A topological leaky-wave antenna based on gyrotropic photonic crystals

Abstract

The application belongs to the field of antennas, and particularly relates to a topological leaky-wave antenna based on a gyromagnetic photonic crystal. The application adopts a single gyromagnetic YIG column to construct a square unit cell, and provides a magnetic field by means of upper and lower magnet layers, the unit cell is adaptively closely arranged into an array antenna, and the boundary in each direction in a rated area is a perfect electric conductor boundary, and a gap array of a leaky-wave region is arranged on the boundary of an excitation source. The topological leaky-wave antenna can be adjusted by adjusting parameters such as a magnetic field, an antenna structure and a frequency, so that the leaky-wave scanning of the antenna is controlled, and the antenna has the characteristics of multi-degree-of-freedom adjustment. The antenna has the advantages of simple structure, good transverse emission effect, overcoming of the phenomenon of open stop band, overcoming of impedance matching, no reflected signal, one-way transmission of waves in a waveguide and the like. The problems of impedance matching and open stop band of the existing leaky-wave antenna are effectively solved.

Description

Technical Field

[0001] The present 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. Gyromagnetic photonic 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 waves.

[0003] Chern insulators are two-dimensional materials with nontrivial topological properties. Their core features are a non-zero Chern number, topologically protected unidirectional edge states, and quantized Hall conductance, exhibiting reflection-free, lossless, unidirectional transmission. By breaking time reversal symmetry (e.g., by introducing magnetism or strong spin-orbit coupling), Chern insulators can form topological gaps in their energy bands, leading to their widespread application in low-energy electronics, topological photonics, and quantum computing.

[0004] Traditional leaky-wave antennas primarily rely on the physical properties of waveguide structures and periodic unit design to control leakage. They achieve electromagnetic energy leakage by artificially disrupting the symmetry of the waveguide structure and introducing physical discontinuities (such as slots or periodic loading) in the waveguide or transmission line. Traditional leaky-wave antennas rarely rely on external magnetic fields, and their control methods are relatively simple. Topological leaky-wave antennas, however, incorporate the principles of topological photonics to achieve unique radiation characteristics through topologically protected edge states or surface states. Topological leaky-wave antennas exploit the topological edge states of topological photonic crystals to achieve unidirectional transmission and leakage of electromagnetic waves. By engineering the symmetry of the photonic crystal units (such as breaking time reversal symmetry and spatial inversion symmetry), topological phase transitions are introduced, resulting in unidirectional edge states. The propagation directionality and robustness of edge states provide a natural advantage for the antenna's radiation. External magnetic fields, mechanical deformation, or electrical control can be used to dynamically control the propagation path and leakage direction of the topological states.

[0005] However, previous designs have the following problems: Traditional leaky-wave antennas often exhibit an open stopband phenomenon. That is, when transmitting vertically, the reflected wave interferes with the incident wave to form a standing wave, significantly reducing 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 property under specific conditions, it has some advantages over traditional antennas, such as overcoming the open stop band phenomenon; overcoming impedance matching and no reflected signal. Due to the existence of topological protection, the waves in the waveguide can only be transmitted in one direction; there are many degrees of freedom for regulation, such as magnetic field, shape, frequency, etc., which can all be used to regulate leaky wave scanning.

[0007] In order to achieve the above purpose, the specific technical solutions of the present invention are 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 magnetic layers are metal plates embedded with magnetic pillars. They are positioned one-to-one with the thickness center of each magnet pillar aligned with the center of a unit cell gyromagnetic YIG pillar, corresponding to two magnet pillars on each layer. The magnetic poles of the magnet pillars embedded in the same layer are aligned. The magnet pillars are fixed in the metal plates and do not contact the gyromagnetic YIG pillars, providing a magnetic field with a magnitude of B > 0T through the upper and lower magnetic layers. The metal plates serve as perfect electrical conductors above and below the functional layers, forming a waveguide cavity.

[0010] The functional layer is composed of periodically arranged unit cells; the planar shape of the unit cell is a square, and a gyromagnetic YIG column is arranged in the center thereof. The interlayer structure of the unit cell is a square metal layer arranged in the center of 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 unit cell is a square lattice, such as Figure 1 (a), whose 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 two Y-axis directions of the rated area are perfect conductor boundaries, and the boundaries of the two X-axis directions of the rated area 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 lightweight 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 slot array of leakage wave areas is opened on the boundary set by the excitation source. The topological leakage wave antenna of the present invention can be adjusted by parameters such as magnetic field, antenna structure, and frequency, 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 has a simple structure; 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 existing leakage wave antennas need 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 cannot achieve continuous scanning from backward to forward). 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 This is a schematic diagram of the structure of the topological leaky wave antenna in the thickness direction of the embodiment;

[0019] Figure 3 Radiation efficiency and leakage rate: (a) The 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 The far-field diagrams of the embodiment are given at 7.5 GHz, 7.6 GHz, and 8.2 GHz respectively;

[0021] Figure 5 For the embodiment of shape-controlled radiation: (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] This embodiment provides a topological leaky-wave antenna based on gyromagnetic photonic crystals, which has a three-layer stacked structure comprising, from top to bottom, an upper magnetic layer, a functional layer, and a lower magnetic layer.

