Far-field accuracy investigation using modulated scattering technique for fast near-field measurements

Near field measurement techniques in conjunction with near-field to far-field transformation algorithms are widely used today. Two of the most important concerns are, firstly, the degree of accuracy achieved, and secondly, the measurement duration. Although high degrees of accuracy can be obtained, the time required to scan completely the near field of an antenna using the classical near-field measurement techniques is rather long. The modulated scattering technique would offer a means to reduce this time by a factor of 10 to 100 while maintaining a reasonable degree of accuracy. Using this technique, however, one introduces further sources of inaccuracy such as the mutual coupling between the elements of the array used to probe the test antenna, and the further limitation of the available measurement dynamic range. In this paper, these two sources of inaccuracy inherent in this technique or other techniques which use a similar set-up, are explored. Multiple reflections between the test antenna and the probe array are ignored. A parabolic reflector is chosen as the test antenna, and an array of dipoles is chosen as the probe antenna in the numerical simulation.     

一种实用的相控阵近场诊断新方法

提出了一种相控阵天线近场诊断的新方法.传统的方法要诊断出相控阵天线单元的激励,必须已知阵列单元的方向图和探头的方向图.文中基于相控阵天线的激励、单元方向图、探头方向图和近场测量数据之间的关系,得到了相控阵天线的激励和近场测量数据之间的耦合方程.利用多项式插值,在不必已知单元方向图和探头方向图的情况下,求解出相控阵天线的单元激励.     

球面近场测试高阶探头补偿算法及其在超宽带探头上的应用

为了提高基于超宽带探头的球面近场天线测试系统精度,相应的探头补偿算法需要考虑超宽带探头的高阶方位模式. 文中采用文献[3]中基于球面波的迭代法方案实现了高效高精度的高阶探头补偿算法,并将其应用到一种工作在2～18 GHz的超宽带双脊喇叭探头中. 同时以偶极子阵列为例,研究了本文算法相较于传统低阶算法的精度优势,测试了该算法在多种条件下的收敛性. 结果显示:在相同条件下,高频端比低频端的高阶补偿效应更加明显;当待测天线完全落在该探头的主瓣6 dB宽度区域内时,算法均可以在几次（小于10）迭代后达到理想的精度. 因此,本文算法可以有效地提高基于超宽带探头的球面近场测试系统的精度,并且具有较高的单机计算效率.     

An overview of near-field antenna measurements

After a brief history of near-field antenna measurements with and without probe correction, the theory of near-field antenna measurements is outlined beginning with ideal probes scanning on arbitrary surfaces and ending with arbitrary probes scanning on planar, cylindrical, and spherical surfaces. Probe correction is introduced for all three measurement geometries as a slight modification to the ideal probe expressions. Sampling theorems are applied to determine the required data-point spacing, and efficient computational methods along with their computer run times are discussed. The major sources of experimental error defining the accuracy of typical planar near-field measurement facilities are reviewed, and present limitations of planar, cylindrical, and spherical near-field scanning are identified.     

Near- and Far-Field Characterization of Planar mm-Wave Antenna Arrays with Waveguide-to-Microstrip Transition

We present the design and characterization of planar mm-wave patch antenna arrays with waveguide-to-microstrip transition using both near- and far-field methods. The arrays were designed for metrological assessment of error sources in antenna measurement. One antenna was designed for the automotive radar frequency range at 77 GHz, while another was designed for the frequency of 94 GHz, which is used, e.g., for imaging radar applications. In addition to the antennas, a simple transition from rectangular waveguide WR-10 to planar microstrip line on Rogers 3003? substrate has been designed based on probe coupling. For determination of the far-field radiation pattern of the antennas, we compare results from two different measurement methods to simulations. Both a far-field antenna measurement system and a planar near-field scanner with near-to-far-field transformation were used to determine the antenna diagrams. The fabricated antennas achieve a good matching and a good agreement between measured and simulated antenna diagrams. The results also show that the far-field scanner achieves more accurate measurement results with regard to simulations than the near-field scanner. The far-field antenna scanning system is built for metrological assessment and antenna calibration. The antennas are the first which were designed to be tested with the measurement system.     

Evaluation des cadences de mesure de champs proches au moyen de sondes modulées

The problems involved in the direct far-field measurements of large antennas have led to the development of the near-field measurement technique. According to this method, the far-field pattern of the antenna is calculated from the near-field measurements close to the antenna. The only inconvenience in this technique is the slow rate of measurements. This slowness is due to the mechanical displacement of the measuring probe or the test antenna. The modulated scattering technique is a method to reduce the measurement time while preserving acceptable levels of accuracy. This article is mainly concerned with estimating the possible measurement rates in typical configurations.     

