Error analysis techniques for planar near-field measurements

A combination of techniques is described for reliably estimating the magnitude of each error arising in planar near-field measurements. They include mathematical analysis, computer simulation, and measurement tests. There are three primary applications for these tests: in designing a measurement facility, the requirements of each part of the measurement system can be specified to meet a given level of accuracy; during actual measurements, the experimenter can identify, and reduce where necessary, potential sources of error in the measurement; and when a measurement has been completed, the estimated uncertainty in the measurement can be obtained with confidence and ease. The latter application has been used in many measurements to verify that the planar near-field technique produces high-accuracy results competitive with any other measurement technique     

天线时域平面近场测试的误差分析

天线时域近场测试技术对误差体系研究的缺失,导致测试结果的不确定度分析一直无法完成.为解决这一问题,以天线时域平面近场测试为例,对时域近场测试的误差进行研究,给出时域测试区别于频域测试技术的四个误差项:探头调制误差、信号源稳定度误差、时间采样间隔误差、时间采样长度误差.在给出误差项后,对误差的产生机理进行了讨论,通过仿真和实测给出了误差对测试结果的影响.     

减小平面近场测量中多次反射误差的新方法

本文给出了用平面近场技术测量超低副瓣天线时,平面近场测量总误差与天线远场方向图副瓣电平的误差方程,并进行了计算机仿真;提出了减小平面近场测量中探头天线与待测天线间多次反射误差和微波暗室电特性误差对超低副瓣天线所引入的测量误差的"自校准法",实验结果说明该方法是解决平面近场测量中多次反射和微波暗室电特性误差较为理想的方法.     

Error analysis for refractive-index profile determination fromnear-field measurements

Refractive-index profiles of diffused optical waveguides are determined by analyzing the near-field pattern of the waveguide. For this method, a computer simulation of measurement errors due to noise, quantization, defocusing, and nonlinearity of the camera system is presented by using data of a typical camera measurement system. The simulation procedure includes signal processing of the measurement intensity profile by means of a cubic spline approximation in order to reduce the influence of the measurement system errors. The residual errors associated with this technique are on the order of a few percent when measuring typical Ti:LiNbO₃ waveguides     

Far-field uncertainty due to random near-field measurement error

Recent planar near-field scanning tests with ultralow-sidelobe antennas have confirmed that random near-field measurement errors will ultimately limit the accuracy of far-field patterns. A formulation is outlined for estimating the spectral signal-to-noise ratio (SNR) arising from noncorrectable near-field random measurement errors. The formulation applies to arbitrarily directive test antennas and probes-even nulling probes. A far-field parameter, called the scan plane coupling factor, may be computed directly from the near-field data, and then used to form the spectral SNR. The accuracy of the spectral SNR is confirmed by simulation and by actual tests with low-sidelobe AWACS array antenna     

Performance enhancement of free space optical communication system using beam-optimized serial relaying in saturated atmosphere with pointing errors

In this paper, the performance improvement of a free space optical communication system with multi-hop and beam optimization has been studied. Novel closed-form expressions for the end-to-end average bit error rate, outage probability and average capacity of multi-hop free space communication system with decode-and-forward relaying are derived. Beam optimization is done using Nelder–Mead simplex algorithm. A composite channel model using atmospheric attenuation, turbulence and pointing errors is used to model the atmospheric impairments. The saturated atmospheric conditions are modeled by negative exponential channel model, and pointing error effects are considered by normalized jitter standard deviation parameter. The performance of the free space optical communication system in terms of end-to-end average bit error rate, outage probability and average channel capacity in saturated atmospheric turbulence conditions and pointing errors is significantly enhanced by using beam-optimized serial relaying with decode-and-forward transmission. The simulation results obtained by Monte Carlo simulation are in agreement with the results obtained from the closed-form expressions.     

