Recognition of Borehole Radar Cable-Related Effects Using Variable Offset Sounding

Conductive cables can influence borehole radar measurements and introduce artifacts into data and therefore must be considered during data analysis and interpretation. This study presents examples of some cable-related effects in data acquired with a radar system that relies on conductive cables for signal transmission. Data show that measurements can be affected when energy radiated from the transmitter antenna induces currents on conductive cables, which can function as an electromagnetic waveguide, allowing fields to propagate along cables and be detected by the receiver antenna. Additionally, periodic artifacts can result when currents traveling on cables reflect at system impedance mismatches.Variable offset soundings (VOS) are not typically conducted during borehole radar studies, but can be useful for recognizing cable-related effects on recorded data and studying propagation characteristics in a borehole. In addition to single-hole VOS measurements, VOS measurements made on the ground surface using E-Plane and H-Plane configurations are shown to have the potential for providing additional insight in regards to coupling mechanisms between borehole antennas and cables.     

Highly Sensitive Pump–Probe Polarimetry: Measurements of Polarization Rotation, Ellipticity, and Depolarization

A highly sensitive polarimetry method for measuring small photoinduced parameters, such as the rotation of the polarization azimuth and changes in the ellipticity and degree of depolarization, is developed on the basis of the pump–probe technique. The sensitivity of the polarimetric method under technical and shot-noise fluctuations of the optical power of the probe beam is analyzed, and optimal settings of the polarimeter are found. The method developed is applied to investigations of nanopolyacetylene films using continuous-wave, picosecond, and femtosecond lasers. Typical angles of polarization rotation were 10^–5–10^–8 rad.     

The Huynen-Fork Polarization Parameters in the Classification of Dielectric Mine-like Objects

We present a polarimetric approach that can be used to characterize subsurface targets by means of ground-penetrating radar. Several quantities related to the Huynen-fork parameters are basic to the study. These quantities are all expressible in terms of the elements of Sinclair matrix S which in turn, can be determined as functions of frequency by an application of the method-of-moment (MoM)—which is briefly reviewed here—to a mine-like object buried at various depths in a soil of specified dielectric and moisture properties. The quantities in question are the Stokes parameters, the elevation, azimuth, and polarizability angles, as well as the polarization ratios and the scattering eigenvalues which optimize the backscattered power. Some of these quantities are studied here and displayed in various graphs. These frequency dependent graphs exhibit useful symmetry properties. The plots of the polarizability angle (β) vs. frequency seem to remain invariant with target depth, and exhibit resonance features that are later shown to agree well with other standard methods to estimate resonances such as Prony method. A simple analysis of the early-time resonances thus estimated is used to obtain acceptable mine dimensions. The agreement found implies that polarimetric techniques, such as present one, can also be used in the arsenal of techniques yielding target-ID clues.     

A Directional Borehole Radar System

In this paper we present the simulation and design of a directional borehole radar. In addition we discuss an imaging method for the radar system. The antenna system contains an electric dipole which is in one direction shielded by a cylindrical perfectly conducting reflector. The radiation pattern of the reflected wavefield is computed by first solving the integral equation. This equation combines the unknown electric surface current density on the reflector and the known incident field from the electric dipole. Once the electric surface current density is known, the radiation pattern of the system is computed using the integral representation over the reflector and the dipole. The radiation patterns for various configurations have been computed in order to find an optimal configuration. A prototype of the antenna system based on an optimal configuration has been built, and the directional radiation pattern has been measured in the plane perpendicular to the antenna system. The measurements were in good agreement with the computations. Subsequently a three dimensional imaging method for the borehole radar is presented. Here a deconvolution is carried out in the angular direction, making use of the computed radiation pattern. Some imaging results will be shown.     

Polarimetric Video Impulse Radar for Landmine Detection

A full-polarimetric ultra wideband GPR front-end has been developed. The technical specifications of the radar have been determined based on the analysis of different GPR scenarios and based on user-oriented demands. The radar has been designed to meet most of these specifications and at the same time to be within a limited budget. The front-end comprises a generator section, a multi-static antenna system and a receiving unit based on a multi-channel sampling converter. The novelty aspects of the radar are: principally new antenna system, use of multiple pulse generators and compensation circuits to improve stability of the system. In comparison with commercially available video impulse GPR systems the key advantages of the front-end are the considerably larger bandwidth, the ability to measure the polarimetric structure of the scattered field and the high precision of scattered field measurements. The front-end is suitable for subsurface imaging with 3D resolution sufficient for antipersonnel mine detection and recognition.     

