超宽带TEM喇叭天线的低频分离回路设计

在超宽带TEM喇叭天线的设计中,往往由于低频性能优化和天线小型化两者难以兼顾,而使得其应用受到限制。该文针对低频的反射问题,基于带通滤波器并联的设计思路,且区别于传统天线末端的低频反馈回路结构,提出在超宽带TEM喇叭天线馈电过渡结构上设计低频分离回路结构,减少低频分量在天线末端的反射,从而改善天线的低频性能。采用该设计思路,对一款超宽带TEM喇叭天线的结构进行改进并实现其优化设计。通过对比改进前后的天线性能,其阻抗带宽的低频降至0.1 GHz,拓展了12.5%,同时天线端口馈电效率提升10%,结果验证了该设计思路和方法对于超宽带TEM喇叭天线低频优化的有效性。最终,对阻抗特性以及该结构在不同频点下电流分布的分析,进一步证实新思路的可行性。     

“飘带”式喇叭天线特性研究

基于TEM喇叭天线的结构特点,兼顾天线辐射性能和轻量化考虑,设计了一种“飘带”式喇叭天线,该设计用两根弯曲的窄带代替了基本模型中的上板。针对“飘带”式喇叭天线的一些重要物理尺寸,利用Ansoft HFSS仿真软件对模型进行了分析。结果表明,该结构进一步改善了喇叭天线的低频性能,展宽了天线的频带。最后分析了“飘带”式喇叭天线的各个参数与天线性能之间的关系,得到了一组优化结果。     

加载TEM喇叭天线的时域分析

TEM喇叭是一种超宽带天线,已广泛应用于瞬态电磁场的研究中.运用时域有限差分法(FDTD)对TEM喇叭天线的时域电磁特性进行了数值研究,比较了两种不同的加载方法对天线性能的影响,为TEM喇叭天线的设计和性能评估提供了参考价值.     

一种末端加载型300MHz/1GHz双频车载超宽带探地雷达天线设计

为满足高速铁路无损探测需兼顾低频探测深度与高频探测精度的要求,采用理论计算与软件仿真结合的方法,设计制作了一种双频带(300MHz/1 GHz)指数型TEM喇叭天线并对其进行了测量。所设计的指数型TEM喇叭天线采用末端加载和适当天线臂切削来实现此超宽带天线的双频带工作。仿真与实测结果表明,天线分别工作在中心为360MHz、带宽约为110MHz的低频带和中心为1 020MHz、带宽约为260MHz的高频带,相对带宽均大于20%。实测天线的接收信号保真度较高,拖尾持续时间短,满足设计要求。此外,这种双频带天线系统可减少雷达系统天线和采样盒等设备的使用数量,降低雷达系统的成本,有较好工程应用前景。     

瞬时超宽带TEM加脊喇叭的时域特性研究

根据瞬时超宽带天线的时域特点,仿真设计了一款超宽带TEM加脊喇叭天线,并对其频域和时域特性进行了初步研究,在频域内实现了3 GHz～18 GHz的超大带宽。在时域内进行了单个喇叭天线的时域信号测试,包括辐射的时域波形和峰峰值方向图。对该类天线的时域特性有了一定的认识。     

双极变张角时域天线设计

传统的超宽带天线概念是在频域下定义的,有些不能作为时域脉冲天线使用.为实现时域天线的定向性、低剖面、小尺寸、可承受高功率等性能,结合领结天线的低剖面特性和TEM喇叭天线的定向辐射特性设计双极变张角时域天线,该天线是根据光导开关的时域响应设计天线激励源的低剖面定向时域超宽带天线,仿真结果表明,该天线是一种高性能的时域天线.     

一种电阻加载的超宽带TEM 喇叭天线

设计了一种基于电阻加载的超宽带TEM 喇叭天线。该天线由两片平滑渐变的金属曲面组成,通过在 馈电端引入微带渐变馈电结构便于同轴线馈电,同时在天线辐射片末端引入电阻加载技术消除天线口面与自由空 间失配引起的反射波能量,有效地改善低频特性,拓展带宽。在理论分析的基础上设计并制作了一副天线样机,实 验测试表明:在0. 1-5GHz 频率范围内,VSWR<2。该天线具有约50:1 的阻抗带宽,并且在0. 75-5GHz 频率范围内 具有良好传输特性。     

超宽带TEM喇叭天线的研究

研究一种超宽带TEM喇叭天线。提出一种无需加载的超宽带TEM喇叭天线的设计思路,理论推导该天线的远区场,由此得到特性阻抗变化与反射系数的关系。利用电磁仿真软件Ansoft HFSS模拟分析,在此基础上,设计一种视轴长度10cm的此类型TEM喇叭天线。测量得到在100～550MHz天线驻波比小于2.0,结果表明此天线在不加载情况下,通过对其结构进行合理的弯曲设计,也能使其具有良好超宽带特性。     

不同参数超宽带反射面天线系统辐射特性

在超宽带反射面天线设计中,首要问题是馈电天线的方向图与反射器匹配。以往在频域上对反射面天线的研究发现,当馈源天线方向图给出约-11 dB的边缘照射时,反射面天线可实现其最佳性能。在参数化模拟了作为馈源的透射电子显微镜(TEM)喇叭天线方向图特性的基础上,根据反射面天线的频域设计准则,相应地加入合适的超宽带反射面天线,对其远场辐射特性进行模拟计算。为了获得尽可能大的远场辐射场,采用计算机仿真技术(CST)数值模拟软件,在0 GHz~1 GHz频率范围内模拟了以不同参数TEM喇叭天线作馈源的超宽带反射面天线的远场辐射特性,并在时域上对其结果进行分析。模拟结果表明,由于其相位中心的不确定性,作为馈源的TEM喇叭天线无法与反射面天线完全匹配,其沿着反射面天线主轴移动时产生的反射面口径场相位和幅度的变化影响着远场辐射场的变化,TEM喇叭天线的遮挡效应也不容忽视。     

