电磁超表面在微波和太赫兹波段雷达散射截面缩减中的应用研究进展

电磁超表面由于其独特的电磁特性为调控电磁波提供了有力工具,合适地设计成编码、随机、相位不连续、完美吸收器等超表面,就能够控制电磁波的散射以及反射特性,实现雷达散射截面的缩减。本文综述了不同的电磁超表面利用漫反射或者吸收等特性实现在微波和太赫兹波段雷达散射截面缩减中的应用。分析表明,编码超表面由不同的数字单元组成,其反射相位差在很宽的频段范围内满足恒定的关系,设计特殊的单元序列使入射的电磁波产生非定向散射,更高bit编码超表面更容易灵活调控电磁波;随机超表面通过调节阵元的尺寸实现宽带移相从而将金属目标特征性强的反射峰打散成一个无规律、杂乱的波,产生漫反射;不连续超表面由于相位不连续可使电磁波发生漫反射或者异常反射;吸收器通过合理设计结构尺寸实现吸收电磁波能量来减小反射。因此电磁超表面在雷达隐身、宽带通讯、成像等方面具有重要的应用前景。最后对电磁超表面在雷达散射截面缩减中应用的发展趋势进行了初步探讨,未来将向着宽带、柔性、大角度等方面发展。     

An ultra-wideband 2-bit coding metasurface using Pancharatnam—Berry phase for radar cross-section reduction

An ultra-wideband 2-bit coding metasurface is designed for radar cross-section (RCS) reduction. The design process is presented in detail, in which a polarization conversion metasurface (PCM) is first proposed. The proposed PCM can realize ultra-wideband circular polarization (CP) maintaining reflection. Moreover, Pancharatnam—Berry (PB) phase will be generated in the co-polarized reflection coefficient by rotating the metallic patches in its unit cells. Thus, based on the PCM, the four coding elements of a 2-bit coding metasurface are constructed using PB phase, and an ultra-wideband PB 2-bit coding metasurface is proposed according to an appropriate coding sequence. The simulated and experimental results show that the coding metasurface has obvious advantages of wideband and polarization-insensitivity. Compared to a metallic plate of the same size, it can achieve more than 10 dB RCS reduction in the frequency band from 9.8 GHz to 42.6 GHz with a relative bandwidth of 125.2% under normal incidence with arbitrary polarizations.     

基于编码超表面的太赫兹宽频段雷达散射截面缩减的研究

本文设计了一种柔性, 非定向低散射的1bit编码超表面, 实现了太赫兹宽频带雷达散射截面的缩减. 这种设计基于对“0”和“1”两种基本单元进行编码, 其反射相位差在很宽的频段范围内接近180°, 为一种非周期的排列方式, 该电磁超表面使入射的电磁波发生漫反射, 从而实现雷达散射截面的缩减. 全波仿真结果表明, 在垂直入射条件下, 编码超表面的镜像反射率低于-10 dB的带宽频段范围为1.0-1.4 THz, 该带宽内超表面相对同尺寸金属板可将雷达散射截面所减量达到10 dB以上, 最大缩减量达到19 dB. 把柔性编码表面弯曲在直径为4 mm的金属圆柱面上, 雷达散射截面的所减量高于10 dB以上的带宽频段范围为0.9-1.2 THz, 仍然可实现宽频带缩减特性. 总之, 编码超表面为调控太赫兹波提供一种新的途径, 将在雷达隐身、成像、宽带通信等方面具有重要的意义.     

宽频带雷达散射截面缩减相位梯度超表面的设计及实验验证

针对相位梯度超表面在隐身技术中的应用,提出通过表面波耦合和异常反射两种机制复合实现宽频带后向雷达散射截面(RCS)缩减,采用开口谐振环进行相位梯度设计,实现了一种二维极化无关相位梯度超表面,在10 GHz附近,超表面通过将垂直入射电磁波耦合为表面波实现RCS缩减,而在大于11 GHz的频率范围内,相位分布的不均匀性使垂直入射的电磁波发生漫反射或者异常反射,降低后向RCS,制作了厚度为2 mm的超表面样品,测试了其反射率曲线和后向RCS,并与相同尺寸的金属板进行了对比,实验结果表明,在宽频段内(9.5—17.0 GHz),超表面在垂直入射情况下可将后向RCS缩减至少10 dB,由于厚度薄、重量轻、频带宽,RCS缩减超表面在隐身新材料和新技术方面具有很大的应用潜力。     

