In this article, a triband frequency selective surface (TBFSS) with narrow band separation is proposed. Pass band frequencies of this TBFSS are 6.9, 8.63 and 10.3 GHz with fractional band width (FBW) of $\text{15.8}\%$, $\text{13.5}\%$, and $\text{10.9}\%$, respectively. Low insertion losses of 0.5, 0.2, and 0.4 dB are observed in the pass bands. These resonant frequencies are adjusted in C and X bands. The unit cell (UC) dimension is $0.2\lambda _0\times 0.2\lambda _0$ which is calculated at lowest transmission zero. Hybrid structural elements are etched on two sides of Rogers 4003 C substrate with $\varepsilon _r$ of 3.38 and thickness of substrate is selected to be 0.406 mm. This design is highly obliquely stable upto $\text{75}^\circ$. It also shows polarization insensitivity to transverse electric (TE) and transverse magnetic (TM) modes of the plane wave. An equivalent circuit is presented for better understanding of the structure and tuning purpose. A prototype is fabricated to measure the frequency response of the TBFSS. Measured and simulated scattering parameter S$_{21}$ exhibit very good match.

中文翻译：

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一种具有高角稳定性和偏振不敏感性的混合元件三频选频面

在本文中，提出了一种具有窄带分离的三带频率选择表面 (TBFSS)。此 TBFSS 的通带频率为 6.9、8.63 和 10.3 GHz，分数带宽 (FBW) 为$\text{15.8}\%$, $\text{13.5}\%$， 和 $\text{10.9}\%$， 分别。在通带中观察到 0.5、0.2 和 0.4 dB 的低插入损耗。这些谐振频率在 C 和 X 波段进行调整。晶胞 (UC) 尺寸为$0.2\lambda _0\times 0.2\lambda _0$这是在最低传输零时计算的。混合结构元件蚀刻在 Rogers 4003 C 基板的两侧$\varepsilon _r$为 3.38，基板厚度选择为 0.406 毫米。这种设计是高度倾斜稳定的$\text{75}^\circ$. 它还显示出对平面波的横电 (TE) 和横磁 (TM) 模式的极化不敏感。为了更好地理解结构和调谐目的，给出了等效电路。制造了一个原型来测量 TBFSS 的频率响应。测量和模拟的散射参数 S$_{21}$ 表现出非常好的匹配。