基于计算机视觉图像精密测量的关键技术研究

虽然计算机视觉系统已经成功地应用于某些检测任务,但由于尺寸畸变和误差的存在,它们一般不被认为是精确的测量工具。本文介绍了精密测量中这些误差的修正方法。第一步是利用神经网络建立图像坐标系的标定模型。然后利用标准件构造学习阶段的神经网络模型,对初始测量的尺寸误差进行建模。最后利用这些模型对测量任务中的测量误差进行校正。     

Spatial statistics of instrument-limited angular measurement errors in phased array radars

The major contributors to the random component of the instrument limited angular measurement errors in electronically scanned phased array radars are reviewed and formulas are developed for statistical modeling of these error sources. The error model employed is applicable to space-fed and certain types of corporate-fed arrays. A comprehensive computer program, embodying this analysis, has been developed for determining these array measurement errors and their spatial correlation statistics, in two angle variables. This program is used to evaluate the statistical behavior of angular errors for some typical situations of interest. The use of angle, frequency, and phase "dithering" for improving the correlation statistics of these arrays is examined. The phase dithering technique is shown to be at least as effective as angle and frequency dithering and has the virtue of being readily implemented in the beam steering computer.     

Displacement errors in antenna near-field measurements and theireffect on the far field

The effects of probe displacement errors in the near-field measurement procedure on the far-field spectrum are studied. Expressions are derived for the displacement error functions that maximize the fractional error in the spectrum for both the on-axis and off-axis directions. The x- y- and z-displacement error in planar scanning are studied and the results are generalized to errors in spherical scanning. Some simple near-field models are used to obtain order-of-magnitude estimates for the fractional error as a function of relevant scale lengths of the near-field, defined as the lengths over which significant variations occur     

近天底干涉SAR动态海面高程测量误差分析

采用近天底的宽刈幅干涉高度计是近年来新发展的海面高程测量技术,与陆地高程测量不同,海浪一直处于随机运动之中,其动态特性会在合成孔径雷达(SAR)成像和干涉处理中引入显著误差。对于厘米级的干涉测量精度要求来说,该误差是主要误差源之一。该文研究了由海面特性引起的高程误差机理及其对于近天底干涉SAR测高精度的影响,建立了运动误差理论模型,同时考虑了电磁偏差与叠掩偏差影响。基于不同SAR工作体制,在不同海况下进行了理论近似仿真,并进行了干涉SAR全链路仿真,全链路仿真结果能够与理论仿真较好地吻合,验证了误差模型的正确。结果显示由海浪引起的误差随着多普勒中心频率近似呈线性变化,且与目标散射加权径向速度成正比。误差不仅与海浪特性相关,还与雷达系统参数相关,这能为未来系统设计、误差预算和海面高程处理提供参考。     

On the radial component of the electric field for a monopole phasedarray antenna focused in the near zone

The near-zone radial and principal spherical components of the electric field for a linear phased array antenna that is focused at one to two aperture diameters in the near zone are investigated. The phased array antenna consists of thin monopole elements, which are analyzed by using the method of moments. A theoretical formulation is described and computer simulation results are presented. The results show that the radial component is negligible in the focused near-field region, which allows the principal component to be accurately computed from knowledge of only the tangential electric field on the focal plane     

A general technique to correct probe position errors in planarnear-field measurements to arbitrary accuracy

A general theoretical procedure is presented to remove known probe-position errors when planar near-field data are transformed to the far field. The measured data are represented as a Taylor series whose terms contain the error function and the ideal spectrum of the antenna. This representation is then assumed to be an actual near-field existing on an error-free regularly spaced two-dimensional scan plane. By inverting the Taylor series, the ideal spectrum in terms of the measured data and the position errors is obtained. The solution is given by an infinite series of an error operator acting on data containing errors of measurement. This error operator is the Taylor series without the zeroth-order term. The nth order approximation to the ideal near-field of the antenna can be explicitly constructed by inspection of the structure of the error operator. Convergence of the approximation is examined. Computer simulations are used to demonstrate the excellent results obtained with this technique, as well as to demonstrate the convergence of the error-corrected fields to the true solution     

基于激光跟踪仪的机床导轨系统误差检测

针对机床导轨系统的误差补偿问题,提出一种基于激光跟踪仪的机床导轨误差检测方法。利用齐次坐标变换的方法建立导轨系统的误差模型,给出6项原始误差与空间误差的关系。在导轨系统的运动平台上选取不共线的3点,并利用激光跟踪仪检测出3点的空间坐标,然后逆用导轨系统误差模型,建立包含所有机床导轨系统原始误差的方程组,进而求得所有空间误差。实验中,分别利用误差检测方法和传统九线法检测导轨系统的偏摆误差,二者的检测结果一致性非常好,且最大差异只有0.74″,证明了该方法的有效性。相对于传统方法,基于激光跟踪仪的机床导轨误差检测方法操作简单、易于实现。     