[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 r = 0.14a of the YIG column, a relative dielectric constant ε1 = 14.3, and a relative magnetic permeability of YIG:

[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.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.

[0028] Figure 1 (b) is a schematic diagram of the topological leaky wave antenna array arrangement of the present invention. The array is an m×n matrix, where m is the number of unit cells in the horizontal X axis and n is the number of unit cells in the vertical Y axis; m≥5, n≥5 are required. a>m×a0, b>n×a0. The 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. Specifically 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 boards 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, the width of the slot units is a1, 0<a1<λ, the slot period p<a1, and the number of slot units s>2. Concrete to 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 position of the holes is symmetrically distributed in the center. The actual object is as follows Figure 2 As shown in (b).

[0030] Figure 2 In (a), the upper and lower magnetic layers are used to apply a magnetic field of B = 0.043T to the YIG. The magnetic layer consists of two 1mm-tall copper plates, one above the other, and a 3mm-thick acrylic plate in the middle to secure the magnets. The upper and lower copper plates prevent the magnets from jumping out during installation. The YIG and dielectric pillars in the functional layer are 7mm tall, and the copper plates securing the pillars are 0.5mm tall. The magnets are ferrite magnets with a height of 3mm and a radius of 4mm.

[0031] exist Figure 3 (a) The orange star position is inserted into the coaxial port probe of the vector network analyzer, and power is fed through the coaxial line. Due to the application of a 0.043T magnetic field, the functional layer phase changes to 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 be calculated. Figure 3(b) shows the radiation frequency curve at a frequency of 7.4GHz-8.4GHz, a magnetic field of 0.043T, 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 radiated from the waveguide like free space is stable. 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 made 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 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 all control the antenna directionality.

[0038] exist Figure 5 Where 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, thus the open stop band phenomenon can be well overcome. Figure 6 (c) shows the far-field distribution diagram of the topological leaky-wave antenna when radiating on the broad side. It can be seen that the directivity of the wave compared to the front and rear side radiation is basically consistent with the broad side radiation. Figure 6 (b) shows 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 very well.

[0043] Overcoming impedance matching: In traditional antenna systems, impedance mismatches between the transmission line and the antenna cause some incident waves to be reflected, forming standing waves. These reflected waves not only reduce transmission efficiency but can also cause antenna heating and signal distortion. This is typically addressed 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 to optimize matching.

[0044] In topological antennas, the Chern insulators used have unidirectional edge states and are defect-immune. This unidirectional propagation prevents the formation of reflected waves, thus fundamentally eliminating the reflection problem.

[0045] The above examples demonstrate that the topological leaky-wave antenna based on gyromagnetic photonic crystals provided by the present invention has proven to be feasible. Furthermore, the present topological leaky-wave antenna features a simple structure, multiple degrees of freedom for adjustment, and overcomes the open-stopband phenomenon and impedance matching issues. It achieves wide-angle leaky-wave scanning characteristics and offers multiple degrees of control (e.g., magnetic field, antenna shape, and frequency can all be used to adjust the leaky-wave directionality).

Claims

1. A topological leaky-wave 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 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 are aligned. 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 B>0T. The metal plates are perfect electrical conductors on the upper and lower layers of the functional layer, used to form a waveguide cavity. The functional layer is composed of a periodic arrangement of primitive cells; the primitive cell has a square planar shape, and a gyromagnetic YIG column is arranged in the center thereof. The interlayer structure of the primitive cell is a square metal layer arranged on the upper and lower bottom surfaces of the gyromagnetic YIG column in an adaptive and centered manner, forming a gap structure in which the upper and lower metal layers sandwich a gyromagnetic YIG column. The primitive cell is a square lattice with a 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 a light material in the middle.

4. The topological leaky-wave antenna based on gyromagnetic photonic crystal according to 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 according to claim 3, characterized in that: The intermediate light material layer is an acrylic board.

6. The topological leaky-wave antenna based on gyromagnetic photonic crystal according to claim 2, 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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