石英晶体元件负载谐振频率测量技术的研究

在分析与对比三种测量石英晶体元件负载谐振频率方法的基础上,设计适用于测量法的π网络与整个测量系统,采用自动网络分析仪测量晶体的阻抗,采用测量法测出负载谐振频率.实验表明,在1 MHz～200MHz频率范围内,系统对负载谐振频率重复测量一致性能达到士1×10-6以内,在30 MHz～200MHz频段,测量误差达到士2×10-6以内.     

适配器对电磁兼容射频传导耦合去耦网络阻抗测量的影响

耦合去耦网络被广泛用于电磁兼容射频传导抗扰度试验,阻抗是其校准的关键参数。为了测量耦合去耦网络的阻抗,适配器被用于连接矢量网络分析仪和耦合去耦网络的受试设备端。目前国内校准实验室普遍没有考虑到适配器对矢量网络分析仪自校准质量的影响,导致高频段阻抗模值测量结果偏差较大。因此,分别基于实验和理论计算原理,设计了同轴转换自校准法和电长度补偿计算修正法用于改善阻抗测量结果。数据表明,上述方法较好地减小了适配器的负面影响,对测量结果起到了改善作用。     

基于矢量网络分析仪功率测量的噪声系数测量方法

现有基于矢量网络分析仪进行噪声系数测量的方法必须依赖标准的噪声源,即Y系数测量法。该文提出一种通过在矢量网络分析仪源端口输出连续波信号,分别测量被测件的信号功率与信号加噪声的功率,结合校准结果和功率测量结果计算获得噪声系数的方法。通过建立测量系统的模型和理论的推导,论述该方法的原理和测量过程的噪声校准,提出的方法不需要使用经过校准具有已知超噪比的噪声源,更简单实用。     

VC环境下Smith阻抗图的实现

主要介绍用于进行电路阻抗分析、匹配网络设计的Smith阻抗图。Smith阻抗图是分析待测器件反射系数、驻波比和阻抗的重要工具，并且常用于矢量网络分析仪中。重点叙述了Smith阻抗图的基本原理、VC的图像处理和在VC环境下绘制Smith阻抗图的方法，并说明了如何在Smith阻抗图中找到某个特定高频电路的负载阻抗。     

一种矢量网络分析仪测量同轴传输线特性阻抗的方法

本文提出了一种应用矢量网络分析仪直接测量同轴传输线特性阻抗新方法.通过建立数学模型,推导出特性阻抗的计算公式,然后经实验验证其方法和测量结果的正确性.     

火工品高频段射频阻抗测试技术?

为测量高频段火工品射频阻抗,根据火工品脚线和矢量网络分析仪的结构特点,设计了火工品专用连接夹具,实现了同轴和平行线的有效连接。并对夹具引入的测量误差进行了修正计算,建立了基于矢量网络分析仪的高频段火工品射频阻抗测试系统。利用此系统,测量了火工品1~18 GHz范围内的射频阻抗,共出现了5个谐振点,在谐振点火工品从电磁环境中吸收的能量最大,为评价火工品在电磁环境中的安全性提供了数据支撑。     

观片灯发光亮度值检测方法的探讨

介绍了两种测量观片灯亮度值的传统方法—亮度计直接测量法和照度计直接测量法,通过总结其优缺点,首次提出了一种利用黑白密度片衰减观片灯照度值的测量方法,该方法测量简便快捷,可对测量精度和量程进行控制。     

高频大电压阻容分压网络的频率特性研究

现代功率分析仪电压测量通道要求同时满足高频、大电压及高精度的测量需求,通道输入级的阻容分压网络对满足这些需求起着关键作用。实验发现,电路的寄生参数对于中高频段测量结果有明显影响,使得测量精度变差。该文将寄生参数考虑进电路,给出分压网络的集总参数模型;基于该模型介绍阻容匹配的必要性,并引入一种新型实用匹配方法。通过PSPICE仿真,分析各参数对分压网络频率特性的影响,并指出影响分压网络测量精度的关键因素。经实物测试,验证分压网络集总参数模型的准确性;DC-1MHz频率范围内,良好匹配的阻容分压网络测量精度达到功率分析仪测量需求。     