Frequency Dependence of the Soil Electromagnetic Properties Derived from Ground-Penetrating Radar Signal Inversion

The accuracy at which the subsurface electromagnetic properties can be identified from full wave inversion of ground penetrating radar (GPR) signals relies on the appropriateness of the model describing their frequency dependence. In this paper, we focus on the characterization of the frequency dependence of the dielectric permittivity and electric conductivity of a sandy soil subject to different water contents from inversion of GPR measurements. Based on previous studies of Lambot et al. the methodology relies on an ultrawide band (UWB) stepped-frequency continuous-wave (SFCW) radar combined with an off-ground monostatic transverse electromagnetic (TEM) horn antenna. Forward modeling of the radar signal is based on linear system transfer functions for describing the antenna, and on the exact solution of Maxwells equations for wave propagation in a horizontally multilayered medium representing the subsurface. Model inversion, formulated by the classical least-squares problem, is carried out iteratively using advanced global optimization techniques. The frequency dependence of the electromagnetic properties of the sandy soil is characterized by performing inversions of the radar signal in different and subsequent limited frequency bands, in which the electromagnetic parameters are assumed to be constant. We observed that over the entire frequency band considered in this study (1–3 GHz), the dielectric permittivity of the sand remains constant with frequency, whatever the water content is. In contrast, the electric conductivity increases significantly from 1GHz to 3 GHz, and this effect increases with water content. The frequency dependence of the electric conductivity may be adequately described using a simple linear relationship. This approach is advantageous since it limits the number of parameters to be optimized in the inverse modeling procedure.     

Six-Port Receiver and Frequency Measurement for Radar Applications at 35GHz

The application of a six-port technology in the receiving part of a radar front-end is described in this paper. This receiver allows measuring magnitude and phase of the radar signal without the need of down-conversion. According to the applications and the availability of the devices needed for assembling the prototype sensor, the frequency of operation was set to 35GHz. The structure of this six-port as well as the calibration and measurement algorithms are described in detail. The accuracy of the phase measurement is 2–10° depending on the power level of the signal. Another key element of the proposed radar sensor is a direct frequency counter. Using this circuit it is possible to measure the frequency of operation with a resolution of 20 bits within 120s. The accuracy of the distance reading of the radar is directly related to the accuracy of the frequency measurement and has reached 0.1mm.     

Specifying the Freshness of Eggs Using Microwave Sensors*

This paper introduces a microwave measurement setup, using three microstrip antennas integrated with a microwave oscillator, and Schottky-diode detectors used as bistatic microwave sensors. We have measured the microwave attenuation (water content) and the bistatic radar cross section (dimensions) of eggs having different storage times (Fig. 1). The measured attenuation (A) for fresh egg, at a frequency of 14.2 GHz is A=8–10 dB; the variation with time is dA [dB]=–0.033T (days), thus nearly –1 dB/30 days. Our next project is to create a microwave device for the automatic selection of old eggs. The basic experimental design and the results of our measurements are discussed.     

基于挠曲线方程的某车载雷达天线质心估算方法

对于车载雷达转塔系统,准确地确定雷达天线的质心位置对转塔的受力分析、设计校核和实际使用都至关重要。文中提出了一种大型雷达天线质心位置估算方法,根据悬臂梁所受集中力的挠曲线近似微分方程,建立转塔系统的数学模型,将测量数据代入模型,所得结果与理论计算结果相差1.83%。该方法不受限于场地和测量设备,计算过程简单,结果准确,可为相关车载雷达天线或相似结构产品的质心位置估算提供理论指导和工程应用参考。     

多通道型偏振成像仪的偏振定标

为了解决多通道型偏振成像仪的偏振定标问题,提出了一种基于积分球无偏光源的偏振定标方法。通过研究偏振光束与光学器件的相互作用,推导出多通道型偏振成像仪的矢量辐射传输模型,确定了需要标定的参数。运用无偏光源标定系统的偏振效应,基于矢量辐射传输模型对中心视场绝对辐射定标系数、光学镜头起偏度和系统低频相对透过率等关键参数进行了标定,通过分析标定结果求解了系统全视场的穆勒矩阵。最后,使用可调偏振度光源验证了仪器典型视场的偏振定标精度。研究结果表明,基于无偏光源的偏振定标方法可以有效提高多通道型偏振成像仪的偏振定标效率;经偏振定标后仪器在目标偏振度低于20%时的偏振测量误差小于1%,满足大气气溶胶测量精度的要求。     

Error Propagation in a Practical Six-Port Device

In this contribution the various influences on the accuracy of the phase measurement unit of a near range precision radar are investigated. The front-end is a monostatic design operating at 34–36.2 GHz. The hardware configuration enables different modes of operation including FM-CW and a single frequency mode with phase and frequency measurement. To achieve a highly accurate distance measurement, attention must be paid to various error sources. Due to the use of a six-port it is rather complicated to determine the corresponding error propagation. In the following the results of investigations on how to achieve an exceptional accuracy of 0.1 mm are described. Especially the error propagation through the six-port is analyzed in detail.     

