Improvement on the wave absorbing property of a lossy frequency selective surface absorber using a magnetic substrate

An equivalent-circuit model is used to analyse the improvement of the wave absorbing performance of the lossy frequency selective surface(FSS) absorber by using a magnetic substrate,showing that it is possible to widen the wave absorbing bandwidth.Three pieces of magnetic substrates are prepared.According to the complex permittivity and permeability,the reflectivity of the corresponding absorber is calculated by the finite difference time-domain(FDTD) method,and the bandwidth of the reflectivity below 10 dB is optimized by genetic algorithm.The calculated results indicate that the wave absorbing performance is significantly improved by increasing the complex permeability of the substrate;the reflectivity bandwidth below 10 dB of the single layer FSS absorber can reach 3.6-18 GHz with a thickness of 5 mm,which is wider than that with a dielectric substrate.The density of the FSS absorber is only 0.92 g/cm 3.Additionally,the absorption band can be further widened by inserting a second lossy FSS.Finally,a double layer lossy FSS absorber with a magnetic substrate is fabricated based on the design result.The experimental result is consistent with the design one.     

A dual-band flexible frequency selective surface with miniaturized elements and maximally flat (Butterworth) response

A dual-band flexible frequency selective surface （FSS） with miniaturized elements and maximally flat （Butterworth） response is presented in this paper. It is composed of three metallic layers, which are fabricated on thin flexible polyimide substrates and bonded together using thin bonding films. The overall thickness of the proposed structure is only about 0.3 mm, making it an attractive choice for conformal FSS applications. All the three layers can constitute a miniaturized- element FSS （MEFSS） and produce the first pass-band with miniaturization property, while the up and bottom layers can constitute a symmetric biplanar FSS and produce the second pass-band with maximally fiat （Butterworth） response. The two pass-bands are independent and there is a wide band spacing up to 30 GHz between them. The principles of operation, the simulated results by using the vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.     

电磁屏蔽用低频比小型化双频带频率选择表面

为满足敏感电子设备对频段密集相邻干扰信号的屏蔽需求,提出了一种低频比双频段带阻频率选择表面（FSS）结构。该结构由介质层和印刷在其两侧并谐振在不同频率的金属导带层构成。通过对两侧金属导带的互补型设计,削弱了两个谐振点间的耦合影响,使该FSS结构具有两个可以独立调节且紧密相邻的阻带,呈现出低频比特点。仿真结果表明,此结构可以实现低至1.16的谐振频率比。基于弯折结构的小型化设计使该FSS的单元尺寸仅为0.071λ,确保所提结构在TE和TM两种极化电磁波照射下,电磁屏蔽效能大于24 dB的入射角度稳定性高达60°。制作了实物并进行测试,实测结果与仿真结果吻合良好,验证了FSS结构设计的可靠性。     

双屏频率选择表面结构的遗传算法优化

双屏频率选择表面能够更好地实现平顶效应和快速下降的边缘,是一种实现雷达舱对探测带外雷达波隐身的有效手段.本文针对双屏频率选择表面(FSS)在电磁波不同角度入射下的宽带通应用,采用遗传算法对FSS介质厚度、介电常数、单元图形、排列周期进行了整体优化,给出优化后的FSS结构和传输特性曲线;同时采用镀膜和光刻技术制备出相应的实验件,在微波暗室进行了测试.结果表明,优化后的结构在保证2 GHz的工作带宽下,对电磁波的入射角度有良好的传输稳定性,这为实现双屏FSS在曲面大角度下的应用奠定了基础. 关键词： 频率选择表面 遗传算法 优化     

一种兼具宽带增益改善和宽带、宽角度低雷达散射截面的微带天线

设计并制备了一种兼具高增益和低雷达散射截面(radar cross section, RCS)的微带天线, 通过给原始微带天线加载双屏频率选择表面(frequency selective surface, FSS)覆层, 使其具有宽带的3 dB增益带宽和宽带、宽角度的低RCS特性. 该FSS单元的上层是四个开口处都焊有电阻的金属环结构, 下层是中间和四边都开缝的金属贴片结构. 上层加载的电阻主要用于吸收雷达入射波, 减缩天线RCS; 下层的贴片和天线地板构成Fabry-Perot谐振腔, 提高天线增益. 在5.75–11.37 GHz频带内, S₂₂<-10 dB, S₁₂<-10 dB; 在11.21–11.54 GHz频带内, S₁₁反射系数相位曲线斜率为正, 幅度模值均在0.86以上. 实验结果表明: 与原始天线相比, 在谐振频点11.73 GHz处, 天线增益提高3.4 dB, E, H面的半功率波束宽度分别减小16°和50°; 天线的3 dB增益带宽为10.00–12.40 GHz, 完全覆盖阻抗带宽. 在4.10–11.30 GHz 频带内, 天线法向RCS均有3 dB以上的减缩, 最大减缩23.08 dB; 4.95 GHz处的单站RCS在-20°–20°的角域、双站RCS 在-37°–37°的角域均有3 dB以上的减缩. 实验结果证实了该FSS覆层可用于同时改善天线的辐射和散射 性能. 关键词： 频率选择表面 低雷达散射截面 高增益 宽带     

