单频激光宽频段频率和强度噪声测量技术

报道了一种mHz至MHz宽频段激光噪声的规范测量技术。通过研制基于迈克耳孙光纤干涉仪的相关延时自外差频率噪声测量装置和具有定标功能的光外差拍频测量装置,结合频谱分析仪和快速傅里叶变换分析仪等标准仪器,规范地测量出了单频激光在mHz至MHz宽频段内的频率和强度噪声特性,并验证了测量结果的准确性。该测量技术有望应用于引力波探测和精密测量等应用中的激光噪声评估。     

Characterization of UXO-like targets using broadband electromagnetic induction sensors

We have inverted broadband electromagnetic induction data over an isolated target to determine its electrical conductivity, magnetic permeability, radius, and depth using a sphere model. Studies using synthetic data of a concentric, broadband, electromagnetic sensor indicate that the technique is dependable and produces fast-converging solutions. The geometrical parameters obtained through this technique are very close to true values, and the electric parameters for noise-free data are correct to within a few percent. When 10% noise is added to the data, the geometric parameters are still well determined, but the electric parameters are poorly resolved, particularly for a sphere that is both conductive and permeable. Tests on the experiment data show that volume-equivalent size and depth to a target can be reasonably estimated for a nonspherical object.     

Detection of broadband planewaves in the presence of Gaussian noiseof unknown covariance: asymptotically optimum tests using the 2-Dautoregressive noise model

This paper addresses the problem of detecting a broadband planewave in noise of unknown spatial and temporal covariance at a linear array of sensors. Results of asymptotic detection theory are applied to derive detectors that approach optimal performance for large data records. A parametric approach is used to model the statistics of the data. A 2-D autoregressive (2DAR) model is chosen to model the noise process. Two broadband planewave signal models are considered. Both models represent the signal as a sum of monochromatic planewaves. In the Gaussian model, the amplitudes are assumed to be Gaussian with a single variance parameter, whereas in the deterministic assumption, they are individual unknown parameters. Detectors based on asymptotic theory are derived for both models. As part of the development of the asymptotically (AS) optimum detector, the Fisher information matrix (FIM) is derived. A proof of the locally asymptotic normal (LAN) property is provided for the Gaussian model probability density function (PDF). Both detectors, however, are AS equivalent to the generalized likelihood ratio test (GLRT), are AS of constant false alarm rate (CFAR), and perform AS as well as the GLRT constructed with full knowledge of the noise statistics. The performance of both detectors are compared with each other and to a standard spatially normalized beamformer in a computer simulation     

Composite microbolometers with tellurium detector elements

A composite microbolometer has been constructed for possible use as a broadband submillimeter radiation detector. Theory, fabrication, and measurement of these devices are discussed, and a finite element thermal model is introduced. The devices utilize nichrome load elements which can be impedance-matched to a planar antenna. The load elements are thermally coupled to tellurium detectors. Room temperature responsivities of 120 V/W and noise equivalent powers (NEPs) as low as 6.7×10^-9 W/√Hz were achieved. Performance appears to be limited by 1/f noise in the Te detector     

Intensity noise in long-wavelength superluminescent sources

Noise in broadband 1.3-μm superluminescent diodes (SLDs) is investigated experimentally, using a balanced detector arrangement to determine the excess noise factor as a function of photodetector current. Measurements were made in both the low-frequency 1/f, regime (<500 kHz) and the high-frequency quantum noise spectral region. The data at higher frequencies are in agreement with predictions of the quantum amplifier model, with values of the spontaneous emission coupling factors ranging from 1.2 to 1.9. It is also found that noise for one polarization of the light is uncorrelated with the noise for the orthogonal polarization over the 0-1 MHz frequency range. This implies that the 1/f, noise is not related to carrier density (gain) fluctuations in the active region of the device. An integrated optic chip design to compensate for the excess intensity noise in fiber gyroscopes is proposed     

Mesure automatique des paramétres de bruit des MESFET hyperfréquences

An automatic noise parameter measurement test set is described in two sections : (i) A novel noise parameter extraction procedure from a set of noise figure measurements is developped. The experimental minimum noise figure is no longer required and the sensitivity to measurement incertainties is found to be very low. (ii) An automatic input tuner with a large number of precalibrated and reproducible positions is designed and realized. The last part give examples of broadband (8 to 17 GHz) noise parameters characterization ofmmic GaAsmesfets when both the automatic tuner and the extraction procedure are used.     

