Prediction of ground multipath parameters from range-gain measurements using Prony?s technique

Prony's technique is used to estimate multipath parameters from range-gain patterns produced by ground multipath interference in line-of-sight radio links. The field distribution at the transmitting antenna side is obtained by digital reconstruction from the range-gain pattern that is recorded, at constant height, along ground surface. The technique is presented as a competitive alternative to the Fourier transform, where much shorter data windows are sufficient for the proposed technique. The technique is validated by calculated and measured range-gain patterns, and the predicted values are in good agreement with the actual ones. Prony's technique produced predictions with comparable errors to the Fourier technique from much smaller data windows.     

NIM反射试验场电性能评估核心技术研究

评测中国计量科学研究院(NIM)新建反射试验场测试装置的准确性,需要足够准确的基准值。通过分析对比矩量法模型与实测模型,设计制作了一种小馈源偶极子天线,根据矩量法准确性与收发天线间距无关这一特性的近场法,分析了近场法在实测中的误差缩减效应,然后据此验证了基准值的准确性(在30 MHz~1 GHz频段24个典型频率点的场地插入损耗偏差小于0.22 dB,相当于天线系数误差小于0.11 dB)。在30 MHz~1 GHz频段10 m距离条件下对NIM新建测试装置的评测结果为:在24个典型频点,水平极化时偏差小于0.26 dB,垂直极化时偏差小于0.34 dB;在频率间隔1 MHz的扫频范围内,垂直极化时偏差小于0.6 dB。     

Two improved algorithms with which to obtain contoured windows for fringe patterns generated by electronic speckle-pattern interferometry

Fringe patterns generated by electronic speckle-pattern interferometry are full of high-spatial-frequency and high-contrast speckle noise. Filtering with contoured windows has proved to be an efficient approach to filtering out speckle noise while retaining the fringe patterns. Furthermore, with contoured windows the contoured correlation fringe pattern method can be used to derive smooth, normalized, consistent fringes. Contoured windows previously were determined by fringe orientation only, and this process generated accumulated errors. We propose two new algorithms with which to obtain the contoured windows according to the fringe intensity slope and the distance ratio to neighboring skeletons. These new techniques can determine contoured windows more precisely.     

A free-space bistatic calibration technique for the measurement ofparallel and perpendicular reflection coefficients of planarsamples

A free-space bistatic measurement system suitable for operation in the frequency range of 5.85-40 GHz is calibrated to measure the parallel and perpendicular reflection coefficients of metal-backed planar samples for obliquely incident waves. The measurement system consists of transmit and receive antennas in the bistatic configuration, mode transitions, precision coaxial cables, and the network analyzer. Diffraction effects of the edges of the sample are minimized by using spot-focusing horn lens antennas, which focus most of the energy on a one-wavelength-diameter circular section of the sample. A new free-space bistatic calibration technique is developed to eliminate errors due to multiple reflections between transmit and receive antennas via the surface of the sample. The effect of defocusing due to the obliquely incident plane wave with focused antennas is minimized by introducing correction factors which modify measured reflection coefficients. Details of the calibration procedure and a discussion of the experimental results obtained for planar samples of Teflon and Eccogel 1365-90 in the frequency range 12.4-18 GHz are presented     

30-1000 MHz field strength standard developed in anechoic chamber

An accurate electric field strength for the frequency range of 30 MHz to 1000 MHz has been developed in a full anechoic chamber with 1-Σ uncertainty less than ±1.9%. Reflection parameters of walls at frequencies below 200 MHz are evaluated experimentally, and the errors due to these waves are compensated in the standard and calibrations of the antennas     

Inkjet-printed patch antenna emitter for wireless communication application

This research focuses on exploring low-cost and rapid production solutions for fabricating emitters for patch antennas for wireless communication applications. Additive manufacturing technique is employed to fabricate two patch antennas using silver nanoparticle ink on FR4 substrate. Finite-element simulation software, HFSS is used to analyse and predict the theoretical performance of the antenna designs for 2.4?GHz MIMO and 6?GHz wireless data transmission. The fabricated antennas have resonant frequencies closely matching the design values. The work provides a viable solution for fabricating emitters and finally antennas commercially using inkjet printing platform, thus overall reducing the cost and simplifying the process.     

