线阵 SAR 三维成像分辨率分析

研究阵列无线 SAR 系统优化问题,关于线阵合成孔径雷达(SAR)使用阵列天线获取观测目标不同入射角的回波信号,能够实现对目标的三维成像.为了获取高分辨率的三维成像结果,研究了线阵 SAR 三维成像分辨率与观测几何的关系.采用线阵 SAR 实现三维成像的信号模型,得到了与线阵 SAR 几何相关的三维分辨率,根据高度向分辨率随着参考视角和线阵角度的变化,得到在线阵角度的三维成像分辨率.并运用运用 MATLAB 仿真平台进行了线阵 SAR 三维成像仿真,结果表明目标三维成像得到了高分辨率的结果.     

相控阵天线方向图的近场功率测量法研究

为解决相控阵天线测量场地受限、技术复杂、难以用于实际工作中的问题,提出了一种近场基于功率测量的方法,使用固定探头接收,利用被测天线自身扫描时接收到的功率值获得不同角度方向图数据,而无需测量相位。以线阵为例,阐述了测量基本原理和配相控制的流程,给出了插值计算公式,定性分析了误差来源和影响,仿真实验结果表明,该方法可有效逼近真实方向图。     

平面阵天线栅瓣性能分析

在相控阵天线设计中,增加阵元间距能提高天线分辨率,但天线波束会出现栅瓣,栅瓣多值性导致目标位置模糊,接收机错误跟踪。因此,阵元间距的合理取值是相控阵天线设计的重要内容。首先建立了阵列天线方向图函数模型,然后推导出矩形阵和三角阵栅瓣出现的位置及不出现栅瓣时阵元间距的取值范围,最后通过MATLAB仿真来验证结论的正确性。     

多重信号分类算法在共形阵列天线中的应用

在天线信号优化设计中,传统的共形阵列天线的信号波达方向(DOA)估计采用了波束扫描技术,需要大量的阵元才能获得较高分辨率,对于有限的阵列孔DOA估计来说,上述技术的分辨率会受到瑞利限制.而多重信号分类(MUSIC)算法,由于充分利用了噪声子空间和信号子空间的正交性,构造了空间谱函数,可以通过谱峰值的搜索来达到DOA估计.对MU-SIC及改进算法进行分析,并且分别在均匀线阵,柱面阵列和锥面阵列天线模型下进行了仿真,结果表明,阵列的排列方式对波达方向的估计性能具有重要的影响.     

阵列天线方向图仿真系统设计与研究

针对阵列天线的布阵问题,设计了一种阵列天线仿真系统,实现了阵列天线设计的可视化操作.通过设置阵元数、波长、阵元间距等天线相关参数,系统能够实现直线、平面、圆形和圆柱四类阵列天线的仿真分析.针对四类阵列天线稀疏布阵问题,系统采用遗传算法,对稀疏阵列天线的方向图特性进行研究.通过系统的仿真,用户可以直观地观察阵列天线方向图...     

超宽带信号功率谱的仿真分析

超宽带(UWB)信号及其功率谱分布是研究超宽带通信系统与其它通信系统频谱共存与兼容问题时,需要考虑的重要因素.根据超宽带信号功率谱的特点,从控制超宽带信号功率谱分布的角度,就高斯单周期脉冲及其各阶导函数、不同的信息调制方式和跳时码参数对超宽带信号功率谱的影响,进行了计算机仿真和分析,并总结出控制超宽带信号功率谱分布的方法,从而为解决超宽带通信系统与其他通信系统频谱共存问题,提供了有益的思想和方法.     

