cone directional antenna based on gyromagnetic photonic crystals. Three dielectric cylinders and a gyromagnetic YIG column are adopted to construct regular hexagonal primitive cells, an upper magnet layer and a lower magnet layer are assisted to provide a magnetic field, the primitive cells are adaptively and tightly arranged into an array antenna, and the boundary of the array antenna where an excitation source is located is set to be a 120-degree zigzag perfect electric conductor boundary. According to the single Dirac cone directional antenna, directional regulation and control of the antenna can be carried out through adjustment of parameters such as a magnetic field, an antenna structure and frequency, and the single Dirac cone directional antenna has the characteristic of multi-degree-of-freedom adjustment; the antenna device can continue to work under the condition that the antenna device has defects, and the robustness is high; the method can be used for directional detection and interference resistance; the structure is simple, the directivity is determined, the direction can be locked as long as a single Dirac cone is generated, and small-angle high-orientation emission is achieved. The problems that an existing directional antenna is relatively low in adjustment degree and insufficient in robustness are effectively solved.

Description

Technical Field

[0001] The invention relates to the field of directional antennas, in particular to a single Dirac cone directional antenna based on gyromagnetic photonic crystals. Background Art

[0002] Gyromagnetic photonic crystals have attracted widespread attention in recent years. The main material used in gyromagnetic photonic crystals is gyromagnetic ferrite, which has a non-reciprocal property, that is, under an external magnetic field, the non-diagonal quantities of its magnetic permeability tensor have opposite signs, resulting in the property that electromagnetic waves can only pass in one direction. By forming an array of non-reciprocal photonic crystals, edge state transmission with unidirectional transmission and immunity to defects can be formed at the edge of the array.

[0003] Typically, in topological photonics, the valley Hall effect, that is, the separation of valley states and the formation of topologically protected valley polarization states, often requires breaking the spatial inversion symmetry in the photonic crystal structure. For example, by introducing different refractive indices in the lattice or changing the geometry, an energy gap can appear in the energy band structure originally at the K point and K' point, thereby forming valley polarization. The valley Hall effect breaks the spatial inversion symmetry, but still retains the time reversal symmetry. However, when the time reversal symmetry is also broken, the phenomenon of a single Dirac cone can be achieved by adjusting the competition between the two symmetries.

[0004] The design methods of traditional directional antennas revolve around antenna structure, beamforming, gain optimization, feeding system and other aspects. For example, reflector antennas and horn antennas usually rely on specific shapes, materials and structures to obtain directivity and gain. Once defects occur in the antenna itself (material and / or structure), it will not work properly, that is, the anti-defect capability is poor; at the same time, reflected signals are easy to generate, and traditional directional antennas need to perform impedance matching to prevent the generation of reflected signals. The single Dirac cone directional antenna is a new type of antenna designed using the principles of topological photonics, relying on the topological properties of materials (such as topological edge states or surface states) to achieve directional radiation. Compared with traditional directional antennas, topological antennas have higher robustness and immunity to defects and environmental disturbances in design, and can also achieve new beam control and directional radiation characteristics. Summary of the invention

[0005] In order to solve the problems existing in the above-mentioned traditional directional antennas, the present invention provides a single Dirac cone directional antenna based on gyromagnetic photonic crystals. Due to its topological protection property under specific conditions, it has some advantages over traditional antennas: strong robustness and can work even when the device has defects; wide application, directional detection and anti-interference, etc.; many degrees of control freedom, for example, magnetic field, shape, frequency, etc. can all control the directionality; simple structure and good directionality.

[0006] In order to achieve the above object, the specific technical solution of the present invention is as follows:

[0007] A single Dirac cone directional antenna based on gyromagnetic photonic crystal has a three-layer stacked structure, which includes an upper magnetic layer, a functional layer and a lower magnetic layer from top to bottom.

[0008] The upper and lower magnet layers are both metal plates embedded with magnet columns, and are arranged one by one on the upper and lower magnet layers of the functional layer in a way that the center of a magnet column in the thickness direction coincides with the center of a unit cell gyromagnetic YIG column. One gyromagnetic YIG column corresponds to two magnet columns in the upper and lower parts. The magnetic poles of the magnet columns embedded in the same magnet layer have the same direction. The magnet columns are fixed in the metal plates and do not contact the gyromagnetic YIG columns, thereby providing a magnetic field through the upper and lower magnet layers, and the magnetic field size is 0.35T<B<0.5T. The metal plates are perfect electrical conductor layers on the upper and lower parts of the functional layer, used to form a waveguide cavity.

