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为了实现超宽带步进变频连续波雷达近场区高分辨率快速成像,提高成像的分辨率,根据步进变频连续波信号发射与传播的特点,采用角谱分析方法,通过对电磁波波动方程进行推导,提出一种适用于超宽带步进变频连续波雷达的成像算法,该算法省去了匹配滤波过程,成像准确。采用HFSS三维电磁场仿真软件进行建模仿真,在仿真结果中采集数据验证成像算法的可行性。结果表明,成像图像中目标能量集中,分辨率高,对于采用的频率范围0.5~1.5GHz,带宽为1GHz的发射信号,理论分辨率为0.15m,实际得到的分辨率约为0.2m。 相似文献
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综合运用多种现代集成器件,采用外差原理设计了分辨率可调的频谱分析仪。为使频谱仪工作于最佳工作状态,提出了滤波带宽和扫频步进频率同步调节的控制技术。SPCE061A单片机通过给AD9850DDS芯片输送控制字,控制其生成步进频率可调的本机振荡信号,经过AD835集成混频器与输入信号混频,由窄带滤波器MAX297滤波取出差频,送入检波电路得到各频率分量有效值。频率测量范围变宽,为0.1 Hz~40MHz;频率分辨率得到提高,10Hz~100KHz7档可调,使每次测试效果最佳;同步调节使操作更简明。 相似文献
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针对无线局域网接收机对低成本和线性度的定制化需求,设计了一款适用于IEEE 802.11 b/g/n/ax标准WLAN接收机的高线性度电流模式混频器;采用零中频接收机架构,电流模式混频器的电路结构主要包括跨导级放大器,混频开关级和跨阻放大器;通过跨导级两种工作状态的转换和跨阻放大器反馈电阻的两种取值变化实现了混频器的四档增益可调;混频开关级选用双平衡无源混频电路以提供良好的线性度;为了解决零中频接收机存在的直流失调问题,加入了一种电流注入式的直流失调校准电路,进一步提高了混频器的线性度;对跨阻放大器中的跨导运算放大器电路进行优化设计以提高其带宽,使跨阻放大器的输入阻抗足够小以保证混频器的线性度;基于180 nm RF CMOS工艺,借助Cadence软件对混频器进行仿真:当本振频率为2.4GHz时,四档增益分别为38dB、32dB、27dB和21dB,中频带宽可达20MHz;噪声系数在高增益的情况下为8.46dB,输入三阶交调点在低增益的情况下可达13.72dBm;仿真结果表明,在较宽的中频带宽下,电流模式混频器取得了良好的线性度性能,满足WLAN接收机的定制化需求。 相似文献
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研究雷达信号调频优化问题,由于合成孔径雷达干扰的欺骗性和复杂性,调制带宽会影响抗干扰性能.为解决上述问题,提出一种调频连续波体制的随机初相与限幅过程相结合的成像雷达抗干扰方法.通过在发射信号中加入随机变化的初始相位、发射诱骗信号截获干扰脉冲并对其进行方位压缩、限幅,然后在方位向上进行逆傅里叶变换和逆滤波并用真实滤波函数进行匹配滤波,最后按照传统调频连续波合成孔径雷达成像方法进行成像.同时通过提高脉冲重复频率增加方位向脉冲积累个数,使成像信干比得到提高,进而使接收端抗干扰性能得到增强.仿真结果证明,与直接进行真实信号匹配滤波相比,加入限幅过程和提高脉冲重复频率使干信比提高了30dB. 相似文献
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从频域角度探讨TH-UWB系统对窄带干扰的抑制能力,采用信号功率谱分析方法,研究UWB系统的调制技术和脉冲成形技术,提出线性组合高斯单周脉冲设计陷波频谱.理论分析及计算机仿真结果表明,合理选择超宽带信号调制方式和脉冲,可在一定程度上提高超宽带系统抗干扰能力.应用提出的线性组合高期单周脉冲作为UWB发射信号,可以有效减小UWB信号对外界的干扰. 相似文献
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Recent years have seen rapid advances in various grid-related technologies, middleware, and applications. The GCC conference has become one of the largest scientific events worldwide in grid and cooperative computing. The 6th international conference on grid and cooperative computing (GCC2007) Sponsored by China Computer Federation (CCF),Institute of Computing Technology, Chinese Academy of Sciences (ICT) and Xinjiang University ,and in Cooperation with IEEE Computer Soceity ,is to be held from August 16 to 18, 2007 in Urumchi, Xinjiang, China. 相似文献
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张涛 《计算机测量与控制》2015,23(1):86-89
为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值. 相似文献
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本文分析了法律数据库的结构和特点,介绍了采用面向对象设计方法和超文本数据库技术开发和实现法律信息库系统将作为重要网络资源之一为不同用户进行法律咨询服务。 相似文献
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In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times. 相似文献
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《中国科学:信息科学(英文版)》2014,(8)
正SCIENCE CHINA Information Sciences(Sci China Inf Sci),cosponsored by the Chinese Academy of Sciences and the National Natural Science Foundation of China,and published by Science China Press,is committed to publishing highquality,original results of both basic and applied research in all areas of information sciences,including computer science and technology;systems science,control science and engineering(published in Issues with odd numbers);information and communication engineering;electronic science and technology(published in Issues with even numbers).Sci China Inf Sci is published monthly in both print and electronic forms.It is indexed by Academic OneFile,Astrophysics Data System(ADS),CSA,Cabells,Current Contents/Engineering,Computing and Technology,DBLP,Digital Mathematics Registry,Earthquake Engineering Abstracts,Engineering Index,Engineered Materials Abstracts,Gale,Google,INSPEC,Journal Citation Reports/Science Edition,Mathematical Reviews,OCLC,ProQuest,SCOPUS,Science Citation Index Expanded,Summon by Serial Solutions,VINITI,Zentralblatt MATH. 相似文献
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正Erratum to:J Zhejiang Univ-Sci C(ComputElectron)2014 15(7):551-563doi:10.1631/jzus.C1300320The original version of this article unfortunately contained mistakes.Algorithm 6 should be as follows:Algorithm 6 FGKFCM-F clustering Input:(1)X={x_1,x_2,…,x_N},,x_iR~d,i=1,2,…,N,the dataset;(2)C,1C≤N,the number of clusters;(3)ε0,the stopping criterion; 相似文献
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《Information & Management》2016,53(6):787-802
Discrepant technological events or situations that entail a problem, a misunderstanding or a difficulty with the Information Technology (IT) being employed, are common in the workplace, and can lead to frustration and avoidance behaviors. Little is known, however, about how individuals cope with these events. This paper examines these events by using a multi-method pragmatic approach informed by coping theory. The results of two studies – a critical incident study and an experiment – serve to build and test, respectively, a theoretical model that posits that individuals use a variety of strategies when dealing with these events: they experience negative emotions, make external attributions, and adopt engagement coping strategies directed at solving the event, eventually switching to a disengagement coping strategy when they feel they have no control over the situation. Furthermore, users’ efforts may result in ‘accidental’ learning as they try to overcome the discrepant IT events through engagement coping. The paper ends with a discussion of the results in light of existing literature, future opportunities for research, and implications for practice. 相似文献