CN118281574A - Millimeter wave near-field low-diffraction focusing beam generation method and system - Google Patents
Millimeter wave near-field low-diffraction focusing beam generation method and system Download PDFInfo
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Abstract
本发明涉及波束调控及毫米波探测领域，尤其是涉及一种毫米波近场低衍射聚焦波束生成方法及系统。该方法利用透射相位调控超表面，通过对透射过超表面的毫米波波束的空间相位进行人为预设的改变和调控，实现对近场波束传播过程的控制，可以实现近场低衍射的聚焦波束的生成，其中的透射相位调控超表面的设计过程包括，利用提出的调控相位分布公式计算调控相位空间分布，确定单个相位区域的离散化相位偏移量和透射相位调控超表面上单个相位区域的超表面单元数量，进而确定单个超表面单元的相位偏移量。与现有技术相比，本发明具有近场波束能量集中、结构复杂度低等优点。
The present invention relates to the field of beam control and millimeter wave detection, and in particular to a method and system for generating a millimeter wave near-field low-diffraction focused beam. The method utilizes a transmission phase control metasurface, and controls the spatial phase of the millimeter wave beam transmitted through the metasurface in an artificially preset manner, thereby controlling the near-field beam propagation process, and generating a near-field low-diffraction focused beam. The design process of the transmission phase control metasurface includes calculating the control phase spatial distribution using the proposed control phase distribution formula, determining the discretized phase offset of a single phase region and the number of metasurface units of a single phase region on the transmission phase control metasurface, and then determining the phase offset of a single metasurface unit. Compared with the prior art, the present invention has the advantages of concentrated near-field beam energy and low structural complexity.
Description
技术领域Technical Field
本发明涉及波束调控及毫米波探测领域，尤其是涉及一种毫米波近场低衍射聚焦波束生成方法及系统。The present invention relates to the field of beam control and millimeter wave detection, and in particular to a millimeter wave near-field low-diffraction focused beam generation method and system.
背景技术Background technique
电磁波在自由空间传播中的衍射等现象会导致电磁波波束的能量在传播过程中发散，降低了电磁波波束的指向性，限制了其在有限区域能量集中能力。因此，在电磁波传播、微波成像、微波能量传输等应用中，电磁波波束的聚焦设计、方法具有重要现实意义。费马原理指出，可以通过控制光波的空间相位来修改光束的波前，推广到更大范围的电磁波，通过控制电磁波的空间相位来调控电磁波的波前，实现对电磁波传播的一定控制。基于广义折射定律，相位调控超表面是由多个亚波长单元组织而成的阵列结构，通过设置每个单元的透射相位或反射相位来实现波束控制。超表面调节电磁波的原理是在界面引入梯度相位，使散射的电磁波在不同位置具有不同的相位差，最终导致具有相同相位的波前发生变化，从而改变电磁波的传播方向。通过设计特定的相位分布，可以实现近场低衍射聚焦波束的生成，传统的波束聚焦方法诸如相控阵天线、电磁介质透镜、环焦反射阵天线等，但它们也有结构庞大、设计难度高和成本高的缺点，而超表面可以基于单个天线实现波束控制。此外，不同形式的超表面可以实现许多不同的功能，如雷达反射截面减小、偏振转换、增益放大等。The diffraction of electromagnetic waves in free space propagation will cause the energy of the electromagnetic wave beam to diverge during the propagation process, reduce the directivity of the electromagnetic wave beam, and limit its ability to concentrate energy in a limited area. Therefore, in applications such as electromagnetic wave propagation, microwave imaging, and microwave energy transmission, the focusing design and method of electromagnetic wave beams are of great practical significance. The Fermat principle points out that the wavefront of the light beam can be modified by controlling the spatial phase of the light wave. It is extended to a larger range of electromagnetic waves. The wavefront of the electromagnetic wave can be controlled by controlling the spatial phase of the electromagnetic wave to achieve a certain control over the propagation of electromagnetic waves. Based on the generalized law of refraction, the phase-controlled metasurface is an array structure composed of multiple sub-wavelength units. Beam control is achieved by setting the transmission phase or reflection phase of each unit. The principle of metasurface regulation of electromagnetic waves is to introduce a gradient phase at the interface so that the scattered electromagnetic waves have different phase differences at different positions, which ultimately causes the wavefront with the same phase to change, thereby changing the propagation direction of the electromagnetic wave. By designing a specific phase distribution, the generation of near-field low-diffraction focused beams can be achieved. Traditional beam focusing methods include phased array antennas, electromagnetic dielectric lenses, and ring-focus reflector array antennas, but they also have the disadvantages of bulky structures, high design difficulty, and high cost. Metasurfaces can achieve beam control based on a single antenna. In addition, different forms of metasurfaces can achieve many different functions, such as radar cross-section reduction, polarization conversion, gain amplification, etc.
因此，近年来电磁波应用中的超表面系统具有重大现实意义，取得了重大发展。其中，文献一“8mm点聚焦透镜天线设计”(马立冬，白佳俊，付云起)提出了基于电磁介质的点聚焦透镜可以实现将透射毫米波集中到一个小的区域内，采用由两个单面透镜合成的双面透镜，材料选用聚四氟乙烯，透镜中的介质均匀，为常数折射率透镜。通过透镜几何形状设计，基于电长度相等原理设计的双曲面透镜，经电磁仿真建模，实现毫米波经过透镜后的波束聚焦。Therefore, in recent years, the metasurface system in electromagnetic wave applications has great practical significance and has made significant progress. Among them, the document "8mm point focusing lens antenna design" (Ma Lidong, Bai Jiajun, Fu Yunqi) proposed that the point focusing lens based on electromagnetic medium can realize the concentration of transmitted millimeter waves into a small area. A double-sided lens composed of two single-sided lenses is used. The material is polytetrafluoroethylene. The medium in the lens is uniform and it is a constant refractive index lens. Through the design of lens geometry, the hyperbolic lens designed based on the principle of equal electrical length is modeled by electromagnetic simulation to realize the beam focusing of millimeter waves after passing through the lens.
文献二“Ku波段电磁聚焦相位梯度超表面设计”(汪竹，王德戌，冉雪红等)提出了一种基于相位梯度超表面阵列的波束聚集设计，电磁波透过超表面时，通过透射相位偏移量呈梯度分布的单元阵列设计。该方法对透射的电磁波实施相位偏移调控，其相位分布公式为聚焦相位：式中，f为焦距，为超表面中心，即参照点相位，λ0为设备应用的波长，通过透射超表面可控制电磁波波前，经过电磁仿真软件仿真，可以实现类似介质透镜对电磁波的聚焦效果。Reference 2 "Ku-band electromagnetic focusing phase gradient metasurface design" (Wang Zhu, Wang Dexu, Ran Xuehong, etc.) proposed a beam focusing design based on a phase gradient metasurface array. When electromagnetic waves pass through the metasurface, the unit array design is designed with a gradient distribution of the transmission phase offset. This method implements phase offset control on the transmitted electromagnetic waves, and its phase distribution formula is the focusing phase: Where f is the focal length, is the center of the metasurface, that is, the reference point phase, and λ 0 is the wavelength of the device application. The wavefront of the electromagnetic wave can be controlled by transmitting the metasurface. After simulation with electromagnetic simulation software, the focusing effect of the electromagnetic wave similar to that of a dielectric lens can be achieved.
文献三“Design and Implementation of a Dual Frequency andBidirectional Phase Gradient Metasurface for Beam Convergence”(Yue H,Chen L,Yang Y Z,He L X,etal.)利用透射型相位梯度超表面单元和反射型相位梯度超表面单元相结合，实现了一种双频双向的波束聚焦设计，在5.6GHz的传输方向和15GHz的反射方向上实现光束会聚。基于频率选择超表面实现两个不同频率波束分别于反射方向汇聚和透射方向汇聚，在两个频率波束的方向实现了峰值增益的增强和-3dB带宽的减小。Reference 3 "Design and Implementation of a Dual Frequency and Bidirectional Phase Gradient Metasurface for Beam Convergence" (Yue H, Chen L, Yang Y Z, He L X, et al.) uses a combination of a transmission-type phase gradient metasurface unit and a reflection-type phase gradient metasurface unit to realize a dual-frequency bidirectional beam focusing design, achieving beam convergence in the transmission direction of 5.6 GHz and the reflection direction of 15 GHz. Based on the frequency selective metasurface, two beams of different frequencies are converged in the reflection direction and the transmission direction respectively, and the peak gain is enhanced and the -3dB bandwidth is reduced in the directions of the two frequency beams.
