分析了对称双屏频率选择表面(FSS)结构如何实现Butterworth型FSS和获得 "平顶"和"陡截止"的 "矩形化"滤波特性。结合平面波展开法与互导纳法, 给出了缝隙阵列导纳和缝隙阵列之间的互导纳。以Y孔形单元为例, 数值计算并分析了FSS屏与中间电介质对Butterworth型FSS的影响; 然后在500 mm×500 mm聚酰亚胺基底镀15μm铜膜, 制作出Y孔型FSS并将其粘贴于介质两侧。用自由空间法测试其传输特性, 测试结果与仿真结果基本一致。当中间电介质电厚度为2.15 mm, 单元周期为7.2 mm×6.235 2 mm, 臂长为3.6 mm, 臂宽为0.8 mm时, 双屏FSS的互导纳与单屏FSS导纳的实部相等, 从而得到Butterworth型FSS。当FSS单元周期增加0.6 mm, 3 dB带宽由3.5 GHz缩减为2.1 GHz时, 截止度增加。分析认为, 对称双屏Butterworth型FSS的设计应遵循以下原则, 即在满足谐振尺寸的前提下采用无加载孔径型单元且单元周期小于0.4λ, 其缝隙长宽比应小于5.5, 中间电介质电厚度约为0.1λ。

This paper researches how to realize the Butterworth type Frequency Selective Surface(FSS) from a symmetric double screen FSS and to obtain the “rectangular” filter characteristics with “flat top” and “steep cut-off”. Combined with the plane wave expansion and mutual admittance methods, the aperture array admittance and the mutual admittance between the arrays were given. Based on the method above, the effects of the FSS screen and the dielectrics media between the FSS screens on the Butterworth FSS were analyzed numerically by taking a common “Y” aperture for an example. Then, a single screen “Y” type FSS was fabricated and pasted on the both sides of media accurately by plating a copper film with thickness of 15 μm on a 500 mm×500 mm polyimide substrate. The free space method was used to test the transmission characteristics, and the simulation results are in good agreement with test ones. Furthermore, when the electrical thickness of the dielectric media was set to be in 2.15 mm, “Y” unit cell period in 7.2 mm×6.235 2 mm, arm length in 3.6 mm, and the arm width in 0.8 mm, the mutual admittance of dual screen FSS is equal to the real part of admittance for a single-screen FSS. As a result, the Butterworth type FSS is obtained successfully. Experiments show that the designed Butterworth type FSS has reduced its -3 dB bandwidth from 3.5 GHz to 2.1 GHz when the cell circle is increased by 0.6 mm. Finally, it suggests that the design of Butterworth type FSS should be to adapt a no-load cell unit with a circle less than 0.4λ on the assumption of resonant sizes, and its radio between gap length and width and the thickness of intermediate electric should be less than 5.5 and about 0.1λ, respectively.