平面波谱恢复算法在平面近场测量中的应用

介绍用于天线平面近场测量的一种近远场变换新算法。该法利用被测天线的平面波谱和口径场幅相分布之间的关系,以及天线口面的约束条件,用G-P迭代算法从平面波谱的置信谱域部分恢复出置信谱域外的平面波谱。这种方法减小了较小截断角下有限扫描面对测量精度的影响,并提高了天线近场测量的效率。     

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.     

天线近远场变换的快速算法

基于考虑探头补偿的平面近远场变换理论,根据实际需要,提出了一种工程实用的平面近远场变换快速算法。通过该算法由近场测量数据变换得到的天线远场方向图,既能达到任意分辨率,又能节约计算内存和提高计算速度。     

基于三次样条插值法的柱面近场测量欠采样修正算法研究

为解决暗室近场测试效率低的问题,本文针对天线近场测量中高效测量方法进行了研究,提出了一种柱面近场欠采样恢复算法。该算法利用高精度的三次样条插值(cubic spline interpolation, CSI)法对未采样的点进行恢复,可减少采样点数,提高测试速度。此外,在柱面近场欠采样恢复CSI求解过程中充分利用系数矩阵的正定、对称等优良特性,使线性方程组的计算量从O(n³)降为O(n),大大提高了CSI的计算效率。最后使用插值后的近场幅度和相位结合柱面近远场变换理论求得天线远场方向图。为验证所提出算法的有效性,试验测试了天线样机,试验结果与理论分析一致。     

光谱相位相干电场重建法的准确相位还原

基于光谱相位相干直接电场重建法(SPIDER)原理,提出采用小波变换和傅里叶变换两种算法互校的方式,确定小波变换法的形状因子和傅里叶变换法的滤波窗口宽度,当两种算法的还原结果一致时,就实现了SPIDER的准确相位还原.通过自制的SPIDER测量仪和自编的SPIDER相位还原软件,实现了对复杂相位的准确还原.     

时域平面近场测量的数值分析方法

本文以H面喇叭为例,研究了天线时域近场的运动状态,用谱域法分析了平面近场分布状况,得出采样原则,为平面近场扫描测量提供了理论依据。介绍了时域平面近场测量的近远场变换公式,包括时域和频域两种计算途径。对各自的优点作出了探讨。运用近远场变换方法计算了时域远场和频域方向图。     

时域近场测量的间接频域算法和直接时域算法研究

时域近远场变换是时域近场天线测量的关键技术。本文对时域近远场变换的间接频域算法和直接时域算法进行了数值模拟和分析。针对开口矩形波导天线的时域近场测量 ,选取时空采样参数和内插公式 ,用两种算法计算时域远场方向图 ,分析周期性、时域混叠问题和扫描面截断效应 ,在相互比较和验证的基础上 ,指出两者的优、缺点及适用的情况。     

基于散射分布函数模型的近远场变换技术研究

全尺寸目标的电磁散射特性测试,需要足够大的测试距离或紧缩场系统,但是建设满足远场条件的室外静态场与室内紧缩场需要巨大的经费投入和很高的技术条件,更无法对飞行器进行现场成像与雷达散射截面(Radar Cross Section,RCS)诊断.针对近距离测试检定飞行器隐身性能的需求,提出了基于散射分布函数模型的近远场变换算法.建立三维散射分布函数模型,采用三维扫描方式记录近场数据,将球面波函数分别在柱坐标系、三维直角坐标系与球坐标系下展开,变换得到目标的远场数据,通过三维逆傅里叶变换与插值算法给出目标的三维重建图像与远场RCS.仿真分析与实验表明,算法准确有效.     

湍流退化图像相位恢复算法研究

为克服气动光学效应对目标图像的影响．把相位恢复算法与气动光学效应机理研究结合起来,用于湍流退化图像的恢复。该算法是通过目标图像的傅里叶变换幅值来恢复目标图像,或等价地,恢复傅里叶变换相位。讨论了两类相位复原算法——迭代傅里叶变换（研）和解相关算法。对现有的解相关算法作了改进。采用共轭梯度法解高斯一牛顿方程,可有效提高算法的收敛速度。研算法不能保证迭代过程总能收敛到正确解,有时会出现停滞现象。将研和解相关算法组合起来,可以克服IFT算法的停滞现象,提高正确收敛率。给出了在信噪比为20dB情况下的湍流退化仿真图像恢复的实例,目标图像能较清晰地恢复出来。实验结果表明该算法具有较好的稳定性和抗噪声能力。     