文献四“Low-Profile Transmitarray Antenna With Cassegrain ReflectarrayFeed”(Wu G B,Qu S W,Yang S W)提出了一种基于环焦副反射阵天线系统的低剖面波束发射阵列天线，其通过具有紧凑环形聚焦的平坦卡塞格伦反射阵列结构实现波形振幅分布调控，通过透射阵列超表面设计实现波形相位分布调控，模拟和测量结果表明，混合配置的天线系统可以实现40％左右的孔径效率，实现低剖面波束的实现。Reference 4 “Low-Profile Transmitarray Antenna With Cassegrain ReflectarrayFeed” (Wu G B, Qu S W, Yang S W) proposes a low-profile beam transmitting array antenna based on a ring-focus sub-reflectarray antenna system. It realizes waveform amplitude distribution control through a flat Cassegrain reflectarray structure with compact ring focusing, and realizes waveform phase distribution control through a transmission array metasurface design. Simulation and measurement results show that the hybrid configuration antenna system can achieve an aperture efficiency of about 40%, realizing the realization of a low-profile beam.
文献五“Ka-Band Wideband Large Depth-of-Field Beam Generation ThroughaPhase Shifting Surface Antenna”(Zhong Y C,Cheng Y J)基于相控超表面提出了一种大景深宽带近场聚焦天线，对透射的电磁波实施相位偏移调控，其相位分布公式为轴锥相位：式中，f为焦距，∈r为介质相对折射率，D为圆形超表面装置直径，Zmax为设计的无衍射距离。进一步基于超表面材料的宽带适用性，通过使用最小均方误差最小化方法来合成超表面元件的相位偏移量分布，运以获得在整个带宽内近似天线孔径上的理想相移，实现了一种宽带、准无衍射范围较大的Ka波段近场聚焦波束生成系统。Reference 5 “Ka-Band Wideband Large Depth-of-Field Beam Generation Througha Phase Shifting Surface Antenna” (Zhong YC, Cheng YJ) proposed a wideband near-field focusing antenna with large depth of field based on phased metasurface, which implements phase shift control on the transmitted electromagnetic wave. Its phase distribution formula is the axis-cone phase: In the formula, f is the focal length, ∈ r is the relative refractive index of the medium, D is the diameter of the circular metasurface device, and Z max is the designed diffraction-free distance. Further based on the broadband applicability of metasurface materials, the phase offset distribution of metasurface elements is synthesized by using the minimum mean square error minimization method to obtain the ideal phase shift on the approximate antenna aperture within the entire bandwidth, realizing a broadband, quasi-diffraction-free Ka-band near-field focusing beamforming system with a large range.
文献六为申请号为CN202310978729.5的中国专利，公开了一种基于高斯光束径向控制的激光雷达装置，通过光相位调制器，对高斯分布的初始激光进行相位调控，实现对激光光束的径向控制，在传播过程可以抑制光斑扩散使得光斑大小维持在较小水平，实现了一种布置灵活的基于激光雷达的低衍射波束生成装置。Document 6 is a Chinese patent with application number CN202310978729.5, which discloses a laser radar device based on radial control of Gaussian beams. Through an optical phase modulator, the phase of the initial laser with Gaussian distribution is controlled to achieve radial control of the laser beam. During the propagation process, the diffusion of the light spot can be suppressed so that the spot size is maintained at a small level, realizing a flexible laser radar-based low-diffraction beam generating device.
但是，上述文献一基于电磁介质几何透镜的方法，现实应用性较低，聚焦方式为点聚焦，聚焦区域小，影响波束的较长距离传输能力；上述文献二和文献三，基于透射型相位超表面的方法，其超表面元件的透射相位偏移量为聚焦相位分布，聚焦方式为点聚焦，聚焦区域小，影响波束的较长距离传输能力；上述文献四，基于环焦副反射阵天线系统的低剖面波束发射阵列天线，结合反射超表面阵列和透射超表面阵列，可以实现对波束的幅度控制和相位控制，但是存在结构尺寸较大，系统复杂度较高的缺点；上述文献五，基于透射型相位超表面的方法，其超表面元件的透射相位偏移量为轴锥相位分布，生成准贝塞尔波束，具有聚焦区域较大的优点，基于超表面宽带适应特性，具有工作频段较宽的优点，但在工作距离内轴上能量强度仍有待提高；上述文献六，基于光相位调制器，通过对初始高斯光束调制特定相位偏移量，实现应用于激光雷达的，光波段的低衍射波束生成装置，而本发明应用基础为毫米波波段，应用场景完全不同。However, the method based on electromagnetic medium geometric lens in the above-mentioned document 1 has low practical applicability, and the focusing mode is point focusing, and the focusing area is small, which affects the long-distance transmission capability of the beam; the above-mentioned documents 2 and 3 are methods based on transmission-type phase metasurfaces, and the transmission phase offset of their metasurface elements is the focusing phase distribution, and the focusing mode is point focusing, and the focusing area is small, which affects the long-distance transmission capability of the beam; the above-mentioned document 4 is a low-profile beam transmitting array antenna based on a ring-focus sub-reflection array antenna system, which combines a reflective metasurface array and a transmission metasurface array to achieve amplitude control and phase control of the beam, but there are some problems. The above-mentioned document five is a method based on a transmission-type phase metasurface, in which the transmission phase offset of the metasurface element is an axial cone phase distribution, which generates a quasi-Bessel beam and has the advantage of a larger focusing area. Based on the broadband adaptability of the metasurface, it has the advantage of a wider operating frequency band, but the on-axis energy intensity within the working distance still needs to be improved; the above-mentioned document six is based on an optical phase modulator, which modulates the initial Gaussian light beam by a specific phase offset to realize a low-diffraction beam generating device in the optical band for application to lidar, while the application basis of the present invention is the millimeter wave band, and the application scenarios are completely different.
综上，如何在现有超表面结构研究的基础上，针对毫米波波段的波束调控，进一步降低天线系统的复杂度和尺度、扩大聚焦区域，提升波束在较长距离上的传输能力，成为本领域需要解决的问题。In summary, how to further reduce the complexity and scale of the antenna system, expand the focusing area, and improve the transmission capability of the beam over a longer distance based on the existing research on metasurface structures for the millimeter wave band has become a problem that needs to be solved in this field.
发明内容Summary of the invention
本发明的目的就是为了克服上述现有技术存在的天线系统复杂度较高、尺度较大、聚焦区域小、影响波束的较长距离传输能力的缺陷而提供一种毫米波近场低衍射聚焦波束生成方法及系统。The purpose of the present invention is to provide a millimeter-wave near-field low-diffraction focused beam generation method and system in order to overcome the defects of the above-mentioned prior art, such as high antenna system complexity, large scale, small focusing area, and influence on the long-distance transmission capability of the beam.
