一种基于改进压缩感知的低信噪比ISAR高分辨成像方法

针对低信噪比下基于压缩感知(CS)的ISAR成像方法性能下降甚至失效的问题,该文提出了一种改进CS的成像方法,即用能量门限分离含目标的距离单元和噪声单元,同时在方位向上用相干投影来提高观测数据的信噪比,利用迭代加权的1-范数优化以增强真实散射点能量并且压制噪声。 改进CS算法适用于强噪声的环境下的ISAR成像,并可利用很少脉冲数获得高分辨的目标像。实测数据处理验证了该方法可以有效克服强噪声与杂波。同时,仅用16个回波脉冲就可得到高分辨ISAR图像,验证了该方法在非常有限脉冲条件下的稳健性。     

利用二维结构稀疏信息的调频步进ISAR高分辨成像新方法

针对已有利用压缩感知理论进行逆合成孔径（Inverse Synthetic Aperture Radar,ISAR）成像方法在低信噪比、欠采样率条件下性能下降严重等问题,依托调频步进波形独有特征并充分利用目标分布的二维结构稀疏信息,提出一种"先方位聚焦后距离分辨"的调频步进ISAR高分辨成像新方法.首先,对回波进行子脉冲脉压,在分析调频步进ISAR回波方位向特有的结构稀疏特征基础上,构建方位向的分布式压缩感知稀疏重构模型;其次,采用分布式压缩感知算法对该模型重构,从而获得低信噪比条件下的方位高分辨成像;最后,利用距离维的回波特征构建任意稀疏重构模型,实现距离向快速成像.由于该方法先进行方位聚焦,再进行距离分辨,并充分利用了目标的结构稀疏性,因此不仅具有抗噪性能强、重构精度高以及采样率低等特点,且避免了越距离单元走动对方位聚焦的影响.仿真与实测数据实验验证了本文方法的有效性.     

基于线性Bregman迭代类的多量测向量ISAR成像算法研究

为实现目标回波数据稀疏时的快速稳健ISAR成像,该文在构建多量测向量ISAR回波模型的基础上,利用压缩感知(Compressive Sensing, CS)中的线性Bregman迭代理论,研究了基于线性Bregman迭代类的多量测向量快速ISAR成像算法。该类成像算法共包括4种算法,首先给出此类算法的整体迭代构架、应用条件以及4种方法之间的联系;其次对此类算法的重构性能、收敛性、抗噪性以及正则化参数选择等方面进行全面的比较分析;最后基于实测数据进行ISAR成像,实验结果表明,与传统单量测向量ISAR成像算法相比,该文算法在低信噪比条件下可在更短的成像时间内获得更高的成像质量。      

基于压缩感知的空间目标三维雷达成像方法

对于稳定飞行的空间目标,俯仰向上的多圈次回波数据是稀疏分布的,从有限的观测数据中反演目标的三维反射率函数是不适定问题,观测噪声也会影响反演的结果,因此传统的FFT算法不再适用,必须引入适当的先验信息才能生成目标的三维图像.文章针对空间目标轨道的运动特性,首先推导了回波俯仰向表达式,然后结合目标散射中心稀疏分布特性和压缩感知原理,提出了一种基于多圈次稀疏观测的空间目标三维成像算法.该方法利用噪声单元估计噪声门限,当观测模型满足约束等距性质时,利用加权迭代的压缩感知算法进行成像处理,生成目标的三维图像.最后结合实测轨道模型,仿真验证了在低信噪比下,基于噪声估计的压缩感知算法能实现对目标三维像的精确重构.     

基于压缩感知的二维联合超分辨ISAR成像算法

在ISAR成像中,距离和方位分辨率分别受发射信号带宽和成像积累角的限制。基于压缩感知(CS)理论,该文提出了一种2维联合超分辨ISAR成像算法。首先建立ISAR观测信号模型并构造2维超分辨字典,然后利用ISAR图像的稀疏先验信息将2维联合超分辨成像建模为最小l1范数的优化问题,最后提出一种快速算法求解该优化问题。该方法进行距离维和方位维的联合处理,有效利用了回波数据的2维耦合信息;通过共轭梯度(CG)运算,快速傅里叶变换(FFT),Hadamard乘积等操作,有效提高了算法的实现效率。仿真和实测实验验证了该算法的有效性。     

