基于超材料吸波体的低雷达散射截面波导缝隙阵列天线∗

摘要

提出利用超材料吸波体减缩波导缝隙阵列天线带内雷达散射截面的设计方法.设计具有超薄(厚度仅为0.01λ，λ为吸波体中心频率对应波长)、无表面损耗层和高吸波率的超材料吸波体，将其加载到波导缝隙天线E面方向辐射缝隙间的金属表面上，并与辐射缝隙保持一定的间距.该加载方式没有破坏天线的口径馈电振幅分布，并利用超材料吸波体对电磁波的强吸收特性降低了天线阵的结构模式项散射.仿真和实验结果表明，加载超材料吸波体后天线阵的反射系数、增益、波瓣宽度保持不变，在x极化和y极化条件下，波导缝隙阵列天线的带内雷达散射截面减缩量均在6 dB 以上，且在−25◦—+25◦范围内天线雷达散射截面均有明显的减缩，鼻锥方向减缩超过10 dB.该研究成果对阵列天线雷达散射截面减缩具有重要的借鉴意义和工程应用价值.%A method of reducing the in-band radar cross section (RCS) of waveguide slot array antenna by utilizing a metama-terial absorber (MA) is presented. A novel ultra-thin (the thickness is only 0.01λ,λis the wavelength corresponding to the MA resonant frequency) MA with high absorptivity and no surface lossy layer is designed;the absorber is composed of two metallic layers separated by a lossy dielectric spacer. The top layer consists of an etched oblique cross-gap patch set in a periodic pattern and the bottom one is a solid metal. Effective impedance of MMA will match the free space impedance by adjusting the dimensions of electric resonant component and magnetic resonant component in the unit cell, and so the reflection will be minimized. Meanwhile, the MMA can obtain a resonant loss to fulfill the high absorption. By finely adjusting the geometric parameters of the structure, we obtain the MA with absorption 99.9%, and its absorbing mechanism being interpreted by analyzing surface current, surface electric field, and volume power loss density distri-bution, respectively. The metallic area between slots in E plane direction of waveguide slot array antenna is covered by MA, and a distance between the radiating slot and the MA is suitably arranged. Antenna radiation performance is kept in good order because this arrangement does not destroy the amplitude distribution of antenna aperture, and the high absorptivity of MA that contributes the reduction of structure mode scattering. Simulation and experimental results demonstrate that the array antenna loaded with MA gets more than 6 dB RCS reduction both in the x-and y-polarized incident conditions; and the RCS of antenna has obviously a reduction from −25◦ to +25◦, the most reduction value exceeds 10 dB in the boresight direction, while the reflectance, gain and beam width are guaranteed. This idea has an important significance and engineering application for the RCS reduction of array antenna.