一种宽角域散射增强超表面的研究

提出并验证了一种基于超表面相位梯度设计以实现宽角域后向雷达散射截面(radar cross section, RCS)增强的设计思路.宽角域RCS增强超表面包含两个区域,分别设计大小相等方向相反的相位梯度,控制-45?和45?方向上的入射电磁波沿入射方向返回;电磁波垂直入射时,在一个区域内耦合为表面电磁波,传播至另一区域再次解耦为垂直反射的自由空间波,分别在-45?, 0?, 45?方向上形成散射峰,实现了在-45?—45?的宽角域范围内的RCS增强.仿真了宽角域RCS增强超表面在电磁波以不同角度入射时的电场分布和单站RCS,测试了加工样品在9—12 GHz频带内不同频点处的单站RCS,和仿真结果基本一致.结果表明:设计的宽角域RCS增强超表面在9—12 GHz的宽带频率范围内,在-45?—45?的宽角域范围内对于x和y极化入射波均有良好的RCS增强效果.     

太赫兹频率编码器

超表面是由亚波长单元组成控制电磁波的人工结构,研究发现通过对其进行编码排列可实现对电磁波能量的任意控制.本文利用四种形状相同、尺寸不同的人字形结构单元,结合其不同相位响应和不同的相位灵敏度设计了太赫兹频率编码器,通过进行特定编码,在频率改变的情况下,实现了对电磁波能量辐射调控.分别设计了1-bit, 2-bit周期和非周期太赫兹频率编码器,通过数值计算和仿真模拟验证了上述特性,而且该结构对太赫兹波辐射主瓣能量有很好的分散作用,可以有效减少雷达散射截面,雷达散射截面缩减在q=0,j=0方向上最大可达29 dB,在太赫兹波隐身中具有巨大应用价值.     

Ultra-wideband RCS reduction using novel configured chessboard metasurface

A novel artificial magnetic conductor(AMC) metasurface is proposed with ultra-wideband 180?phase difference for radar cross section(RCS) reduction. It is composed of two dual-resonant AMC cells, which enable a broadband phase difference of 180?±30?from 7.9 GHz to 19.2 GHz to be achieved. A novel strategy is devised by dividing each rectangular grid in a chessboard configuration into four triangular grids, leading to a further reduction of peak bistatic RCS. Both fullwave simulation and measurement results show that the proposed metasurface presents a good RCS reduction property over an ultra-wideband frequency range.     

Ultra-wideband low radar cross-section metasurface and its application on waveguide slot antenna array

A novel approach devoted to achieving ultra-wideband radar cross section reduction(RCSR) of a waveguide slot antenna array(WGSAA) while maintaining its radiation performance is proposed. Three kinds of artificial magnetic conductors(AMCs) tiles consisting of three types of basic units resonant at different frequencies are designed and arranged in a novel quadruple-triangle-type configuration to create a composite planar metasurface. The proposed metasurface is characterized by low radar feature over an ultra-wideband based on the principle of phase cancellation. Both simulated and measured results demonstrate that after the composite metasurface is used to cover part of the antenna array, an ultrawideband RCSR involving in-band and out-of-band is achieved for co-and cross-polarized incident waves based on energy cancellation, while the radiation performance is well retained. The proposed method is simple, low-cost, and easy-tofabricate, providing a new method for ultra-wideband RCSR of an antenna array. Moreover, the method proposed in this paper can easily be applied to other antenna architectures.     

Design of multi-band metasurface antenna array with low RCS performance

In this paper, a multi-band metasurface(MS) antenna array with low radar cross section(RCS) performance is proposed and measured. Firstly, a 44 antenna array is composed of four 22 Jerusalem cross structure antenna arrays working at different frequency bands, which is aimed at enhancing the bandwidth effectively. Then, each antenna can be seen as a unit of MS in spite of adding the feeding structure. Based on phase cancellation principle, the MS is arranged into a chessboard configuration in order to realize wideband RCS reduction. Thus, excellent radiation and scattering characteristics are obtained simultaneously. Simulated and measured results indicate that this work provides a novel method to achieve bandwidth expansion as well as wideband RCS reduction of the antenna array.     