相控阵雷达宽窄带测速匹配技术研究

针对宽带测速情况下有时无输出以及窄带测速跳谱线的问题,分析了两种现象产生的机理,并提出用窄带测速数据提高宽带测速精度的方法,解决了宽带波门套不住目标的现象,保证了宽带测速的连续输出;同时,为了解决窄带测速跳谱线带来的窄带测速模糊问题,提出了用宽带测速数据进行辅助判决的解决方法;最终,通过宽窄带测速数据相互匹配突破了工程应用中面临的技术难题,对提高雷达的测量精度和探测能力具有重要意义。     

脉冲干扰下的宽带接入网上行信道误码率研究

脉冲干扰是宽带接入网上行信道数据传输性能受限的因素之一,基于对脉冲噪声干扰影响宽带接入网上行信道特性的研究,推导了其特征函数模型。建立了脉冲噪声干扰下的系统仿真模型,在16进制QAM调制下,仿真得到了载噪比与误码率的曲线,并对系统模型的BER仿真曲线结果进行了分析。为提高宽带接入网系统性能和故障诊断提供了有效的理论依据。     

窄带连续波干扰下宽带接入网上行信道MER研究

窄带连续波是宽带接入网上行信道的典型干扰。为了研究此时的宽带接入网系统性能,推导了窄带连续波干扰的特征函数模型,并以此为依据,建立了系统模型,获得了基于窄带噪声的宽带接入网上行信道QPSK系统调制误码率(MER)与载噪比(C/N)的关系曲线,并对系统模型的MER仿真曲线进行了分析。为提高宽带接入网系统性能和排查干扰提供了有效的理论依据。     

传声器阵列校准技术研究

气动噪声通常为宽频噪声,设计的阵列需要同时满足对高低频信号的测量需求,在确定了阵列测量频率范围的情况下,设计相应的阵列形式。在风洞气动噪声试验技术中,基于传声器阵列的噪声源定位技术是核心试验技术,噪声源定位的精准度主要取决于传声器阵列校准技术。传声器相位阵列安装之后,由于传声器频率响应和灵敏度不同,前置放大器、电缆的铺设、电源和信号调理器的频率响应以及传声器在阵列中的安装影响,会引起数据采集系统各测量通道间固有的相位差和幅值差。修正传声器的相位差和幅值差使得所有的传声器幅频响应一致,保证试验结果的准度。     

A mobile wide-band measurement system for urban man-made noise

This paper describes in detail the criteria for the design of a mobile laboratory for the characterization and measurement of man-made electromagnetic noise in the urban, suburban, and rural environment. A significant difference from previous similar measurements is the bandwidth of the receiving system, which is here of the order of 1 MHz. A simple model is proposed to describe the impulsive noise together with a series of experiments to validate the model and determine the significant necessary parameters. The detailed requirements for each of the subsystems of the mobile laboratory are discussed and some typical results obtained in trial runs are presented.     

A Mobile Wide-Band Measurement System for Urban Man-Made Noise

This paper describes in detail the criteria for the design of a mobile laboratory for the characterization and measurement of manmade electromagnetic noise in the urban, suburban, and rural environment. A significant difference from previous similar measurements is the bandwidth of the receiving system, which is here of the order of 1 MHz. A simple model is proposed to describe the impulsive noise together with a series of experiments to validate the model and determine the significant necessary parameters. The detailed requirements for each of the subsystems of the mobile laboratory are discussed and some typical results obtained in trial runs are presented.     

