A single Dirac cone directional antenna based on gyromagnetic photonic crystal

Abstract

The present invention relates to the field of directional antennas, specifically a single Dirac cone directional antenna based on gyromagnetic photonic crystals. The present invention uses three dielectric columns and one gyromagnetic YIG column to construct a regular hexagonal unit cell, and uses upper and lower magnet layers to provide a magnetic field. The unit 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 outgoing wave is generated, the direction will be locked to achieve high directional emission at a small angle. It effectively solves the problem of relatively low adjustment degree and insufficient robustness of existing directional antennas.

Description

Technical Field

[0001] The present 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. These crystals primarily utilize gyromagnetic ferrites, which exhibit a nonreciprocal property: under an applied magnetic field, the off-diagonal quantities of their magnetic permeability tensor have opposite signs, resulting in a unidirectional transmission of electromagnetic waves. Arraying these nonreciprocal photonic crystals allows for unidirectional, defect-immune edge state transmission at the edges of the array.

[0003] Typically, in topological photonics, the valley Hall effect, which separates valley states and forms topologically protected valley polarization states, often requires breaking spatial inversion symmetry in the photonic crystal structure. For example, by introducing different refractive indices or changing the geometry in the lattice, energy gaps can appear in the band structure originally at the K and K' points, thereby forming valley polarization. The valley Hall effect breaks spatial inversion symmetry but retains time reversal symmetry. However, when 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 aspects such as antenna structure, beamforming, gain optimization, and feeding systems. For example, reflector antennas and horn antennas usually rely on specific shapes, materials, and structures to obtain directivity and gain. Once defects appear 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 easily generated, and traditional directional antennas require 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. It relies on the topological properties of the material (such as topological edge states or surface states) to achieve directional radiation. Compared with traditional directional antennas, topological antennas have higher design robustness and immunity to defects and environmental disturbances, and can 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.; multiple degrees of freedom of control, such as magnetic field, shape, frequency, etc., can all control directionality; simple structure and good directionality.

[0006] In order to achieve the above object, the specific technical solutions of the present invention are 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 magnetic layers are metal plates embedded with magnetic pillars. They are arranged one-to-one above and below the functional layer, with the thickness center of each magnetic pillar aligned with the center of a unit cell gyromagnetic YIG pillar. Each gyromagnetic YIG pillar corresponds to two magnet pillars, one above and one below. The magnetic poles of the magnet pillars embedded in the same magnetic layer are aligned. The magnet pillars are fixed in the metal plates and do not contact the gyromagnetic YIG pillars, thus providing a magnetic field through the upper and lower magnetic layers with a magnitude of 0.35T < B < 0.5T. The metal plates serve as perfect electrical conductors above and below the functional layers, forming a waveguide cavity.

[0009] The functional layer is composed of periodically arranged unit cells; the planar shape of the unit cell is a regular hexagon, and a gyromagnetic YIG column and three dielectric columns that do not touch each other are provided therein. The interlayer structure of the unit 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 unit cell, a, is greater than 0, and the antenna operating frequency changes with changes in a. A diagonal of the unit cell's regular hexagon serves as the longitudinal Y-axis, and the midline of the opposite side perpendicular to it serves as the transverse X-axis. The three dielectric pillars are initially positioned at the left, upper right, and lower right, respectively, forming an equilateral triangle with the center of the triangle serving as the coordinate origin. θ is the angle of counterclockwise rotation of the three dielectric pillars around the center. The gyromagnetic YIG pillar and the three dielectric pillars are cylindrical. The radius r of the gyromagnetic YIG pillar satisfies 0 < r < 0.5a, and the radius r' of the dielectric pillar satisfies 0 < r' < r. The distance d between the centers of the circle of the gyromagnetic YIG pillar and the dielectric pillar 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 the primitive cells: Adaptively spliced ​​and arranged in sequence within the rated area based on the sides of a regular hexagon. The number of primitive cells in both the X-axis and Y-axis directions must be greater than 5. The setting boundary where the excitation source is located must be a 120° sawtooth perfect conductor boundary formed by regular hexagons arranged along the X-axis. The other sides of the rated area are open boundaries with no shape requirements. For aesthetics or ease of processing, a rectangular array can be made.

[0012] Furthermore, the upper and lower magnet layers are sandwich structures with a lightweight 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 adjusted using simulation software 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 upper and lower magnet layers to provide a magnetic field. 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 the 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 even 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 This is a diagram of the original cell and structure of a single Dirac cone directional antenna in an embodiment;

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

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

[0019] Figure 4 1 is a radiation pattern of a single Dirac cone directional antenna according to an embodiment;

[0020] Figure 5 This is a sample defect example test diagram of a single Dirac cone antenna in 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 in the embodiment. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is described in detail below with reference to 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 by the primitive cells finally forms a single Dirac cone directional antenna.

[0025] In this embodiment, the unit cell 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, and 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 permittivity 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.μ 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, 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 unit cells as shown in the figure below: 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 electric conductor boundary. It 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 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 apply a magnetic field of B = 0.4T to the YIG. The magnet layers consist of two 1mm-tall copper plates, one on top and one on the bottom, and a 3mm-thick acrylic plate in the middle to hold the magnets. The copper plates prevent the magnets from attracting each other during installation. The magnets are made of neodymium iron boron, are 3mm tall, and have a radius of 4mm.

[0032] The height of the gyromagnetic YIG columns and dielectric columns in the middle functional layer are both 7 mm. 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 columns and dielectric columns).

[0033] Among them, this embodiment omits the upper metal layer of the intermediate 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, it improves the convenience of the assembly process on the one hand, and improves the lightweight of the overall antenna on the other hand.