[0009] The functional layer is composed of periodically arranged primitive cells; the planar shape of the primitive cell is a regular hexagon, in which a gyromagnetic YIG column and three dielectric columns that do not touch each other are arranged, and the interlayer structure of the primitive cell is that a regular hexagonal metal layer is adaptively aligned above and below the gyromagnetic YIG column and the three dielectric columns, forming a gap structure in which the upper and lower metal layers clamp the gyromagnetic YIG column and the three dielectric columns.

[0010] The lattice constant of the primitive cell is a>0, and the antenna operating frequency changes with the change of a; a diagonal line of the regular hexagon of the primitive cell is taken as the longitudinal Y axis, and the midline of the opposite side perpendicular to the diagonal line is taken as the transverse X axis: the initial positions of the three dielectric columns are respectively positive left, upper right and lower right, and the three dielectric columns form an equilateral triangle, and the center point of the equilateral triangle is the coordinate origin; θ is the angle of the three dielectric columns rotating counterclockwise around the center. The gyromagnetic YIG column and the three dielectric columns are all cylinders, the radius r of the gyromagnetic YIG column satisfies 0<r<0.5a, the radius r' of the dielectric column satisfies 0<r'<r, and the center distance between the gyromagnetic YIG column and the dielectric column is d, which satisfies r+r'<d<0.5a-0.5r'. A single Dirac cone is formed by adjusting the parameters a, B, r', r, d and θ.

[0011] Arrangement period of primitive cells: Adaptively spliced ​​and arranged in sequence based on the sides of regular hexagons in the rated area, requiring that the number of primitive cells in the X-axis direction and the Y-axis direction are both greater than 5, and satisfying that the setting boundary where the excitation source is located is a 120° sawtooth perfect conductor boundary formed by regular hexagons arranged along the X-axis direction, and the other sides of the rated area are open boundaries with no requirements; for the sake of aesthetics or ease of processing, it can be made into a rectangular array.

[0012] Furthermore, the upper and lower magnet layers are sandwich structures with a light material in the middle.

[0013] Furthermore, the upper metal layer of the intermediate functional layer and the metal layer of the upper magnetic layer are a common metal layer, or the lower metal layer of the intermediate functional layer and the metal layer of the lower magnetic layer are a common metal layer.

[0014] Furthermore, the single Dirac cone formed by adjusting the parameters a, B, r', r, d and θ is used to adjust the directivity of the antenna.

[0015] In summary, the present invention uses three dielectric columns and one gyromagnetic YIG column to construct a regular hexagonal primitive cell, and uses the upper and lower magnet layers to provide a magnetic field, so that the primitive cells are adaptively and tightly arranged into an array antenna, and the array antenna boundary where the excitation source is located is set to a 120° sawtooth perfect conductor boundary. The single Dirac cone directional antenna of the present invention can be adjusted by parameters such as magnetic field, antenna structure, and frequency to control the directionality of the antenna, and has multi-degree-of-freedom adjustment characteristics; it can continue to work when the antenna device has defects, and has high robustness; it can be used for directional detection and anti-interference; it has a simple structure and determined directionality. As long as a single Dirac cone is generated, the direction of the outgoing wave will be locked in the wave vector direction corresponding to the single Dirac cone, achieving high directional emission at a small angle. It effectively solves the problem of relatively low adjustment degree and insufficient robustness of existing directional antennas. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The single Dirac cone directional antenna primitive cell and structure diagram of the embodiment;

[0017] Figure 2 is a schematic diagram of an interlayer cross-section of a single Dirac cone directional antenna of an embodiment;

[0018] Figure 3 The supercell structure and energy band diagram of the embodiment;

[0019] Figure 4 is a radiation pattern of a single Dirac cone directional antenna of an embodiment;

[0020] Figure 5 This is a sample defect example test diagram of a single Dirac cone antenna of an embodiment;

[0021] Figure 6 Schematic diagram of directional detection of a single Dirac cone antenna in an embodiment;

[0022] Figure 7 This is an anti-interference test diagram of the single Dirac cone antenna of the embodiment. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0024] A single Dirac cone directional antenna based on gyromagnetic photonic crystal, such as Figure 1As shown, the antenna array built from primitive cells ultimately forms a single Dirac cone directional antenna.