An examination of the theory and practices of planar near-fieldmeasurement

Using computer simulation, several fundamental issues in planar near-field measurement are examined. The results indicate that some of the prevailing views of practices regarding the evanescent modes, the sampling and filtering of data, and the selection of the location and directivity of the probe are incomplete or misleading. In particular, the merits of using smaller low-directivity probes in conjunction with a closer probe-to-antenna distance have been found to be unduly overlooked     

基于物理光学法的近场多入多出雷达成像模拟

针对点目标扩展函数(PSF)不能有效分析复杂目标在毫米波近场多入多出(MIMO)雷达成像中的散射机理问题，研究了一种基于近场物理光学散射计算数据的毫米波MIMO雷达成像模拟方法。该方法利用近场物理光学方法，获得包含阵列构型和目标散射信息的近场计算数据，并通过近场MIMO成像处理器实现近场MIMO成像的全过程模拟。利用D波段“T”字型二维稀疏MIMO阵对复杂的三维目标开展了近场成像实验，仿真和实验结果表明，模拟结果与实际成像结果有很好的一致性。该方法能够分析近场MIMO成像系统的成像性能，为近场MIMO成像的阵型设计提供支撑，揭示复杂目标的近场散射特性与成像机理。     

Modified $theta $-Scanning Technique for First/Third-Order Probes for Spherical Near-Field Antenna Measurements

This paper presents a modified $theta $-scanning technique for first/third-order probes for spherical near-field antenna measurements. Unlike the traditional $theta $-scanning technique, this new scanning technique gives a possibility, due to the cutoff property of the azimuthal spherical modes, to filter out the influence of the undesired third-order azimuthal modes of the probe near the poles of the measurement sphere. Without increasing the measurement time, the technique allows reducing the errors caused by the application of the computationally efficient first-order probe correction technique (incorrectly) to first/third-order probes. The technique is optimal for spherical near-field systems, that employ, for example, an open-ended rectangular (or square) waveguide probe, that closely approximates a first/third-order probe, and apply the well-known first-order probe correction technique. In such systems, compared to the traditional $theta $-scanning technique, the modified $theta $-scanning technique can be used to significantly reduce the errors caused by the incomplete probe correction.      

Study on Magnetic Probe Calibration in Near-field Measurement System for EMI Application

Near-field measurement, as an efficient method for studying the electromagnetic interference (EMI) problem, is becoming increasingly important. The calibration of the near-field probe is a critical part in the measurement procedure. This paper presents a fast and effective calibration method of magnetic probe. The factors that influence the calibration method is analyzed and discussed. Two kinds of calibration structures are designed and fabricated to determine the probe factor (PF) of two magnetic probes, which are horizontal magnetic field probe and vertical magnetic field probe, respectively. Moreover, PF is obtained through comparing the measurement data with the simulation data of the same calibration structure. Another sample is designed and fabricated to verify the obtained PF and the calibration method. The measurement results match simulation results well with the relative errors at the “large signal region” less than 20%, which indicates a good accuracy of the calibration method.     

Test zone field compensation

Test zone field (TZF) compensation increases antenna pattern measurement accuracy by compensating for extraneous fields created by reflection and scattering of the range antenna field from fixed objects in the range and by leakage of the range RF system from a fixed location in the range. TZF compensation can be used on fixed line-of-sight (static) far-field, compact, and near-field ranges. Other compensation techniques are seldom used in practical measurement situations because they are limited in the amount of compensation they provide. These techniques do not adequately model the type of extraneous field present in the range or require increased measurement time and equipment necessary to implement the technique. TZF compensation overcomes these limits as follows. The TZF is measured over a spherical surface encompassing the test zone using a low gain probe. The measured TZF is used antenna pattern measurements to compensate for extraneous fields. TZF compensation theory is presented and demonstrated using measured data     

Accurate determination of planar near-field correction parametersfor linearly polarized probes

A procedure used by the US National Bureau of Standards (NBS) for accurately determining the plane-wave receiving parameters of both single- and dual-port linearly polarized probes is described. Examples are presented, and the effect of these probe receiving characteristics in the calculation of the parameters for the antenna under test is demonstrated using the required planar near-field theory. The planar near-field theory necessary to accomplish probe correction and to formulate probe parameter errors is presented in a concise and meaningful way to help understand when probe correction is or is not needed     

基于扫描探针显微镜的近场超空间分辨指纹光谱技术研究现状

基于扫描探针显微镜的近场超空间分辨指纹光谱技术在分子识别及组分鉴别方面具有极大的应用前景.扫描探针显微技术与不同的光谱联合使用,发展出了不同的具有纳米级分辨的指纹光谱技术,其中包括针尖增强拉曼散射光谱技术、纳米级分辨率的傅里叶变换红外光谱技术及散射式的扫描近场太赫兹光谱技术.这三种散射式的扫描近场光学显微技术在实现方式上有所不同,在近场指纹识别方面可以相互补充.该综述主要对三种近场超空间分辨指纹光谱技术的特点进行了深入地分析和比较,并且对这三种技术的研究现状及应用进行了总结.     