本发明的目的可以通过以下技术方案来实现：The purpose of the present invention can be achieved by the following technical solutions:
根据本发明的第一方面，提供一种毫米波近场低衍射聚焦波束生成方法，包括以下步骤：According to a first aspect of the present invention, there is provided a millimeter wave near-field low-diffraction focused beam forming method, comprising the following steps:
确定毫米波波束的目标波束参数，所述目标波束参数包括频率/波长参数和调控目标参数，所述调控目标参数包括聚焦区域范围长度；Determining target beam parameters of the millimeter wave beam, wherein the target beam parameters include frequency/wavelength parameters and control target parameters, wherein the control target parameters include a focal area range length;
基于所述目标波束参数，利用调控相位分布公式计算调控相位空间分布；Based on the target beam parameters, calculating the control phase spatial distribution using a control phase distribution formula;
基于所述目标波束参数，确定透射相位调控超表面的尺寸参数，同时确定透射相位调控超表面的超表面单元数量和单个超表面单元的尺寸参数，进而确定所述透射相位调控超表面上单个相位区域的超表面单元数量；Based on the target beam parameters, determining the size parameters of the transmission phase control metasurface, and simultaneously determining the number of metasurface units of the transmission phase control metasurface and the size parameters of a single metasurface unit, and then determining the number of metasurface units in a single phase region on the transmission phase control metasurface;
基于所述调控相位空间分布，确定单个相位区域的离散化相位偏移量；Based on the regulated phase spatial distribution, determining a discretized phase offset of a single phase region;
基于所述离散化相位偏移量和所述单个相位区域的超表面单元数量，确定单个超表面单元的相位偏移量；Determine a phase offset of a single metasurface unit based on the discretized phase offset and the number of metasurface units in the single phase region;
基于所述单个超表面单元的相位偏移量，完成透射相位调控超表面的设计；Based on the phase offset of the single metasurface unit, the design of the transmission phase control metasurface is completed;
获取待调控波束，利用设计好的透射相位调控超表面，将相应的相位偏移量附加至所述待调控波束，实现对所述待调控波束的调控，生成近场低衍射聚焦波束。The beam to be regulated is obtained, and the corresponding phase offset is added to the beam to be regulated using the designed transmission phase regulation metasurface, so as to achieve regulation of the beam to be regulated and generate a near-field low-diffraction focused beam.
作为优选的技术方案，所述调控相位分布公式为：As a preferred technical solution, the phase distribution adjustment formula is:
式中，表示调控相位空间分布公式，k为波数，λ为待调控波束的波长，调控相位平面与波束传播方向垂直，ρ为调控相位平面上的点相对波束中轴的离轴距离，(x,y)为调控相位平面上的点与波束中轴的相对坐标，α为用以控制波束聚焦的程度的可调参数，为调控装置中心的参考点相位。In the formula, represents the spatial distribution formula of the control phase, k is the wave number, λ is the wavelength of the beam to be controlled, the control phase plane is perpendicular to the beam propagation direction, ρ is the off-axis distance of the point on the control phase plane relative to the beam axis, (x, y) is the relative coordinate of the point on the control phase plane and the beam axis, α is an adjustable parameter used to control the degree of beam focusing, It is the reference point phase of the control device center.
作为优选的技术方案，当相位偏移量大于2π时，相位分布公式为：As a preferred technical solution, when the phase offset is greater than 2π, the phase distribution formula is:
式中，为向下取整符号。In the formula, The floor symbol.
作为优选的技术方案，所述聚焦区域范围长度的计算公式为：As a preferred technical solution, the calculation formula for the focus area range length is:
且近场调控条件为：And the near-field control conditions are:
Zmax<(2D2)/λZ max <(2D 2 )/λ
式中，Zmax表示聚焦区域范围长度，D为正方形相位调控超表面的边长尺寸，λ为待调控波束的波长。Where Z max represents the length of the focusing area, D is the side length of the square phase control metasurface, and λ is the wavelength of the beam to be controlled.
根据本发明的第二方面，提供一种毫米波近场低衍射聚焦波束生成系统，包括毫米波发射天线装置，所述系统用于实现所述的毫米波近场低衍射聚焦波束生成方法，所述系统还包括透射相位调控超表面装置，所述透射相位调控超表面装置利用所述的方法设计组成，According to a second aspect of the present invention, a millimeter wave near-field low diffraction focused beam forming system is provided, comprising a millimeter wave transmitting antenna device, the system is used to implement the millimeter wave near-field low diffraction focused beam forming method, the system also includes a transmission phase control metasurface device, the transmission phase control metasurface device is designed and composed using the method described,
所述毫米波发射天线装置用于发射特定波长的初始毫米波波束，所述初始毫米波波束经初次传播后得到待调控波束，所述透射相位调控超表面装置用于将相应的相位偏移量附加至所述待调控波束，实现对所述待调控波束的调控，其中，所述透射相位调控超表面与所述毫米波波束的传播方向垂直，所述透射相位调控超表面装置的中心与所述毫米波波束的中轴为同轴，所述透射相位调控超表面装置与所述毫米波发射天线装置的间距小于0.01m。The millimeter-wave transmitting antenna device is used to transmit an initial millimeter-wave beam of a specific wavelength. The initial millimeter-wave beam obtains a beam to be controlled after initial propagation. The transmission phase control metasurface device is used to add a corresponding phase offset to the beam to be controlled to achieve control of the beam to be controlled, wherein the transmission phase control metasurface is perpendicular to the propagation direction of the millimeter-wave beam, the center of the transmission phase control metasurface device is coaxial with the central axis of the millimeter-wave beam, and the distance between the transmission phase control metasurface device and the millimeter-wave transmitting antenna device is less than 0.01m.
作为优选的技术方案，所述系统还包括天线接收装置，用于接收近场低衍射聚焦波束，所述近场低衍射聚焦波束经过所述透射相位调控超表面装置调控后得到。As a preferred technical solution, the system also includes an antenna receiving device for receiving a near-field low-diffraction focused beam, wherein the near-field low-diffraction focused beam is obtained after being controlled by the transmission phase control metasurface device.
作为优选的技术方案，所述透射相位调控超表面装置包括[(2N-1)×M]×[(2N-1)×M]个边长为L、厚度为d的正方形超表面单元，所述透射相位调控超表面装置包括[(2N-1)]×[(2N-1)]个相位区域，单个所述相位区域包括M×M个所述正方形超表面单元。As a preferred technical solution, the transmission phase control metasurface device includes [(2N-1)×M]×[(2N-1)×M] square metasurface units with a side length of L and a thickness of d, and the transmission phase control metasurface device includes [(2N-1)]×[(2N-1)] phase regions, and a single phase region includes M×M square metasurface units.
作为优选的技术方案，所述正方形超表面单元的尺寸参数为亚波长数量级，所述透射相位调控超表面的尺寸参数在应用波长范围实现的传输系数相位偏移量范围为[0,2π]，且传输系数幅度>0.8。As a preferred technical solution, the size parameters of the square metasurface unit are of sub-wavelength order, and the size parameters of the transmission phase control metasurface achieve a transmission coefficient phase offset range of [0, 2π] in the application wavelength range, and the transmission coefficient amplitude is >0.8.
作为优选的技术方案，所述相位偏移量利用调控相位分布公式获取，所述调控相位分布公式为：As a preferred technical solution, the phase offset is obtained by adjusting the phase distribution formula, and the adjusting phase distribution formula is:
式中，表示调控相位空间分布公式，k为波数，λ为待调控波束的波长，调控相位平面与波束传播方向垂直，ρ为调控相位平面上的点相对波束中轴的离轴距离，(x,y)为调控相位平面上的点与波束中轴的相对坐标，α为用以控制波束聚焦的程度的可调参数，为调控装置中心的参考点相位。In the formula, represents the spatial distribution formula of the control phase, k is the wave number, λ is the wavelength of the beam to be controlled, the control phase plane is perpendicular to the beam propagation direction, ρ is the off-axis distance of the point on the control phase plane relative to the beam axis, (x, y) is the relative coordinate of the point on the control phase plane and the beam axis, α is an adjustable parameter used to control the degree of beam focusing, It is the reference point phase of the control device center.
作为优选的技术方案，当相位偏移量大于2π时，相位分布公式为：As a preferred technical solution, when the phase offset is greater than 2π, the phase distribution formula is:
式中，为向下取整符号。In the formula, The floor symbol.
与现有技术相比，本发明具有以下有益效果：Compared with the prior art, the present invention has the following beneficial effects:
1、本发明利用透射相位调控超表面，通过对透射过超表面装置的毫米波波束空间相位进行人为预设的改变和调控，实现对近场波束传播过程的控制，可以实现近场低衍射聚焦波束的生成，其中，本发明中的应用波长灵活可调，聚焦参数可调，调控相位分布可以根据实际需要进行调整，且无需涉及天线设计，系统复杂度较低，应用范围广，适用性强；1. The present invention utilizes a transmission phase control metasurface to artificially preset changes and control of the spatial phase of the millimeter-wave beam transmitted through the metasurface device, thereby controlling the near-field beam propagation process and generating a near-field low-diffraction focused beam. The application wavelength in the present invention is flexibly adjustable, the focusing parameters are adjustable, and the control phase distribution can be adjusted according to actual needs, without involving antenna design. The system has low complexity, a wide range of applications, and strong applicability.
