Transient Analysis of a Directional Coupler Using a Coupled Mlcrostrip Slot Line in Three-Dimensional Space (Short Paper)

In recent MIC techniques, double-sided MIC has been studied because its advantages in propagation characteristics are greater than that conventional MIC's. A coupled microstrip slotline is one of them. Its application to various circuit elements has often been discussed. But the coupled microstrip slotline is essentially three-dimensional structure, so the analysis demands a rigorous three-dimensional treatment. Also, the recent high-speed pulse technique demands analysis in the time domain. The present paper treats a directional coupler using the coupled microstrip slotline in three-dimensional space and time. The results of the directional coupler analysis is presented with the complicated time variation of the three-dimensional electromagnetic field. So, the mechanism of the directional coupling phenomena that is produced by the propagation characteristics of the even and odd modes is presented in the time domain, In particular, the instantaneous diagram of the Poynting vector details the energy flow in the transient process. For the analysis of the characteristics of the complex microwave device, these results present the utilities of the various field distributions that are obtained by the three-dimensional vector analysis in the time domain.     

Transient analysis of nonuniform transmission lines with nonlinear terminal networks

A semi-analytical method in time domain is presented for analysis of the transient response of nonuniform transmission lines. In this method, the telegraph equations in time domain is differenced in space domain first, and is transformed into a set of first-order differential equations of voltage and current with respect to time. By integrating these differential equations with respect to time, and precise computation, the solution of these differential equations can be obtained. This method can solve the transient response of various kinds of transmission lines with arbitrary terminal networks. Particularly, it can analyze the nonuniform lines with initial conditions, for which there is no existing effective method to analyze the time response so far. The results obtained with this method are stable and accurate. Two examples are given to illustrate the application of this method.     

线天线及天线阵的时域传输线矩阵法分析

本文针对线天线及天线阵的频域分析方法的缺点，首次将时域传输线矩阵法应用到这一领域，应用时域ＴＬＭ法时，只需经过一次运逄就可以得到天线及天线阵各个区域的场特性，本文计算方法及数值结果表明，运用时域ＴＬＭ法可以对各种大型天线阵进行有效的分析，便于工程应用。     

基于变换域选择的干扰抑制技术

在无线通信系统中存在各式各样的干扰,尤其在军事通信中。不同类型干扰信号在时／频域具有不同的信号特征。现有的干扰抑制算法都是在特定域上进行干扰抑制。研究了一种基于变换域选择的干扰抑制算法,并提出了一种改进的度量选择算法,该算法可以有效地选择最佳变换域去抑制干扰。这种算法简单、且容易实现,复杂度也比较低。仿真结果表明这种算法对于抑制不同的干扰有较好的性能。     

A fast encoding algorithm for fractal image compression using theDCT inner product

In this paper, a fast encoding algorithm is developed for fractal image compression. At each search entry in the domain pool, the mean square error (MSE) calculations of the given range block and the eight dihedral symmetries of the domain block are obtained simultaneously in the frequency domain, in which the redundant computations are all eliminated in the new encoding algorithm. It is shown in software simulation that the encoding time is about six times faster than that of the baseline method with almost the same PSNR for the retrieved image. The fast algorithm is performed to deal with the eight dihedral symmetries at each search entry. Therefore, it can be applied to various enhanced algorithms which are equipped with quadtree, classification, and other mechanisms.     

Vers la simplification spatiale des tarifs téléphoniques (un exercice de style)

This paper is divided into three parts: first, a presentation of the trends which appear in the evolution of telephone pricing: presently, spatial or geographical complexity together with relative simplicity in the time domain; in the future a growing simplification in the spatial domain together with a growing weight of the time (duration and time of the day). Secondly, different pricing schemas are described. In every case, there only remaind a few charging zone and quantitative results are discussed. The limiting case of complete postalization (no influence of distance) is examined. The consequence of a decrease in the tax unit is also considered. It would allowed for a more convenient taxation of short duration calls. In conclusion, foreseeable implications of modernizing telephone pricing are evaluated. Local disparities in telephone consumption are evidenced and transfers of revenues would therefore take place between the various categories of users.     

