A hybrid scheme of signal process techniques to improve the measurement accuracy of antenna radiation patterns inside an anechoic chamber

Abstract

Antenna measurement inside an anechoic chamber can significantly suffer from measurement inaccuracy due to the scattering from the shielding walls and internal structures, if the space is not sufficiently large and the absorbers have not significantly reduced the multipath signals, which raises multipath interference. This paper develops a hybrid scheme that integrates the concepts of signal processing techniques including time gating, matrix pencil and multiple signal classification methods to reduce the multipath effects and improve the measurement accuracy. Characteristic comparison between individual method as well as the hybrid scheme will be performed based on experimental examinations.     

A 100-1000 MHz field strength standard for an anechoic chamber

A 100-1000 MHz range field strength standard using a short broadband dipole antenna has been developed for use in an anechoic chamber. The broad bandwidth of the standard antenna reduces calibration time and reduces the calibration differences which occur when the standard antennas must be changed for broadband calibration. The enclosure of the system in the anechoic chamber eliminates the interaction of the radiation with the neighboring environment, and ensures that the measurements are unaffected by weather. Error, due to reflection waves from each of the walls, the floor, and the ceiling of the chamber, was reduced by measuring the insertion loss with very closely spaced antennas, and by compensating the near-field effect theoretically. This frequency range is covered by only two standard antennas, and the field strength standard has been established with one-sigma uncertainty within ±1.6%     

5m法微波暗室性能研究

在研究暗室性能评估指标的测试标准基础上,制定5 m法暗室性能评估指标的测试方案,通过对5 m法暗室的归一化场地衰减、场地电压驻波比和场均匀性进行测试和分析,验证了5 m法暗室在电磁兼容测试中的可行性。     

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     

Radiated immunity tests: reverberation chamber versus anechoic chamber results

This paper concerns the comparison between reverberation chamber (RC) and anechoic chamber (AC) measurements: In particular, the case of an immunity test is considered. A two-wire transmission line is adopted as a device under test (DUT), and the current induced on the line by the external field is monitored to construct a possible susceptibility profile. Both the averaged current over stirrer rotation and the maximum current are considered to show how robust the RC measurement is against the positioning and the orientation of the DUT inside the chamber. As expected from theory, the maximum value is related to the average one by means of the number of the independent positions of the stirrer. Finally, it is highlighted how in the RC it is possible to lose some worst case situations, related to a particular incident field polarization and incoming direction, and the underestimation of the induced current depends upon the chosen number of stirrer positions.     

NIM球面近场法天线校准装置的测量不确定度评定

介绍了中国计量科学研究院（NIM）开发的一套精密球面近场扫描法天线校准装置(400 MHz～110 GHz)在测量天线归一化方向图（限于幅度）时的不确定度评定。以“自我比较法”为基础,简介了探头、安装对准、数据采样和射频系统等引入的18个不确定度分量的评定结果,重点针对天线暗室反射引入的不确定度不易评估的难题,基于射线追踪法提出了一种分析、测量和计算相结合的“干扰法”。评估结果表明该套近场系统在-40 dB副瓣电平内,重复性优于0.1 dB (26 GHz)、在忽略探头极化误差时的扩展不确定度优于2.7 dB。最后分析了球面近场天线测量的不确定度特点。     

消声水池声场的仿真计算

消声水池的声场计算对消声水池尺寸的确定和所敷设的吸声材料参数的选择十分重要。利用虚源方法建立了消声水池声场计算的声场模型,该模型考虑了二次反射、吸声系数随入射角变化、有指向性声源等多种情况。利用声场模型对水池的声场进行了计算,分别考虑了点声源、吸声系数随入射角变化、二次反射和指向性声源等情况。通过对不同条件下消声水池声场的计算仿真,分析了不同因素对水池自由场的影响,得到了具有一定应用价值的结论。     