时域天线阵的测试及其结果分析

将时域天线组成阵列是改善超宽带雷达技术性能一条行之有效的途径;研究时域天线阵辐射或接收的波形变换和畸变规律．是十分必要的;利用虚拟仪器技术,采用1．abView软件平台,使用模块化设计思想．实现一套慕于示波器和转台协调工作的时域天线阵自动测试系统的设计;通过对灭线阵测试结果进行分析,并与FDTD的仿真结果进行对比,得出关于时域天线阵有价值的结论。     

基于拉普拉斯分布天线阵列下MIMO性能研究

多天线系统是可以克服多径干扰的影响并增加频谱使用效率的系统.MIMO系统的容量增加主要取决于无线电信道的空间相关性性能.主要研究了MIMO天线阵列系统的性能,包括MIMO空间时间相关性和天线阵列配置,推导了当角能量遵循拉普拉斯分布时均匀线性阵列、均匀圆阵的衰落相关性解析公式,并分析了两种天线阵列下的系统信道容量.通过计算机程序模拟仿真验证了分析结果,验证结果表明当阵元间距增大或者衰减因子减小(角度扩展增大)时,空间衰落相关性减小,系统信道容量增大,提升了系统性能.     

超宽带冲激无线电相关接收器的仿真比较

超宽带相关接收器的设计是超宽带冲激无线电接收机实现信号接收的关键之一,针对使用二阶高斯脉冲的超宽带冲激无线电相关接收器的特点,建立了相应的仿真模型,在Simulink平台下实现了对超宽带冲激无线电相关接收器的模拟,采用了T-R(发送-参考)自相关和互相关三种相关接收机方案,分别通过高斯噪声信道和多径信道进行相关仿真,对比了各种相关接收器的脉冲检测效果,验证了相关检测技术从噪声环境中提取超宽带信号的能力,为超宽带相关接收机系统的优化设计提供了参考.     

三维接收天线阵列信道模型下的空域相关性

建立三维接收天线阵列的空间信道模型,将以往的信道建模方向推广到空间域,给出该信道模型的通用数学表达式。针对该通用形式,将来波信号角度描述扩展到俯仰角和方位角,推导该信道模型下空域相关系数的数学表达式,显示接收天线阵的形状对空域相关系数的影响。分析当来波信号的功率谱(俯仰角和方位角)分别为均匀、高斯、拉普拉斯分布时的空域相关系数,给出了数值仿真结果。     

Miniaturized coplanar waveguide‐fed disk monopole antenna for ultra‐wideband applications with improved wireless local area network band rejection

In this article, we first propose a miniaturized coplanar waveguide‐fed disk monopole antenna with overall size of 14 mm × 22 mm. Measurement results show that the antenna has an ultrawide impedance bandwidth from 3 to 12 GHz and omnidirectional radiation pattern. Next, we introduce two U‐shaped slots in the ground plane of the antenna to provide an improved band rejection in the wireless local area network frequency band. Experimental results indicate that the proposed band notch antenna has maximum voltage standing wave ratio (VSWR) of 25 in the desired rejection band. Measured gain for the proposed band notch antenna is around 0 dB and reduces to ?15dB in the desired rejection band. Time domain performance of both the initial antenna and band notch antenna is also examined and the best detection template is presented. Computed total fidelity factors for both the initial and band notch antenna are greater than 0.9. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013     

A new feature extraction method for odour classification

A new method for real time classification of volatile chemical substance traces is presented. The method is based on electrochemical signals of an array of semiconductor gas sensors. In these sensor signals characteristic patterns of different substances are hidden. There are non-linear correlative relationships between the measured sensor signals and the chemical substances which are treated using two methods derived from statistical learning theory (Support Vector Machine - SVM, Maximum Likelihood Estimation - MLE) for the detection of the substance characteristics in the sensor signals. A key criterion for the presented pattern recognition is a newly developed type of features, which is specially adapted to the low frequency signals of semiconductor sensors. The presented features are based on the evaluation of the range of the transient response in the sensor signals in the frequency domain.To derive the new features, both real measurement data and synthetic generated signals were used. In the experiments the focus was set on the creation of reproducible sensor signals to get characteristic signal patterns. Synthetic signals were derived from a Gaussian Plume Model. With the new features, training data sets were calculated using the classification methods SVM and MLE. With these training data sets new sensor measurements may be assigned to the substances which are to be sought. The advantage of the presented method is that no feature reduction is needed and no loss of information occurs in the learning process.The classification results based on the new features have been compared with the classification based on a conventional method for feature extraction. It was proved that the recognition rate of the substances used with the new feature type is higher.The substance classification is primarily limited by the sensitivity of the semiconductor sensors, because sufficiently large sensor signals must have been provided to obtain appropriate substance patterns. At the present stage of development the method presented is suitable for the classification of substance groups, such as nitro aromatics or alcohols, but not for specific substances.     

