双层频率选择表面电磁特性数值模拟研究

给出了一种分析有介质加载的不同栅格外形双层频率选择表面电磁特性的数值模拟方法.介质分离区内前向波和反向波分别关于相应的频率选择表面是周期的,确定了矢量传输及衰减模的表述形式.应用电磁场边界条件获得不同Floquet模系数的矩阵表达式,推导出一组耦合的积分方程,利用矩量法求解得到结构的电磁散射特性.模拟结果表明,由于层间介质内电磁场衰减模的耦合,双层FSS结构的电磁传输特性较单层有很大的改善.     

对称双层FSS的传输特性分析

应用模匹配方法,研究了关于中心层面对称的双层频率选择表面(FSS)的传输特性。讨论了各介质层厚度改变对频率选择表面频响特性的影响,指出通过修正双层FSS的有关介质参数,可以有效地改善传输带宽的稳定性并缩小传输曲线谐振区的深沟。     

基于频率选择表面的宽角扫描阵列

设计并加工了一种基于双层频率选择表面(frequency selective surface, FSS)的一维Vivaldi阵列天线.首先采用周期边界条件分析无限大阵列中的单元特性, 利用等效传输线原理和广义散射参数矩阵来设计优化加载在Vivaldi阵列上方的介质宽角匹配层.然后, 在所加载的双层介质匹配层表面直接印制FSS结构使阵列扫描特性得到极大改善.仿真和实测结果表明, 一维Vivaldi阵列中心单元在7~12 GHz的有源驻波比均小于2.5, 在8~10 GHz波束扫描范围能够达到±60°.仿真结果还表明:采用双层FSS结构的Vivaldi阵列与未加载匹配层的Vivaldi阵列相比, 在7~11.5 GHz增益有2~4 dB的提高; 同时在扫描至±60°时, FSS结构的加载使得阵列在对应扫描角下的交叉极化下降了5~10 dB.     

双层频率选择表面的优化设计

为了使双层缝隙型频率选择表面在大角度入射时具有更小的传输损耗,利用带通滤波器的原理为双层FSS建立传输线等效模型,确定了层间的最佳距离。介质的不同加载方式及不同的介电常数都会对双层FSS的频率响应有较大影响,同时,两层传输曲线的耦合方式会影响频率响应曲线中心的传输损耗。仿真结果表明,在层间距离一定的情况下,介质厚度越薄,介电常数越小,频率响应曲线中心的传输损耗也越小。同时,增大通带带宽可以改善双层FSS在大角度入射时的通带中心凹陷程度。     

一种新型双层微带定向耦合器

提出了一种新型双层微带结构的3 dB定向耦合器.此耦合器由两层带有耦合缝隙和寄生单元的介质板背对背放置.通过增加耦合面积和引入寄生单元补偿电容起到了均衡奇、偶模相速提高了耦合度,实现了宽频的3 dB紧耦合.通过优化设计,在频带范围内,此双层微带定向耦合器的定向性优于普通的耦合微带线定向耦合器.设计结果在450～860 ...     

双层错位频率选择表面的电磁特性分析

针对双层频率选择表面(FSS)在曲面应用中容易出现单元错位问题,基于耦合积分方程建立错位FSS结构的理论分析模型,分析了双层错位FSS的电磁特性.采用谱域矩量法并结合周期性边界条件,将各层单元表面电流的计算范围限定在一个周期内;对于错位层FSS单元被周期边界截断的情况,考虑了周期边界上导体表面电流的连续性;选用RWG(Rao-Wilton-Glisson)基函数描述导体表面的感应电流,以实现对任意形状FSS单元的数值计算.以方环形贴片单元为例验证了算法的准确性,并考察了周期边界的电流连续性对FSS电磁特性的影响,分析了层间距、入射极化方向和错位量等参数对错位FSS结构散射特性的影响.     