之江实验室声学实验室设计和性能测试

之江实验室声学实验室包括消声室、半消声室、混响室和听音室,结合实验楼整体布局,确定了声学实验室内部结构尺寸,提出了声学设计性能要求,为类似声学实验室的设计和规划提供参考。建成后,按照JJF 1147、JJF 1143和GB/T6881.1-2002分别对消声室、半消声室、混响室和听音室声学性能进行了测试,结果表明,该声学实验室达到了预期设计目标,可提供高精度的声学环境,为之江实验室开展相应的声学研究提供了基础环境条件支撑。     

Assessment of a TD-Based Method for Characterization of Antennas

Antenna-characterization measurements are traditionally performed in the frequency domain (FD) through a vector network analyzer (VNA) in an anechoic chamber. Nevertheless, the high cost of the required setup strongly limits the possibility of using this approach. Starting from these considerations, a time-domain (TD)-based approach for characterizing antennas without using an anechoic chamber is assessed. As a matter of fact, instruments operating in TD are usually less expensive than VNAs; nevertheless, with appropriate data processing, they provide as much information. Particularly, it is demonstrated that the selection of an optimal time windowing is the main factor that guarantees a high accuracy level in the corresponding FD. The proposed approach leads to the accurate evaluation of the reflection scattering parameter S ₁₁(f) from time-domain reflectometry (TDR) data. The experimental validation is tested on a commercial radio-frequency identification (RFID) reader antenna, and the results are compared with reference VNA measurements performed in an anechoic chamber. The ultimate goal of this paper is to demonstrate that, through calibrated TDR measurements, along with an optimal time windowing, an accurate antenna characterization can be achieved.     

不同界面形状分层消声覆盖层声特性的实验研究

研究了不同界面形状的分层消声覆盖层的吸声性能。制备了三角形、半圆形、矩形和平面形等不同界面形状的分层消声覆盖层,并在声管中测试了其水声吸声系数。结果表明:在研究的频率范围内,非平面界面形状的分层消声覆盖层吸声性能优于平面界面形状的分层消声覆盖层的吸声性能,其中,半圆形界面形状的分层消声覆盖层吸声效果最好。原因在于声波在非平面界面上会发生波型转化,使声衰减能力弱的纵波转化为声衰减能力强的切变波,引起较大的剪切变形,入射波能量被大量地消耗。研究说明,合理设计分层消声覆盖层界面形状可以提高其水声吸声性能。     

混合型空腔结构覆盖层吸声性能研究及其优化设计

基于有限元法研究了以空气为背衬的混合型空腔结构覆盖层的吸声特性。建立了具有混合型空腔结构的覆盖层有限元模型,对其进行吸声特性数值仿真分析。结果表明,该空腔结构的吸声特性明显优于相同穿孔率的单腔结构。通过优化设计,进一步提升了混合型空腔结构覆盖层在全频段的吸声性能,并得到了若干覆盖层结构参数影响其吸声性能的规律。     

消声水池中弹性球回声的测量与标定

在消声水池中对直径范围为2cm～5cm的钢球进行了回声测量。对长脉冲和短脉冲入射声信号的回声信号进行了分析比较。研究了目标的弹性作用在这两种情况下对回声的影响。通过对标准钢球回声测量结果与解析计算结果的比较,检验了消声水池目标回声测量的精度,并为其他非标准目标回声测量提供对比标定的依据。     

满足新标准的智能电能表射频电磁场抗扰度测试系统设计

该文针对GB/T17215.211-2006的要求,提出一种以电波暗室为核心的电能表射频电磁场抗扰度测试系统方法。给出了硬件配置和软件流程图,分析了关键技术。由于LabVIEW的开放性,该系统可以应用于不同的EUT和仪器配置。     

Procedural aspects of the certification of anechoic chambers

The error in measuring the characteristics of anechoic chambers by plotting radiation patterns is analyzed. It is shown that the result of measurements is an estimate of the local reflectivity with errors, due to the nonuniqueness of the solutions of the initial measurement equations and the discreteness of the measurement data obtained. Ways of reducing the errors in estimating the local and integral reflectivities are proposed.     