[0025] In this example, the original cell ( Figure 1 a) The lattice constant a=17.5 mm, the radius of the gyromagnetic YIG column r=0.14a, the radius of the dielectric column r'=0.8r, the center distance between the gyromagnetic YIG column and the dielectric column d=0.35a, the initial positions of the three dielectric columns are positive left, upper right and lower right, respectively, the three dielectric columns form an equilateral triangle, and θ is the angle of the three dielectric columns rotating counterclockwise around the center.

[0026] The relative dielectric constants of the gyromagnetic YIG column and the dielectric column are ε1=14.3 and ε2=4.4 respectively. The relative permeability tensor of YIG is:

[0027]

[0028] where μ r =1+(ω0+iαω)ω m / ((ω0+iαω) 2 -ω 2 ), κ=ωω m / ((ω0+iαω) 2 -ω 2 ),ω m =γM s ,ω0=γH0,γ=1.76×10 11 s -1 T -1 , α=0.0088. r represents the diagonal component of the relative permeability tensor, κ represents the off-diagonal component of the relative permeability tensor, ω m represents the saturated Larmor precession frequency, ω0 represents the Larmor precession frequency, H0 is the external magnetic field, γ is the gyro magnetic ratio, α is the damping coefficient, ω is the operating frequency, and M s is the saturation magnetization.

[0029] The single Dirac cone directional antenna based on gyromagnetic photonic crystal designed in this embodiment has a top view of the arrangement of the functional layer primitive cells as shown in FIG. Figure 1 As shown in b, the array is a 29*12 array with θ=10.3° (29 is the number of primitive cells in the X-axis direction, and 12 is the number of primitive cells in the Y-axis direction), and the lower boundary is a 120° sawtooth PEC perfect conductor boundary, which is used for directional emission by generating eigenmode electromagnetic waves within a specific wave vector range in the array.

[0030] Figure 2 The schematic diagram of the interlayer structure of the single Dirac cone directional antenna of this embodiment is divided into three layers, the upper and lower magnetic layers and the middle functional layer. The plates are bonded and fixed with copper tape. The excitation source is welded on Figure 1 b The position of the orange five-pointed star, where energy is supplied through the coaxial line of the vector network analyzer (model ZNB20).

[0031] The upper and lower magnet layers are used to apply a magnetic field B = 0.4T to YIG. The magnet layer is composed of two 1mm high copper plates and a 3mm thick acrylic plate in the middle to fix the magnet. The upper and lower copper plates are used to place the magnets to attract each other during installation. The magnet material is neodymium iron boron, with a height of 3mm and a radius of 4mm.

[0032] The height of the gyromagnetic YIG column and the dielectric column in the middle functional layer are both 7 mm, and the lower metal layer is a perforated copper plate with a height of 0.5 mm, which is used to fix the four columns (YIG column and dielectric column).

[0033] Among them, this embodiment omits the upper metal layer of the middle functional layer, and adopts a lightweight acrylic plate structure with an intermediate sandwich for the upper and lower magnetic layers, without affecting the overall antenna performance: on the one hand, it improves the convenience of the assembly process, and on the other hand, it improves the lightweight of the overall antenna.

[0034] The single Dirac cone directional antenna of the present invention is based on gyromagnetic photonic crystal, and its working principle is as follows:

[0035] like Figure 3 (a) is a supercell formed by an array of 16 primitive cells with θ = 10.3. The left and right sides of the supercell are periodic boundary conditions, and the top and bottom are open boundary conditions and perfect conductor boundary conditions, respectively. By performing a parametric scan of the supercell of 16 units in the irreducible Brillouin zone, we can obtain Figure 3 (b) The corresponding energy band, in which 8.9 GHz-9.5 GHz corresponds to the state of a single Dirac cone. When the excitation source generates excitation in this frequency band, the body state corresponding to the single Dirac cone will be excited in the array.