基于分布式压缩感知的窄带LFMCW旋翼成像方法

针对窄带LFMCW体制雷达旋翼成像问题,研究了一种基于分布式压缩感知(DCS)的窄带LFMCW旋翼ISAR成像方法。在该方法中,根据窄带LFMCW体制雷达成像与传统脉冲体制回波模型上的差异,基于转速参数估计和压缩感知理论,建立了LFMCW体制雷达旋翼回波稀疏基以及稀疏表示模型,在此基础上,研究了相应的ISAR成像方法。在该算法中,首先提取出脉压后旋翼所在距离单元内的回波,通过自相关思想并利用图像熵完成对旋翼目标叶片个数和旋翼转速的估计;然后对于方位欠采样条件时传统方法不适用于LFMCW雷达的旋翼成像问题,根据旋翼转速信息构建出窄带LFMCW分布式稀疏基,将Dechirp后的回波信号通过DSOMP算法进行重构,实现最终成像。仿真结果验证了所研究方法的可行性和有效性。     

基于压缩感知的宽带成像雷达Chirp信号回波的压缩和重构

针对宽带成像雷达chirp信号回波按照带通采样定理采样得到的数据量大所导致的存储压力大的问题,本文提出基于压缩感知的chirp信号回波压缩和重构方法,首先就回波是否可压缩,利用chirplet变换分析了chirp信号回波的稀疏性,在信号稀疏的基础上,应用chirplet变换给出了可应用于压缩感知的稀疏字典及其简化形式,并证明了所给出的简化形式稀疏字典满足信号重构的条件。最后给出了回波的压缩和重构方法并结合ISAR成像进行了数字实验,先在目标转动加平动模型下,进行了数据的压缩和重构,通过比较重构信号和原信号的时域波形、高分辨距离像和ISAR成像结果,验证了本文的方法。最后仿真分析了重构误差随信噪比的变化曲线,说明了本文的方法对信噪比的要求。      

基于贝叶斯压缩感知的ISAR自聚焦成像

针对ISAR自聚焦成像,该文提出一种基于贝叶斯压缩感知的高分辨率成像算法。首先利用目标图像的稀疏特性构建级联形式的稀疏先验模型,同时将相位误差建模为均匀分布模型;然后基于最大后验准则,依据贝叶斯压缩感知理论交替迭代求解目标图像和相位误差。与传统稀疏方法相比,所提算法进一步利用了目标图像的联合稀疏信息,将ISAR CS成像转化为MMV联合稀疏优化问题的求解,可以有效改善自聚焦的精度以及成像质量。仿真结果验证了该算法的有效性。     

基于压缩感知的稀疏孔径认知ISAR成像方法

针对运用压缩感知理论对ISAR目标成像时不同目标所需观测维数和积累时间不同的问题,提出了一种基于压缩感知的稀疏孔径认知ISAR高分辨成像方法。在对目标稀疏特性认知的基础上,构建了基于目标横向稀疏度和观测积累时间的随机观测矩阵,并给出了成像质量评估标准,实现了对有限雷达资源条件下ISAR目标的高分辨认知成像。仿真结果表明,利用该方法成像,不仅可以减少雷达成像发射脉冲数,而且可以有效减少目标成像的时间,同时还能获得高质量的目标ISAR像。     

基于稀疏贝叶斯方法的脉间捷变频ISAR成像技术研究

传统捷变频成像方法具有高旁瓣、低分辨率的缺点。鉴于捷变频ISAR回波信号的稀疏性,该文基于原始数据的2维压缩感知方案,在贝叶斯原理框架下,用稀疏贝叶斯算法方差成分扩张压缩方法(ExCoV)实现捷变频ISAR像的重建。贝叶斯框架下的稀疏重构算法考虑了稀疏信号的先验信息以及测量过程中的加性噪声,因而能够更好地重建目标系数。作为一种新的稀疏贝叶斯算法,ExCoV不同于稀疏贝叶斯学习(SBL)算法中赋予所有的信号元素各自的方差分量参数,ExCoV方法仅仅赋予有重要意义的信号元素不同的方差分量,并拥有比SBL方法更少的参数,克服了SBL算法参数多时效性差的缺点。仿真结果表明,该方法能克服传统捷变频成像缺点,并能够实现低信噪比条件下的2维高精度成像。     

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