共形超表面机理、设计及其在目标RCS减缩中的实验研究

Conformal and stealth techniques have promised vital applications and compelling requirements in the realm of military, aviation, and communication. To realize a significant reduction of radar cross section (RCS) under the conformal situation, we propose the academic idea of popularizing the conformal gradient metasurface (CGMS) in the stealth applications. In this regard, firstly, the analytical model is established and the influence rules of coupling efficiency, cell-to-cell coupling, transmission and scattering properties, loss as well as bandwidth as a function of the curvature, shape and position of a CGMS are also investigated in depth, aiming to obtain the excitation and working mechanisms, illustrate the operation principle over the control electromagnetic waves and also establish the design method for CGMS. Secondly, the stealth mechanisms and scattering control mechanisms of the CGMS are studied. To actualize the minimal total RCS, we concentrate on obtaining a group of optimal impedance and phase distributions based on the methods of ray tracing, genetic algorithm, particle swarm algorithm and the compensation principles for impedances and phases, respectively. Thirdly, we realize the conformal cloaks based the established design method combining the optimal impedance and phase distributions. Afterwards, the RCS of the targets coated by designed conformal cloaks will be measured to experimentally demonstrate the broadband high-performance RCS reductions. This project is expected to afford new routes and methods for broadband and high-performance cloaking characteristics and the research achievements will open a new way for metasurface applications, exhibiting comprehensive scientific research meanings and considerable engineering values.

共形技术和隐身技术在军事、航天、通信领域具有重要的应用前景和迫切需求。针对共形条件下目标RCS减缩实现这一课题，本申请率先提出了基于共形梯度超表面（CGMS）实现隐身的学术思想。围绕这一主题，首先建立CGMS的理论分析模型，研究电磁波与CGMS的耦合效率、单元互耦、传输、散射、损耗、带宽随共形面曲率、形状、位置的变化规律，得到CGMS的激发和工作机理，阐明其电磁波操控机理和新物理特性，建立其设计方法；其次研究CGMS的隐身以及散射控制机理，以最小RCS为目标函数，基于射线追踪，遗传、粒子群算法以及相位、阻抗补偿原理计算优化得到超表面的最佳相位、阻抗分布；最后基于CGMS的设计方法和相位、阻抗分布，实现共形隐身衣并完成对目标的赋形和样品测试，验证宽带高性能RCS减缩特性。本项目可望为宽带高性能隐身提供新的技术途径和实现方法，开辟超表面新的应用领域，具有广泛的科学研究意义和可观的工程应用价值。

提出了共形梯度超表面概念，基于射线追踪法建立了包裹任意形状物体的共形超表面相位补偿机理、设计方法、曲面到平面参考面的最小失真映射以及曲面超表面单元近似平面设计的准则。探索了共形超表面的散射控制机制，依据该方法设计超表面单元的位置、方位角和相位，曲率引起的光程和扭曲电磁波前可以重新得到纠正和恢复。为进行验证，设计、加工了多款具有不同功能共形超表面样品并在微波段对包裹超表面披衣的金属圆柱进行数值和实验表征。超表面单元具有超宽带工作带宽（8.17–22.1GHz）和近100%的交叉极化转换效率（效率大于93.5%）。研制的共形超散射体能将入射波对称高定向地散射到两个方向上，与裸金属圆柱相比，预定方向散射强度增强一个数量级以上，展现出宽频、高效双波束散射增强功能，验证了方法的正确性和鲁棒性。提出了基于旋转抛物梯度、螺旋线性相位梯度打散电磁波来降低目标雷达横截面（RCS减缩）的学术思想，其中几何贝尔（PB）相位解决了全极化问题，抛物梯度子阵和数字超表面结合解决了RCS减缩领域的复杂优化难题，多谐振技术和色散工程方法解决了电磁隐身器件的超宽带工作，最终旋转抛物梯度超表面实现了超宽带、全极化固有均一漫反射隐身，且粒子群算法优化的相位分布趋近于抛物梯度相位分布，进一步验证了抛物梯度方法的正确性、固有性和鲁棒性，具有重要的国防应用价值。最后，基于建立的共形设计与漫反射新方法，全面探索了共形漫反射在宽频RCS减缩隐身中应用，设计了多款柱面共形隐身衣和多功能器件进行验证。实验结果表明抛物梯度数字超表面10dB RCS减缩带宽达102.7%。透明柔性复合相位超表面在x和y极化下的5dB RCS减缩带宽分别为7.5-10.6GHz和7.4-11.7GHz。抛物梯度共形超表面x、y极化波下超表面在13-15.6 GHz范围内均可以实现近10dB的RCS缩减。率先将可调技术与梯度超表面结合提出了可调梯度超表面概念，系统研究了其电磁特性与调控机理。提出了正交极化串扰抑制方法，设计了多种极化不相关性各向异性超表面，实现了复杂的辐射调控和多功能特性。