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.%We have designed and fabricated a broadband low radar cross section (RCS) metamaterial absorber with polarization-independent characteristic based on electromagnetic resonance. The absorbing mechanism is investigated by means of electric as well as magnetic field distributions and retrieval algorithm. Absorbing and RCS properties of this absorber are performed by waveguide experiment and free space measurements, respectively. Theoretical analysis indicates that the absorber can produce electric and magnetic resonances in different locations for fixed frequency, while for different frequencies, it can provide energy losses in different dielectric layers, which effectively lowers the electromagnetic couplings and consequently keep the strong absorbing properties in a wide frequency range. Experimental results show that the designed absorber with 3-layer structure achieves a frequency range which is 4.25 times as that of 1-layer absorber with absorptivity above 90%, its relative bandwidth for RCS reduction above 10dB is 5.1%. The cell size and thickness of the designed absorber are very small, i.e., 0.17 and 0.015 of the working wavelength. Thus the low-RCS property of the absorber is wide-angle and polarization-independent. In addition, the working frequency range of the absorber can be adjusted by properly designing the layers.
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