2、相比于传统的介质电磁透镜系统和阵列天线系统，本发明运用相位调控超表面能够有效降低天线系统的复杂度和尺度，且可加载在已有天线系统中，具有一定实用性；2. Compared with the traditional dielectric electromagnetic lens system and array antenna system, the present invention uses the phase-controlled metasurface to effectively reduce the complexity and scale of the antenna system, and can be loaded into the existing antenna system, which has certain practicality;
3、本发明采用的调控相位分布公式，相比于传统的超表面波束聚焦设计中使用的聚焦相位，在工作距离内具有聚焦距离更长的优势，能够扩大聚焦区域，提升毫米波波束在较长距离上的传输能力；3. The control phase distribution formula adopted by the present invention has the advantage of longer focusing distance within the working distance compared to the focusing phase used in the traditional metasurface beam focusing design, which can expand the focusing area and improve the transmission capability of the millimeter wave beam over a longer distance;
4、本发明利用特有的调控相位分布公式调控相位偏移量、设计透射相位调控超表面，相比于已有的超表面波束聚焦设计中使用的贝塞尔波束生成相位，本发明具有生成波束的轴上能量强度峰值更高的优势；4. The present invention uses a unique control phase distribution formula to control the phase offset and design a transmission phase control metasurface. Compared with the Bessel beam generation phase used in the existing metasurface beam focusing design, the present invention has the advantage of generating a higher peak energy intensity on the axis of the beam;
5、相比于传统的高斯光束径向控制的光相位调制设计，本发明设计毫米波波段，波段光调制器已有较多产品，而毫米波波段中波束相位调控装置较少，有较大创新意义。5. Compared with the traditional Gaussian beam radially controlled optical phase modulation design, the present invention is designed for the millimeter wave band. There are many products of band optical modulators, but there are fewer beam phase control devices in the millimeter wave band, which has great innovative significance.
附图说明BRIEF DESCRIPTION OF THE DRAWINGS
图1为本发明实施例中的毫米波近场低衍射聚焦波束生成系统结构示意图；FIG1 is a schematic diagram of the structure of a millimeter-wave near-field low-diffraction focused beam forming system in an embodiment of the present invention;
图2为本发明实施例中的仿真实验流程图；FIG2 is a flow chart of a simulation experiment in an embodiment of the present invention;
图3为本发明实施例中的仿真实验附加本实施例的相位偏移量示意图；FIG3 is a schematic diagram of a phase offset of a simulation experiment in an embodiment of the present invention and an embodiment of the present invention;
图4为本发明实施例中的仿真透射相位调控超表面装置的相位偏移区域示意图；FIG4 is a schematic diagram of a phase shift region of a simulated transmission phase control metasurface device in an embodiment of the present invention;
图5为本发明实施例中的仿真未调控高斯波束传播仿真结果图；FIG5 is a diagram showing simulation results of unregulated Gaussian beam propagation in an embodiment of the present invention;
图6为本发明实施例中的仿真实验附加聚焦相位偏移量后波束传播仿真结果截面图；FIG6 is a cross-sectional view of a beam propagation simulation result after adding a focusing phase offset in a simulation experiment in an embodiment of the present invention;
图7为本发明实施例中的仿真实验附加轴锥相位偏移量后波束传播仿真结果截面图；7 is a cross-sectional view of the beam propagation simulation result after the axis-cone phase offset is added in the simulation experiment in the embodiment of the present invention;
图8为本发明实施例中的仿真实验附加本实施例相位偏移量后波束传播仿真结果截面图；FIG8 is a cross-sectional view of a beam propagation simulation result after adding a phase offset of the embodiment of the present invention to the simulation experiment in the embodiment of the present invention;
图9为本发明实施例的仿真实验中不同传播距离的波束中心复电场强度对比图；FIG9 is a comparison diagram of complex electric field intensities at beam centers at different propagation distances in a simulation experiment of an embodiment of the present invention;
图10为本发明实施例的仿真实验中不同传播距离的1/e^2波束半径对比图；FIG10 is a comparison diagram of 1/e^2 beam radii at different propagation distances in a simulation experiment of an embodiment of the present invention;
图11为本发明实施例的透射型相位调控超表面单元的结构示意图；FIG11 is a schematic structural diagram of a transmission-type phase control metasurface unit according to an embodiment of the present invention;
图12为本发明实施例的超表面单元的透射幅度、透射相位与设计参数变化曲线图；FIG12 is a graph showing changes in transmission amplitude, transmission phase, and design parameters of a metasurface unit according to an embodiment of the present invention;
图13为本发明实施例的超表面单元的透射幅度与频率、设计参数变化曲线图；FIG13 is a graph showing changes in transmission amplitude, frequency, and design parameters of a metasurface unit according to an embodiment of the present invention;
图14为本发明实施例的超表面单元的透射相位与频率、设计参数变化曲线图。FIG14 is a graph showing changes in transmission phase, frequency and design parameters of a metasurface unit according to an embodiment of the present invention.
具体实施方式Detailed ways
下面结合附图和具体实施例对本发明进行详细说明。本实施例以本发明技术方案为前提进行实施，给出了详细的实施方式和具体的操作过程，但本发明的保护范围不限于下述的实施例。The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.
实施例Example
本实施例提供一种毫米波近场低衍射聚焦波束生成方法，利用该方法设计组成相应的透射相位调控超表面装置，也即透射型相位偏移超表面装置(特定相移量分布)，将透射相位调控超表面装置与毫米波发射天线装置、天线接收装置共同构成图1示出的毫米波近场低衍射聚焦波束生成系统，利用该系统能够实现前述方法，具体步骤如下：This embodiment provides a millimeter-wave near-field low-diffraction focused beamforming method, which is used to design a corresponding transmission phase control metasurface device, that is, a transmission-type phase shift metasurface device (specific phase shift distribution), and the transmission phase control metasurface device, a millimeter-wave transmitting antenna device, and an antenna receiving device together constitute a millimeter-wave near-field low-diffraction focused beamforming system shown in FIG. 1. The system can be used to implement the aforementioned method, and the specific steps are as follows:
(1)确定所需调控的毫米波波束参数，即目标波束参数，目标波束参数包括频率/波长参数和调控目标参数，调控目标参数包括聚焦区域范围长度Zmax；(1) Determining the millimeter wave beam parameters to be regulated, namely, the target beam parameters, the target beam parameters including the frequency/wavelength parameters and the regulation target parameters, the regulation target parameters including the focal area range length Z max ;
(2)基于所需调控的毫米波波束参数，利用本实施例提供的调控相位分布公式计算调控相位空间分布；(2) Based on the millimeter wave beam parameters to be regulated, the regulated phase spatial distribution is calculated using the regulated phase distribution formula provided in this embodiment;
(3)基于所需调控的毫米波波束参数和所需的聚焦区域范围长度，确定透射相位调控超表面装置的长、宽边长尺寸参数D，同时确定透射相位调控超表面的超表面单元数量和单个超表面单元的尺寸参数(边长为L、厚度为d)，进而确定透射相位调控超表面上单个相位区域有M×M个结构相同的超表面单元；(3) Based on the required millimeter-wave beam parameters and the required focal area range length, the length and width dimension parameters D of the transmission phase control metasurface device are determined, and at the same time, the number of metasurface units of the transmission phase control metasurface and the dimension parameters of a single metasurface unit (side length L and thickness d) are determined, and then it is determined that a single phase area on the transmission phase control metasurface has M×M metasurface units with the same structure;
(4)基于调控相位空间分布，计算单个相位区域的离散化相位偏移量；(4) Based on the spatial distribution of the regulated phase, the discretized phase offset of a single phase region is calculated;
(5)基于离散化相位偏移量和单个相位区域的超表面单元数量，计算单个超表面单元的相位偏移量；(5) calculating the phase offset of a single metasurface unit based on the discretized phase offset and the number of metasurface units in a single phase region;
(6)基于单个超表面单元的相位偏移量，完成透射相位调控超表面装置的设计和组成；(6) Based on the phase offset of a single metasurface unit, the design and composition of the transmission phase control metasurface device are completed;
(7)将毫米波发射天线装置、透射相位调控超表面装置初步组合成为低衍射聚焦波束生成系统：(7) The millimeter-wave transmitting antenna device and the transmission phase control metasurface device are preliminarily combined into a low-diffraction focused beam forming system:
毫米波发射天线装置为馈源天线装置，用于发射特定波长的初始毫米波波束，图1中示出的是多张角馈源天线装置，初始毫米波波束经初次传播后得到待调控波束，其中，发射天线装置发射的初始毫米波波束在近场情况下为可以近似为高斯波束考虑的有向波束，需要确定的参数包括所需调控的毫米波波束的频率/波长参数、高斯波束的束腰半径参数ω0，上述参数用于确定调控相位的空间分布；The millimeter wave transmitting antenna device is a feed antenna device, which is used to transmit an initial millimeter wave beam of a specific wavelength. FIG. 1 shows a plurality of angular feed antenna devices. After the initial millimeter wave beam is initially propagated, a beam to be regulated is obtained. The initial millimeter wave beam transmitted by the transmitting antenna device is a directional beam that can be approximated as a Gaussian beam in the near field. The parameters that need to be determined include the frequency/wavelength parameters of the millimeter wave beam to be regulated and the beam waist radius parameter ω 0 of the Gaussian beam. The above parameters are used to determine the spatial distribution of the regulated phase.