A two probes scanning phaseless near-field far-field transformationtechnique

An innovative and effective technique to determine the far-field of a radiating system from near-field intensity data is introduced, analyzed, and tested. The approach is based on the simultaneous measurement of the amplitude of the voltages received by two different probe antennas moving over a single scanning surface in the near zone and performs the phase retrieval of the near-field by assuming as unknown the plane wave spectrum of the field. The radiated field is then straightforwardly evaluated. As compared to the existing phaseless measurement techniques, the use of two different probes makes it possible to avoid the need for a second scanning surface and thus allows the use of smaller (and cheaper) anechoic chambers. Furthermore, the measurement time is essentially equal to that required by conventional techniques based on the measurement of the complex near-field. The reliability and the effectiveness' of the approach are investigated and discussed and the key factors affecting its behavior are highlighted. In particular, the relevance of the difference between the plane wave spectra (PWS) of the two probe antennas in ensuring an acceptable reliability of the solution, with respect to the starting point of the procedure, is outlined. Finally, the effectiveness of the approach is confirmed by an extensive numerical analysis, which also shows the stability of the solution against data noise     

近场辐射电磁干扰模态测试系统设计

提出近场辐射电磁干扰模态测试方法,设计近场模态检验测试系统,采用近场电磁场头对待测设备进行扫描式测量,获得待测设备的近场电磁场分布情况,并根据测得电磁场强度大小可分析得到待测设备的辐射EMI模态。实验结果表明,该方法可对电子电路的近场辐射EMI模态进行有效识别和检验,分别得到近场辐射共模噪声和差模噪声EMI模态,为辐射电磁干扰噪声的抑制提供有益参考。     

Electric field probes--A review

Electric field probes consisting of a dipole antenna, RF detector, nonperturbing transmission line, and readout device have been implemented in a variety of ways. Three orthogonal dipoles are generally used in anE-field probe to provide a response which is nearly isotropic for all polarizations of the incident field. Diode detectors have been used with electrically short or resistivity loaded dipoles to produce very broadband devices (0.2 MHz to 26 GHz). Thermocouple detectors are used to provide true time-averaged data for high peak-power modulated fields. Optical fibers, together with a suitably modulated light source, may be used to form a wide-band nonperturbing data link from the dipole and detector to a remote readout. Application ofE-field probes range from the measurement of fields in living animals exposed to nonionizing radiation to the measurement of fields in air for electromagnetic compatability or radiation safety purposes. Probes are available that can measure field strengths from less than 1 V/m to over 1000 V/m (rms).     

A First/Third-Order Probe Correction Technique for Spherical Near-Field Antenna Measurements Using Three Probe Orientations

A probe correction technique is described for spherical near-field antenna measurements based on sampling the near field for three probe orientations in each measurement direction. The technique applies to odd-order probes whose radiated field contains (significant) power only in the first (mu = plusmn1) and third- order (mu = plusmn3) azimuthal spherical modes. The technique is ideally suited as an optional probe correction technique for high-accuracy measurements in existing measurement systems that employ a rectangular or square waveguide probe and the traditional first-order probe correction technique.     

聚焦离子束在光纤探针制备技术中的应用

本文概述了利用聚焦离子束制备用于近场光学显微镜光纤探针的方法,讨论了探针的锥型刻蚀、孔径控制和特殊结构加工等;论述了聚焦离子束的工作原理和在光纤探针高精度加工方面的优势。利用此技术制备的光纤探针的锥型和针尖孔径精确可控,并具有高光洁度,高通光效率等特点。     

Tip-Shape Reconstruction for a Laterally Vibrating SPM Probe

This study is concerned with the tip-shape reconstruction for the shear-force scanning probe microscope and the near-field scanning optical microscope, in which the probe executes lateral vibrations. The spatial resolution of the microscopes is directly dependent on the tip radius. A reconstruction method is proposed that employs specially designed test structures and is based on deconvolution. The method is used to generate images of tungsten and nickel wire probes, fabricated by electrochemical etching, and near-field optical-fiber probes. The results are verified by TEM imaging of the probes. By the same approach, correlation is revealed between reconstructed probe aperture and resolution for the near-field optical microscope.     

Tailoring modal power distribution in common-core waveguide arrays

In this paper, the scattering matrix method (SMM) is used to analyze the modal properties of evanescently coupled waveguide arrays with cores spaced equidistant from a common central core. Propagation constants and field distributions of the fundamental in-phase supermodes are obtained for waveguide arrays comprising three, four, five, six, and seven cores. The authors show how the coupling strength among individual cores can be controlled by adjusting the properties of the central core, thereby providing a means of tailoring the near-field mode profile. By properly selecting the parameters of the central core, the authors also show how an equal power distribution among all cores can be achieved. A seven-core waveguide array is discussed in detail including the effects of varying core spacing and central core parameters on the supermodes and dispersion properties of the array.