基于多步相位恢复的激光远场焦斑测量方法

为了实现激光远场焦斑的高精度测量,提出一种基于多步相位恢复的激光远场焦斑测量方法。理论推导了基于多步相位恢复的激光远场焦斑重构模型,其中为了解决焦斑计算中出现的欠采样问题,引入了线性调频z变换(CZT)技术,相较于传统的快速傅里叶变换(FFT)补零计算,此方法避免了计算冗余。同时,提出一种基于多步相位恢复的激光远场焦斑重构算法,并仿真分析了扫描步长和探测位置数对所提方法收敛性的影响,确定了最佳扫描步长和探测位置数。为了验证所提方法的有效性,搭建了基于纯相位型液晶空间光调制器(SLM)的实验验证装置,实验结果和理论值的相关系数为0.9976。同时,所提方法与传统长焦距透镜成像法相比,测量精度更高,可为激光远场焦斑高精度测量提供一种技术手段。     

A plane-polar approach for far-field construction from near-field measurements

It is well-known that the far field of an arbitrary antenna may be calculated from near-field measurements. Among various possible nearfield scan geometries, the planar configuration has attracted considerable attention. In the past the planar configuration has been used with a probe scanning a rectangular geometry in the near field, and computation of the far field has been made with a two-dimensional fast Fourier transform (FFT). The applicability of the planar configuration with a probe scanning a polar geometry is investigated. The measurement process is represented as a convolution derivable from the reciprocity theorem. The concept of probe compensation as a deconvolution is then discussed with numerical results presented to verify the accuracy of the method. The far field is constructed using the Jacobi-Bessel series expansion and its utility relative to the FFT in polar geometry is examined. Finally, the far-field pattern of the Viking high gain antenna is constructed from the plane-polar near-field measured data and compared with the previously measured far-field pattern. Some unique mechanical and electrical advantages of the plane-polar configuration for determining the far-field pattern of large and gravitationally sensitive space antennas are discussed. The time convention exp (j omega r) is used but is suppressed in the formulations.     

基于傅立叶变换频移特性的平面近场测试方法

为了满足快速和无相测试现场天线的需求,文中提出了一种基于傅立叶变换频移特性的平面近场测 试方法。该方法采用多探头技术,利用各个通道的移相,达到天线角域的移动,实现了任意指向角信号的采集,具有 测试快速、使用便捷的特点,特别适用于天线的大规模生产测试和现场测试等。对一个标准喇叭天线进行了平面近 场扫描测量,对比了用传统近场数据处理插值方式得到的和用频移性质得到的天线远场方向图(E 面)。实验显示, 该方法具有与传统近场测试方法相同的效果,能有效地测试天线方向图。     

Phaseless bi-polar planar near-field measurements and diagnosticsof array antennas

Antenna near-field measurements typically require very accurate measurement of the near-field phase. There are applications where an accurate phase measurement may not be practically achievable. Phaseless measurements are beginning to emerge as an alternative microwave antenna measurements technique when phase cannot be directly measured. There are many important aspects for successful implementation of a phaseless measurement algorithm. This paper presents appropriate phaseless measurement requirements and a phase retrieval algorithm tailored for the bi-polar planar near-field antenna measurement technique. Two amplitude measurements and a squared amplitude optimal sampling interpolation method are integrated with an iterative Fourier procedure to first retrieve the phase information and then construct both the far-field pattern and diagnostic characteristics of the antenna under test. In order to critically examine the methodologies developed in this paper, phaseless measurement results for two different array antennas are presented and compared to results obtained when the near-field amplitude and phase are directly measured     

On the characterization of a reflector impulse radiating antenna (IRA): full-wave analysis and measured results