UWB antenna and MIMO antennas with bandwidth,band‐notched,and isolation properties for high‐speed data rate wireless communication: A review

The prospective of ultrawide band (UWB) technology is enormous due to its remarkable advantages such as the capability of providing high‐speed data rates at short transmission distances with low power dissipation. The swift growth in wireless communication systems has made UWB an exceptional technology to replace the conventional wireless technologies in today's use. UWB bandwidth (3.1‐10.6 GHz) covers most of the communication applications. High frequency of operation with high level of miniaturization has enhanced the interest in designing high performance antennas. There is a growing demand for small and low cost UWB antennas that are able to provide satisfactory performance in both time and frequency domains. The trend in recent wireless systems, including UWB based systems, are to build small, low‐profile integrated circuits so as to be compatible with portable wireless devices. Transformation of UWB in MIMO achieved high data rate and solved the problem of multipath propagation. The main reason for writing this review is to investigate various UWB methods and band rejection approaches on a single platform. Some of the isolation enhancement approaches are also included in article due to the requirement in MIMO antennas.     

Beamforming of UWB pulse array and its implementation

This paper firstly introduces a realistic ultra-wideband (UWB) pulse model and discusses the principle of sensor array beamforming for UWB pulse signals. Then the differences between a UWB pulse array and narrowband sinusoidal array are studied. Based on it, the problem of realizing a digital and applicable variable delay circuit (VDC) to compensate the channel propagation delay accurately for UWB pulse array beamforming is addressed. In our work, fractional sample delay compensation filters (FDCF) are combined with delay lines to build up accurate VDCs. As a result, the Lagrange interpolation method based on maximally flat criterion is found to be most suitable for the fixed beam steering; and Farrow structure is recommended to satisfy the need of rapid beam adjustment. In the simulation experiments, two kinds of directivity pattern for an UWB pulse array are studied and compared with that of sinusoidal array. The effectiveness of the presented scheme is verified by the simulation results, which show that the VDC implementation by digital lines and FDCF can remarkably improve the performance of the directivity patterns of UWB pulse array especially for the system with low sampling rate.     

A compact asymmetric slot dual band antenna fed by CPW for PCS and UWB applications

A compact slot antenna with an overall dimension of 30 × 30 × 1.6 mm³ is proposed for dual band applications. The radiating element is a hexagonal shape patch which protrudes from a Co‐Planar Waveguide (CPW) feed into a step shape slot. The slot is basically rectangular in shape and is extended by inserting rectangular cuts of different sizes on the ground plane around it. The ultrawide impedance bandwidth is achieved using asymmetric feed line along with extended rectangular cuts around the slot. For realizing the second band for personal communication system applications (near 1.9 GHz), a metallic stub of quarter wave length is attached at the top of the slot. The measured impedance bandwidth (for S₁₁ < ?10 dB) is 110 MHz (1.86–1.97 GHz) for the first band and 9 GHz (3.0–12.0 GHz) for the second band. The antenna is further characterized by omnidirectional radiation patterns in the H‐plane, dumb‐bell shape radiation patterns in the E‐plane and a peak gain of 3–5 dBi over the ultrawideband. All the measured results are found to be in good agreement with the simulated results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:243–254, 2015.     