Non compact single-layers of dielectric spheres electromagnetc behaviour

Single layer of dielectric spheres is a recognized model for the basic understanding of some aspects of photonic crystals. Here we present a systematic study of the effect of compacting in the electromagnetic transmission of dielectric spheres monolayers. Experiments were performed in the microwave domain (from 10 GHz to 30 GHz) with glass spheres of high dielectric permittivity ε = 7. Time Domain Finite Integration (TDFI) calculations were also accomplished. Experimental data and TDFI calculations agreement provides a double check on the lack of experimental artefacts and the correctness of simulation settings. Following the evolution of the lower frequency spectral peak with layer compacting ratio, we established three different electromagnetic regimes. For the higher and lower compacting ratio regimes, the peak frequency matches isolated sphere pure resonances, while for intermediate values of compacting, some transition between these two modes takes place. Extending the study to the complete frequency range, we find that sphere single layers transmission spectra become closer to isolated sphere scattering calculations as the compacting ratio is decreased. However as the agreement remains imperfect even for our lowest compacting measurable layer, we conclude that some structure contribution cannot be neglected even for low compact layers.     

双带频率选择表面设计

为了实现频率选择表面(FSS)的双带特性,设计了由矩形栅格和三圆环组合单元FSS。对FSS的谱域求解方法进行了详细的描述。采用谱域法分析了不同角度和极化入射波下FSS的频率响应性能。结果表明,所设计的FSS对于不同入射角度和极化电磁波具有稳定的双带、平顶传输及陡峭下降边缘特性。双带特性大致表现为1.8～5.4GHz的阻带和5.4～20.0GHz的通带。阻带谐振频率稳定在3.1GHz左右,而通带在-4dB的平顶传输带宽达14.3GHz以上。其陡峭下降边缘特性表现为S波段信号强烈反射,而其他波段信号通过,从而实现多波段通讯。该结构FSS可应用于卫星通信、雷达罩及其他相关领域。     

微波低通高阻复合材料构件的设计与性能验证

随着海洋环境武器装备隐身发展的需要, 开展具有微波低通高阻特性的复合材料构件设计与研究显得重要而迫切. 文章首先设计了一种中空六边形周期性结构, 以此为基础设计了一个由面层、中空六边形环周期层1、中间层、中空六边形环周期层2、面层组成的新型复合双层频率选择表面(FSS)结构件. 其上层FSS的结构参数为中空六边形环边长3.0 mm, 线宽度0.5 mm, 缝隙宽度0.4 mm; 下层FSS的结构参数为中空六边形环的边长3.2 mm, 线宽度0.5 mm, 缝隙宽度1.0 mm. 模拟结果表明: 该复合材料构件具备优良的低频透过性与高频屏蔽性快速转换的特性, 能够获得优异的低通高阻性能, 同时在45°范围内具备优良的角度不敏感性. 最后制备和实验验证得到了0–2 GHz低频段具有95.6%高透过性、同时在7.05–18 GHz高频段具有10 dB 以上屏蔽性能的复合材料构件, 对具有隐身特性的新型滤波电磁功能构件的研制具有重要价值.     

一种性能稳定的新型频率选择表面及其微带天线应用

设计了一种基于分形树结构的高性能频率选择表面(frequency selective surface,FSS),并将其作为微带天线的空间滤波器,同时改善天线的辐射与散射性能.该FSS单元是由两层金属及其中间介质组成,上、下层金属采用金属柱连结,整体构成树枝状分形结构.通过优化参数,得到了一种宽带、极化无关、宽入射角、小型化的超薄FSS,厚度只有约0.017λ.将该FSS应用于微带天线后,天线的相对带宽拓展到40%,工作频段内的增益得到改善,9.6 GHz时,天线的增益提高了6.7 dB,同时,天线工作频带内的雷达散射截面(radar cross section,RCS)也得到了明显减缩,最大减缩为12.7 dB.实验结果与仿真结果符合得较好,证实了该空间滤波器具有提高宽带天线增益、增强天线定向性、改善天线带宽与降低天线带内RCS的效果,可以应用于宽带天线带内辐射与散射性能的同时改善.     