There is a growing demand for impulse radiating antennas (IRAs) to receive and transmit short pulses. The basic concepts of IRA are reviewed and the far-field pattern versus frequency of an ideal IRA is characterized based on the fundamental properties of IRA. It is shown that the transmitted pulse is ideally in the form of a time derivative of the input pulse. The physical optics simulation results show that the far-field characteristics of a parabolic reflector are very close to an ideal IRA if it is fed properly. The reflector IRA was constructed, analyzed and measured at UCLA. The near-field and far-field characteristics of the reflector IRA are studied using both the method of moments (MoM) full-wave simulations and the frequency domain measurements. In this paper, the radiation mechanism of the reflector IRA is studied using a detailed current distribution on the parabolic reflector and the feeding structure at different frequencies. Applying either the calculated current distribution on the reflector IRA or the measured near-field results, it is seen that the aperture field intensity of the parabolic reflector is not the same in the two principle planes and as a result the beam-widths in the two principle planes are different. The far-field patterns of the antenna are measured and the calculated far-field patterns support the measured results. The calculated current distribution results provide a guideline on how to properly change the feeding structure to achieve a more uniform aperture field and increase the antenna radiation efficiency.     

Far-field pattern determination from the near-field amplitude ontwo surfaces

The possibility of determining the far field of radiating systems by measuring only the near-field amplitude is investigated. The main difficulties of the problem are examined in some detail and a new near-field/far-field transformation technique is developed, based on the measurement of the near-field amplitude over two surfaces surrounding the antenna under test. The accuracy of the far-field reconstruction results are related both to the distance between such surfaces and to some a priori information concerning the near-field phase and/or the radiating system. The information on the radiating system allows relaxation of the need for any information on the near-field phase provided that the distance between the measurement surfaces is high enough. Conversely, the knowledge of a more or less corrupted near-field phase allows reduction of such distances without affecting the accuracy of the far-field reconstruction. Numerical examples validating the effectiveness of the developed algorithm are provided for the planar scanning case     

Linear spiral sampling for the bipolar planar near-field antennameasurement technique

This paper investigates linear spiral sampling for bipolar planar near-field antenna measurements. This sampling scheme is, depending on range implementation, the most rapid polar near-filed data acquisition mode. The near-field to far-field transformation is performed using a modified optimal sampling interpolation (OSI)/fast Fourier transform (FFT) approach. Measured far-field pattern results for a waveguide-fed slot array antenna are presented and are shown to have excellent agreement with results obtained from a conventional bipolar measurement     

基于未知源域重构的无相位近场测量技术

天线的远场对于研究天线辐射特性具有重大意义,由于远场的直接测量有着诸多限制,近场测量技术计算远场因其简洁准确的特点得到广泛应用. 然而,传统的近场测量技术要求获取近场区的幅度和相位分布才能发挥作用,随着天线频率的升高,人们想要在近场区获取准确的相位信息变得十分困难. 为了解决该技术难题,文中提出一种无相位近场测量技术. 利用一个封闭面上的幅度信息重建或猜测出包围待测天线的球面切向电场分布,并采用遗传算法进行全局优化,其最初为四组随机数据,经过数次优化后将逐渐接近准确结果. 仿真结果表明,本文方法能够在忽略相位信号的前提下,计算出准确的远场辐射特性.     

FFT applications to plane-polar near-field antenna measurements

The four-point bivariate Lagrange interpolation algorithm was applied to near-field antenna data measured in a plane-polar facility. The results were sufficiently accurate to permit the use of the FFT (fast Fourier transform) algorithm to calculate the far-field patterns of the antenna. Good agreement was obtained between the far-field patterns as calculated by the Jacobi-Bessel and the FFT algorithms. The significant advantage in using the FFT is in the calculation of the principal plane cuts, which may be made very quickly. Also, the application of the FFT algorithm directly to the near-field data was used to perform surface holographic diagnosis of a reflector antenna. The effects due to the focusing of the emergent beam from the reflector, as well as the effects of the information in the wide-angle regions, are shown. The use of the plane-polar near-field antenna test range has therefore been expanded to include these useful FFT applications     

基于多个分数阶次的复杂光场相位恢复算法

给出了一种基于多个分数阶次的复杂光场相位恢复迭代算法。首先利用输入面和两个较高分数阶输出面上的强度信息,恢复出输入面相位分布的轮廓,然后再利用输入面和两个较低分数阶输出面,进一步恢复出相位分布的细节。分别针对具有缓变相位、随机相位分布的光场,进行了二维相位分布的恢复,都得到了良好的恢复结果。最后在一维情形下分析了探测噪声和光路位置调整误差对算法稳定性的影响。