介质损耗对频率选择表面传输特性的影响

应用模匹配技术,研究了Y形缝隙平面周期阵列夹嵌于均匀有耗介质层中心的夹心频率选择表面(FSS)结构对平面波的传输特性。讨论了介质层对结构中心谐振频率、传输带宽、以及传输损耗的影响规律。相同介电常数的介质材料在有耗和无耗情况下的模拟分析结果清楚表明介质本身的损耗是影响FSS结构损耗特性的主要因素。     

双阻带红外频率选择表面的设计

为实现在中、远红外两个大气窗口的低透过率,设计了一种基于六边形环状结构的双屏红外频率选择表面（FSS）,利用CST电磁软件进行仿真分析,发现该FSS在3~5 m和8~14 m两个波段内的平均透过率低于2.5%,实现了红外波段的双阻带;采用表面电流模式分析法和有效介质理论分析了该FSS的滤波机理,发现不同谐振点处由于屏间耦合或屏内单元间的耦合在谐振单元表面感应出对称分布的电流从而使散射总场增强,形成增强型反射,即比较理想的红外光阻带;最后研究了电磁波的极化方式、入射角度、介质属性以及结构参数对FSS传输特性的影响。结果表明该FSS具有良好的偏振稳定性和角度稳定性,介质属性和结构参数对其传输特性有较大影响。     

带有多层介质衬底FSS的损耗和带宽特性分析

本文简要介绍应用模匹配方法分析带有多层介质衬底的FSS频率响应技术,在此基础上研究带有多层介质衬底的平面Y形缝隙周期阵列对平面波的频率传输特性。重点讨论介质层厚度变化对FSS传输损耗及带宽的影响。     

FSS对TE极化波传输特性的实验研究

通过实验测试,从单元的尺寸、形状、介质加载以及各参数对入射角的敏感性等方面,初步探讨了频率选择表面(Frequency Selective Surfaces,简称FSS)对TE波的传输特性.结果表明,FSS的谐振频率主要由单元的尺寸和形状确定;介质加载使得FSS平板的谐振频率降低;加载不同厚度的介质对FSS的透波率和谐振频率影响不同;对称加载介质能提高FSS的传输特性对入射角的稳定性.     

含电磁双各向异性介质衬底的FSS特性分析

运用谱域Galerkin法对含电磁双各向异性介质衬底的频率选择表面(FSS)进行了分析,概述了算法的基本实现过程,直接以Maxwell方程为基础,逐步推导出该周期结构中的谱域格林函数.文中在衬底介质参数的变动下,对一系列FSS反射系数进行了有效计算,计算结果表明了介质衬底的电磁各向异性特性对FSS频率选择特性的影响.     

频选膜拼接工艺误差对复材天线罩电性能的影响

加载频率选择表面(FSS)薄膜的复合材料天线罩在实际制作过程中,需将若干FSS薄膜结构进行拼接以构成一个整体,FSS膜的拼接工艺误差则对天线罩的电性能产生实质性的影响。文中设计了一款X波段的A夹层平板复合材料天线罩,并建立了由拼接工艺误差带来的FSS膜搭接和FSS膜缝隙的电磁仿真模型,研究了不同拼接工艺对复合材料天线罩的透波率、电磁波传输特性的影响以及对天线辐射特性的影响。研究结果表明：天线罩中的FSS薄膜结构的拼接错位对电磁波传输影响明显,会明显降低天线主瓣增益和天线罩透波率;当入射电磁波的极化方向与FSS薄膜结构的搭接缝方向相同时,FSS膜结构对天线罩透波率影响较大,当极化方向与FSS薄膜结构的搭接缝方向垂直时,则其对天线罩透波率影响较小;两块FSS膜结构边缘搭接的相对位置和搭接距离对天线方向图有明显影响;两块FSS薄膜结构边缘无搭接且存在缝隙则对天线罩透波率影响较小。该研究对复合材料天线罩的制造工艺具有工程指导意义。     

A Miniaturized and Polarization Independent Electromagnetic Shield for C and X-Band Applications

This paper proposes a miniaturized, polarization independent and dual band frequency selective surface (FSS) based electromagnetic shield. A corrugated FSS and zigzag square ring (ZSR) are arranged in back-to-back configuration over single-layered low-profile dielectric. This configuration not only offers shielding for both C and X-band but also achieves stable polarization independent response for these bands. Simulated and measured results verify its 30 dB average shielding over a wide band and 60° polarization independency alongside. More importantly, the equivalent circuit model analysis and analytical parameterization of this dual band configuration is also investigated. The modelling and simulations are in line with measurements that makes it as a potential shield for C and X-band wireless applications including SATCOMs, Microwave filters and many others.