[0036] exist Figure 1 (b) Insert the coaxial line port probe of the vector network analyzer at the orange star, and feed the power through the coaxial line. Since there is an eigenmode at the single Dirac cone, it can stimulate body propagation, and the wave vector range of the corresponding body mode is very small. The wave vector corresponds to the propagation direction of the electromagnetic mode in free space. The small wave vector range corresponds to the outgoing wave with a small angle range in free space.

[0037] Figure 4(a) is the radiation of the embodiment antenna, where the upper rectangular area is air, and the lower rectangular area is the embodiment antenna array, which is excited by the source at the position of the orange five-pointed star. In the antenna sample, the rotation angle of the dielectric column is θ=10.3, the applied magnetic field is 0.4T, and the feeding is performed by a vector network analyzer. The body mode is successfully excited at 8.9GHz, and the body mode propagates into the free space as a highly directional wave. (b) The figure shows the far field diagram on the plane. According to the solution, the equivalent wavelength of f=8.9GHz at B=0.4T is 33.708mm; in order to calculate the far field, we select a semicircle with a radius of 1000mm, which is much larger than 10 times the equivalent wavelength. We place this semicircle on the exit surface and place 181 points every 1° to detect the energy corresponding to different positions. Finally, the normalized directional diagram is drawn. It can be seen that at 8.9GHz, corresponding to the field diagram, a highly directional wave is generated near 41°. Figure (c) shows that in the frequency band from 8.9 GHz to 9.5 GHz, the outgoing waves have a small angular range and a bandwidth of 0.6 GHz.

[0038] Figure 5 To explore the robustness of the antenna in the example, (a)-(c) the defects in the functional layer are gradually increased, and (d) a PEC is inserted into the functional layer. From (a) to (c), the defects in the functional layer gradually increase from 8 unit cells to 18 and then to 29. It can be seen that the corresponding Ez field diagram below still has good directivity; this shows that the single Dirac cone directional antenna has a certain degree of immunity to internal defects, which is the result of topological protection. Similarly, a PEC rod is added horizontally to the sample, as shown in Figure (d), and the corresponding Ez field diagram radiated energy still has good directionality. The single Dirac cone directional antenna is highly robust to defects and PECs, which is a feature that traditional directional antennas do not have.

[0039] Directional detection and anti-interference:

[0040] The most typical application of single Dirac cone directional antenna is radar detection, such as Figure 6 In the two figures (a)(b), the yellow five-pointed star and the blue five-pointed star are two signal sources that transmit energy, and the red five-pointed star is a receiving probe. Due to the asymmetry of the single Dirac cone, only one electromagnetic wave corresponding to the direction of the valley can be incident from the free space into the functional layer and become a body wave, which can be detected by the receiving probe. However, since the emission sources at other positions do not satisfy the momentum matching relationship, their energy is strongly reflected at the interface between the free space and the sample, so that the energy cannot be detected at the receiving probe. Therefore, this high directivity can be used to determine the position of the target, which is particularly advantageous in long-distance detection.

[0041] Another typical application of single Dirac cone directional antenna is anti-interference. Figure 7In (a), there are two sources, 1 and 3, where 1 is the target source and 3 is the interference source. When the two sources excite electromagnetic waves at the same time, the waves of the two sources will interfere with each other in free space and affect the reception. However, when the waves pass through the functional layer, the antenna has a filter-like effect and can only filter out waves in one direction, so it can effectively filter out interference waves in other directions. Figure 7 (b) gives the corresponding s21 and s23. It can be clearly seen that the transmission gap between s21 and s23 is about 15 dB between 8.7 GHz and 9.5 GHz, which is very different.

[0042] It can be seen from the above embodiments that the single Dirac cone directional antenna based on gyromagnetic photonic crystal provided by the present invention is feasible, and has the characteristics of multi-degree-of-freedom adjustment (such as magnetic field, antenna structure, frequency, etc. can cause the corresponding single Dirac cone energy band structure to produce frequency offset, thereby changing the emission direction to regulate the directivity), high robustness (continue to work when the antenna device has defects); can be used for directional detection and anti-interference; simple structure, determined directionality, as long as a single Dirac cone is generated, the direction of the outgoing wave will be locked in the wave vector direction corresponding to the single Dirac cone, achieving small-angle highly directional emission.