利用矢量网络分析仪单端口校准误差项提取二端口网络的S参数

提出了一种利用矢量网络分析仪单端口校准误差项提取互易二端口网络S参数的方法。该方法要求在不同的参考平面上分别进行两次单端口校准,然后利用两次单端口校准的误差项求解二端口网络的S参数,通过实验验证该方法的正确性。该方法可应用于负载牵引和噪声参数测量过程中阻抗调配网络的S参数提取。     

矢量网络分析仪时域测量技术分析与MATLAB仿真

矢量网络分析仪因具有频率测量范围宽、测试精度高等优点,被广泛应用与射频微波领域.时域测量技术作为其一项重要的拓展功能,在进行时间域分析及解决特定场景下的测试问题时十分有用.分析了矢量网络分析仪的时域测量理论基础,探究了时、频域转换及时域选通实现的原理及方法,同时通过使用MATLAB软件对整个过程进行了仿真,实现了时域选...     

Impedance measurements with second-order harmonic oscillator fortesting food sterility

In this paper, we present a simple interface circuit for measuring impedance based on a second-order harmonic oscillator. The circuit is intended for testing the sterility of aseptically packed food products, where it must measure the conductivity changes of the packaged food in a nondestructive way. The measured impedance is modeled as a low-ohmic resistor (representing the conductivity of the food) in series with a capacitor (the walls of the food container). The oscillator is built with fast current-feedback operational amplifiers (CFOA). To measure the resistive component of the impedance, an AC-to-DC converter is realized with a wide frequency range analog multiplier. The presented experimental results prove that with this interface circuit an accurate measurement of the impedance components can be achieved in a frequency range up to 10 MHz. The range of the resistive component is from a few ohms up to 200 ohms; the range of the capacitive component is from 50 pF up to 300 pF     

Synthetic TDR Measurements for TEM and GTEM Cell Characterization

This paper describes the main features of the time-domain reflectometry (TDR) measurement technique and, in particular, the TDR analysis performed using a proper operating mode of the vector network analyzer (VNA), which is called synthetic TDR. Furthermore, some results of reflection measurement, which aim to characterize the impedance behavior of transverse electromagnetic (TEM) and gigahertz TEM cells by means of a commercial VNA in time-domain mode, are presented     

Novel and Simple High-Frequency Single-Port Vector Network Analyzer

Portable, accurate, and relatively inexpensive highfrequency vector network analyzers (VNAs) have great utility for a wide range of applications, encompassing microwave circuit characterization, reflectometry, imaging, material characterization, and nondestructive testing to name a few. To meet the rising demand for VNAs possessing the aforementioned attributes, we present a novel and simple VNA design based on a standing-wave probing device and an electronically controllable phase shifter. The phase shifter is inserted between a device under test (DUT) and a standing-wave probing device. The complex reflection coefficient of the DUT is then obtained from multiple standing-wave voltage measurements taken for several different values of the phase shift. The proposed VNA design eliminates the need for expensive heterodyne detection schemes required for tunedreceiver-based VNA designs. Compared with previously developed VNAs that operate based on performing multiple power measurements, the proposed VNA utilizes a single power detector without the need for multiport hybrid couplers. In this paper, the efficacy of the proposed VNA is demonstrated via numerical simulations and experimental measurements. For this purpose, measurements of various DUTs obtained using an X-band (8.2–12.4 GHz) prototype VNA are presented and compared with results obtained using an Agilent HP8510C VNA. The results show that the proposed VNA provides highly accurate vector measurements with typical errors on the order of 0.02 and 1$^{circ}$ for magnitude and phase, respectively.      

AC Impedance Behaviour of Black Diamond Films

The first measurement of impedance on free-standing diamond films from 0.1 Hz to 10 MHz up to 300℃ were reported. A wide range of chemical vapour deposition (CVD) materials were investigated, but here we concentrate are well fitted to a RC parallel circuit model and the equivalent resistance and capacitance for the diamond films have been estimated using the Zview curve fitting. The results show only one single semicircle response at each temperature measured. It was found that the resistance decreases from 62 MΩ at room temperature to 4 kΩ at300℃, with an activation energy around 0.51 eV. The equivalent capacitance is maintained at the level of 100 pF up to 300℃ suggesting that the diamond grain boundaries are dominating the conduction. At 400℃, the impedance at low frequencies shows a linear tail, which can be explained that the AC polarization of diamond/Au interface occurs.     