基于FEKO的频率步进导引头回波仿真

频率步进雷达(SFR)导引头通过在频域进行带宽合成,距离分辨力显著提高,可以分辨出复杂目标的细节特征,从而进行抗干扰分析与目标识别。在进行SFR回波信号仿真时,要求回波模型能符合并反映目标的细节特征,目标不能等效为点目标,而散射中心提取法则意味着散射点的舍弃和合并,对目标的细节描述并不准确,为此提出基于FEKO的复杂目标回波信号产生方法。根据频率步进雷达信号时域特征,推导出直接利用FEKO的散射场数据进行时域回波计算的数学模型,并使用FEKO提取目标在各种入射角度下的散射场幅度和相位信息进行存储,在仿真时直接调用散射场数据进行时域回波计算,从而得到复杂目标的高拟真度回波信号模型,在空空导弹数字仿真、半实物仿真和抗干扰研究中具有实用意义。     

雷达技术体制发展创新的理论基础探讨

研究了雷达自诞生以来各种新技术体制发展创新的历程;提出了雷达电磁信号波形与目标信息关系的基本模型;在此基础上,探讨了雷达系统技术体制发展创新的理论基础。认为,寻找选择能够采集目标新信息的电磁信号波形(时频域、空间域、极化域或它们的联合域),并形成新电磁信号波形回波的信号处理和目标新信息提取方法,是雷达系统技术体制发展创新的理论基础。     

FDTD calculation of scattering from frequency-dependent materials

An efficient method to include frequency-dependent materials in finite difference time domain calculations based on the recursive evaluation of the convolution of the electric field and the susceptibility function has previously been presented. The method has been applied to various materials, including those with the Debye, Drude, and Lorentz forms of complex permittivity, and to anisotropic magnetized plasmas. Previous demonstrations of this approach have been confined to total field calculations in one dimension. In this paper the recursive convolution method is extended to three-dimensional scattered field calculations. The accuracy of the method is demonstrated by calculating scattering from spheres of various sizes composed of three different types of frequency-dependent materials     

辛时域多分辨率算法在波导结构仿真中的应用

文中基于Daubechies紧支撑尺度函数的辛时域多分辨率(symplectic multiresolution time-domain,S-MRTD)算法,在时间方向上采用优化的3级3阶的辛算子进行离散,以减少时间步的迭代次数,在空间方向上采用小波尺度函数展开算法进行离散.给出了S-MRTD算法的三维迭代公式,并将其...     

A low-frequency analog for a Gunn-effect oscillator

After a brief introduction to the Gunn effect and an explanation of the proposed equivalent circuit of the Gunn diode, a low-frequency (5 Hz) lumped-circuit analog is described. The analog is able to simulate the initiation and circuit quenching of the domain, the transit time of a dipole domain, and the dynamic negative-resistance characteristic associated with the domain. Thus the analog can qualitatively account for many properties of the dipole domain modes. A short section also shows how, within certain limitations, the LSA mode can be investigated by means of the analog. The analog enables the behavior of the Gunn diode to be studied under various forms of loading, and the results to be related to a wide range of actual diodes in microwave circuits by a simple scaling process. The sciencies of various modes can be compared. Photographs are presented of an oscilloscope display showing the relevant current and voltage waveforms (including the domain voltage) for a pure resistive load, a parallel resonant load, and a series inductive load. The provision for a direct display of domain voltage means that a particularly clear visual distinction is possible between transit-time and circuit-quenched modes of oscillation. Tuning by variation of the external load is demonstrated; the importance of the semiconductor's current peak-to-valley ratio and of the choice of transit time in determining the efficiency in a given mode is illustrated. A possible explanation for the reported observation of subharmonics is provided by the analog, on the basis of alternate modes, i.e., a cycle of circuit-quenched operation followed by a cycle of transit-time operation. The limitations of the analog are discussed together with ways in which some of them could be overcome.     

