Topological leaky-wave antenna based on gyromagnetic photonic crystal

Abstract

The invention belongs to the field of antennas, and particularly relates to a topological leaky-wave antenna based on gyromagnetic photonic crystals. A single gyromagnetic YIG column is adopted to construct square primitive cells, an upper magnet layer and a lower magnet layer are assisted to provide a magnetic field, the primitive cells are adaptively and closely arranged into the array antenna, boundaries in all directions of a rated area are perfect electric conductor boundaries, and a slot array of a leaky wave area is formed in the boundary of an excitation source. According to the topological leaky-wave antenna, leaky-wave scanning 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 topological leaky-wave antenna has the characteristic of multi-degree-of-freedom adjustment; the waveguide has the advantages that the structure is simple, the transverse emergent effect is good, the open-stop band phenomenon is overcome, impedance matching is overcome, no reflection signal exists, and waves in the waveguide can only be transmitted in a one-way mode. The problem that an existing leaky-wave antenna needs impedance matching and has an open stop band is effectively solved.

Description

Technical Field

[0001] The invention belongs to the field of antennas and relates to a leaky-wave antenna, in particular to a topological leaky-wave 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 waves can only pass in one direction.

[0003] Chern insulators are two-dimensional materials with non-trivial topological properties. Their core features are non-zero Chern number, topologically protected unidirectional edge states and quantized Hall conductance, which exhibits non-reflection and lossless unidirectional transmission. By breaking the time reversal symmetry (such as introducing magnetism or strong spin-orbit coupling), Chern insulators form topological gaps in the energy band and are widely used in low-energy electronic devices, topological photonics and quantum computing.

[0004] Traditional leaky wave antennas mainly rely on the physical properties of waveguide structures and periodic unit designs to control leakage. They achieve leakage of electromagnetic wave energy by artificially destroying the symmetry of waveguide structures and introducing physical discontinuities (such as slotting and loading periodic structures) on waveguides or transmission lines. Traditional leaky wave antennas rarely rely on external magnetic fields, and the control methods are relatively simple. However, topological leaky wave antennas combine the principles of topological photonics and achieve unique radiation characteristics through topologically protected edge states or surface states. Topological leaky wave antennas use the topological edge states of topological photonic crystals to achieve unidirectional transmission and leakage of electromagnetic waves. By designing the symmetry of photonic crystal units (such as destroying time reversal symmetry and space inversion symmetry), topological phase changes are introduced to form unidirectional edge states. The propagation directionality and robustness of edge states provide natural advantages for the radiation of antennas. External magnetic fields, mechanical deformation or electrical control methods can be used to dynamically control the propagation path and leakage direction of topological states.

[0005] However, the previous design has the following problems: For traditional leaky wave antennas, the open stopband phenomenon usually occurs, that is, when the vertical emission occurs, the reflected wave interferes with the incident wave to form a standing wave, which greatly reduces the leaky wave efficiency. Traditional leaky wave antennas require impedance matching to prevent the generation of reflected signals. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned traditional leaky wave antennas, the present invention provides a topological leaky wave antenna based on gyromagnetic photonic crystals. Due to its topological protection properties under specific conditions, it has some advantages over traditional antennas, such as overcoming the open stop band phenomenon; overcoming impedance matching, no reflected signal, and due to the existence of topological protection, the waves in the waveguide can only be transmitted in one direction; there are many degrees of control freedom, for example, magnetic field, shape, frequency, etc. can all be used to control the leaky wave scanning.

[0007] In order to achieve the above object, the specific technical solution of the present invention is as follows:

[0008] A topological leaky wave 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.

[0009] 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 B>0T. The metal plates are perfect electrical conductor layers on the upper and lower parts of the functional layer, used to form a waveguide cavity.

[0010] The functional layer is composed of periodically arranged primitive cells; the plane shape of the primitive cell is a square, and a gyromagnetic YIG column is arranged in the center thereof. The interlayer structure of the primitive cell is that a square metal layer is adaptively and centrally aligned on the upper and lower bottom surfaces of the gyromagnetic YIG column, forming a gap structure in which the upper and lower metal layers clamp a gyromagnetic YIG column.

