填充介质的厚屏频率选择表面传输特性

Transmission properties of thick-screen frequency selective surface with filling dielectrics

为了改善厚屏频率选择表面(FSS)的滤波特性,实现FSS在雷达天线罩上的应用,设计了具有圆孔单元的厚屏FSS结构,并将其单元内填充介质,制备出了相应的实验件。理论分析时,首先建立等效问题;接着用Floquet定理将无限大厚屏FSS上所有阵列单元的场展开为无穷多个平面电磁波;然后在单元边界处强加边界条件;最后用矩量法求解等效的磁场积分方程。在微波暗室测试后,发现测试值与计算值基本一致。结果表明:中心频率的变化主要取决于单元间距、入射角和介电常数等3个参数;其中,当单元间距由30mm增加到36mm,电磁波的入射角由10°增加到30°,填充介质的介电常数由2.5增加到7.0时,中心频率分别减小了2.1,1.5,1.9GHz;另外,单元直径增大使得带宽增加,当单元直径由14mm增加到17mm,带宽增加了1.2GHz。可以看出,改善厚屏FSS的传输特性是多参数优化的问题,如果合理选择填充介质并适当选取其他参数,能够获得理想的传输特性。

In order to improve the filtering characteristics of Frequency Selective Surfaces（FSSs） and to realize their applications to bandpass radomes,a thick-screen FSS with circle slot elements filled with dielectric materials was designed and a corresponding experimental FSS sample was produced.In theoretical analysis for the thick-screen FSS,an equivalent problem was established,then the Floquet’ s theorem was employed to expand the field from the infinite array elements into an infinite number of plane wave.Furthermore,the boundary condition was enforced at aperture boundarys,and the method of mements was used to solve the equivalent magnetic-field integral equation.A test was carried out in a microwave darkroom,and measured results show that it is in good agreement with calculated ones.The results show that the center frequency mainly depents on interelement spacings,incidence angles and dielectric permittivities.When three parameters increase from 30 mm to 36 mm,10° mm to 30° mm,2.5 mm to 7.0 mm respectively,the center frequency can be reduced by 2.1,1.5 and 1.9 GHz correspondingly.Moreover,the bandwidth is related to the shape of the element.When the diameter of element changes from 14 mm to 17 mm,it increases 1.2 GHz.It is concluded that improving transmission characteristics of thick-screen FSS is a task on optimizing various parameters.It can obtain optimal transmission properties by choosing filling dielectrics and other parameters appropriately.