一种新型探地雷达天线的设计仿真

结合探地雷达(GPR)的发射信号,设计了一款工作频率范围为0.7~1.2 GHz的角锥喇叭天线。对喇叭天线结构参数的设计过程进行了分析,并利用电磁仿真软件Ansoft HFSS对其行建模仿真。仿真结果表明:在喇叭天线工作频率范围内,天线的驻波比小于1.4,在中心频率955 MHz下喇叭天线的增益最大达到11 d B左右,满足实际探地雷达对天线系统的要求。该天线具有频带宽、电压驻波比低、增益高、方向性强等优点。     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

Critical Stage Rule-Based Real Time Dispatch（RTD）System in Highly-Mixed-Products （HMP） FAB

An improving utilization and efficiency of critical equipments in semiconductor wafer fabrication facilities are concerned. Semiconductor manufacturing FAB is one of the most complicated and cost sensitive environments. A good dispatching tool will make big difference in equipment utilization and FAB output as a whole. The equipment in this paper is In-Line DUV Scanner. There are many factors impacting utilization and output on this equipment group. In HMP environment one of the issues is changing of reticule in this area and idle counts due to load unbalance between equipments. Here we'll introduce a rule-based RTD system which aiming at decreasing the number of recipe change and idle counts among a group of scanner equipment in a high-mixed-products FAB.     

GaAsSb/InAlAs PA DHBTs Grown by Production MBE

The epi material growth of GaAsSb based DHBTs with InAlAs emitters are investigated using a 4 × 100mm multi-wafer production Riber 49 MBE reactor fully equipped with real-time in-situ sensors including an absorption band edge spectroscope and an optical-based flux monitor. The state-of-the-art hole mobilities are obtained from 100nm thick carbon-doped GaAsSb. A Sb composition variation of less than ± 0.1 atomic percent across a 4 × 100mm platen configuration has been achieved. The large area InAlAs/GaAsSb/InP DHBT device demonstrates excellent DC characteristics,such as BVCEO＞6V and a DC current gain of 45 at 1kA/cm2 for an emitter size of 50μm × 50μm. The devices have a 40nm thick GaAsSb base with p-doping of 4. 5 × 1019cm-3 . Devices with an emitter size of 4μm × 30μm have a current gain variation less than 2% across the fully processed 100mm wafer. ft and fmax are over 50GHz,with a power efficiency of 50% ,which are comparable to standard power GaAs HBT results. These results demonstrate the potential application of GaAsSb/InP DHBT for power amplifiers and the feasibility of multi-wafer MBE for mass production of GaAsSb-based HBTs.     

Noise character analysis and the restraint of self-pulsation laser diodes

We calculate the Langevin noise sources of self-pulsation laser diodes, analyze the effects of active region noise and saturable-absorption region noise on the power fluctuation as well as period fluctuation, and propose a novel method to restrain the noise effects. A visible SIMULINK model is established to simulate the system, The results indicate that the effects of noise in absorption region can be ignored; that with the increase of DC injecting current, the noise effects enhance power jitter, and nevertheless, the period jitter is decreased; and that with external sinusoidal current modulating the self-pulsation laser diode, the noise-induced power jitter and period jitter can be suppressed greatly. This work is valuable for clock recovery in all-optical network.     

High-quality single-crystal CdSe nanoribbons and their optical properties

Large-scale synthesis of single-crystal CdSe nanoribbons is achieved by a modified thermal evaporation method, in which two-step-thermal-evaporation is used to control CdSe sources＇ evaporation. The synthesized CdSe nanoribbons are usually several micrometers in width, 50 nm in thickness, and tens to several hundred micrometers in length. Studies have shown that high-quality CdSe nanoribbons with regular shapes can be obtained by this method. Room-temperature photolumines-cence indicates that the lasing emission at 710 nm has been observed under optical pumping （266 nm） at power densities of 25-153 kW/cm^2. The full width half maximum （FWHM） of the lasing mode is 0.67 nm     

Propagation of hermite-cosh-gaussian beams passing through ABCD optical system with an annular aperture

By using the expansion of the aperture function into a finte sum of complex Gaussian functions, the corresponding analytical expressions of Hermite-cosh-Gaussian beams passing through annular apertured paraxially and symmetrically optical systems written in terms of ABCD matrix were derived, and they could reduce to the cases with squared aperture. In a similar way, the corresponding analytical expressions of cosh-Gaussian beams through annular apertured ABCD matrix were also given. The method could save more calculation time than that by using the diffraction integral formula directly.     

Influence of polarization extinction ratio on distributed polarization coupling detection

Distributed polarization coupling in polarization-maintaining fibers can be detected by using a white light Michelson interferometer. This technique usually requires that only one polarization mode is excited. However, in practical measurement, the injection polarization direction could not be exactly aligned to one of the principal axes of the PMF, so the influence of the polarization extinction ratio should be considered. Based on the polarization coupling theory, the influence of the incident polarization extinction on the measurement result is evaluated and analyzed, and a method for distributed polarization coupling detection is developed when both two orthogonal eigenmodes are excited.     

Call for Papers

正Communications—VLSI Researches and industries of telecommunications have been growing rapidly in the last 20 years and will keep their high growing pace in the next decade.The involved researches and developments cover mobile communications,highway and last-mile broadband communication,domain specific communications,and emerging D2D M2M communications.Radio communication steps into its