为满足窗口吸收体在通信、雷达和天线等领域中面临的高选择性和可调控性能方面的需求，本论文针对当前窗口吸收体在高选择性设计和加载有源器件中的技术瓶颈展开深入研究。通过对等效介质理论、传输线理论、频率选择窗口吸收体( Frequency Selective Rasorber , FSR)透波和吸波原理进行基础研究，结合频率选择表面(Frequency Selective Surface, FSS)方法，设计并实现了高选择性、可切换模式的频率选择窗口吸收体。

针对高选择性性能的提升，设计了一种吸-透-吸(A-T-A)型频率选择窗口吸收体，其通带位于S波段。通过在无损层中引入二阶带通响应并优化叉指谐振器，设计了一种具有高选择性通带的双极化FSR。在八边形环结构中引入并联谐振，成功实现了窗口吸收体的高选择性设计。在3.5 GHz时获得了0.78 dB的低插入损耗值，S₂₁>-3 dB带宽在3.41-3.67 GHz。S₁₁<-10 dB的范围为2.2到8.2 GHz，同时获得了通带左右的两个吸收带宽，吸收率大于80%的吸收带的工作频段为1.95-3.27 GHz（相对带宽50.6%）和3.8-8.4 GHz（相对带宽75.4%）。通过对窗口吸收体在不同数据下的S参数进行了仿真、分析和论证，最后进行了样品加工与实验验证。实验数据与仿真数据吻合良好，证明了A-T-A型频率选择窗口吸收体的有效性和高选择性。

针对与有源器件结合的FSR应用问题，设计了一种加载PIN二极管的有源频率选择窗口吸收体，其工作频率在3 GHz-6 GHz。该窗口吸收体能够根据二极管的通断状态分别实现吸波模式和吸收模式，从而实现了吸波与吸收的可调控。在二极管开启状态下，所呈现出来的S参数与A-T-A型频率选择窗口吸收体并无差异。在4.56 GHz处，S₂₁约为-1.89 dB，证明可以以低插入损耗传输。同时，通过仿真结果可以观察到S₂₁在传输频点两侧的提升及衰减曲线陡峭，传输聚焦于4.56 GHz单频点，可以有效筛选此频点处的电磁波。反射系数S₁₁<-10 dB带宽为3-6.12 GHz（相对带宽为68.4%）。通过对不同工作频点的电场强度与表面电流分布进行分析，深入探讨了所设计窗口吸收体的工作机理与性能。

这两种设计为窗口吸收体的性能提升和应用拓展提供了理论基础和实现途径。通过对两种窗口吸收体的全面设计、仿真分析，为窗口吸收体在雷达隐身、天线设计、微波

成像等领域的应用提供了参考。

To address the challenges of achieving high selectivity and tunable performance in window absorber for applications in communication, radar, and antenna systems, this thesis delves into the design limitations of current window absorber, focusing on high-selectivity performance and the integration of active components. By leveraging equivalent medium theory, transmission line theory, and the transmission and absorption principles of Frequency Selective Rasorber (FSR), and combining these with the Frequency Selective Surface (FSS) design methodology, this work successfully develops frequency-selective window absorber with high selectivity and mode-switching capabilities.

For improving selectivity, an Absorptive-Transmissive-Absorptive (A-T-A) type frequency-selective window absorber operating in the S-band is proposed. By introducing a second-order bandpass response in the lossless layer and optimizing the interdigitated resonator design, a dual-polarized FSR with a highly selective passband is achieved. Parallel resonance is incorporated into the octagonal ring structure to realize the high-selectivity design. A low insertion loss value of 0.78 dB was obtained at 3.5 GHz, and the S₂₁>-3 dB bandwidth was 3.41-3.67 GHz. The range of S₁₁<-10 dB is 2.2 to 8.2 GHz, while obtaining two absorption bandwidths around the passband, the absorption rate of more than 80% of the absorption band is 1.95-3.27 GHz (relative bandwidth 50.6%) and 3.8-8.4 GHz (relative bandwidth 75.4%). Through the simulation, analysis and demonstration of the S-parameters of the window absorber under different data, the sample processing and experimental verification are carried out. The experimental data agree well with the simulation data, which proves the effectiveness and high selectivity of A-T-A frequency selection window absorber.

To explore the integration of active components, a second design is presented: an active frequency-selective window absorber incorporating PIN diodes, operating within the frequency range of 3 GHz-6 GHz. The window absorber can realize the absorption mode and rasorber mode respectively according to the on-off state of the diode, so the absorption and rasorber can be regulated. When the diode is on, there is no difference between the S-parameter presented and the A-T-A type frequency selection window absorber. At 4.56 GHz, the S₂₁ is about -1.89 dB, proving that it can be transmitted with low insertion loss. At the same time, through the simulation results, it can be observed that the rise and decay curves of S₂₁ on both sides of the transmission frequency are steep, and the transmission is focused on a single frequency point of 4.56 GHz, which can effectively screen electromagnetic waves at this frequency point. The reflection coefficient S₁₁<-10 dB bandwidth is 3-6.12 GHz (68.4% relative bandwidth). By analyzing the electric field intensity and surface current distribution at different operating frequencies, the working mechanism and performance of the designed window absorber are discussed.

These two designs provide the theoretical basis and implementation methods for improving the performance and expanding the applications of window absorbers. Through comprehensive design and simulation analysis of the two types of window absorbers, they provide a reference for the application of window absorbers in fields such as radar stealth, antenna design, and microwave imaging.