Radar cross section measurements using near-field radar imaging

In this paper a technique to obtain the far-field scattering signature of bodies, using near-field measurements, is proposed. The method is based on near-field radar imaging techniques. The backscattered field data are collected in a controlled environment over a large frequency band and aspect angle using a near-field antenna. A focused radar image of the body is generated. Probe correction to compensate for the radiation pattern of the interrogating antenna is conducted during the two-dimensional imaging of the object. The contribution from each scattering center to the total backscattered far-field is obtained from the radar image. The proposed technique is applied to obtain the far-field radar cross section (RCS) for an object from near-field measurements conducted in an anechoic chamber at the University of Pretoria, South Africa     

大型风冷冷水机组工况试验室声学设计

以实际工程为例,介绍了在大型风冷冷水机组性能试验室中如何进行试验室声学设计,在满足大型风冷机组性能试验的基础上,在兼顾工况试验所需要的温度变化、湿度变化以及气流组织需要的同时,考虑噪声测试的特殊需要,采取合理组织气流走向等技术措施,保证大型空调冷冻设备性能试验室内的声场效果达到预期要求。     

消声瓦声参数匹配与水下目标的回波消声效果

覆盖消声瓦是水下目标隐身的一个主要方法,对敷瓦消声效果的预报是敷瓦工程的一个重要环节。预报的关键是对消声瓦吸声效果的数值分析和目标回波强度的计算方法。本文分析了消声瓦的吸声机理,据此,采用传递矩阵法和参数匹配方法求得敷瓦多层结构在任意方向的反射系数,再通过物理声学方法计算目标回波强度,给出预报值,并同实验结果进行了比较。     

一种新的消声室声压级的计算方法

根据国标JJF 1147-2006计算反平方律声压级时出现了不符合常识的现象,提出一种新的计算消声室内声压级的方法,将声压级随着距离的衰减量与声压级在空气中的衰减量分开计算,并且使用声压级偏差的平方和最小为判据计算反平方律声压级.此方法能很好地改变上述现象,而且在低中高频具有普遍性.     

Amplification and calibration for miniature E-field probes

The amplification and signal-conditioning system for a miniature nonperturbing RF E-field probe is described. A simple calibration procedure using an X-band slotted waveguide is presented. It requires less power and space than conventional techniques requiring antenna measurements in an anechoic chamber. Measurement results demonstrate relatively small field perturbation due to the probe; and a region in the waveguide where the field is relatively uniform and suitable for calibration. Calibration accuracy is further established by comparing results with those obtained from antenna measurements in an anechoic chamber. To establish the calibration technique, the probe-amplification system is analyzed, leading to a gain equation relating the output voltage and measured field intensity, which is experimentally verified     

Scattering simulations in inhomogenous volumes for scanning near-field optical microscopy

Abstract

This paper describes finite-element techniques to simulate scattering of electromagnetic radiation from objects in inhomogeneous solution spaces. The motivation for the work is the development of software to model field interactions at surfaces for scanning near-field optical microscopes. The calculation is performed in a computational anechoic chamber—a finite volume surrounded by an absorbing layer to simulate free space. The volume may consist of any configuration of materials, including lossy dielectrics and ferrites. The first step in the procedure is to find a distribution of element current sources consistent with the absorbing boundaries that generate the desired unperturbed wave solution. The base solution is not limited to simple plane waves. It may consist of any valid electromagnetic disturbance including mixed propagating and evanescent waves. The second step is to introduce one or more scattering objects and to solve finite-element equations for the perturbed fields. One advantage of the approach is that the boundaries need only absorb the scattered field components. Another useful feature for the microscopy calculations is that the method is equally effective for near and far fields. In simulations of small object scattering the absorbing boundary can be at a distance much less than a wavelength.