多径衰落条件下两种常规测向方法的误差问题

讨论了莱斯多径衰落信道模型在两类常规测向技术中的应用。利用常规测向技术对信噪比的特定要求,分析了具有莱斯分布特性衰落信道对比相、比幅测向误差抖动的影响,给出了其分布函数,并通过仿真指出其应用限制。最后就工程应用中所关心的模型参数获取和采样点数确定等问题作一论述。     

An experimental investigation of three eigen DF techniques

The comparative direction-finding (DF) performance of multiple signal classification (MUSIC), ROOT-MUSIC, and estimation of signal parameters via rotational invariance techniques (ESPRIT) is considered. Data were collected from two target transmitters operating simultaneously. The objective of the experiment was to evaluate multipath resolution capability using measurement precision equivalent to that found in modern radio direction-finding systems     

Sensitivity analysis of the maximum likelihood direction-findingalgorithm

A first-order analysis is performed of the sensitivity of the maximum likelihood (ML) direction-finding algorithm to system errors which cause differences between the array manifold used by the algorithm and the true array manifold. The effect of such errors on the directions-of-arrival (DOA) estimates is investigated. The ability of the ML algorithm to resolve two closely spaced sources in the presence of phase and gain errors in the array elements or in the receivers, or errors in the element locations, is analyzed. A formula for computing the failure threshold of the algorithm as a function of source separation and other system parameters is derived and tested by simulation. The analysis assumes that the exact covariance matrix of array element outputs is known     

一种矢量调制移相器的反馈补偿设计方法

针对矢量调制移相器存在的移相误差和增益波动问题,提出一种矢量调制移相器的反馈补偿设计方法.在分析了矢量调制的移相原理及影响移相精度和增益稳定性的误差因素的基础上,根据反馈补偿原理对误差因素进行补偿校正.首先通过自动化的测试和处理流程,得到移相器的相位和增益误差特性表,然后将该误差特性表反馈至移相器监控单元,最后监控单元利用插值算法和归一化原理实现对误差量的补偿校正.对采用该方法设计的移相器进行实际测试,结果表明：其移相精度小于1°,增益随相位变化波动小于0.4 dB,对比补偿校正之前,移相精度和增益稳定性得到了大幅提高和改善,从而验证了该方法的有效性.     

多层快速多极子算法的改进措施

 为精确求解散射问题,采用混合场积分方程（CFIE）、多层快速多极子算法（MLFMA）和共轭梯度算法（CG）的收敛技术。基于传统多层快速多级子算法,详细研究了二维拉格朗日插值节点数对计算精度的影响,并改进了插值方法,在不同的层采用不同的插值节点数;提出了在不同的层采用不同的精度控制来计算多级子模式数;分析了稀疏矩阵的对称性对内存使用的影响以及磁场积分方程对迭代初始值的选择。数值计算结果表明以上改进可较大幅度地提高计算精度和计算效率,同时降低内存使用,可满足复杂目标电磁散射计算要求。     

Angle-of-Arrival Estimation Using an Adaptive Antenna Array

A direction-finding technique is presented that is capable of simultaneously estimating the arrival angles of multiple signals. Pulsed as well as continuous signals can be handled with the signal form only approximately specified. An adaptive antenna array is used as a processing device in the estimation technique. The effect of input signal and feedback loop parameters upon estimate bias is discussed.     

Interplanetary type III radio bursts observed from high southern heliographic latitudes

Type III radio bursts observed from high southern latitudes are analyzed for the first time. The continual observation of these radio bursts by Ulysses from after the Jupiter swing-by to 50°S latitude argues for a wide latitudinal directivity of type III radiation. From this high latitude perspective, type III radio sources that lie in the far hemisphere of the Sun with respect to Ulysses are unambiguously resolved for the first time. Using the Ulysses direction-finding capabilities, the radio source locations in the 3-D heliosphere are derived for a radio event on 31 January 1994 when Ulysses was 45°S latitude. The source locations describe a spiral-like trajectory originating from the far side of the Sun. The angular radii of these radio sources are compared to angular radii that were previously derived from in-ecliptic observations.     

改进谢别德插值方法在地磁图构建中的应用

构建地磁图是地磁/惯性组合导航研究的一项重要内容,为了提高地磁导航中地磁基准图的精度,本文分析研究了改进谢别德插值算法,简要概述了数字地磁图的构建原则,并将改进谢别德插值算法应用到地磁图构建中.通过实验验证,发现该方法与距离加权反比插值算法、克里格插值算法相比,具有较好的插值效果.由此,初步判定改进谢别德插值算法在地磁...     