透射相位调控超表面装置用于将相应的相位偏移量附加至接收到的待调控波束，实现对待调控波束的调控，生成近场低衍射聚焦波束，其中，近场低衍射聚焦波束在一定的近场距离内，相比未调制的波束，波束能量更集中，轴上能量更强；The transmission phase control metasurface device is used to add the corresponding phase offset to the received beam to be controlled, so as to control the beam to be controlled and generate a near-field low-diffraction focused beam, wherein the near-field low-diffraction focused beam has more concentrated beam energy and stronger on-axis energy than the unmodulated beam within a certain near-field distance;
本实施例中低衍射聚焦波束生成系统还包括天线接收装置，用于接收近场低衍射聚焦波束。In this embodiment, the low-diffraction focused beam forming system further includes an antenna receiving device for receiving a near-field low-diffraction focused beam.
需要注意的是，透射相位调控超表面与毫米波波束的传播方向垂直，整个透射相位调控超表面装置的中心与毫米波波束的中轴为同轴的空间关系，透射相位调控超表面装置与毫米波发射天线装置之间距离d0<0.01m。It should be noted that the transmission phase control metasurface is perpendicular to the propagation direction of the millimeter wave beam, the center of the entire transmission phase control metasurface device is coaxial with the central axis of the millimeter wave beam, and the distance d 0 between the transmission phase control metasurface device and the millimeter wave transmitting antenna device is <0.01m.
前述的调控相位分布公式为：The aforementioned control phase distribution formula is:
k＝2π/λ (2)k＝2π/λ (2)
式中，表示调控相位空间分布公式，k为波数，λ为待调控波束的波长，调控相位平面与波束传播方向垂直，ρ为调控相位平面上的点相对波束中轴的离轴距离，(x,y)为调控相位平面上的点与波束中轴的相对坐标，α为用以控制波束聚焦的程度的可调参数，为调控装置中心的参考点相位。In the formula, represents the spatial distribution formula of the control phase, k is the wave number, λ is the wavelength of the beam to be controlled, the control phase plane is perpendicular to the beam propagation direction, ρ is the off-axis distance of the point on the control phase plane relative to the beam axis, (x, y) is the relative coordinate of the point on the control phase plane and the beam axis, α is an adjustable parameter used to control the degree of beam focusing, It is the reference point phase of the control device center.
相位分布函数对于一些坐标点的相位调制量(相位偏移量)会大于2π，由于在透镜透过率函数中，相位的变换作用表现在自然常数e的复指数虚部上，即k＝2π/λ为波数，λ为所调制波束的波长，因此在现实实现中相位分布可以将大于2π的相位点压缩至[0,2π]范围内，公式为：The phase modulation (phase offset) of the phase distribution function for some coordinate points will be greater than 2π, because in the lens transmittance function, the phase transformation effect is manifested in the complex exponential imaginary part of the natural constant e, that is, k = 2π/λ is the wave number, λ is the wavelength of the modulated beam, so in actual implementation, the phase distribution can compress the phase points greater than 2π to the range of [0,2π], and the formula is:
式中，为向下取整符号。In the formula, The floor symbol.
关于上述调控相位空间分布公式中的可调参数α，可以用以控制波束聚焦的程度，其中，生成的聚焦波束的聚焦区域长度为：The adjustable parameter α in the above formula for regulating the spatial distribution of the phase can be used to control the degree of beam focusing, wherein the focal region length of the generated focused beam is:
式中，Zmax表示聚焦区域范围长度，D为正方形相位调控超表面的边长尺寸，为了有效调控波束满足：Where Z max represents the length of the focusing area, and D is the side length of the square phase control metasurface. In order to effectively control the beam,
且满足近场调控条件：And meet the near-field control conditions:
改变可调参数α，可以控制聚焦区域范围长度，进而控制波束聚焦的程度。By changing the adjustable parameter α, the length of the focusing area can be controlled, thereby controlling the degree of beam focusing.
透射相位调控超表面装置通过一定尺寸的单个的具有一定相位偏移量的透射式超表面单元组合而成。其中，整个透射相位调控超表面装置的中心应当与所调控波束的中心轴线同轴，也即待调控波束相对于相位调控超表面装置为正入射。The transmissive phase control metasurface device is composed of a single transmissive metasurface unit of a certain size with a certain phase offset. The center of the entire transmissive phase control metasurface device should be coaxial with the central axis of the beam to be controlled, that is, the beam to be controlled is normally incident relative to the phase control metasurface device.
其中，若干个相邻单元的相位偏移量可以设为相同，组成一个虚拟的相位区域。单个相位区域的相位偏移量由上述相位分布公式确定，(xi,yj)为单个相位区域的中心点与波束中轴的相对坐标。通过整个相位调控超表面装置的相位分布，实现透射过装置后的毫米波低衍射聚焦波束的生成。The phase offsets of several adjacent units can be set to be the same to form a virtual phase region. According to the above phase distribution formula Sure, ( xi , yj ) is the relative coordinate of the center point of a single phase region and the center axis of the beam. Through the phase distribution of the entire phase-controlled metasurface device, the generation of a millimeter-wave low-diffraction focused beam after passing through the device is achieved.
本实施例提供的透射相位调控超表面装置包括[(2N-1)×M]×[(2N-1)×M]个边长为L、厚度为d的正方形超表面单元，也即超表面装置由多个超表面单元组成[(2N-1)×M]行、[(2N-1)×M]列的阵列实现，也可以认为是由(2N-1)行、(2N-1)列的相位区域阵列组成(单个相位区域包括M×M个超表面单元)，其中第N行、第N列的相位偏移区域的中心即为透射相位调控超表面装置的几何中心。因此，对于透射相位调控超表面装置的整体尺寸，厚度为d，长和宽均为：The transmission phase control metasurface device provided in this embodiment includes [(2N-1)×M]×[(2N-1)×M] square metasurface units with a side length of L and a thickness of d, that is, the metasurface device is implemented by an array of multiple metasurface units consisting of [(2N-1)×M] rows and [(2N-1)×M] columns, and can also be considered to be composed of a phase region array of (2N-1) rows and (2N-1) columns (a single phase region includes M×M metasurface units), where the center of the phase offset region of the Nth row and the Nth column is the geometric center of the transmission phase control metasurface device. Therefore, for the overall size of the transmission phase control metasurface device, the thickness is d, and the length and width are both:
D＝[(2N-1)×M]×L (7)D＝[(2N-1)×M]×L (7)
其中，单个相位偏移单元为正方形的透射型相位调控超表面单元，其尺寸和具体的超表面结构设计应当满足具体波段的相位调控需求，具体有：Among them, a single phase shift unit is a square transmission-type phase control metasurface unit, and its size and specific metasurface structure design should meet the phase control requirements of a specific band, specifically:
(1)单元尺寸为亚波长数量级；(1) The unit size is of sub-wavelength order;
(2)通过改变超表面结构尺寸参数可以对装置的设计工作波长的电磁波，实现[0,2π]的传输系数相位偏移量调控；(2) By changing the size parameters of the metasurface structure, the transmission coefficient phase offset of the electromagnetic wave of the designed working wavelength of the device can be controlled in the range of [0,2π];
(3)满足上一条相位偏移量覆盖范围的同时，在应用波长保持传输系数幅度>0.8，即透射损耗较小。(3) While satisfying the phase offset coverage range in the previous paragraph, the transmission coefficient amplitude is kept > 0.8 at the application wavelength, that is, the transmission loss is small.
