球面近场天线测量系统校准中的一类不确定度分析

球面近场天线测量系统多探头校准时,校准用天线角度偏差会引起探头幅度相位一致性的测量不确定度.本文建立了典型的FDTD天线仿真模型,获取了包含幅度和相位信息的3D方向图仿真数据,仿真数据表明:在角度误差较小时,增益、相位误差和空间角度误差呈近似线性关系.其次,频率越高,增益和相位误差越大.本文依据仿真给出了6GHz以内标准不确定度分量概算公式,分析表明:即使考虑近场效应,本文所列概算公式也是稳妥的.     

多探头球面近场测试系统校准方法及对准角度误差分析

针对多探头球面近场天线测试系统的通道不一致性提出了校准方法,并对对准角度误差引入的近场测量幅度相位误差进行了仿真分析。分析表明,当对准角度误差Δφ=0. 5°时,引入的近场测量幅度误差0. 1dB,相位误差1°。采用高精度转台机械臂并结合激光对准等技术手段,可以将对准角度误差控制在±0. 1°之内,近场测量幅度误差及相位误差也将大幅减小。     

一种低交叉极化小口径超宽带天线的设计

在高精度近场法天线测量、平面波发生器应用等场合,工作频段通常受限于近场探头。为了克服开口波导探头的带宽限制,出现了基于Vivaldi天线的超宽带、小口径天线作为近场探头。然而,常见的Vivaldi天线是非对称结构,导致交叉极化性能较差。设计了一款低交叉极化小口径超宽带天线,采用5层对称结构改进了传统Vivaldi天线的非对称性,利用贝塞尔曲线设计渐变槽辐射结构、加载电阻和贴片以及刻蚀矩形斜槽,减小了交叉极化比和天线驻波,改善了天线辐射方向性图。该探头口径宽70 mm、长201 mm,在0.9～6 GHz频段内天线仿真所得交叉极化比优于40.9 dB,增益为-5.5～9.53 dBi,端口反射系数幅度低于-10 dB,其辐射方向性图在全频段不开裂、主波束指向不变。     

对流量测量不确定度评估中若干名词术语的看法

根据VIM(3rd)、JJF 1001-2011和JJF 1059.1-2012,对《ISO/TR 7066-1:1997 Assessment of uncertainty in calibration and use of flow measurement devices-Part1:Linear calibration relationships》、ISO 5168:2005和GB/T 29820.1-2013,对其中的若干术语、定义和符号作了初步分析,提出了一些不同看法和修改意见;分别对ISO/TR 7066-1和ISO 5168中关于“随机误差”、“系统误差”、“标准偏差和方差”;“不确定度和不确定度评定”、“重复性测量条件”,以及“灵敏度”和“线性校准方程”等定义和注解的表述进行了讨论。     

三天线法环天线校准系统建立及测量结果不确定度评定

在350kHz~30MHz频段内,为了准确得到环天线所处位置的场强,环天线的天线系数需要校准。三天线法是一种校准天线系数的绝对方法,需要3个环天线,两两组对测量,且不需要任何参考标准。介绍了三天线法校准环天线的原理,基于矢量网络分析仪建立校准系统,并评定校准系统的测量结果不确定度。基于K(i,j)的计算公式复杂,很难计算出其引入的不确定度,因此采用数字电磁学代码(NEC)建模评定K(i,j)的不确定度。评定结果表明,在350kHz~30MHz频段内4个典型频点的扩展不确定度小于0.81dB(k=2)。     

X波段空中辐射场测量中的天线设计与应用

为减小空中微波辐射场测量时极化失配带来的影响,设计了一种低轴比微带圆极化阵列天线,该天线在9.7GHz,3dB波束宽度约45°,轴比低至0.1dB。天线功率容量大于1.5kW,常温(26℃)和低温(-6℃)时天线轴比偏差小于0.1dB。应用该天线可以将极化失配不确定度减小到0.1dB以内,并具有较强的环境适应性,适用于X波段空中辐射场精确测量。     

18~26.5GHz功率密度标准装置

介绍了中国计量科学研究院研究建立的18~26.5 GHz功率密度标准装置,重点是相对于现有的1~18GHz标准装置,在喇叭天线增益确定、净功率确定、谐波抑制、场地性能改善和确认方面所作的改进工作。通过测量场地电压驻波比和探头线性,验证了标准装置的可靠性。与1~18 GHz标准装置的比对结果显示,两套标准装置在18 GHz的一致性满意,验证了18~26.5 GHz标准装置的准确性。此外还初步评估了校准结果的不确定度,校准结果的护展不确定度为0.48 dB(k=2)。     

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。     

吸波涂层雷达反射率原位测量技术

目的 为满足吸波涂层在装机条件下雷达反射率原位测量的迫切需求,提出一种基于天线近场测试的雷达反射率原位测量技术。方法 设计小型化超宽带天线、收发去耦结构以及屏蔽罩,构建原位测量探头,并与微波扫频模块和数据处理模块集成,研制出雷达反射率手持式宽频测量仪并。结果 经对比验证,在-17～0 dB反射率范围以及2～18 GHz频率范围内,该测量仪测量结果与弓形系统测量结果偏差小于1.5 dB。结论 该测量仪适用于厚度为1.5 mm以内已涂覆涂层雷达反射率的准确测量。     