An estimate of the instant when gravitational impulses occur taking anomalous errors into account

The probability of making a reliable estimate when measuring the unknown instant of the occurrence of a gravitational impulse with a partially known initial phase for cryogenic resonant gravitational antennas is calculated. The theory of overshoots of stationary random processes is used to analyze anomalous errors, assuming Gaussian additive interference. __________ Translated from Izmeritel’naya Tekhnika, No. 3, pp. 7–10, March, 2007.     

基于小波变换的结构模态参数识别

及时、准确地识别出结构的模态参数是结构健康监测与损伤识别的重要前提。小波分析是众多识别方法中较优越的一种，因其在时一频两域都具有表征信号局部特征的能力，近年来这一方法在线性及非线性系统的参数识别中开始应用。探讨了基于小波脊（Ridge）与小波骨架（Skeleton）的模态参数识别方法，针对小波变换中遇到的边端效应问题，提出了基于自回归滑动平均模型（ARMA）的“预测延拓”方法，并以美国土木工程师学会（ASCE）提供的Benchmark模型为例进行了数值模拟。结果表明，本文提出的方法可以有效地抑制小波边端效应，通过小渡变换可以准确地识别出结构的模态参数。     

Practical considerations in pulse-echo radar for short rangesensing

In this paper, we present the principle of operation, design, and testing of a pulse echo radar unit that utilizes the properties of short helical antennas. Data was captured for targets approaching the radar at three different controlled velocities, three different target sizes, and three radar range gate settings. These data reveal the expected Doppler frequency as well as a second anomalous frequency. The effects of multipath signals, separated transmit and receive antennas, and direct antenna coupling are used to explain this anomalous frequency. These effects are mathematically simulated, and the results compare favorably with the test data     

Viewing Strategy and Window Effects on Dynamic Visual-Inspection Accuracy

Equally-spaced product units, moving on a belt at a uniform velocity, were exposed for visual inspection over a fixed viewing window. Viewing windows were equal to the product unit interspacing and twice this distance to give respectively 1 and 2 product units within the window. Three different belt speeds were used. Subjects performed short runs of visual inspection using their self-directed strategies of viewing the sequence of product units and then these subjects repeated all conditions of this task using a “directed viewing strategy.” Improved viewing discipline was expected from this “directed” strategy and eye motion monitoring was employed to verify that the subjects used the “directed” strategy. Inspection errors of each type were observed under twelve experimental conditions. Both types of errors were found to be greater with: 1) the smaller viewing window, 2) self-directed viewing strategies in contrast to the “directed” strategy, and 3) higher belt velocities. Contrasts were also made between error types and between high- and low-performing subject groups. Inferences on the apparent cost of each error type were made from these data and compared with rational objectives. Economic implications are shown for these viewing-strategy and viewing window effects.     

Numerical model estimating the capabilities and limitations of the fast Fourier transform technique in absolute interferometry

Anumerical model was developed to emulate the capabilities of systems performing noncontact absolute distance measurements. The model incorporates known methods to minimize signal processing and digital sampling errors and evaluates the accuracy limitations imposed by spectral peak isolation by using Harming, Blackman, and Gaussian windows in the fast Fourier transform technique. We applied this model to the specific case of measuring the relative lengths of a compound Michelson interferometer. By processing computer-simulated data through our model, we project the ultimate precision for ideal data, and data containing AM-FM noise. The precision is shown to be limited by nonlinearities in the laser scan.     

损耗地面上线天线的一种近似计算方法

在普遍镜像法分析地面上垂直天线特性的基础上，提出了一种修正的镜像法，该方法能提高计算的速度．通过仿真计算以及对测量结果的比较，发现VLF天线输入阻抗随着地面电导率的改变而明显变化，而且大地的形状和地质在一定程度上影响VLF天线的发射效率。     

Amplitude Estimation by a Multipoint Interpolated DFT Approach

This paper focuses on the amplitude estimation by a multipoint interpolated discrete Fourier transform (DFT) method. Accurate results are obtained using the weighted multipoint interpolated DFT (WMIpDFT) method with maximum sidelobe decay windows. In addition, using the WMIpDFT method with maximum sidelobe decay windows, it is mathematically proven that the systematic errors affecting the amplitude estimation decrease as the number of interpolation points and/or the window order increases. Computer simulations confirm the accuracy of the derived expressions. Moreover, the influence of white Gaussian noise on the amplitude estimations has been analyzed by means of computer simulations.     