[0011] The primitive cell is a square lattice, such as Figure 1 (a), whose lattice constant a0>0, the antenna operating frequency changes with the change of a0; the midline of one opposite side of the primitive cell square is the longitudinal Y axis, and the midline of the other opposite side is the transverse X axis; the primitive cells are adaptively spliced ​​and arranged in the rated area in the X-axis and Y-axis directions based on the square sides of the primitive cells, and the boundaries of the rated area in the two Y-axis directions are perfect conductor boundaries, and the boundaries of the rated area in the two X-axis directions are also perfect conductors; wherein, a slot array of the leakage wave area is opened on the boundary where the excitation source is set.

[0012] Furthermore, the gyromagnetic YIG column is a cylinder, and its radius r satisfies 0<r<0.5a0.

[0013] Furthermore, the upper and lower magnet layers are sandwich structures with a light material in the middle.

[0014] 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.

[0015] Furthermore, simulation software is used to adjust the parameters a0, B, r and the structural parameters of the slot array to adjust the performance of the entire topological leaky-wave antenna.

[0016] In summary, the present invention uses a single gyromagnetic YIG column to construct a square 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 boundaries in the four directions of the rated area are perfect electrical conductor boundaries, and a gap array of leaky wave areas is opened on the boundary set by the excitation source. The topological leaky wave antenna of the present invention can be adjusted by parameters such as magnetic field, antenna structure, frequency, etc., so as to perform leakage wave scanning control of the antenna, and has multi-degree-of-freedom adjustment characteristics; because it has the property of topological protection, it has some characteristics that are superior to existing antennas, and the structure is simple; the lateral emission effect is good, and the open stop band phenomenon is overcome; impedance matching is overcome, and there is no reflected signal. Due to the existence of topological protection, the waves in the waveguide can only be transmitted in one direction; it effectively solves the problem that the existing leaky wave antenna needs to perform impedance matching and have an open stop band (such as some antennas have no edge states at the position k=0 in the energy band, and continuous scanning from backward to forward cannot be achieved). BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the structure of the primitive cells of the functional layer of the present invention and their arrangement;

[0018] Figure 2 It is a schematic diagram of the structure of the topological leaky wave antenna in the thickness direction of the embodiment;

[0019] Figure 3 For radiation efficiency and leakage rate: (a) Figure shows the selection of input and output when calculating radiation efficiency and leakage rate (b) radiation efficiency (c) leakage rate (d) Ez field distribution diagram when radiation efficiency is greater than 90%;

[0020] Figure 4 As the far-field diagram of the embodiment, the far-field diagrams at 7.5 GHz, 7.6 GHz, and 8.2 GHz are respectively given;

[0021] Figure 5 For the shape-controlled radiation of the embodiment: (a) shows the relationship between the height of the functional layer and the hole height, (b) gives the three-dimensional far-field distribution at 0.7h and 0.9h;

[0022] Figure 6 To overcome the open stopband effect in an embodiment: (a) is a schematic diagram of the open stopband during frequency scanning, (b) is a leakage rate near the wide side radiation, and (c) is a two-dimensional far-field distribution diagram. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is described in detail below.

[0024] The present embodiment provides a topological leaky wave antenna based on gyromagnetic photonic crystal, which is a three-layer laminated structure including an upper magnetic layer, a functional layer and a lower magnetic layer from top to bottom.

[0025] The functional layer is composed of a periodic arrangement of primitive cells of a square lattice, such as Figure 1 As shown in (a), the YIG column in this embodiment is a cylindrical column. The topological leaky wave antenna specifically designed in this embodiment has a lattice constant a0=25 mm, a radius of the YIG column r=0.14a, a relative dielectric constant of YIG is ε1=14.3, and a relative magnetic permeability of YIG is:

[0026]

[0027] 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.

[0028] Figure 1 (b) is a schematic diagram of the topological leaky wave antenna array arrangement of the present invention, which is an m×n matrix, where m is the number of primitive cells in the horizontal X axis, and n is the number of primitive cells in the vertical Y axis; m≥5, n≥5 are required. a>m×a0, b>n×a0. The part with an extra integer multiple of the lattice constant is used to enhance the transmission effect of the edge state, and the orange five-pointed star is the position of the excitation source. Concretely applied to the topological leaky wave antenna array of this embodiment, the m×n matrix is ​​a 25×10 array, a=10.25a0, b=25.25a0.

