摘要:
为进一步提高传统Salisbury屏的吸波性能,本文提出了利用高阻抗表面在特定频率同相反射的特性,替代原有结构中的金属平板设计多频带Salisbury屏的方法.通过分析不同频率电磁波经高阻抗表面反射后空间电磁场的场强分布,说明可以通过共用Salisbury屏的损耗层,在高阻抗表面同相反射的特征频率附近引入新的吸收带.以不同尺寸方形周期结构的单频和双频高阻抗表面为例,从仿真和实验两个方面验证了多频带Salisbury屏设计的可行性,且实验和仿真结果十分符合.结果表明,多频带Salisbury屏基本保留了原有的吸波性能,同时又引入了新的吸收峰,吸收峰的位置和数量与高阻抗表面同相反射的频带位置和数目有关.与传统的Salisbury屏相比,在材料增加厚度不足1 mm 的情况下,多频带Salisbury屏的设计使反射率小于?10 dB的吸波带宽由8.5 GHz增加到10.1 GHz,且实现了向长波方向的拓展,最低频率由7.5 GHz拓展到5.98 GHz.
Abstract:
High impedance surface, due to its unique property of in-phase reflection at some frequency, could be used in de-signing multiband Salisbury screen by replacing the metallic ground plane in a traditional structure, which is proposed, in this paper, to enhance the microwave absorbing performance of the conventional Salisbury screen. First, electromag-netic wave field intensity of different frequency in space after being reflected by a high impedance surface is analyzed, which implies that new absorption bands can be introduced at about the frequencies of in-phase reflection by sharing Salisbury screen’s resistive sheet, without adding extra lossy materials such as lumped elements or others. Then, by taking a single band high impedance surface at 6.25 GHz and a dual-band high impedance surface at 6.27 and 8.17 GHz, which are both composed of patches array with varying periodic size and a thickness of 0.6 mm, the multiband Salisbury screens can be constructed utilizing a conventional one with an absorbing peak at about 10.5 GHz. The reflectivity of these multiband absorbers are simulated by employing the commercial CST microwave studio and later measured using a reflectivity measurement system comprising two polarized horns and a vector network analyzer. Experimental results agree well with the simulations, and all results verify that the method presented at the beginning is effective. Results also show that new additional absorptions appear at the frequencies where microwaves are nearly reflected in phase from the high impedance surface, with the same number of the in-phase reflection bands. Meanwhile, the original microwave absorbing capability of the traditional Salisbury screen is reserved mostly. Compared to the single band high impedance surface, the dual-band high impedance surface performs better in the design as the absorbing bandwidth is wider and the absorbing frequency is lower. With an additional thickness of the high impedance surface (no more than 1 mm), the total absorption bandwidth of the multiband Salisbury screen with a reflection below ?10 dB increases from 8.5 to 10.1 GHz, and the lowest frequency with 10 dB absorption falls from 7.5 to 5.98 GHz. So it could be concluded that the design of multiband Salisbury screen is helpful to widen the absorption, especially towards the lower frequency direction.
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