采用蒙特卡洛法评定转基因水稻样品中NOS终止子的测量不确定度

采用蒙特卡洛方法(MCM)实施“概率分布传播”来评定转基因水稻样品中NOS终止子的测量不确定度,解析转基因成分测量不确定度的概率分布。评定结果表明:NOS终止子的相对含量为2.95%,非常接近理论含量(3%),而且其标准不确定度为2.13×10^-4,远小于1.00×10^-2。在95%的包含概率下,NOS终止子的相对含量分布在2.91%～3.00%非常窄的包含区间内,充分说明测量质量好,测量结果可靠;NOS终止子相对含量的概率分布呈标准正态分布,揭示转基因成分测量条件满足GUM法的假设,MCM和GUM法都可以应用于转基因成分测量不确定度评定。     

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     

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%     

Requirements imposed on the anechoic factor of anechoic chambers when measuring backscattering patterns

The quantitative requirements imposed on the echo suppression of an anechoic chamber when measuring the scattering indicatrix are obtained using a four-ray model of the interaction between the object being measured and the anechoic chamber. It is shown that, depending on the bistatic scattering, these requirements may be stricter or less rigorous than the similar requirements for antenna measurements. Translated from Izmeritel'naya Tekhnika, No. 1, pp. 43–44, January, 1996.     

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     

一种双频MIMO天线的T型枝节解耦设计

本文设计了一种T型枝节解耦的双频MIMO天线.两个工作频段分别覆盖WLAN频率2.45 GHz/5.2 GHz/5.8 GHz.低频谐振单元为倒F天线,通过在低频枝节上增加短截线,用以产生高频谐振,实现双频工作.将天线单元沿水平方向对称放置形成二单元的MIMO天线,并采用在两个天线单元之间添加T型枝节的方法进行解耦.对...     

Super Compact UWB Monopole Antenna for Small IoT Devices

This article introduces a novel, ultrawideband (UWB) planar monopole antenna printed on Roger RT/5880 substrate in a compact size for small Internet of Things (IoT) applications. The total electrical dimensions of the proposed compact UWB antenna are 0.19 λ_o × 0.215 λ_o × 0.0196 λ_o with the overall physical sizes of 15 mm × 17 mm × 1.548 mm at the lower resonance frequency of 3.8 GHz. The planar monopole antenna is fed through the linearly tapered microstrip line on a partially structured ground plane to achieve optimum impedance matching for UWB operation. The proposed compact UWB antenna has an operation bandwidth of 9.53 GHz from 3.026 GHz up to 12.556 GHz at −10 dB return loss with a fractional bandwidth (FBW) of about 122%. The numerically computed and experimentally measured results agree well in between. A detailed time-domain analysis is additionally accomplished to verify the radiation efficiency of the proposed antenna design for the ultra-wideband signal propagation. The fabricated prototype of a compact UWB antenna exhibits an omnidirectional radiation pattern with the low peak measured gain required of 2.55 dBi at 10 GHz and promising radiation efficiency of 90%. The proposed compact planar antenna has technical potential to be utilized in UWB and IoT applications.     

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.     

Dual wideband coplanar waveguide-fed notched antennas with asymmetrical grounds for multi-band wireless application

A novel single-layer planar monopole antenna is proposed for dual wideband operation. The antenna is a notched patch fed by a coplanar waveguide with two asymmetrical ground planes. The parametrical effects of the size of two such grounds and an embedded notch on the impedance matching condition have been examined theoretically. By fabricating and measuring the prototypes of the proposed antenna, two bands with 10 dB return loss bandwidths of about 490 MHz centred at 2.13 GHz band and of about 99.2% ranging from 3.32 to 6.9 GHz were obtained. A stable radiation pattern and average gains of greater than 2.6 and 4.8 dBi, respectively, over the two operating bands have also been obtained. These properties make the antenna suitable for multi-frequency wireless operation.     

Short backfire antenna with microstrip Clavin feed

A single short backfire antenna has an enclosed structure with no sharp projections and approximately 15 dBi gain, making it attractive for handheld radio monitoring and other man-portable applications. However, a microstrip patch fed short backfire antenna had a broad E-plane radiation pattern main lobe, leading to a loss of gain and low aperture efficiency. The antenna was studied using a commercially available Method of Moments software. Adding eight parasitic wires inside the cavity of a short backfire was found to narrow the E-plane radiation pattern main lobe, making it more like the H-plane radiation pattern and increasing the peak gain by 1.5 dB. A single proof of concept antenna was built at 1.49 GHz, which had a bandwidth of 2.3%, aperture efficiency of 78% and was shown to have equalised principal plane main lobes.