     

周期性单负介质平板层的传输特性

利用传输矩阵法研究了无色散的周期性单负介质平板层的传输特性。研究表明当晶格常数与波长可比拟时电磁波很难通过,而当波长远大于晶格常数时通过相邻界面倏逝模电场的耦合作用,可使一定频率的电磁波产生耦合共振导致隧穿。在波长很长时可将性质差异的介质平板层进行均匀化处理,并给出其等效介电常数和等效磁导率,进而讨论左手材料的实现条件。     

基于耶路撒冷十字图案FSS宽带RAS的设计与性能研究北大核心CSCD

设计并制备了一种基于耶路撒冷十字图案的频率选择表面(FSS)吸波结构。吸波结构基本单元是由石墨烯耶路撒冷十字结构、高发泡聚氨酯泡沫和金属铝板组成。通过电磁仿真软件,探究了FSS的单元结构参数对吸波结构电磁性能的影响。仿真结果表明,吸波结构的相对带宽和吸收效果可以通过改变FSS单元参数来调节。采用遗传算法对FSS吸波结构进行参数优化并制备了吸波结构样件。利用单喇叭测试系统对样件的反射率进行了测试,测试结果与仿真结果基本一致,结果表明该吸波结构在反射率为-20 dB以下的相对带宽为0.72,且在8.6~18.0 GHz的频率范围内均可达99%以上的吸收效果。     

A numerical absorbing boundary condition for finite difference andfinite element analysis of open periodic structures

In this paper we present a novel approach to deriving local boundary conditions, that can be employed in conjunction with the Finite Difference/Finite Element Methods (FD/FEM) to solve electromagnetic scattering and radiation problems involving periodic structures. The key step in this approach is to derive linear relationships that link the value of the field at a boundary grid point to those at the neighboring points. These linear relationships are identically satisfied not only by all of the propagating Floquet modes but by a few of the leading evanescent ones as well. They can thus be used in lieu of absorbing boundary conditions (ABCs) in place of the usual FD/FEM equations for the boundary points. Guidelines for selecting the orders of the evanescent Floquet modes to be absorbed are given in the paper. The present approach not only provides a simple way to derive an accurate boundary condition for mesh truncation, but also preserves the banded structure of the FD/FEM matrices. The accuracy of the proposed method is verified by using an internal check and by comparing the numerical results with the analytic solution for perfectly conducting strip gratings     

Eigenmode confinement in the dielectrically apertured Fabry-Perot microcavity [VCSEL]

The three-dimensional (3-D) optical confinement of the dielectrically apertured Fabry-Perot microcavity is analyzed by considering electromagnetic coupling between the confined region and parasitic waveguide modes that exist outside the aperture. If the cavity length is close to one-half the emission wavelength and for large enough aperture sizes, all parasitic waveguide modes can be evanescent except one which couples only weakly to the emitting region. If the aperture diameter is too small, loss of optical confinement is predicted, and the optical mode size at which this occurs can be estimated from the cavity length and the relative shifts in the vertical resonances inside and outside the apertured region.     

A reconfigurable slot aperture design over a broad-band substrate/feed structure

A novel dual-band reconfigurable aperture (RECAP) design is introduced for operation over a two-octave bandwidth. The proposed RECAP consists of interleaved crossed-slot elements for dual-polarized and broad-band array operation without grating lobes. The dimensions of the array elements can be reconfigured by using radio-frequency switches such as microelectromechanical systems or PIN diodes. The array elements along with the switches are integrated into the top layer of a multilayered composite structure consisting of passive, resistively loaded frequency selective surface (FSS) elements that form a broad-band ground plane system. Excitation is provided through a broad-band balanced/matched feed, and reconfiguration allows for broad-band operation using the same FSS substrate. Besides the FSS substrate, shorting pins can be employed within the cavity to enhance gain performance. Significant analysis and understanding of the FSS/slot array configuration is presented along with measurements that should serve as a reference in future developments of these layered arrays.     

含各向异性介质衬底频率选择表面的直线法分析

运用直线法对一以单轴各向异性介质层为衬底的频率选择表面(FSS)进行了分析,考虑到介质层的各向异性,文中对直线法的常用方式作出了一定的修改,并详细介绍了整个方法实现过程。最后,对几套不同介电参数的FSS进行了计算,考虑了介质衬底的各向异性对FSS电磁特性的影响。