频率选择表面(Frequency Selective Surface, FSS)可以在工作频段内低损耗透射电磁波，并在工作频段外将电磁波散射至远离入射波的方向，从而实现一定的电磁隐身和抗干扰能力，但是散射波存在被探测及成为干扰源的可能，为了解决这一问题，FSS吸波体的概念被提出。基于FSS设计的吸波体既可以将工作频段内的电磁波低损耗透射，也可以将工作频段外的电磁波完全吸收，因此，相比FSS，FSS吸波体在电磁隐身和抗干扰领域更具有优势。本文基于FSS的工作原理，设计出多种频率响应的FSS吸波体。主要的工作内容概括为以下三点：

(1) 研究了可以实现宽带吸收的低剖面频率选择表面吸波体(Frequency Selective Absorber, FSA)。通过特征模分析提取多组正交的特征模式，分析其谐振和辐射特性。对于一对有效模式下，垂直入射时，FSA的垂直入射吸收率在8.92-14.75 GHz内大于90%；斜入射时，FSA的斜入射吸收性能随入射角增大迅速恶化。改进FSS的排布方式使有效模式数量增加至两对，垂直入射时，FSA在6.2-21.1 GHz内大于90%；45°斜入射时，FSA在6.2-21.1 GHz内的吸收率大于80%。

(2) 研究了可以实现在工作频段内传输，工作频段外吸收电磁波的具有单透射带的双极化频率选择表面雷达吸波体(Frequency Selective Rasorber， FSR)。基于等效电路分析，对八边型环FSS的结构进行改造，使其在平面波的激励下产生并联谐振，达到了带内高透射、带外吸收的阻抗条件。在垂直入射时，|S₂₁|在9.62-11.72 GHz内大于-3 dB，|S₁₁|在5.2-14.8 GHz内小于-10 dB；在5.02-8.80 GHz和12.94-14.89 GHz频段内，吸收率大于80%；当入射角等于40°时，|S₁₁|和|S₂₁|曲线保持稳定。

(3) 研究了分别具有单透射带和双透射带的双极化FSR。基于交叉偶极子型FSS和对称谐振器分别实现了透射频带中心在3 GHz、4 GHz、5 GHz和6 GHz的单透射带FSR；基于交叉偶极子型FSS和非对称谐振器分别实现了透射频带中心在3 GHz与5 GHz、4 GHz和6 GHz的双透射带双极化FSR。

研究结果表明，设计的FSA、单透射带FSR和双透射带FSR可分别在宽频率范围内抑制带外干扰信号，同时又能高效传输特定频段的带内信号，所设计的FSR在电磁隐身和抗干扰领域有广泛的应用。

Frequency Selective Surfaces (FSS) can transmit electromagnetic waves with low loss within their operating frequency range, and scatter electromagnetic waves away from the incident wave direction outside the operating frequency range, thus achieving certain electromagnetic stealth and anti-interference functions. However, the scattered waves may still be detected and become sources of interference. To solve this problem, the concept of FSS absorber was proposed. Based on FSS design, absorbers can not only transmit electromagnetic waves with low loss within the operating frequency range, but also completely absorb electromagnetic waves outside the operating frequency range. Therefore, compared with FSS, FSS absorbers have more advantages in the field of electromagnetic stealth and anti-interference. In this paper, various FSS absorbers with multiple frequency responses are designed based on the working principle of FSS. The main work can be summarized as follows:

(1) Firstly, a low-profile frequency selective absorber (FSA) capable of wideband absorption is studied. Multiple sets of orthogonal characteristic modes are extracted through characteristic mode analysis, and their resonant and radiating characteristics are analyzed. For a pair of effective modes, the vertical incidence absorption rate of FSA is greater than 90% within 8.92-14.75 GHz, and the oblique incidence absorption performance of FSA deteriorates rapidly with the increase of incidence angle. The layout of FSS is improved to increase the number of effective modes to two pairs. When vertically incident, FSA is greater than 90% within 6.2-21.1 GHz, and when obliquely incident at 45°, the absorption rate of FSA is greater than 80% within 6.2-21.1 GHz.

(2) A dual-polarized Frequency Selective Rasorber (FSR) with a single transmission band that can transmit within the working frequency range and absorb electromagnetic waves outside the working frequency range is studied. Based on equivalent circuit analysis, the structure of the octagonal ring FSS is modified to achieve the impedance condition of high transmission within the band and absorption outside the band under the excitation of plane waves. When vertically incident, |S₂₁| is greater than -3 dB within 9.62-11.72 GHz, and |S₁₁| is less than -10 dB within 5.2-14.8 GHz. The absorption rate is greater than 80% within 5.02-8.80 GHz and 12.94-14.89 GHz. When the incidence angle is 40°, the S₁₁ and S₂₁ curves remain stable.

(3) A dual-polarized FSR with a single transmission band and a double transmission band is studied. Based on cross-dipole FSS and symmetric resonator, single transmission band FSR with transmission band center at 3 GHz, 4 GHz, 5 GHz, and 6 GHz are respectively achieved. Based on cross-dipole FSS and asymmetric resonator, dual transmission band FSR with transmission band center at 3 GHz and 5 GHz, 4 GHz, and 6 GHz are respectively achieved.

The research results indicate that the designed FSA, single-passband FSR, and double-passband FSR can respectively suppress out-of-band interference signals within a wide frequency range, while efficiently transmitting in-band signals in specific frequency bands. The designed FSR has a wide range of applications in the fields of electromagnetic invisibility and anti-interference.

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