[0034] The present invention is based on a single Dirac cone directional antenna of a 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 sweep on the supercell of 16 units in the irreducible Brillouin zone, we can obtain Figure 3 (b) 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) Inserting a probe into the coaxial port of a vector network analyzer at the orange star and feeding power through the coaxial line, the presence of an eigenmode at the single Dirac cone can stimulate bulk propagation, with the corresponding bulk mode having a very small wave vector range. The wave vector corresponds to the propagation direction of the electromagnetic mode in free space. A small wave vector range corresponds to an outgoing wave with a small angular range in free space.

[0037] Figure 4(a) shows the radiation from the example antenna, where the upper rectangular area is air and the lower rectangular area is the example antenna array. The antenna is excited by the source at the orange star. The dielectric rods in the antenna sample are rotated at an angle of θ = 10.3°, and the applied magnetic field is 0.4 T. Feeding is performed using a vector network analyzer. A bulk mode is successfully excited at 8.9 GHz, propagating into free space as a highly directional wave. (b) shows the far-field diagram for this plane. The equivalent wavelength at B = 0.4 T and f = 8.9 GHz is 33.708 mm. To calculate the far field, a semicircle with a radius of 1000 mm, significantly greater than 10 times the equivalent wavelength, is selected. This semicircle is placed on the exit surface, and 181 points are placed every 1° to detect the energy corresponding to different positions. Finally, the normalized radiation pattern is plotted, showing that at 8.9 GHz, a highly directional wave is generated near 41°, corresponding to the field pattern. 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 embodiment, (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 directionality; 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 in the sample, as shown in Figure (d). The corresponding Ez field diagram still has good directionality in its radiation energy. 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 Figures (a) and (b), the yellow and blue five-pointed stars represent two energy-emitting signal sources, respectively, and the red five-pointed star represents the receiving probe. Due to the asymmetry of the single Dirac cone, electromagnetic waves in only one valley can be incident from free space into the functional layer and transform into bulk waves, thereby being detected by the receiving probe. However, since the energy from the emitting sources at other locations does not satisfy the momentum matching relationship, it is strongly reflected at the interface between free space and the sample, making it impossible for the receiving probe to detect the energy. Therefore, this high directivity can be used to determine the position of the target, which is particularly advantageous in long-range 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 from the two sources will interfere with each other in free space, affecting the reception. However, when the waves pass through the functional layer, the antenna has a filter-like effect, which only filters out waves in one direction, thereby effectively filtering out interference waves in other directions. Figure 7 (b) shows 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] The above embodiments show that the single Dirac cone directional antenna based on gyromagnetic photonic crystals provided by the present invention is feasible and has multiple degrees of freedom adjustment (for example, the magnetic field, antenna structure, frequency, etc. can all cause the corresponding single Dirac cone band structure to produce a frequency offset, thereby changing the emission direction to regulate the directionality), high robustness (continues to operate even with defects in the antenna device); can be used for directional detection and anti-interference; and has a simple structure and predetermined directionality. As long as a single Dirac cone is generated, the direction of the outgoing wave is locked to the wave vector direction corresponding to the single Dirac cone, achieving highly directional emission at a small angle.

Claims

1. A single Dirac cone directional antenna based on gyromagnetic photonic crystal, characterized by: 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 magnetic layers are both metal plates embedded with magnetic columns. They are arranged one-to-one on the upper and lower magnetic layers of the intermediate functional layer, with the center of each magnetic column aligned with the center of a unit cell gyromagnetic YIG column in the thickness direction. One gyromagnetic YIG column corresponds to two magnetic columns, one on the upper and one on the lower. The magnetic poles of the magnetic columns embedded in the same magnetic layer have the same direction. The magnetic 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 magnetic layers. The magnetic field magnitude is 0.35T < B < 0.5T. The metal plates are perfect electrical conductor layers above and below the functional layers, used to form a waveguide cavity. The functional layer is composed of a periodic arrangement of unit cells. The unit cell has a regular hexagonal planar shape, and is provided with a gyromagnetic YIG column and three dielectric columns that do not touch each other. The interlayer structure of the unit cell is that a regular hexagonal metal layer is provided above and below the gyromagnetic YIG column and the three dielectric columns, and is adaptively aligned to form a gap structure in which the upper and lower metal layers sandwich the gyromagnetic YIG column and the three dielectric columns. The lattice constant of the unit cell is a>0, and the antenna operating frequency changes as a changes. A diagonal line of the regular hexagon of the unit cell is used as the longitudinal Y-axis, and the midline of the opposite side perpendicular to the diagonal line is used as the transverse X-axis. The initial positions of the three dielectric columns are respectively at the positive left, upper right, and lower right, and the three dielectric columns form an equilateral triangle with the center point of the equilateral triangle as 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 cylindrical. 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 distance between the center of the circle of 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: Within the rated area, they are adaptively arranged in sequence based on the sides of a regular hexagon. The number of primitive cells in both the X-axis and Y-axis directions must be greater than 5. The setting boundary where the excitation source is located must be a 120° sawtooth perfect conductor boundary formed by regular hexagons arranged along the X-axis. The other sides of the rated area are open boundaries with no shape requirements.

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

3. The single Dirac cone directional antenna based on gyromagnetic photonic crystal according to claim 2, characterized in that: The intermediate light material layer is an acrylic board.

4. The single Dirac cone directional antenna based on gyromagnetic photonic crystal according to 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 according to claim 1, characterized in that: The a=17.5 mm, θ=10.3°, magnetic field B=0.4 T, d=0.35a, r=0.14a, r'=0.8r, 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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