基于十字单元的可调谐互补屏频率选择表面

为实现频率选择表面（FSS）工作频点的可调谐，将环型孔径FSS负载分离后形成感性表面与容性表面，利用两者之间的耦合机制设计了一种互补屏FSS。建立了互补屏FSS等效电路模型，定性分析了它的变频机理。采用耦合积分方程法计算了负载贴片旋转角，耦合电介质厚度和相对介电常数对互补屏传输特性的影响。利用镀膜与光刻方法在耦合电介质两侧制备容性表面与感性表面，并用自由空间法测试250 mm×250 mm样件的传输特性。计算与测试结果均表明：当十字贴片从0°旋转至10°，互补屏FSS的谐振频点会从18.2 GHz向低频漂移至14.8 GHz。当耦合电介质的物理厚度从0.1 mm变化到1 mm时，互补屏FSS的容性表面和感性表面之间的耦合效应逐渐消失。耦合电介质相对介电常数增加使互补屏间的耦合增强，其工作频点向低频漂移。实验显示：随着负载贴片旋转角的变化，互补屏FSS能够实现主动变频功能，为设计和制备主动FSS提供借鉴。

Tunable complementary frequency selective surfaces based on cross-elements

To tune the operating frequency of a Frequency Selective Surface (FSS), the load impedance of the loop slot FSS forms was separated to an inductive surface and a capacitive surface, and the coupling mechanism between the two surfaces was used to develop a Complementary FSS(CFSS). An equivalent circuit model of the CFSS was established and its tunable resonance mechanism was analyzed quantitatively. The influences of the rotating angle of the load patch, coupled dielectric thickness and the relative dielectric constant on the transmission characteristics of the CFSS were calculated accurately by using the coupled integral equation method, then the inductive surface and the capacitive surface were fabricated on both sides of the coupled dielectric by the coating and lithography methods. The transmission response of a 250 mm × 250 mm CFSS prototype was measured by using the free space method. The calculated and measured results show that the CFSS resonance will be tuned from 18.2 GHz to 14.8 GHz by rotating the cross patch from 0 degree to 10 degree. The coupling effect between the capacitive surface and the inductive surface will disappear by increasing the physical thickness of the coupling dielectric from 0.1 mm to 1 mm. With increasing the relative dielectric constant of the coupling medium, the coupling between the CFSSs will be strengthened and the operating frequency will shift to lower frequencies. It concludes that the CFSS can realize the active resonance conversion function as the rotating angle changes, which provides references for the design and manufacture of active FSSs.