High performance data compression method with pattern matching for biomedical ECG and arterial pulse waveforms

Biomedical waveforms, such as electrocardiogram (ECG) and arterial pulse, always possess a lot of important clinical information in medicine and are usually recorded in a long period of time in the application of telemedicine. Due to the huge amount of data, to compress the biomedical waveform data is vital. By recognizing the strong similarity and correlation between successive beat patterns in biomedical waveform sequences, an efficient data compression scheme mainly based on pattern matching is introduced in this paper. The waveform codec consists mainly of four units: beat segmentation, beat normalization, two-stage pattern matching and template updating and residual beat coding. Three different residual beat coding methods, such as Huffman/run-length coding, Huffman/run-length coding in discrete cosine transform domain, and vector quantization, are employed. The simulation results show that our compression algorithms achieve a very significant improvement in the performances of compression ratio and error measurement for both ECG and pulse, as compared with some other compression methods.     

蝶形天线的计算机仿真设计

蝶形天线是在脉冲型探地雷达中广泛采用的一种宽带天线。本文采用时域有限差分算法(FDTD)结合PML吸收边界条件分析了蝶形天线在高斯脉冲激励下的时域特性,通过傅立叶变换,计算出天线的方向图和在不同频率下的输入阻抗,结果表明FDTD算法用于分析蝶形天线是有效的。     

A half cut design of low profile UWB planar antenna for DCS/PCS/WLAN applications

A miniaturized half cut coalesced kite shaped printed antenna is presented for the ultrawide band (UWB) characteristics. The proposed design bears a compact and small physical dimension of 25 (L) × 9 (W) × 1.6 (h) mm³. This structure produces higher impedance bandwidth as compared to the corresponding full structure of the antenna design. The variation of ground plane dimension is studied to get the optimized results of the antenna. The measured impedance bandwidth (return loss <10 dB) of the proposed antenna is found to be 16.12 GHz in the frequency range 1.02 to 17.14 GHz. The average measured gain for this design is 3.12 dBi for the entire band of operation. The far field radiation patterns are also presented at 1.18, 3.1, 6.85, and 10.6 GHz. The antenna performances are first analyzed by the CST Microwave Studio, the simulation software based on finite integration technology (FIT) and then the optimized structure is fabricated for the measurements. The proposed design structure reveals the recent state of art by using the half cut technique which not only miniaturizes the size but also covers the whole UWB range to be used for many wireless systems.     

Crack band model of fracture in irregular lattices

An irregular lattice model is used to simulate mode I fracture in softening materials, such as concrete. Lattice geometry is based on a three-dimensional Voronoi discretization of the material domain. The Voronoi diagram provides scaling rules for the elemental stiffness relations, leading to an elastically uniform representation of the material for simple modes of straining. Fracture is represented using a crack band approach, in which the dimensions of the crack band are also scaled according to the Voronoi diagram. The material is viewed as homogeneous and the energy dissipation mechanisms active at finer scales are lumped into a cohesive crack relation. This energy conserving crack band approach is objective with respect to the irregular geometry of the lattice. Model accuracy and performance are demonstrated through simulated fracture testing of concrete specimens under uniaxial tension and flexural loadings. Basic qualities of the simulation approach, demonstrated here for homogeneous models of concrete, are applicable toward simulating fracture in multi-phase systems where material features are explicitly modeled.     

Regulation performance limitation of networked time-delay systems with incomplete information

In this paper, the regulation performance limitation of networked time-delay systems is studied. The communication network is mainly affected by parameters such as packet dropouts, encoding-decoding, interference signal, and channel noises. Non-minimum phase zeros, unstable poles, and time delay are all considered for a given plant. The corresponding regulation performance expression is derived using coprime factorization and spectral decomposition techniques in the frequency domain. The results indicate that the regulation performance of the system is related to the inherent characteristics of the given plant, including non-minimum phase zeros, unstable poles, and time delay. Additionally, network communication parameters such as white Gaussian noise, packet dropouts, encoding-decoding, and external interference signals all affect the regulation performance of networked time-delay systems. Finally, some simulation examples are provided to demonstrate the effectiveness of the theory.