本实施例不涉及具体的超表面结构设计，而涉及的单个超表面单元的相位偏移量，依照本实施例提出的相位分布公式和提出的设计方法确定。This embodiment does not involve a specific metasurface structure design, but involves a phase offset of a single metasurface unit, which is determined according to the phase distribution formula and the design method proposed in this embodiment.
其中，M×M个相邻超表面单元组成一个虚拟的相位区域，相同相位区域内的超表面单元采用相同的相位偏移量设计，即相同的结构。单个相位区域所需的相位偏移量，基于本实施所提出的相位偏移量分布公式计算得到。单个相位区域所需的相位偏移量，由区域的几何中心的坐标带入上述公式计算得到。Among them, M×M adjacent metasurface units form a virtual phase region, and the metasurface units in the same phase region adopt the same phase offset design, that is, the same structure. The phase offset required for a single phase region is calculated based on the phase offset distribution formula proposed in this implementation. The phase offset required for a single phase region is calculated by substituting the coordinates of the geometric center of the region into the above formula.
需要说明的是，在其他一些实施例中，出于减少超表面结构制造难度的目的，可以减少相位分布的离散化精度，也即，不必以单个超表面单元的数量作为连续相位偏移量分布的离散化网格数，实际上可以使若干相邻超表面单元使用相同结构、实现相同的相位偏移量。以此降低所需生产的特定结构的超表面单元的数量，降低生产难度。It should be noted that in some other embodiments, in order to reduce the difficulty of manufacturing the metasurface structure, the discretization accuracy of the phase distribution can be reduced, that is, it is not necessary to use the number of single metasurface units as the number of discretized grids for the continuous phase offset distribution. In fact, several adjacent metasurface units can use the same structure and achieve the same phase offset. In this way, the number of metasurface units of a specific structure that need to be produced is reduced, and the production difficulty is reduced.
接下来提供一种基于77GHz毫米波波束近场低衍射聚焦波束生成仿真系统，验证前述的低衍射聚焦波束生成方法及系统的有效性，验证流程如图2所示，具体为：Next, a near-field low-diffraction focused beamforming simulation system based on a 77GHz millimeter-wave beam is provided to verify the effectiveness of the aforementioned low-diffraction focused beamforming method and system. The verification process is shown in FIG2, specifically:
本实施例应用高斯波束准光路设计方法进行仿真实验，高斯波束传播是基于傍轴近似理论来求解亥姆霍兹波动方程。傍轴近似理论认为从馈源发出的电磁波主要集中在靠近传播轴一个角度范围之内。在近轴近似的条件下，基模高斯波束在柱坐标下的表达式为：This embodiment uses the Gaussian beam quasi-optical path design method to perform simulation experiments. Gaussian beam propagation is based on the paraxial approximation theory to solve the Helmholtz wave equation. The paraxial approximation theory believes that the electromagnetic waves emitted from the feed source are mainly concentrated within an angle range close to the propagation axis. Under the condition of paraxial approximation, the expression of the fundamental mode Gaussian beam in cylindrical coordinates is:
R＝z+(πω2)/(zλ) (9)R＝z+(πω 2 )/(zλ) (9)
式中，z为传播方向的传播距离坐标，ω为高斯波束束腰半径，λg为基模高斯波束波长，R为高斯波束的波前曲率半径，为基模高斯波束附加相移。本实施例中所调制的高斯波束的空间场强分布由上述公式产生，其中波束波长λ＝c/(77×109)＝0.0039m。Where z is the propagation distance coordinate in the propagation direction, ω is the waist radius of the Gaussian beam, λg is the wavelength of the fundamental mode Gaussian beam, and R is the wavefront curvature radius of the Gaussian beam. The phase shift is added to the fundamental mode Gaussian beam. The spatial field intensity distribution of the modulated Gaussian beam in this embodiment is generated by the above formula, wherein the beam wavelength λ = c/(77×10 9 ) = 0.0039 m.
本实施例基于角光谱理论运用分步长傅里叶变换方法(SSFM)进行波束传播仿真实验，SSFM波束传播仿真是基于菲涅尔传播中的菲涅尔积分公式：This embodiment uses the fractional-step Fourier transform method (SSFM) to perform a beam propagation simulation experiment based on the angular spectrum theory. The SSFM beam propagation simulation is based on the Fresnel integral formula in Fresnel propagation:
式中，U1(x1,y1)为初始复电场横向空间分布，U2(x2,y2)为传播z距离后的复电场横向空间分布，应用卷积理论和傅里叶变换理论上述传播公式可以化为：Where U 1 (x 1 ,y 1 ) is the initial complex electric field transverse spatial distribution, and U 2 (x 2 ,y 2 ) is the complex electric field transverse spatial distribution after propagation distance z. Applying convolution theory and Fourier transform theory, the above propagation formula can be transformed into:
U2(x2,y2)＝F-1{F{U1(x1,y1)} H(fx,fy)} (11)U 2 (x 2 ,y 2 )＝F -1 {F{U 1 (x 1 ,y 1 )} H(f x ,f y )} (11)
式中，转换函数H(fx,fy)可表示为：Where, the conversion function H(f x ,f y ) can be expressed as:
式中，fx为空间频谱X轴上的空间频率坐标，fy为空间频谱Y轴上的空间频率坐标。Where fx is the spatial frequency coordinate on the X-axis of the spatial spectrum, and fy is the spatial frequency coordinate on the Y-axis of the spatial spectrum.
以此理论可以将波束传播仿真通过对横向复电场的分步长的傅里叶变换实现。Based on this theory, beam propagation simulation can be realized by performing a step-by-step Fourier transform of the transverse complex electric field.
根据图1展示的一种基于相控超表面的毫米波近场低衍射聚焦波束生成系统，根据图2建立波束传输仿真系统，其中具体的仿真参数为：According to the millimeter-wave near-field low-diffraction focused beam forming system based on phased metasurface shown in FIG1 , a beam transmission simulation system is established according to FIG2 , where the specific simulation parameters are:
波长为3.9mm，即频率为77GHz，高斯波束束腰半径为20mm，仿真网格单元步长为0.2mm，仿真网格数为2048×2048，横向仿真区域尺寸为0.4094m×0.4094m正方形区域。涉及本实施例的透射型超表面单元的仿真，设置超表面单元为正方形单元，边长1.3mm，整体超表面装置为由多个超表面单元组成的(13×3)×(13×3)的单元阵列。其中，以相邻3×3个超表面单元为一个相位区域，也即整体超表面装置由13×13的相位偏移区域组成，超表面装置的相位偏移量设计由相位分布公式和相位区域的中心坐标确定。The wavelength is 3.9mm, that is, the frequency is 77GHz, the Gaussian beam waist radius is 20mm, the simulation grid unit step size is 0.2mm, the number of simulation grids is 2048×2048, and the lateral simulation area size is a 0.4094m×0.4094m square area. In the simulation of the transmission-type metasurface unit of this embodiment, the metasurface unit is set as a square unit with a side length of 1.3mm, and the overall metasurface device is a (13×3)×(13×3) unit array composed of multiple metasurface units. Among them, adjacent 3×3 metasurface units are used as a phase region, that is, the overall metasurface device is composed of 13×13 phase offset regions, and the phase offset design of the metasurface device is determined by the phase distribution formula and the center coordinates of the phase region.