基于电磁谐振分离的宽带低雷达截面超材料吸波体

基于超材料的电磁谐振特性, 设计、制作了一种极化无关的宽带低雷达散射截面 (radar cross section, RCS)超材料吸波体. 通过场分布和反演法分析了其吸波机理, 利用波导法和空间波法测试了其吸波率和RCS特性. 理论分析表明: 在平面波的作用下, 该吸波体对某一吸波频率在不同的位置分别提供电谐振和磁谐振, 对不同的吸波频率, 利用不同的介质层提供主要的能量损耗, 从而有效减弱了电磁耦合, 保证了宽频带的强吸收特性. 实验结果表明: 设计的三层结构吸波体吸波率达90%以上的带宽是单层结构的4.25倍, RCS减缩10 dB以上的带宽为5.1%, 其单元尺寸为0.17λ, 厚度仅为0.015λ. 该吸波体的低RCS特性还具有极化无关、宽入射角的特点, 且通过改变吸波体的夹层结构可以实现工作带宽的灵活调节. 关键词： 超材料吸波体 雷达散射截面 宽带 电磁谐振     

电磁带隙结构在天线雷达散射截面减缩中的应用

 提出了一种使用电磁带隙结构来减小微带印刷对称阵子天线雷达散射截面的方法。该方法利用电磁带隙结构的带阻特性,使其能作为天线的地板,在带外(非谐振)时,电磁带隙结构对入射电磁波起滤波作用。仿真和实验的结果表明,电磁带隙结构能保证天线在带内辐射不受影响的同时,还大幅度地降低了天线带外的雷达散射截面。     

Real-time programmable coding metasurface antenna for multibeam switching and scanning

Novel electromagnetic wave modulation by programmable dynamic metasurface promotes the device design freedom, while multibeam antennas have sparked tremendous interest in wireless communications. A programmable coding antenna based on active metasurface elements (AMSEs) is proposed in this study, allowing scanning and state switching of multiple beams in real time. To obtain the planar array phase distribution in quick response, the aperture field superposition and discretization procedures are investigated. Without the need for a massive algorithm or elaborate design, this electronically controlled antenna with integrated radiation and phase-shift functions can flexibly manipulate the scattering state of multiple beams under field-programmable gate array (FPGA) control. Simulation and experimental results show that the multiple directional beams dynamically generated in the metasurface upper half space have good radiation performance, with the main lobe directions closely matching the predesigned angles. This metasurface antenna has great potential for future applications in multitarget radar, satellite navigation, and reconfigurable intelligent metasurfaces.     

Ultrawideband Spin-Decoupled Coding Metasurface for Independent Dual-Channel Wavefront Tailoring

Achieving distinct functionalities for electromagnetic (EM) waves with opposite handedness in a broad frequency range is highly desirable and essential for modern wireless communications and radar stealth. However, available functional meta-devices still suffer from the issues of locked functionalities or spin-decoupled properties but with limited bandwidth. Here, a spin-decoupled coding metasurface is presented for achieving independently spin-controlled functionalities with high efficiency in an ultrawide frequency band. By synthesizing the Jones matrix, it is predicted that two half-wave plates with a phase difference of 90° can form a 1-bit coding metasurface operating for orthogonal spins independently. As proofs of concept, two meta-devices are implemented by the metasurface in the microwave region. The first meta-device performs as a spin-decoupled beam deflector while the second one shows an ability to generate spin-decoupled multi-beams carrying desired orbital angular momentums. Both of the designed meta-devices can operate in the whole band of 7.5–18.5 GHz (with relative bandwidth of 80%), which, to the best knowledge, is so far the broadest bandwidth that can be achieved by spin-decoupled metasurfaces. This may trigger interest and open opportunities for advanced functional meta-devices in practical applications, for example, multichannel metasurface antennas, or multifunctional low-scattering devices in microwave region.     

基于拓扑优化设计的宽频吸波复合材料

本文基于拓扑优化方法设计并制备了一种宽频吸波复合材料,该吸波复合材料由高强玻璃纤维透波板、电阻损耗型超材料、聚氨酯泡沫和碳纤维反射板组成.仿真及测试结果表明,该吸波复合材料在2–18 GHz频段内的平板反射率均小于-12 dB.并且由于采用高强玻璃纤维及碳纤维复合材料作为面板层,聚氨酯泡沫作为芯材,因此该吸波复合材料不仅在较宽频带内对电磁波具有高的吸收率,同时还具有质量轻、耐高温、耐低温、耐湿热、抗腐蚀等特点,便于实现吸波与力学性能及耐环境性能的兼容,具有一定的工程应用价值.     