The interpolated fast Fourier transform: a comparative study

The properties of five interpolating fast Fourier transform (IFFT) methods (IFFT) are studied with respect to their systematic errors and their noise sensitivity, for a monofrequency signal. It is shown that windows with small spectral side lobes do not always result in a better overall performance of the IFFT method and that time-domain estimators can be more efficient than the analyzed IFFT methods     

Analysis of shadow and direct-feed radiation mutual coupling in paraboloid antennas

By considering the shadow region of diffracted rays and direct-feed radiation, the calculation of the power coupling between skew paraboloid antennas is modified. The skew configuration means there is an angle between the axes of two antennas, and the two antennas are placed in the back of half-space of each other. It is illustrated by considering the coupling between two identical front-fed symmetric paraboloid antennas, each of which is fed by a TE11 mode circular waveguide. The result can be used as guidance for the installation disposition of multiple antennas.     

VHF Loop Antenna Loss Measurements

The product of the loss ratios of two very small loop antennas, oriented such that their axes coincide, is given approximately by L1L2 = A(1.5)-2(1 + k2d2)-2(kd)6 where L1 and L2 are the dissipative power loss ratios of the loops, d is the spacing between the loops, and k = 2?/wavelength. A is the insertion loss measured between the ports of the two loops including their matching networks. The loops are assumed to be impedance-matched to the generator and to the load, respectively. A relationship is developed which takes into account the effects of the receiving loop current on the transmitting loop mesh. This makes possible measurements with more closely spaced loops than otherwise, without incurring intolerable errors. The minimum useful spacing depends on the loss ratios, being greater for more efficient antennas. For small antennas with practical loss ratios, the measurements can be made on the laboratory bench or in production test without special antenna test facilities. A more nearly exact field expression due to F. M. Greene is utilized for loops of appreciable size.     

Comparative robustness study of planar antennas

Is it possible to produce a planar dipole-like antenna with a reduced conductive area without any loss in either robustness or performance? The objective is to reduce the amount of expensive conductor to be used when applying a meshing technique to the printing of antennas. In this context, robustness means that the characteristics are maintained when the antenna is damaged, for example if it is scratched. This is particularly important for radio frequency identification tags in logistic systems. A general antenna robustness evaluation methodology, based on numerical simulations of a large number of randomly damaged antennas, is used for the antenna comparisons. The antenna performance degradation, based on the return loss (S₁₁) at 868 MHz, is monitored for some basic planar antennas. Finally, we show that it is possible to produce robust low-cost antennas using wire replacements for the solid planar antennas and thus, provided that the robustness requirement is moderate, replace the solid antenna with a thin conductor analogue     

A new refractometer by combining a variable length vacuum cell anda double-pass Michelson interferometer

A new refractometer with a variable length vacuum cell has been developed to eliminate errors caused by deformations in optical windows of the cell. The refractive index of air is determined by measuring the changes in the optical path difference between the air of interest and a vacuum as a function of the changes in the cell length. An optical phase modulation technique and a dark fringe detection method are used to obtain a high resolution in measuring the optical path difference by a double-pass Michelson interferometer. A combined standard uncertainty of 5×10^-9 in the measurement of the refractive index of air has been achieved     

Refractive index measured by laser beam displacement at λ=1064 nm for solvents and deuterated solvents

The refractive index of a liquid is determined with 0.0003 accuracy from measurements of laser beam displacement by a liquid-filled standard 10 mm spectrophotometer cell. The apparatus and methods are described and the results of measurements at λ=1064 nm and T=25.0 °C for 30 solvents and deuterated solvents are presented. Several sources of potential systematic errors as large as 0.003 are identified, the most important being the curvature of the liquid cell windows. The measurements are analyzed accounting for the significant imperfections of the apparatus.     

基于共轭虚拟阵列的稳健波束形成方法

针对提高阵列天线波束性能问题,本文提出了基于共轭虚拟阵列的信号导向矢量扩展方法.利用共轭虚拟阵元扩展阵列,增大了阵列孔径却不改变实际阵元数,降低了副瓣电平并且不会增加天线制造成本.在虚拟阵列的基础上对信号导向矢量进行扩展,使阵列波束形成效果更加稳健.本文通过在有无干扰以及存在幅度和相位误差情况下对11个阵元阵列天线进行...