Radiation properties of microstrip patch antenna covered with an anisotropic dielectric layer and a plasma sheath

By using SO-FDTD method, radiation properties of microstrip patch antenna covered with an anisotropic dielectric layer and a plasma layer are investigated. Simulation results show that the resonant frequency of antenna covered with a plasma layer varies with different plasma parameters. It has been indicated that the frequency offset of antenna is as high as 120 MHz when plasma frequency changes from 1 GHz to 8 GHz. The effect on antenna covered with an anisotropic dielectric layer is analyzed, while altering the dielectric constant or thickness of dielectric layer. Finally, the peak gain of antenna in complex plasma environment is presented in detail.     

Influence of substrate process tolerances on transmission characteristics of frequency-selective surface

Frequency-selective surface （FSS） is a two-dimensional periodic structure consisting of a dielectric substrate and the metal units （or apertures） arranged periodically on it. When manufacturing the substrate, its thickness and dielectric constant suffer process tolerances. This may induce the center frequency of the FSS to shift, and consequently influence its characteristics. In this paper, a bandpass FSS structure is designed. The units are the Jerusalem crosses arranged squarely. The mode-matching technique is used for simulation. The influence of the tolerances of the substrate＇s thickness and dielectric constant on the center frequency is analyzed. Results show that the tolerances of thickness and dielectric constant have different influences on the center frequency of the FSS. It is necessary to ensure the process tolerance of the dielectric constant in the design and manufacturing of the substrate in order to stabilize the center frequency.     

Absorption properties of carbonyl-iron/carbon black double-layer microwave absorbers

Double-layer materials were devised in order to improve the absorbing properties of electromagnetic wave absorbing plates. The double-layer wave absorbing materials are composed of a matching layer and an absorption layer. The matching layer is the surface layer through which most of the incident waves can enter, and the absorption layer beneath it plays an important role in incident wave attenuation. The total thickness of the double layer is the sum of the thicknesses of these two layers. Carbonyl iron (CI) and carbon black (CB) were used as absorbents in the matching and absorption layers, respectively. The structures of the CI and CB particles were analyzed using scanning electron microscopy and transmission electron microscopy; the dielectric properties and absorption mechanisms were also studied. In the testing frequency range 2-18 GHz, the results show that the double-layer absorbers have two absorption peaks, and the positions and values of these peaks change with the content level of the absorbents. When the mass fraction of CI in the matching layer is 50% and the total thickness of the absorber is 4 mm, the effective absorption band (below −8 dB) reaches 5.5, 5.8, and 6.5 GHz. Where the mass fraction of CB is 50% or 60% and the mass fraction of CI is 70%, the bandwidth with reflection loss below −4 dB is larger than 10 GHz.     

基于树枝结构单元的超材料宽带微波吸收器

本文设计并制作了一种基于树枝结构单元的超材料宽带微波吸收器.该超材料吸收器采用夹层结构,由按六边形密集排布的金属树枝阵列、双层介质基板和金属薄膜组成.通过调节树枝单元的几何参数和金属树枝阵列的排布方式,可以出现三个吸收峰,实现三频工作.通过调节三个吸收峰工作的频率形成宽频吸收,采用夹层结构提高吸收效率,从而对垂直入射到超材料表面的微波实现高吸收.实验表明吸收器的反射曲线从9.79 GHz到11.72 GHz出现了反射率小于10%的较宽吸收带,透射曲线恒等于0,吸收率大于90%的带宽为1.93 GHz.这种 关键词： 树枝状结构 夹层结构 吸收效率 吸收带宽     

Terahertz bandpass filters using double-stacked metamaterial layers

Bandpass filters are reported based on double-stacked metamaterial layers separated by an air gap for operation at terahertz frequencies. Several stacking configurations were investigated designed for a ~0.5 THz center frequency. The filters exhibited improved spectral transmission properties when compared with conventional ones based on single metamaterial layers. 3 dB bandwidth of ~78 GHz and sidelobe suppression ratio >16 dB were determined when symmetric or asymmetric double layers were stacked. We demonstrate that superior frequency selectivity can be achieved when metamaterial layers with different unit cells are used. Good agreement was found between measured and simulated transmission response.     