由于相位是相对值，本实施例考虑相位调控装置的中心的相位参考值为0，即采用的相位偏移量分布公式即为：Since the phase is a relative value, this embodiment considers that the phase reference value of the center of the phase control device is 0, that is, The phase offset distribution formula used is:
其中，可调参数α设为0.4704，k＝2π/λ为波数。Among them, the adjustable parameter α is set to 0.4704, and k = 2π/λ is the wave number.
同时，出于比较的目的，针对轴锥相位偏移量分布公式为：At the same time, for comparison purposes, the distribution formula for the axis-cone phase offset is:
其中，参数θ设为0.0666rad；Among them, the parameter θ is set to 0.0666rad;
针对聚焦相位偏移量分布公式为：The formula for focusing phase offset distribution is:
由于针对相位分布公式参数的调整会改变所调制波束的聚焦程度，对于基于轴锥相位偏移量的波束调控，其最大无衍射距离为：Since the adjustment of the phase distribution formula parameters will change the focusing degree of the modulated beam, the maximum diffraction-free distance for beam steering based on the axicon phase offset is:
Zmax＝D/(2 tanθ) (16)Z max = D/(2 tanθ) (16)
在本实施例中，相位分布公式和轴锥相位分布公式基于性能比较的目的，设置最大无衍射距离相同，即In this embodiment, the phase distribution formula is and the axis-cone phase distribution formula For the purpose of performance comparison, the maximum diffraction-free distance is set to be the same, that is,
在本实施例中由于明确了波束半径，考虑D/2＝20mm，在一般应用中D为相位调控超表面装置的几何尺寸，设置参数α和参数θ，针对聚焦相位，设置焦距参数f为：In this embodiment, since the beam radius is clear, considering D/2=20 mm, in general applications, D is the geometric size of the phase-controlled metasurface device, and the parameters α and θ are set. For the focusing phase, the focal length parameter f is set as:
f＝Zmax/2＝0.15 m (18)f＝Z max /2＝0.15 m (18)
在仿真过程中，通过在仿真的复电场横向分布中，乘以自然常数e的复指数可以实现附加相位偏移量，因此相位的变换作用表现在自然常数e的复指数虚部上其中波数k＝2π/λ。In the simulation process, the additional phase shift can be achieved by multiplying the complex exponential of the natural constant e in the simulated complex electric field lateral distribution. Therefore, the phase shift effect is manifested in the imaginary part of the complex exponential of the natural constant e. Where the wave number k = 2π/λ.
本实施例基于基模高斯波束的表达式，仿真原始波束，基模高斯波束表达式为：This embodiment simulates the original beam based on the expression of the fundamental mode Gaussian beam. The expression of the fundamental mode Gaussian beam is:
式中，A0为归一化参数，为波束半径，为瑞利距离，(x,y)为横向空间坐标，z为传播方向的传播距离坐标，ω0为高斯波束束腰半径。以上述表达式E(x,y,0)＝A0(1/ω0)exp{-(x2+y2)/ω0 2}作为初始波束的归一化横向复电场分布。In the formula, A0 is the normalization parameter, is the beam radius, is the Rayleigh distance, (x, y) is the transverse spatial coordinate, z is the propagation distance coordinate in the propagation direction, and ω 0 is the Gaussian beam waist radius. The above expression E(x, y, 0) = A 0 (1/ω 0 ) exp{-(x 2 +y 2 )/ω 0 2 } is used as the normalized transverse complex electric field distribution of the initial beam.
如依据图2建立的仿真系统所示，由上述的相位偏移量分布公式和整体超表面装置的参数的配置，可以生成本实施例的、轴锥相位的、聚焦相位仿真相位调控超表面装置，其中每个装置及装置外未被调控的区域，整体0.4094m×0.4094m尺寸的横向仿真区域，仿真为2048×2048的相位偏移量矩阵。如图3所示为基于本发明相位偏移量分布公式和装置设计方法仿真得到的实际尺寸的相位调控装置示意图；如图4所示为基于本发明相位偏移量分布公式和装置设计方法仿真得到的相位调控装置的相位偏移量分布示意图。As shown in the simulation system established according to FIG2, the above-mentioned phase offset distribution formula and the configuration of the parameters of the overall metasurface device can generate the axonic phase, focusing phase simulation phase control metasurface device of this embodiment, wherein each device and the uncontrolled area outside the device, the overall lateral simulation area of 0.4094m×0.4094m size, is simulated as a 2048×2048 phase offset matrix. FIG3 is a schematic diagram of a phase control device of actual size obtained by simulation based on the phase offset distribution formula and device design method of the present invention; FIG4 is a schematic diagram of the phase offset distribution of the phase control device obtained by simulation based on the phase offset distribution formula and device design method of the present invention.
如图2所示，首先将初始的高斯波束通过前述的分步傅里叶传播仿真方法进行传播dz＝0.01m的仿真，仿真从馈源天线装置到超表面装置之间的配置距离d0＝0.01m，此时得到待调控波束，通过将相应相位偏移量附加到待调控波束实现对初始波束的空间相位调控，其过程也是透射型相位偏移超表面装置的仿真过程。调制后的波束，通过前述的分步傅里叶传播仿真方法进行传播方向上的仿真，仿真步长dz设置为0.01m，仿真距离为0.01m至1m，由此仿真过程可以得到使用不同相位偏移公式的透射型相移超表面的聚焦波束生成系统，传播不同距离的横向电场强度空间分布的仿真结果。如图5所示为未经调控的初始波束经过传播仿真的传播方向波束场强横截面结果图；如图6所示为经过聚焦相位偏移量调控的波束经过传播仿真的传播方向波束场强横截面结果图；如图7所示为经过轴锥相位偏移量调控的波束经过传播仿真的传播方向波束场强横截面结果图；如图8所示为经过本发明相位偏移量调控的波束经过传播仿真的传播方向波束场强横截面结果图。As shown in FIG2 , the initial Gaussian beam is firstly simulated by propagating dz=0.01m through the aforementioned step-by-step Fourier propagation simulation method, and the configuration distance d 0 =0.01m between the feed antenna device and the metasurface device is simulated. At this time, the beam to be regulated is obtained, and the spatial phase regulation of the initial beam is realized by adding the corresponding phase offset to the beam to be regulated. This process is also the simulation process of the transmission-type phase-shifted metasurface device. The modulated beam is simulated in the propagation direction through the aforementioned step-by-step Fourier propagation simulation method, and the simulation step dz is set to 0.01m, and the simulation distance is 0.01m to 1m. From this simulation process, the focused beam generation system of the transmission-type phase-shifted metasurface using different phase offset formulas can be obtained, and the simulation results of the spatial distribution of the transverse electric field intensity at different propagation distances can be obtained. As shown in Figure 5, it is a graph showing the beam field strength cross section result in the propagation direction of the uncontrolled initial beam after propagation simulation; as shown in Figure 6, it is a graph showing the beam field strength cross section result in the propagation direction of the beam controlled by the focusing phase offset after propagation simulation; as shown in Figure 7, it is a graph showing the beam field strength cross section result in the propagation direction of the beam controlled by the axial cone phase offset after propagation simulation; as shown in Figure 8, it is a graph showing the beam field strength cross section result in the propagation direction of the beam controlled by the phase offset of the present invention after propagation simulation.