[0029] Press the function layer Figure 1 (b) The structure is built, and the interlayer structure is as follows Figure 2As shown in (a), 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 is supplied with energy through the coaxial line of the vector network analyzer (model ZNB20). The period of the slot units arranged in an array is p, and the width of the slot units is a1. If 0<a1<λ, the slot period p<a1, and the number of slot units s>2. In this embodiment: the upper boundary is opened with a slot array of a1=9.6mm (quarter wavelength), the slot period p=0.8a0, and the number of slots is s=20; the left and right lower boundaries of the functional layer are supported by copper strips with a thickness of 1cm and a height of 7mm, and the length and width are the same as the antenna size; the leakage wave boundary is a perforated copper plate with a thickness of 1mm, and the holes are symmetrically distributed in the center. The actual object is as follows Figure 2 (b) as shown.

[0030] Figure 2 (a) The upper and lower magnet layers are used to apply a magnetic field B = 0.043T to YIG. The magnet layer consists 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 prevent the magnet from jumping out during the installation process. The height of the YIG and dielectric columns in the functional layer is 7mm, and the height of the copper plate fixing the column is 0.5mm. The magnet is a ferrite magnet with a height of 3mm and a radius of 4mm.

[0031] exist Figure 3 (a) The coaxial line port probe of the vector network analyzer is inserted at the position of the orange five-pointed star, and power is fed through the coaxial line. Due to the application of a 0.043T magnetic field, the functional layer phase changes into a Chern insulator phase, which will generate edge states propagating at the upper edge. When the wave propagates to the leaky wave region, since the mode corresponding to the edge state is located above the light cone, it is a fast wave and can be radiated into the air.

[0032] In order to calculate the radiation efficiency and leakage rate, this embodiment selects two lines located before and after the periodic slot array (leaky wave area) in the topological leaky wave antenna, such as Figure 3 As shown in (a), by integrating the energy density of these two lines, Pin and Pout can be obtained. Substitute the solved values ​​into the following formula:

[0033] η=1-P out / P in =1-exp(-2αL)=1-exp(-4π(α / k0)(L / λ0))

[0034] Where L is the length of the antenna, α is the leakage rate, k0 is the vacuum wave number, and λ0 is the vacuum wavelength.

[0035] The radiation efficiency and leakage rate can then be calculated. Figure 3(b) shows the radiation frequency curve at a frequency of 7.4 GHz-8.4 GHz, a magnetic field of 0.043 T, and a hole height of h. The yellow area is the area where the radiation efficiency is higher than 90%, which coincides with the frequency range of the photonic band gap. Figure 3 (c) shows the leakage rate curve in the same frequency range. In the frequency range of the photonic band gap, the leakage rate changes very little and is almost unchanged, indicating that the wave radiates stably from the waveguide like free space. Figure 3 (d) is the Ez field distribution diagram of the yellow area in Figure (b). It can be seen that there is first a unidirectionally transmitted edge state, which meets the requirements within the photon band gap, and its emission has good directionality.

[0036] Figure 4 The far-field distribution is given. Through modeling and simulation in CST, the YIG column is placed in a rectangular cavity composed of copper plates, and a periodic slot array is opened on the upper side plate. By calculating the electric field far field at 7.5GHz-8.2GHz, we obtain the far-field radiation pattern of the topological leaky wave antenna. Figure 4 As shown, it can be seen that there is a good beam scanning phenomenon in the 0.7 GHz frequency band from 7.5 GHz to 8.2 GHz, and the beam scanning angle is -35° to 23°, with a total scanning angle of 53°.

[0037] There are many degrees of control freedom, such as magnetic field, antenna shape, frequency, etc., which can control the antenna directionality.

[0038] exist Figure 5 Here, h2 represents the opening height, and h is the YIG column height. Figure 5 (b) shows the three-dimensional far-field distribution at two heights of h2=0.7h and 0.9h, and it is obvious that the beam deflects as the structure changes.

[0039] Figure 3 (d) shows the field pattern distribution at f = 7.55 GHz, 7.72 GHz, and 8.12 GHz under a magnetic field of 0.043 T. It can be seen that the beam deflects as the frequency changes.

