A high selectivity frequency selective rasorber (FSR) with an ultraminiaturized unit based on 2.5 dimensional (2.5-D) parallel resonator (PR), exhibiting low insertion loss passband between two absorption bands, is investigated. The lossy unit is realized by inserting a 2.5-D strip-type PR structure into the center of each side of the metal square ring and loaded with resistors connected at the four corners. The novel 2.5-D PR consists of interdigitated capacitors and strip metal wire connecting the other side of the lossy layer obtained by using metallized vias. The 2.5-D PR can effectively alleviate the congestion of the single-sided structures and achieve a high degree of miniaturization by means of tortuous extension inductance structure; as an additional feature, the values of L and C can be independently adjusted to determine the passband frequency allowing to provide additional degree of freedom to the design. An equivalent circuit model is proposed to analyze its operating principle. The dimensions of the miniaturized unit are 0.13 λ _f × 0.13 λ _f × 0.16 λ _f (being λ _f the free space wavelength at the passband). A transmission window with low insertion loss of 0.125 dB is obtained at 4.65 GHz under normal incidence. The fractional bandwidth for −10 dB reflection is about 96%. The miniaturized FSR satisfies the characteristic of polarization insensitivity (TE and TM) and angular insensitivity (up to 45°). A prototype of miniaturized FSR has been manufactured and measured, showing a reasonable agreement with simulations.

中文翻译：

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基于叉指型2.5-D并联谐振器的超小型化高选择性吸收器

研究了一种基于 2.5 维 (2.5-D) 并联谐振器 (PR) 的超小型化单元的高选择性频率选择性吸收器 (FSR)，在两个吸收带之间表现出低插入损耗通带。有损单元是通过在金属方环的每一侧的中心插入一个2.5-D条形PR结构并在四个角处加载连接的电阻来实现的。新颖的 2.5-D PR 由叉指型电容器和带状金属线组成，该金属线连接通过使用金属化通孔获得的有损层的另一侧。2.5-D PR可以有效缓解单面结构的拥塞，通过曲折的延伸电感结构实现高度小型化；作为附加功能，L 和 C 的值可以独立调整以确定通带频率，从而为设计提供额外的自由度。提出了等效电路模型来分析其工作原理。小型化单元的尺寸为0.13 λ _f × 0.13 λ _f × 0.16 λ _f (被λ _f通带处的自由空间波长）。在垂直入射下，在 4.65 GHz 处获得了具有 0.125 dB 低插入损耗的传输窗口。-10 dB 反射的分数带宽约为 96%。小型化的 FSR 满足偏振不敏感（TE 和 TM）和角度不敏感（最大 45°）的特性。小型化 FSR 的原型已经制造和测量，显示出与模拟的合理一致性。