Claims

1. A single Dirac cone directional antenna based on gyromagnetic photonic crystal, characterized in that: It is a three-layer laminated structure, which includes an upper magnetic layer, a functional layer and a lower magnetic layer from top to bottom; The upper and lower magnet layers are both metal plates embedded with magnet columns, and are arranged one by one on the upper and lower magnet layers of the middle functional layer in a way that the center of a magnet column in the thickness direction coincides with the center of a unit cell gyromagnetic YIG column, and one gyromagnetic YIG column corresponds to a total of two magnet columns on the upper and lower sides; the magnet columns embedded in the same magnet layer have the same magnetic pole direction, and the magnet columns are fixed in the metal plates and do not contact the gyromagnetic YIG columns, thereby providing a magnetic field through the upper and lower magnet layers, and the magnetic field size is 0.35T<B<0.5T; the metal plates are perfect electrical conductor layers on the upper and lower sides of the functional layer, and are used to form a waveguide cavity; The functional layer is composed of periodically arranged primitive cells; the plane shape of the primitive cell is a regular hexagon, in which a gyromagnetic YIG column and three dielectric columns that do not touch each other are arranged, and the interlayer structure of the primitive cell is that a regular hexagonal metal layer is arranged above and below the gyromagnetic YIG column and the three dielectric columns in an adaptive alignment, forming a gap structure in which the upper and lower metal layers clamp the gyromagnetic YIG column and the three dielectric columns; The lattice constant of the primitive cell is a>0, and the antenna operating frequency changes with the change of a; a diagonal line of the regular hexagon of the primitive cell is taken as the longitudinal Y axis, and the midline of the opposite side perpendicular to the diagonal line is taken as the transverse X axis: the initial positions of the three dielectric columns are respectively positive left, upper right and lower right, and the three dielectric columns form an equilateral triangle, and the center point of the equilateral triangle is the coordinate origin; θ is the angle of the three dielectric columns rotating counterclockwise around the center together; the gyromagnetic YIG column and the three dielectric columns are all cylinders, the radius r of the gyromagnetic YIG column satisfies 0<r<0.5a, the radius r' of the dielectric column satisfies 0<r'<r, and the center distance between the gyromagnetic YIG column and the dielectric column is d, which satisfies r+r'<d<0.5a-0.5r'; a single Dirac cone is formed by adjusting the parameters a, B, r', r, d and θ; Arrangement period of primitive cells: Adaptively spliced ​​and arranged in sequence based on the sides of regular hexagons in the rated area. The number of primitive cells in the X-axis and Y-axis directions is required to be greater than 5, and the setting boundary where the excitation source is located is a 120° serrated perfect conductor boundary formed by regular hexagons arranged along the X-axis direction. The other sides of the rated area are open boundary shapes with no requirements.

2. The single Dirac cone directional antenna based on gyromagnetic photonic crystal as claimed in claim 1, characterized in that: The upper and lower magnet layers are sandwich structures with light materials in the middle.

3. The single Dirac cone directional antenna based on gyromagnetic photonic crystal as claimed in claim 1, characterized in that: The intermediate light material interlayer is an acrylic plate.

4. The single Dirac cone directional antenna based on gyromagnetic photonic crystal as claimed in claim 1, characterized in that: The upper metal layer of the intermediate functional layer and the metal layer of the upper magnetic layer are a common metal layer, or the lower metal layer of the intermediate functional layer and the metal layer of the lower magnetic layer are a common metal layer.

5. The single Dirac cone directional antenna based on gyromagnetic photonic crystal as claimed in claim 1, characterized in that: The a=17.5 mm, θ=10.3°, magnetic field B=0.4 T, d=0.35 a, r=0.14 a, r'=0.8 r, and the relative dielectric constants of the gyromagnetic YIG column and the dielectric column are ε1=14.3 and ε2=4.4 respectively.

6. The single Dirac cone directional antenna based on gyromagnetic photonic crystal according to claim 1, characterized in that: The single Dirac cone formed by adjusting the parameters a, B, r', r, d and θ is used to adjust the directivity of the antenna.

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