[0040] Changing the magnetic field applied by the antenna will also cause the outgoing wave of the same antenna structure at the same frequency to be deflected.

[0041] Overcoming the open stopband phenomenon: Figure 6 In (a), a schematic diagram of the beam deflection of a traditional leaky wave antenna during frequency scanning is given. When the wave is deflected to the vertical emission direction, it can be seen that the radiation efficiency of the beam is greatly reduced compared to the front and rear sides.

[0042] Since the edge states of the Chern insulator have strong topological protection properties, i.e., unidirectional transmission and defect immunity, reflection is prohibited in the wave transmission path, and there will be no standing wave phenomenon, so the open stopband phenomenon can be well overcome. Figure 6 (c) shows the far-field distribution of the topological leaky-wave antenna when radiating on the wide side. It can be seen that the directivity of the wave compared to the front and rear side radiation is basically consistent with the wide side radiation. Figure 6 (b) It can be seen that near the wide-side radiation, the leakage rate of the radiated wave remains almost unchanged, which also proves that the topological leaky-wave antenna has overcome the open-stopband phenomenon well.

[0043] Overcoming impedance matching: In traditional antenna systems, the impedance mismatch between the transmission line and the antenna will cause part of the incident wave to be reflected, forming a standing wave. This reflected wave will not only reduce the transmission efficiency, but may also cause problems such as antenna heating and signal distortion. It is usually necessary to optimize the matching by designing an impedance matching network (such as using a tuned inductor, capacitor or balun) or adjusting the geometric parameters of the antenna and transmission line.

[0044] In the topological antenna, due to the use of Chern insulator, its edge state is unidirectional and defect-immune. The unidirectional propagation makes it impossible for reflected waves to form, so the reflection problem is fundamentally eliminated.

[0045] It can be seen from the above embodiments that the topological leaky wave antenna based on gyromagnetic photonic crystal provided by the present invention is proven to be feasible. And the topological leaky wave antenna of the present invention has the characteristics of simple structure, multi-degree-of-freedom adjustment, overcoming the open stopband phenomenon, overcoming the impedance matching problem, realizing the large-angle leaky wave scanning characteristics, and multiple degrees of control freedom (for example, magnetic field, antenna shape, frequency, etc. can all regulate the leaky wave directivity).

Claims

1. A topological leaky wave 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 functional layer in a manner 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 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 B>0T; 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 square, and a gyromagnetic YIG column is arranged in the center thereof; the interlayer structure of the primitive cell is a square metal layer arranged in the center of the upper and lower bottom surfaces of the gyromagnetic YIG column adaptively and aligned to form a gap structure in which the upper and lower metal layers clamp a gyromagnetic YIG column; The primitive cell is a square lattice, and its lattice constant a0>0, and the antenna operating frequency changes with the change of a0; the midline of one opposite side of the primitive cell square is the longitudinal Y axis, and the midline of the other opposite side is the transverse X axis; the primitive cells are adaptively spliced ​​and arranged in the rated area in the X-axis and Y-axis directions based on the square sides of the primitive cells, and the boundaries of the rated area in the two Y-axis directions are perfect conductor boundaries, and the boundaries of the rated area in the two X-axis directions are also perfect conductors; wherein, a slot array of the leakage wave area is opened on the boundary where the excitation source is set.

2. The topological leaky wave antenna based on gyromagnetic photonic crystal according to claim 1, characterized in that: The gyromagnetic YIG column is a cylinder, and its radius r satisfies 0<r<0.5a0.

3. The topological leaky wave antenna based on gyromagnetic photonic crystal according to claim 1, characterized in that: The upper and lower magnet layers are sandwich structures with light materials in the middle.

4. The topological leaky wave antenna based on gyromagnetic photonic crystal as claimed in claim 3, 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 topological leaky wave antenna based on gyromagnetic photonic crystal as claimed in claim 3, characterized in that: The intermediate light material interlayer is an acrylic plate.

6. The topological leaky wave antenna based on gyromagnetic photonic crystal according to claim 1, characterized in that: The simulation software is used to adjust the parameters a0, B, r and the structural parameters of the slot array to adjust the performance of the entire topological leaky-wave antenna.

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