Performance analysis of QAM in a two-wave with diffuse power fading environment

This letter investigates the average bit error rate (BER) performance of quadrature amplitude modulation in a two-wave with diffuse power (TWDP) fading environment. In TWDP fading, the received signal is composed of two specular components in addition to the diffuse component. The cumulative distribution function of TWDP fading is used to derive the BER expression in closed-form. Numerical and simulation results are presented to show the impact of different TWDP fading scenarios on the error performance.     

观测站存在位置误差条件下基于MDS的多站时差定位算法

为了降低无源定位中观测站站址误差对定位精度产生的不良影响,论文提出了一种基于多维尺度分析的多站无源时差定位解析算法。算法建立了存在站址误差时关于目标位置的线性方程组,推导了方程误差与时差测量误差和站址误差之间的关系式,将误差的统计特性融入到新的加权矩阵之中,使用加权最小二乘方法对目标位置进行了求解。仿真实验表明,算法对于小测量误差具有无偏性,其定位精度能够达到克拉美罗下界,相对于Ho K C的解析算法具有更好的稳健性。      

Useful Bounds on the Performance of a Spread-Spectrum Mobile Communication System in Various Fading Environments

Previous results on the spread-spectrum system for mobile communication proposed by Cooper and Nettleton have been obtained by computer simulation. In this paper, closed-form bounds on the bit error rate are derived for flat, Rayleigh, and Rician fading conditions. For more general types of fading, the saddle point method is used. Since the bounds are easily computed, they are more useful than computer simulations for analyzing system performance.     

基于Gerchberg-Papoulis算法的平面近场截断误差修正方法研究

在平面近场天线测量中,有限扫描面截断是影响测量精度的主要误差源之一,找到解决截断误差的方法是天线测量的研究重点之一.文中将平面近场天线测量中由有限区域内的场求平面波谱的过程抽象为带限函数外推的数学模型,从实际测量中的近远场变换理论出发,论证了GP（Gerchberg-Papoulis）算法应用在平面近场测量中在理论上是切实可行的.将GP算法应用在平面近场天线测量中,并分析了不同迭代次数算法的修正情况.结果表明,随着算法迭代次数的增多,可信角域外计算方向图与理论方向图差别明显减小.因此,本文的方法能够明显减小平面近场测量中截断误差的影响.除此以外,还分析了误差对算法收敛性的影响,结果表明,误差对算法修正效果影响较大.     

DTF型太阳光度计测量大气光学参数的对比验证及误差分析

DTF型系列太阳光度计在合肥地区测量大气气溶胶光学厚度(AOT)和可降水量(PWV),并与其它测量仪器进行对比验证,各仪器之间测量结果日变化趋势具有很好的一致性.对比分析结果显示:太阳光度计之间测量气溶胶光学厚度和可降水量的均方根误差都在8％以内;太阳光度计测量的可降水量与微波辐射计测量的水汽含量进行对比,均方根误差约5％.通过对比验证和误差分析,DTF型太阳光度计测量AOT和PWV具有较高的可靠性.     

平面近场天线多任务测试系统工程设计

提出了一种平面近场天线多任务测试系统的工程设计方法,该方法通过增加多功能天线测试控制器和远控微波开关对传统平面近场测试系统进行升级,使其具备对平面相控阵雷达天线多频点、多波位、多通道一次最多可测试35个天线方向图的测试能力。对新引入的幅相误差及扫描面截断误差进行了计算分析。大型相控阵天线的实测结果表明,在提高测试效率的同时,其测试精度亦能满足测试要求。     

激光双脉冲DSPI系统性能分析Ⅰ:误差及控制

分析研究了动态散斑相关条纹图的数字化、量化、空间相移误差及散斑随机噪声等因素对双脉冲激光数字散斑干涉系统位相重建精度的影响,并提出了控制测量误差的方法。