基于吸聚一体的低散射传输型透镜设计

通过传输型超表面透镜与电路模拟雷达波吸收器的集成设计,提出了一种兼具透射波前变换与带外雷达散射截面减缩特性的微波复合材料设计方法。透镜采用亚波长分布的周期性单元,由梯度相位补偿对透射波进行调节,进而获得平面波前与球面波前之间的互易变换。并且,使用透镜在波前变换频带以外低频端的反射特征,结合单个有耗层设计,构造了电路模拟吸波器。选用一副缝隙耦合馈电的微带贴片天线单元作为初级馈源天线,观察到复合材料的波前变换特性可在宽频带范围内产生主瓣增益增强效果。与透镜相比,电路模拟吸波器的引入使得复合材料针对TE与TM极化分别可在130.68%与155.11%的频率范围内获得雷达散射截面减缩效果。通过全波模拟和实验测量,验证了辐射增益增强与雷达散射截面减缩效果,表明了复合材料吸聚一体设计的有效性。     

基于开口椭圆环的高效超宽带极化旋转超表面

电磁波的极化态在信号传输和灵敏度测量中有非常重要的应用价值. 本文设计、仿真并实验验证了微波频段基于开口椭圆环谐振器的极化旋转超表面. 理论上, 将多阶表面等离子谐振和高阻抗表面相结合, 解释了多谐振点、高效率极化旋转的物理机理. 数值上, 通过对结构参数的仿真分析, 给出了运用开口椭圆环结构设计多频段、超宽带高效极化旋转超表面的方法. 所设计和制作的超表面能够在相对带宽104.5%的频率范围内实现大于85%的极化旋转效率. 这些工作将为极化操控超表面的设计和应用提供重要帮助.     

均匀磁化等离子体与雷达波相互作用的数值分析

采用平板几何对不同磁场强度下等离子体对电磁波的吸收、反射和透射特性进行了数值分析.结果表明,不同磁场可以显著改变等离子体对不同频率的雷达波的吸收和反射特性.当雷达波频率接近等离子体高混杂频率时,磁化等离子体将对该波产生强的共振吸收,带宽在2GHz左右,吸收比可达90%以上.因此,通过适当调整磁场强度、等离子体密度和碰撞频率,可实现较宽雷达波段的等离子体隐身 关键词： 电磁波 磁化等离子体 共振吸收 等离子体隐身     

人工磁导体正交布阵的宽带低雷达截面反射屏

基于互补开口谐振单环 (complementary split ring resonator, CSRR) 的电磁特性, 设计了一种新型人工磁导体 (artificial magnetic conductor, AMC) 结构 CSRR-AMC. 通过与方形贴片人工磁导体的反射相位对比发现, 该结构在X极化和Y极化波垂直照射条件下可分别实现小型化和多同相反射频带. 基于此特性, 设计了一种仅由单一CSRR-AMC结构组成的宽带低雷达截面反射屏. 该设计将相邻CSRR-AMC单元正交化排布, 通过优化单元结构实现宽带相位对消, 降低后向散射能量. 测试结果表明, 样品在7.38–10.47 GHz 范围内后向RCS减缩量达到10 dB以上, 相对带宽达到34.6%, 为宽带低反射屏设计提供了新的方法. 关键词： 人工磁导体 相位对消 宽带 雷达截面减缩     

一种兼有高增益和宽带低散射特征的波导缝隙天线设计

设计了一种同时具备高增益和宽带低散射特征的波导缝隙天线.将蚀刻有互补开口谐振环的方形贴片人工磁导体正交布阵得到宽带低雷达截面积(RCS)反射屏并以之代替原天线的全金属反射板,通过优化反射屏的加载方式,在展宽天线工作频带、提高天线增益的同时,实现了宽频域范围内天线鼻锥方向RCS减缩.实测结果表明:加载低RCS反射屏的缝隙天线工作带宽增加了100 MHz,前向增益提高了3.2 dB,在5.52—6.63GHz范围内RCS减缩量达10 dB以上,减缩带宽达到20%.     

基于宽带吸波体的微带天线雷达散射截面缩减设计

利用加载集总电阻的方式设计出一种极化稳定且宽入射角的宽带超材料吸波体(wide-band metamaterial absorber, WBMA), 在平面波垂直入射时, 其吸波半波功率带宽达12.7 GHz, 吸波率大于90%的带宽达10.42 GHz, 峰值吸波率达99.9%. 将其与微带天线共基板共接地板的方式加载, 制备出WBMA微带天线, 实现了天线宽频域内雷达散射截面(radar cross section, RCS)大幅缩减. 仿真与实测结果表明: 将WBMA加载于微带天线后, 天线的前向增益提高了0.53 dB, 整体辐射特性基本保持不变; 在不同极化波下, 天线的工作频带带内和带外等宽频域(6.95-17.91 GHz)内的单站RCS缩减大于3 dB以上, 最大缩减值达21.2 dB; 在天线的中心频点8 GHz处± 48°的宽角域内, 双站RCS缩减效果明显, 很好地实现了天线的宽频域大角度的隐身设计.