近地面1 km高度处折射率梯度与地面气象参数统计关系的研究

近地面大气折射率梯度是影响无线电系统性能的重要因素.为研究近地面折射率梯度与地面气象参数温湿压的关系，利用太原地区1986—1995年的探空数据，拟合出近地面折射率梯度与地面气象参数的关系模型.拟合分析结果表明:太原地区近地面1 km高度处折射率梯度与地面气象参数的线性关系优于与地面折射率的指数关系；从与地面气象参数的线性模型中可以直观地看出折射率梯度受地面温湿压影响的权重.通过研究近地面折射率梯度与地面气象参数的统计关系，可更快捷地通过地面温湿压评估近地面无线电视距，从而进一步为大气折射的研究提供支持，为优化无线电系统规划设计提供支撑.     

Decoupling Method Between Digital Signals on FPCB and Mobile Handset Antenna

Digital harmonics, which may reduce the radio frequency sensitivity of a system, can be coupled with an antenna in a mobile handset. This letter presents a decoupling method for increasing the isolation between digital harmonics on a flexible printed circuit board (FPCB) and an antenna in terms of the ground mode current and the concept of reaction. We model the signal and ground lines in an FPCB as a loop circuit exciting a ground mode current and demonstrate a simple but efficient decoupling method for reducing the excited ground mode current.     

干扰走廊对地面警戒雷达干扰效果仿真分析

针对干扰走廊是干扰地面警戒雷达的一种有效的手段,给出地面警戒雷达遭受干扰走廊干扰的模型,利用雷达探测距离来衡量地面警戒雷达受干扰情况,并结合实例进行仿真分析.     

A Multiscale Curvature Algorithm for Classifying Discrete Return LiDAR in Forested Environments

One prerequisite to the use of light detection and ranging (LiDAR) across disciplines is differentiating ground from nonground returns. The objective was to automatically and objectively classify points within unclassified LiDAR point clouds, with few model parameters and minimal postprocessing. Presented is an automated method for classifying LiDAR returns as ground or nonground in forested environments occurring in complex terrains. Multiscale curvature classification (MCC) is an iterative multiscale algorithm for classifying LiDAR returns that exceed positive surface curvature thresholds, resulting in all the LiDAR measurements being classified as ground or nonground. The MCC algorithm yields a solution of classified returns that support bare-earth surface interpolation at a resolution commensurate with the sampling frequency of the LiDAR survey. Errors in classified ground returns were assessed using 204 independent validation points consisting of 165 field plot global positioning system locations and 39 National Oceanic and Atmospheric Administration-National Geodetic Survey monuments. Jackknife validation and Monte Carlo simulation were used to assess the quality and error of a bare-earth digital elevation model interpolated from the classified returns. A local indicator of spatial association statistic was used to test for commission errors in the classified ground returns. Results demonstrate that the MCC model minimizes commission errors while retaining a high proportion of ground returns and provides high confidence in the derived ground surface     

Comparison of Computed RF Current Flow on a Power Line With Full Scale Measurements

Reradiation of an MF/AM broadcast transmitter's signal by a power transmission line can cause serious pattern distortion. A computer model of a power line, developed and tested against scale model measurements over highly conductive ground, has been used to assess the pattern distortion to be expected from a power line proposed for construction, to identify those towers on an existing power line which carry strong RF currents, and to design "detuningn devices to suppress such currents. The accuracy of the computer model's "predictions" is tested in this paper against full-scale measured RF current flow on the skywires of a real power line. A toroidal current probe is described which is suitable in the MF band for current measurement on a large steel lattice structure such as a power line tower. Instrumentation is described for the measurement of either current magnitude only, or of both magnitude and phase. Thus the current flowing on a power line tower is readily measured by this method. Measurements of skywire current are compared with computations using a highly conductive "perfect" ground model, and using the Sommerfeld-Norton ground model for "lossy" ground of conductivity 10 millisiemens/metre and relative permittivity 15. The two ground models result in similar current distributions, with the peaks and minima in the standing wave pattern at the same positions on the skywire. The lossy ground model results in somewhat less current flow due to the damping introduced into the resonant behaviour of the power line.     