一种介质-金属加载圆孔单元厚屏频率选择表面

厚屏频率选择表面能较好地改善FSS带宽性能,是实现隐身雷达天线罩的有效手段.为了全面掌握厚屏FSS的传输特性,给FSS的工程应用提供可靠依据,本文设计了一种介质-金属加载圆孔单元的厚屏频率选择表面.采用矩量法对此结构进行分析计算,主要研究了加载金属直径、加载介质厚度、电磁波入射角等几个参数对厚屏FSS传输特性的影响规律.仿真实验结果表明:带宽、中心频率及其透过率都对填充介质直径、加载金属直径、加载介质厚度、电磁波入射角和不同排列方式有不同程度的敏感性,可以通过合理调整加载金属直径及加载介质厚度来获得较宽的通带和较高的透过率.这为实现厚屏FSS在曲面隐身雷达天线罩上的应用提供了一种有价值的借鉴.     

High-Breakdown-Voltage Submicron InGaAs/InP Double Heterojunction Bipolar Transistor with ft=170GHz and fmax=253GHz

The layer structure of InGaAs/InP double heterojunction bipolar transistor (DHBT) is designed to enhance the frequency performance and breakdown voltage. The composition-graded base structure is used to decrease the base transit time. The InGaAs setback layer and two highly doped InGaAsP layers are used to eliminate the conduction band spike of the collector. The submicron-emitter InGaAs/InP DHBT is fabricated successfully. The base contact resistance is greatly decreased by optimization of contact metals. The breakdown voltage is more than 6V. The current gain cutoff frequency is as high as 170GHz and the maximum oscillation frequency reached 253GHz. The DHBT with such high performances can be used to make W-band power amplifier.     

Analysis of Frequency Selective Surfaces with Metallic and Dielectric Losses at Millimeter Wave Range

In this paper, a theoretical analysis of scattering from a doubly frequency selective surfaces (FSS) with dielectric and metallic losses in the millimeter wave range is presented. The theoretical analysis involves the solution of the electric field integral equation relating the induced current in the FSS in the presence of anisotropic dielectric layers. The method of moment is employed to obtain numerical results. The frequency selective surface structure considered is composed by conducting patch elements sandwiched between two anisotropic dielectric layers. Three different anisotropic materials are considered: Epsilam-10, Alumina, and Sapphire. The sapphire presents low losses when compared with the other two dielectric materials. The most common metals, as copper and aluminum, are considered in this analysis. None significant metallic losses were observed for any considered metal. Numerical results are presented for the scattering characteristics and for dielectric and metallic losses parameters.     

Design of broadband microwave absorber utilizing FSS screen constructed with coupling configurations

The design of a frequency selective surface (FSS) screen constructed using a coupling configuration to implement a broadband microwave absorber is presented in this paper. The reflectivity representation recognizes the characterization of the absorber. Simulation and measurement results are presented and analyzed. A coupling FSS screen is introduced in order to obtain a better bandwidth and absorption. The bandwidth with the reflectivity below ?10?dB could get 5.45?C18?GHz, compared with the 6.28?C18?GHz of the absorber with square patches FSS, provided that the thickness of the absorber is 4?mm.     

估算线筒式介质阻挡放电场强和电子平均动能的方法

利用静电场模型对线筒式介质阻挡放电电场强度进行了计算,并对电子平均动能进行了估算。通过对单双介质阻挡放电(DBD)的对比,发现在相同的放电条件下,双介质DBD产生的电场强度和电子平均动能比单介质DBD的要大。这就很好地解释了在相同的放电参数下,甲苯的降解效率在双介质DBD中要比单介质DBD中大。     

������Ͳʽ�����赲�ŵ糡ǿ�͵���ƽ�����ܵķ���

The electric field strength and electron mean kinetic energy in co-axial dielectric barrier discharge (DBD) were estimated based on static electric filed model. Through the comparison of the single dielectric layer DBD with the double dielectric layer DBD, it was found the electric field strength and electron mean kinetic energy in double dielectric layer DBD are greater than that in the single dielectric layer DBD under the same electrode configuration and discharge conditions. The calculation results can successfully applied to explain the toluene degradation efficiency in double dielectric layer DBD is larger than that in the single dielectric layer DBD under the same discharge parameters.