大型相控阵雷达阵面平面度测量方法研究

阵面平面度是天线阵面设计的关键指标,其准确测量是指标校核的重要手段。文中从大型相控阵雷达的阵面平面度的测量需求出发,分析了现有常规测量手段在各型雷达中的适应性,并结合工程实际应用阐述了各方法在实际测量中的关键点,为同类应用时方法的选取和使用提供了依据。同时,针对现代大型相控阵雷达的设计特点,提出了平面度测量的未来趋势。     

Verification methods and antenna horizontal beamwidth of across-the-road radar for traffic speed enforcement in China

Across-The-Road (ATR) radar is the most common type of traffic speed measurement devices used in China for traffic law enforcement. Its speed measurement accuracy is highly concerned by drivers, lawyers, policemen and metrologists as well. Among those influence factors, antenna horizontal beamwidth is an important one, which has not been taken into account in the current verification regulation of ATR radar in China. In this paper, the current verification methods of ATR radar in China are firstly introduced, and the reason for the field measurement error of ATR radar is analyzed. The speed measurement error of ATR radar related to antenna horizontal beamwidth is investigated in details, and theoretically calculated in various combinations of installation angles and horizontal beamwidths. Field tests with three equal-distanced piezo sensors each lane as triggering reference have also been performed on two ATR radar samples with horizontal beamwidth 5° and 10° respectively. The results of theoretical analysis and field tests verify that antenna horizontal beamwidth smaller than 6° is a precondition for accurate and reliable field measurements, which has also been added to the newly published pattern approval regulation of ATR radar in China.     

雷达天线系统离心风机气动噪声研究

基于FW-H方程,对离心风机进行气动声学理论分析,结合噪声测试方法,对某雷达天线系统进行噪声试验研究分析.测试数据表明,噪声和振动加速度频谱图分布较为接近,噪声振动能量峰值频率均为离心风机叶片基频的倍频,即雷达天线系统噪声主要来源于离心风机的气动噪声.通过改变均热板上翅片与风机叶片边缘的间距和调节风机转速,对单个离心风...     

航空多角度偏振辐射计的偏振定标

研究了航空多角度偏振辐射计的辐射定标方法,以消除其自身引入的偏振效应,提高偏振辐射计的测量精度.首先,根据引入仪器偏振效应的主要因素推导了含定标系数的仪器探测方程,由仪器在0°和90°两个状态下对同一信号的探测方程求解了定标系数表达式,并设计了仪器分别处于两个状态下获取信号、求解定标系数的定标方法.最后,分别针对非偏振光源和完全线偏振光源的测试数据求解了所有的定标系数,使用可调偏振度光源验证了偏振定标结果.结果显示,该仪器偏振测量精度不低于o.5％,满足仪器精度指标要求.     

波导裂缝天线单元结构设计

随着现代雷达技术的发展,波导裂缝天线单元之间的间距越来越小,安装位置精度越来越高,常规的结构形式很难满足波导裂缝天线单元结构设计的新需求,迫切需要一种新的结构形式来解决上述问题.文中在分析波导裂缝天线结构设计新需求的基础上,提出了一种新的结构形式,对开缝波导管、负载和波导同轴变换器进行了结构设计研究,并对波导裂缝天线单...     

A High-Speed Continuous Wave GPR

In this work an innovative high speed continuous wave stepped frequency GPR has been designed and implemented with the aim of overcoming the low speed issue of wide bandwidth CW-SF GPRs. It is based on a structure combining a Digital Direct Synthesizer (DDS), a Phase Lock Loop (PLL) and a quadrature modulator (I/Q Modulator). The radar is an L-S band GPR able to scan a 1 GHz bandwidth (1500–2500 MHz) with 200 steps in 10 ms. The system has been developed for automatic synthetic aperture radar (SAR) imaging of historical-artistic interest structures. Some system tests and laboratory tests on a realistic masonry setup were carried out in order to asses the performances of this system.     

某有源相控阵气象雷达天线结构设计

随着科学技术的进步和现代雷达的发展,有源相控阵雷达因功能全面,战术指标优良,越来越多地运用在气象领域。但由于大型相控阵天线成本很高,限制了该类型天线的应用,因此能否研发出高性能、低成本的有源相控阵天线关系到其在民品市场中的应用与推广。文中以有源相控阵气象雷达天线为例,分析其结构设计需求,针对其结构设计难点,设计了一种性价比高的天线结构,并对天线阵面进行总体优化布局,对天线骨架,高频箱,裂缝波导,天线阵面吊装和三维布线等方面进行了详细叙述。     

某相控阵雷达车机动性设计

某相控阵雷达具有集成度高、天线口径大、质量重等特点,其机动性设计是个难题.文中通过对天线阵面进行合理分块并选择合适的折叠方式,设计并使用一套天线自动展/收和调平的自动架设/撤收的液压系统,运用MSC·ADAMS运动分析软件对天线展/收机构进行仿真分析和优化设计,使该雷达车的机动性达到了指标要求,并已通过整机工程实施对其进行了验证.该系统可靠性高,性能优越,对类似雷达车的机动性设计具有一定的参考意义.