Direction of arrival tracking below the ambiguity threshold

We present an algorithm for direction-of-arrival (DOA) tracking that allows operation below the ambiguity threshold of the direction-finding (DF) system. Using multiple target tracking techniques, the algorithm turns the most likely DOAs of each measurement into multiple potential tracks and then selects the true track as that with the maximum cumulative likelihood. The improvement offered by the algorithm, namely the extension of the ambiguity-free signal-to-noise ratio (SNR) domain, is demonstrated in several simulated experiments using several array structures, including a sparse array and a uniform linear array     

An operational system implementation of the ESPIRIT DF algorithm

The practical implementation of the ESPRIT algorithm into direction-finding system architecture is considered. In particular, the problems of phase ambiguity resolution for extended array separations and multidimensional azimuth/elevation estimation are addressed. Generalized solutions for these problems are proposed, and a bearing quality indicator that provides a measure of credibility associated with each angle-of-arrival estimate is developed. Plots of computer simulated performance are presented in order to assess the probability of detection, of failure to alarm, and of false alarm as a function of azimuthal separation and period of signal observation     

Test Results with an Experimental Direction-Finding System

A direction-finding system was built that can simultaneously estimate the arrival angles of two incident signals. It is conceptually straightforward to extend the system to cases with greater numbers of signals. The system is designed to work with uncorrelated signals whose form is unknown, e.g., two communications signals residing in the same bandwidth. Pulsed as well as continuous signals can be handled. The technique involves the determination of the received signal's correlation matrix as an intermediate step. Pattern range tests were performed to determine angle estimate bias and accuracy.     

Performance of diversely polarized antenna arrays for correlatedsignals

The performance of direction finding systems in a correlated signal environment utilizing diversely polarized antenna arrays is investigated. The Cramer-Rao bound (CRB) is used to evaluate the accuracy of the estimated directions of arrival (DOAs). Compact closed form formulas are presented for the CRB corresponding to the joint estimation of the DOAs, signal covariance matrix, signal polarization parameters, and noise variance. The CRB is evaluated numerically for selected examples, to provide insights into the potential improvement in direction-finding accuracy due to polarization diversity     

基于双曲正弦函数的拓扑优化在热传导结构设计中的应用

电子设备的热传导结构设计是解决飞机电子设备热防护问题的有效方法,基于经验的传统设计方法存在设计周期长,获得的结果性能并不一定优等问题,因此将拓扑优化应用在飞机电子设备散热设计中,能够快速获取较优的结构布局。建立基于双曲正弦函数(sinh函数)插值模型的热传导拓扑优化数学模型,将该模 型的算法应用于二维、三维热传导算例,并通过 MATLAB编程进行算法实现;该模型与SIMP模型和RAMP模型进行对比,并应用于机载 LRM 模块导热拓扑优化设计。结果表明：基于sinh函数的插值模型较 SIMP插值模型精确,较RAMP插值模型的迭代次数少,能更好地解决热传导结构拓扑优化设计问题。     

The Effect of Ground Reflections and Scattering on an Interferometer Direction Finder

The azimuth and elevation angles of an airborne beacon transmitter can be determined using a direction finder comprised of two orthogonal interferometers located near the earth's surface. In this paper we consider the reflection of the incident electromagnetic field by the earth's surface and the resultant effect on the direction-finding system. The analysis yields an upper bound or limit to the interferometer phase error and the corresponding error in bearing angle that can result because of specular reflection and diffuse scattering.     

流固耦合数据交换的插值精度影响因素研究

提出了一种投影-形函数插值的新方法,用发展了三维线性插值方法。又包括使用优化插值和常体积转化等6种插值方法,从表征多种不同网格质量和待插值函数值情况的角度,进行了插值精度验证的应用研究,探索了网格质量和待插值函数值对插值精度的影响程度。研究结果表明,投影-形函数插值方法的效果很好;流/固的网格质量及其匹配状况在很多情况下对插值精度的影响要远大于插值方法本身。     

An Analysis of Wide-Band Microwave Monopulse Direction-Finding Techniques

This paper presents the concept, theory of operation, characteris tic equations, and error analysis of four wide-band monopulse techniques. The basic techniques described, which include pure amplitude monopulse, phase and amplitude monopulse (two-and three-channel configurations), and pure phase monopulse interferometer, are particularly applicable to monopulse direction finding systems that require frequency coverage over several octaves and open-loop angle bearing of several degrees. Sufficient detail and working formulas are included to permit a trade-off analysis to be made between the direction-finding techniques for selection in specific hardware applications.     

数控系统中空间任意平面圆弧插补算法

以往的数控系统只能插补平行坐标平面的圆弧,本文根据坐标系旋转的原理,提出了一种可以插补任意平面圆弧曲线、且可以满足控制实时性要求的插补算法,以简化编程,提高加工精度。     

A method for improving extended Kalman filter performance forangle-only passive ranging

A relatively simple method is presented which eliminates previously reported (Oct. 1985) erratic estimation performance associated with Cartesian formulations of the extended Kalman filter (EKF) for the 2D angle-only emitter location problem. The technique is based on an initialization procedure which combines a priori probability density function (pdf) information with single measurement a posteriori pdf information in a manner which is more efficient than the EKF. Simulation results are presented which demonstrate the utility of the technique as compared with a previously offered modified gain EKF     

非等间距相关系数AR(p)序列预测方法

针对非等间距时间序列预测中存在误差较大的问题,本文建立了非等间距相关系数AR(p)序列预测方法,详细讨论了非等间距相关系数AR(1)序列和AR(2)序列的预测公式和误差估计。大量计算表明,本文方法与通过插值将非等间距序列变换为等间距序列进行预测的传统方法相比,具有更高的预测精度。      

双机协同无源定位的飞行试验方法研究

分析了基于测向交叉定位的双机协同无源定位原理,构建了误差模型,给出了影响定位误差的因素。并从双机定位基线、目标机进入距离和目标机进入方位三个因素进行了双机协同无源定位误差的仿真。通过基于定位精度要求的试飞剖面设计,给出了两种典型的双机协同无源定位试飞航线,并给出试飞结果评估的方法和流程。