天基雷达相干地杂波模型研究

地杂波特性对天基雷达（SBR）的地面动目标指示（GMTI）功能有很大影响。该文深入研究了SBR相干地杂波的模拟方法,在经典的星载雷达空间几何模型的基础上提出了适用于模拟特定距离门杂波特性的杂波仿真模型,并给出了在该模型下的SBR相干地杂波仿真方法,分析了SBR的多普勒频率特性。该模型提高了相干地杂波模拟的实用性。仿真得到的距离-多普勒二维杂波图证实了该模型的正确性和有效性。     

Elastic waves interacting with buried land mines: a study using the FDTD method

A three-dimensional (3-D) finite-difference model for elastic waves in the ground has been developed and implemented. The model has been created to supplement the development of a sensor that uses elastic waves to detect buried land mines. The model is used to investigate the propagation characteristics of elastic waves in the ground and to explore the interaction of elastic waves with buried land mines. When elastic waves interact with a buried mine, a strong resonance occurs at the mine location. The resonance can be used to enhance the mine's signature and to distinguish the mine from clutter. Results presented in this paper explain the features of elastic wave propagation in the ground and show the interaction of elastic waves with both an anti-personnel mine and an anti-tank mine.     

Closed-Form Expressions for the Total Power Radiated by an Electrically Long Multiconductor Line

Two analytical solutions based on transmission-line theory for the total power radiated by a multiconductor line above a ground plane are proposed. The line is not assumed to be electrically short or close to the ground plane, thus making the proposed model suitable for assessing the emission/immunity of actual transmission lines employed in industrial contexts such as in the automotive domain, railway lines, and power-distribution lines. The model allows an imperfect ground plane to be considered through the complex-image approximation together with propagation losses. Numerical and experimental results are provided as a validation, while an empirical rule to assess the accuracy of the results is proposed. The two expressions aim at allowing fast parametric analysis of radiation during the design phase of the electrical and geometrical configuration of an unshielded multiconductor transmission line.      

静电放电模拟器电路建模分析

从实际的静电放电模拟器结构出发,根据接触放电时静电放电电流的主要特征,考虑到静电模拟器本身、连接线及回路电缆与地平面间产生的分布参数的影响,建立了一个新的静电放电模拟器等效电路模型,并用PSPICE软件对等效电路进行模拟分析,得到了与实测波形基本一致的电流波形.利用该模型讨论了各分布参数对放电电流的影响.结果表明:模拟器体电阻与地间的电感对电流波形影响不大,因此可以忽略,但其与地之间的分布电容对电流波形的低频段有重要影响;连接线分布参数对电流波形的第一峰值及波形光滑度都有影响;回路电缆分布参数主要影响了电流波形中第二个波峰峰值及其位置.     

Accurate power supply and ground plane pair models [for MCMs]

In this paper, we derive a theory and method for the use of two-dimensional (2-D) discrete transmission lines (TL's) or discrete coupled transmission lines (CTL's) in modeling power supply and ground planes accurately. If the stray coupling between power or local ground and global ground is not significant, the discrete TL's model is used. Otherwise the discrete CTL's model is used. An arbitrarily shaped plane pair is discretized into a 2-D TL or CTL array by an automatic mesh algorithm. The equivalent distributed circuit, including skin loss effect at high frequencies, represents this power ground plane pair. The theory is extended to be applicable to a generic multiple dielectric layer structure. The model computation results are in excellent agreement with S parameter measurements for practical frequency ranges, including the first major resonant nulls and peaks. The null or peak of the S parameter frequency response represents the test port interaction with the resonant standing wave of these planes at that frequency. The resultant S parameter data of these models can be condensed into a simpler N port equivalent circuit to represent a larger hierarchical power and ground plane network for fast simulation     

Empirical Near Ground Path Loss Modeling in a Forest at VHF and UHF Bands

Near ground radio wave propagation is examined in a tropical plantation experimentally at VHF and UHF bands. The propagation loss with forest depth is empirically analyzed using an integrated model combining both the foliage induced effect and the ground effect. Several well-known empirical foliage models are compared and analyzed. It is observed that the fitted ITU-R model taking into account the ground reflection, can provide a close approximation to the path loss in a tropical palm plantation. However, the accuracy of this model becomes poor when lateral wave dominates in the VHF band. A modification to the ITU-R model is then proposed taking into consideration the lateral wave effect. The modified model is verified using measured and published data, and found to have higher accuracy for large foliage depth in the VHF band as compared to the existing empirical foliage models.      

Optimization of the quadrifilar helix antenna

Experimental data on the quadrifilar helix antenna have led to an optimum pitch angle and an optimum ground plane size. The ground plane size is an important parameter, and its optimum diameter is about three times the diameter of the helix. The optimum pitch angle is about35deg. Beam patterns and ellipticity data are given for the optimized model. Bandwidth is about 4:1.     