Harmonic impedance measurement using a thyristor-controlled short circuit

An effective and easy-to-implement method for measuring power system harmonic impedances is presented. The method uses a thyristor to create a controlled short circuit at the measurement point. The short circuit produces a pulse current and a voltage distortion, which are then used to estimate the system impedance. The strength of the current pulse is controlled through the thyristor firing angle so that enough signal energy is available for precise measurement and yet the disturbance is small enough not to cause power quality problems. The method can be implemented into a portable impedance measurement device. Computer simulations and lab tests were used to verify the effectiveness of the method. A criterion for determining the frequency range of reliable measurements using the proposed device is also established.     

一种利用S参数测量平衡RFID标签天线阻抗的优化方法

针对测量平衡RFID标签天线阻抗的准确性问题,提出了一种利用s参数测量的优化方法。该方法将平衡RFID标签天线等效为双端口网络,通过联合使用端口短路、开路延伸方法测量S参数,根据拐点选取最邻近数据并进行区间的数据拟合,从而计算出天线阻抗。首先 h1 进行了测量理论分析．然后设计了实物测量场景（915MHz频段的RFID天线）,并将该优化方法与传统的Bahm方法、无延伸单端口方法、延伸单端口方法进行了对比。结果表明,在工作频段内,该优化方法所测的标签天线的阻抗实部,虚部与仿真结果基本一致,比传统的Balun2及单端口等测摄方法准确;在工作频段外,所测阻抗实部仍然与仿真结果接近,尽管阻抗虚部与仿真结果存在一定的偏差。     

Impedance characteristics and electrical modelling of multi-walled carbon nanotube/silicone rubber composites

Multi-walled carbon nanotube (MWCNT)-filled silicone rubber (SR) composites were prepared by solvent evaporation method, with different MWCNT concentrations from 0.5 wt% to 6.5 wt%. Alternating current (AC) electrical properties of samples with interdigital electrodes were measured in the frequency range from 20 Hz to 1 MHz. Impedance spectroscopy analysis reveals a frequency-independent percolation transition between 2.0 wt% and 2.9 wt%. Samples above the percolation threshold exhibit more regular variations: the magnitude of impedance decreases gradually with frequency in the low-frequency range, and then decreases as a power law beyond a critical frequency, with the exponent in a limited range indicating the AC universality of disordered solids; the plots of real and imaginary parts of impedance fit semicircles well in the complex plane, implying semiconductive behaviours. Over the concentration range tested, a multi-stage circuit model consisting of resistor–capacitor (RC) networks is proposed to simulate the electrical responses of samples. The validity of the modelling approach is verified by comparing simulation results to experimental results, and is further supported by the analysis of the characteristic frequency. The use of equivalent circuits in modelling provides a further insight into the conducting network inside nanocomposites and more valuable guidance for the design of correlative devices.     

The four-frequency process for coupled-duals using error-corrected S-parameter measurements

Although the four-frequency measurement process has been used successfully on coupled dual crystals from 9.4 MHz to 21.4 MHz, discrepancies between the crystal data and filter data at 45 MHz and 57.5 MHz suggested an error problem associated with the measurement system. To eliminate the errors, a twelve-term error model was chosen and the equations were derived for use with an automatic network analyzer. The details of the direct deviation of the four-frequency measurement process are given in which the two resonator frequencies and the synchronous peak separation frequency (SPSF) of a coupled dual crystal are calculated from the two frequencies of the zeros of the short-circuit driving point impedance, and the two frequencies of the zeros of the open-circuit driving point impedance. Determination of the four frequencies from the error-corrected S parameters is discussed, as well as the analysis of an external capacitor placed across the output circuit to obtain a more convenient distribution of the four frequencies. A comparison is made between data taken on the original fixture and data taken on an automatic network analyzer using error-corrected S parameters.     

Norton-Corrected Measurement of Complex Impedances of a Large Format Bolometer Array

We report on our efforts to measure simultaneously a well-calibrated complex impedance of a large number of detectors in a long wavelength bolometer array. The array is described in other presentations. A method for correcting the complex impedance measurements of bolometers and calorimeters has been presented by Lindeman et al. (Rev. Sci. Instrum. 78:043105, [2007]) using a Thévenin equivalent circuit to represent the bias network. We have built on this method for superconducting bolometers with a Norton equivalent circuit and have used it to improve our impedance data. We further describe our method for extracting a Norton-corrected complex impedance as a function of frequency from a stream of multiplexed time-ordered data. This method is well-suited to producing simultaneous complex impedance measurements for a large number of detectors.