脉冲干扰下的宽带接入网上行信道MER研究

脉冲干扰严重影响实际通信过程中宽带接入网上行信道的系统性能。基于特征函数理论,推导脉冲干扰的数学模型,并模拟实现脉冲干扰对宽带接入网上行信道的干扰特性。设计和构造宽带接入网上行信道的通信系统平台。得出脉冲干扰下的宽带接入网上行信道16QAM系统的调制误码率(MER)与载噪比(C/N)关系的仿真曲线。仿真结果验证了设计的正确性,同时表明脉冲噪声对系统的影响受到脉冲个数和幅度的制约。     

Simple and highly sensitive method for wavelength measurement of low-power time-multiplexed signals using optical amplifiers

We describe a simple method for the wavelength measurement of optical signals that is easily capable of measuring a 1-nW average power optical signal with a wavelength resolution of 0.1 pm/Hz/sup 1/2/ while maintaining a large measurement range in excess of 12 nm. The system uses an erbium-doped fiber amplifier to increase the signal level before being measured with a wide-band edge filter. This technique is well suited to the measurement of low duty cycle time-multiplexed signals such as those in multiplexed fiber sensor systems. We show that the measurement of the amplified signal is improved despite the broadband nature of the amplified spontaneous emission noise. We show for the first time that the addition of an amplifier can increase the detection capabilities of the edge filter method beyond the shot noise limit of an unamplified measurement.     

Broad-band detection based on two-dimensional mixed autoregressivemodels

Two detectors for broadband plane waves in colored noise fields that use a linear array are described. The signal spectrum, arrival angle, and noise field coloration are not known a priori. Using a two-dimensional mixed autoregressive model, a generalized-likelihood-ratio test and its weak-signal equivalent, the Rao test, are derived. The performances of the proposed detectors are shown by computer simulations to be superior to those of conventional Fourier-based methods. Detection results for real data are presented     

Technique of enhancing the noise immunity of broadband communications systems

A technique is considered for enhancing the noise immunity of broadband communications systems with repetition. This technique is based on generating a broadband noise-like signal in the transmitting circuit of the system and adaptive compensation of broadband localized interferences in the receiver. In this case, an adaptive variation of transmitter carriers is conducted in each of the channels. The gain in noise immunity provided by the technique proposed was calculated in comparison with other known techniques.     

微波放大器Rn-Gn模型噪声参数的准确提取

对微波放大器Rn—Gn噪声模型以及噪声参数的提取方法进行了研究,自行研制了精密的阻抗变换器,组建了一套新的噪声系数测量系统,采用加权最小二乘法准确提取出放大器的噪声参数。实验测量结果稳定、可靠,在不同频点下可以得到包括最小噪声系数在内的四个噪声参数,并节省了测量时间,为微波低噪声放大器的设计提供了更加可靠的基础数据。     

一种宽带单脉冲雷达测角方法

针对实际宽带单脉冲雷达的测角问题,在介绍宽带单脉冲测角原理基础上,说明了标定的具体做法,并从函数的角度分析了标定方法的理论有效性;给出了使用标定结果的测角方法并分析了该方法的误差;最后给出了实测数据的测角结果.测角结果与实际情况相符合,验证了测角方法的有效性.     

A spatial filtering approach to robust adaptive beaming

The problem of controlling the superresolution in adaptive beamformers is treated. A straightforward method is presented that works for both narrowband and broadband arrays. The method is based on forming the blocking matrix in a general sidelobe canceller structure using a spatial FIR filter. The suppression of this spatial filter and the implicit noise of the leaky least-mean-square algorithm together determine the beamformer     

Analysis of the cyclic short-term variation of indoor power line channels

The purpose of this paper is to analyze the properties of indoor power line communications channels when they are used for broadband transmission. It will be shown that these channels exhibit a short-term variation, due to the fact that high-frequency parameters of electrical devices depend on the instantaneous amplitude of mains voltage. This phenomenon leads to a channel model proposal based on a linear periodically time-varying system and cyclostationary random noise. A measurement system, designed to capture these time variations in real power networks, and some of the most significant results obtained with it, are presented. In addition, a statistical analysis of the measurements performed in several indoor power line scenarios is included, so that the relevance of time variations in actual channels can be evaluated.