此外，本实施例针对透射型相移超表面装置的具体设计，提供一个具体的仿真实例进行验证，该结构设计仅作说明验证，本发明不涉及超表面单元的具体结构设计：In addition, this embodiment provides a specific simulation example for verification of the specific design of the transmission-type phase-shift metasurface device. The structural design is only for illustration and verification, and the present invention does not involve the specific structural design of the metasurface unit:
本实施例考虑了如图11的一种透射型相位调控超表面单元，单个单元的结构设计由三层相同结构层叠而成，层叠结构可以在不过多损失透射能量的同时，提升单元的相位偏移量覆盖范围。对于单层结构，分为正面金属贴片结构、中心基层、背面金属贴片结构，其中正面和背面金属贴片结构相同。金属贴片结构分为外侧金属方环和中心圆形金属贴片。在固定其他结构参数的同时，通过改变中心圆形金属贴片的半径参数，可以实现对透射波束附加特定的相位偏移量，即透射型相位调控超表面单元。在本实施例的仿真中，基于电磁仿真软件CST进行建模仿真。具体结构参数为，金属贴片层厚度为0.008mm，金属方框宽度w＝0.02mm，金属方环外边与中心基层边长相同，金属贴片层设置采用金(au)材料，中心基层采用相对介电常数ε＝2.1，损耗正切值为0.0002的聚四氟乙烯材料，中心基层长、宽边长L＝1.3mm，厚度d＝3×0.35mm，中心圆形金属贴片半径参数为r。通过改变r的大小，改变超表面单元的性能，控制单元的透射相位。This embodiment considers a transmission-type phase-control metasurface unit as shown in Figure 11. The structural design of a single unit is composed of three layers of the same structure stacked together. The stacked structure can improve the phase offset coverage of the unit without losing too much transmission energy. For a single-layer structure, it is divided into a front metal patch structure, a central base layer, and a back metal patch structure, wherein the front and back metal patch structures are the same. The metal patch structure is divided into an outer metal square ring and a central circular metal patch. While fixing other structural parameters, by changing the radius parameter of the central circular metal patch, it is possible to add a specific phase offset to the transmitted beam, that is, a transmission-type phase-control metasurface unit. In the simulation of this embodiment, modeling and simulation are performed based on the electromagnetic simulation software CST. The specific structural parameters are as follows: the thickness of the metal patch layer is 0.008mm, the width of the metal square frame is w = 0.02mm, the outer edge of the metal square ring is the same as the side length of the central base layer, the metal patch layer is set with gold (au) material, the central base layer is made of polytetrafluoroethylene material with a relative dielectric constant ε = 2.1 and a loss tangent value of 0.0002, the length and width of the central base layer are L = 1.3mm, the thickness is d = 3 × 0.35mm, and the radius parameter of the central circular metal patch is r. By changing the size of r, the performance of the metasurface unit is changed, and the transmission phase of the unit is controlled.
在CST仿真软件中对上述结构进行建模设置，边界条件设置为周期边界，对单元中心圆形金属贴片单元的半径参数r进行步进参数仿真，该单元在77GHz处的传输系数的幅度和相位随参数r的变化如图12所示。如图可见，考虑电磁波波束正入射时，改变半径参数r在0.05mm至0.62mm之间变化，经超表面单元的透射后的电磁波相位变化可以覆盖[0,2π]，且透射幅度在0.84以上，结果可知满足相位偏移量覆盖范围的同时，应用波长保持透射损耗较小，该单元设计可以满足相位调控的使用需求。图13为该单元在75GHz～79GHz，改变改变半径参数r所得的传输系数幅度仿真结果；图14为该单元在75GHz～79GHz，改变改变半径参数r所得的传输系数相位仿真结果，仿真结果表明，此单元设计可以在77Ghz以外的一定频段内也具有有效的相位调控能力，具有一定的宽频带适应能力。The above structure is modeled and set in CST simulation software, the boundary condition is set as periodic boundary, and the radius parameter r of the circular metal patch unit in the center of the unit is simulated by step parameters. The amplitude and phase of the transmission coefficient of the unit at 77GHz are shown in Figure 12 as the parameter r changes. As can be seen from the figure, when the electromagnetic wave beam is positively incident, the radius parameter r changes from 0.05mm to 0.62mm, and the phase change of the electromagnetic wave after transmission through the metasurface unit can cover [0,2π], and the transmission amplitude is above 0.84. The results show that while meeting the coverage range of the phase offset, the application wavelength keeps the transmission loss small, and the unit design can meet the use requirements of phase regulation. Figure 13 shows the transmission coefficient amplitude simulation results of the unit at 75GHz~79GHz, changing the radius parameter r; Figure 14 shows the transmission coefficient phase simulation results of the unit at 75GHz~79GHz, changing the radius parameter r. The simulation results show that this unit design can also have effective phase regulation capabilities in a certain frequency band outside 77Ghz, and has a certain wide-band adaptability.
如图9所示为未经调控的初始波束、经过聚焦相位偏移量调控的波束、经过轴锥相位偏移量调控的波束、经过本发明相位偏移量调控的波束，通过本实施例传播仿真系统后，各自仿真波束中心复电场强度与传播距离的结果图；如图10所示为未经调控的初始波束、经过聚焦相位偏移量调控的波束、经过轴锥相位偏移量调控的波束、经过本发明相位偏移量调控的波束，通过本实施例传播仿真系统后，各自1/e^2波束半径与传播距离的结果图。As shown in Figure 9, an uncontrolled initial beam, a beam controlled by the focusing phase offset, a beam controlled by the axial cone phase offset, and a beam controlled by the phase offset of the present invention are respectively simulated as the result graphs of the complex electric field intensity at the center of each beam and the propagation distance after passing through the propagation simulation system of this embodiment; as shown in Figure 10, an uncontrolled initial beam, a beam controlled by the focusing phase offset, a beam controlled by the axial cone phase offset, and a beam controlled by the phase offset of the present invention are respectively simulated as the result graphs of the 1/e^2 beam radius and the propagation distance after passing through the propagation simulation system of this embodiment.
通过实验结果可以得知，本实施例提供的系统能够用于毫米波近场低衍射聚焦波束生成，该系统经过仿真场景验证，待调控波束通过特定相位偏移量分布的透射型相位偏移超表面装置，相比于未经调控的高斯波束，可以实现工作距离内波束中心光强的提升和波束半径的减小，即低衍射聚焦波束的生成。本实施例提出的超表面装置相位分布公式，经过仿真场景验证，相比轴锥相位分布，在工作距离内可以实现更高的波束中心电场强度以及更小的波束半径。同时，聚焦相位分布虽然具有最高的波束中心电场强度以及最小的波束半径，但是由于点聚焦特性，其聚焦特性维持距离最短。因此本实施例提出的超表面装置相位分布公式在仿真实施例中表现出较强的创新性和实用性，相比领域经典方法具有一定优势。本实施例提供的方法及系统具有近场波束能量集中、结构复杂度低的优点，在毫米波雷达、毫米波近场成像、毫米波检测等领域具有广泛应用前景。It can be known from the experimental results that the system provided in this embodiment can be used for millimeter-wave near-field low-diffraction focused beam generation. The system has been verified by simulation scenarios. The beam to be regulated passes through a transmission-type phase-shifted metasurface device with a specific phase offset distribution. Compared with an unregulated Gaussian beam, it can achieve an increase in the center light intensity of the beam within the working distance and a reduction in the beam radius, that is, the generation of a low-diffraction focused beam. The phase distribution formula of the metasurface device proposed in this embodiment has been verified by simulation scenarios. Compared with the axis cone phase distribution, a higher beam center electric field intensity and a smaller beam radius can be achieved within the working distance. At the same time, although the focusing phase distribution has the highest beam center electric field intensity and the smallest beam radius, due to the point focusing characteristics, its focusing characteristics maintain the shortest distance. Therefore, the phase distribution formula of the metasurface device proposed in this embodiment shows strong innovation and practicality in the simulation embodiment, and has certain advantages over the classical methods in the field. The method and system provided in this embodiment have the advantages of concentrated near-field beam energy and low structural complexity, and have broad application prospects in the fields of millimeter wave radar, millimeter wave near-field imaging, and millimeter wave detection.
以上详细描述了本发明的较佳具体实施例。应当理解，本领域的普通技术人员无需创造性劳动就可以根据本发明的构思作出诸多修改和变化。因此，凡本技术领域中技术人员依本发明的构思在现有技术的基础上通过逻辑分析、推理或者有限的实验可以得到的技术方案，皆应在由权利要求书所确定的保护范围内。The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.
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