Capacitance of a circular symmetric model of a via hole including finite ground plane thickness

The capacitance of a simplified model of a via hole is calculated based on an integral equation approach for the surface charge density. The formulation of the problem is based on an integral equation for the surface charges combined with an analytical solution at the ground plane opening. The finite ground plane thickness is explicitly taken into account. Numerical data are obtained for a large range of realistic geometrical data. The relative importance of the contribution to the total capacitance coming from the ground plane opening is explicitly evaluated. It is found that the via capacitance is proportional to the square root of its height, at least for the range of geometrical data considered.<>     

Two-stage MAS technique for analysis of DRA elements and arrays on finite ground planes

A two-stage method of auxiliary sources (MAS) technique is proposed for analysis of dielectric resonator antenna (DRA) elements and arrays on finite ground planes (FGPs). The problem is solved by first analysing the DRA on an infinite ground plane (IGP) and then using this solution to model the FGP problem     

Simplified terrain identification and component fatigue damage estimation model for use in a health and usage monitoring system

Improved reliability of military ground vehicle systems is often in direct conflict with increased functionality and performance. Health and Usage Monitoring Systems or HUMS are being developed to address this issue. Traditionally, HUMS applications have been limited to high-cost equipment such as aircraft. In order to apply a HUMS to a relatively inexpensive military ground vehicle, simplified algorithms that derive terrain exposure from a basic set of sensors and estimate fatigue damage accumulated on components whose loading comes primarily from terrain have been developed. Various inputs and statistical parameters are evaluated for this model based on accuracy of terrain identification and quality of fatigue prediction on an example component. The generalized process and recommendations for application of this model to military ground vehicle systems are discussed.     

Space/ground systems as cooperating agents

Within NASA and the European Space Agency (ESA), it is agreed that autonomy is an important goal for the design of future spacecraft, and that this requires on-board artificial intelligence. NASA emphasises deep space and planetary rover missions, while ESA considers on-board autonomy as an enabling technology for missions that must cope with imperfect communications. ESA's attention is on the space/ground system. A major issue is the optimal distribution of intelligent functions within the space/ground system. This article describes the multi-agent architecture for space/ground systems (MAASGS). A MAASGS agent may model a complete spacecraft, a spacecraft subsystem or payload, a ground segment, a spacecraft control system, a human operator, or an environment. The MAASGS architecture has evolved through a series of prototypes. This study recommends that the MAASGS architecture should be implemented in the operational Dutch Utilisation Centre.     

基于集群架构的地海杂波数据存储系统

为了实现对海量地海杂波原始数据、特性分析数据、模型数据等管理,文中提出基于Oracle RAC的集群架构构建地海杂波数据存储系统,依据地海杂波数据以及研究分析的特点,从集群架构、逻辑架构、数据存储技术、数据检索等方面进行设计。对构建的数据库模拟产生1 000 000条记录进行了测试分析,验证了数据库的性能,为地海杂波特性分析提供高性能的数据服务奠定基础。     

A Physical-Optics Model for Double-Bounce Scattering From Tree Stems Standing on an Undulating Ground Surface

In this paper, a model for prediction of radar backscatter from coniferous forests in the VHF and UHF band is proposed. The model includes the double-bounce scattering originating from vertical stems standing on an undulating ground surface and is based on a physical-optics approach. The model can be used to assess the importance of ground topography in synthetic aperture radar (SAR) imagery of forests, and it is applicable to SAR systems using horizontally transmit and receive polarization (HH). The model was validated against data from the airborne SAR systems CARABAS-II and LORA. Precision measurements of ground topography and forest characterization at a single tree level were used as model input to simulate SAR images. The simulated images were compared to radar data in the frequency bands 22–82 and 225–470 MHz, and it was found that the model could predict much of the variation in backscatter observed in images ($R^{2} = hbox {0.44}$ and 0.65 at best, for the lower and higher frequency band, respectively), which should be compared to $R^{2} approx hbox {0.1}$ if the same model, but assuming a flat ground, was used. The results thus indicate that ground topography must be considered when predicting the variations in backscatter in the SAR images studied. The model did, however, fail to predict the absolute values of the backscattered intensity. The reason for the discrepancy is believed to be the value chosen for stem dielectric constant and unmodeled effects due to wave attenuation, tilting stems, and small-scale surface roughness.      

Concerning the horizontal electric field of lightning

In lightning investigations we need simple yet reasonably accurate expressions for the horizontal electric field for an imperfectly conducting ground plant. The Cooray-Rubenstein (see Radio Sci., vol.27, no.4, p.529-38, 1992, and IEEE Trans. Electromag. Compat., vol.38, no.8, p.531-535, 1996) prediction model involves only the horizontal electric field expression for a perfectly conducting ground, the surface impedance, and the tangential magnetic field also for a perfectly conducting ground. We develop an exact version of this relationship and show analytically how and under what conditions it reduces to the CR expression