不同接地体冲击接地阻抗的时域分析

用时域有限差分(FDTD)法对接地体冲击接地阻抗进行了时域分析.计算了脉冲泄流时不同接地体的冲击接地阻抗(TGR),并分析了接地体自身形状及电磁参数对TGR的影响.通过分析得到如下结论:在接地体上下表面埋深相同,表面积相同,但接地体形状不同时,TGR基本相同;体积相同,表面积越大,TGR越小,但用刻槽方法使表面积增大不能减小TGR;非金属接地体电导率足够大时具有与导体一样的泄流效果;接地体磁导率变化对TGR影响很小.     

一种新的二相码旁瓣抑制滤波器

二相编码是一种在雷达脉冲压缩中得到广泛应用的波形,但是一般的二相码波形的旁瓣抑制算法只适用于短码(如Barker码等),且设计得到的滤波器阶数比较高。本文提出了一种新的基于时域综合的二相码旁瓣抑制滤波器,能适用于各种长度的二相码,包括m序列等。文中给出了m序列和Barker码旁瓣抑制滤波器结果,并与现有的滤波器性能进行了比较。     

Stability of discretized partial element equivalent EFIE circuitmodels

The instabilities associated with integral equation techniques for-the solution of electromagnetic problems in the time domain are well known. Instabilities may be due to either the numerical technique used for the time integration, or problems created by the discrete representation for the numerical solution of the problem. In this paper, we concentrate on the discretization issue. The stability problem occurs for various discretizations and formulations. Here, we use the partial element equivalent circuit (PEEC) formulation of the electric field integral equation (EFIE) in the circuit domain. This leads to a better understanding of the issues at hand. We show why the discretized model can be unstable and we suggest a circuit motivated technique to stabilize the solution     

Techniques de calibration et de traitement des signaux pour la mesure de I’efficacite de blindage des cables au moyen de methodes temporelles

The purpose of this paper is to show the influence of the various time domain parameters on the precision of the result in the frequency domain for the determination of the transfer impedance of the coaxial cable. In the first part of the paper the conversion is made through the discrete Fourier transform. The ratio of the spectrum of the cross talk voltage and the spectrum of the disturbing current is computed to obtain the transfer impedance of the cable. In the second part we purpose some techniques for increasing the dynamic range of the characteristic of the transfer impedance. The average and the determination of the Dirac response of the cable are commented on few examples which summarize the main important point of this method.     

时域有限差分法分析平面周期性结构电磁特性

本文阐述了如何用时域有限差分法分析平面周期结构的电磁特性.FDTD方法与周期性边界条件、吸收边界条件结合,构成分析各种周期性结构电磁特性准确、有效的通用工具.但为了在时域表示宽带信号的周期性边界条件,必须引入辅助场量并加以适当变形才可建立时域迭代式.文中以平面双周期频率选择表面为例,给出了计算思路和结果.     

空时编码技术在OFDM系统中的研究

正交频分复用（OFDM）技术是一种多载波调制技术,其子载波之间相互正交,可以高效地利用频谱资源。空时编码是一种用于多发射天线的编码技术,该编码在多根发射天线和各个时间周期的发射信号之间能够产生空间域和时间域的相关性,从而使接收机克服多入多出（MIMO）信道衰落和减少发射误码率。这两种技术的结合,实现了最大分集增益,误码性能得到很好改善,而且具有系统实现复杂度低的特点。     

隐蔽直扩通信研究

在对直扩信号能够被检测截获的原因进行深入分析的基础上,针对现有各种直扩信号盲检测截获方法的关键所在,提出通过对直扩信号进行加扰和改变扩频码码速相结合的方法来改变其时域统计特性及其频域、谱相关域特征增强其通信隐蔽性的思想方法,并对经过处理后的直扩信号的特性进行了模拟探讨分析。     

仿真软件在微波技术教学中的应用

本文以微波负载单支节匹配和时域反射仪为例,以同轴线为传输线,建立几何模型,用软件数值仿真,分别从频域和时域研究同轴线传输特性参数,目的是借助仿真软件理解微波传输物理量在频域和时域中不同的表现形式,用可视化的仿真结果帮助理解物理内涵,同时把仿真软件结合实际应用,以此提高学生在电磁场和微波技术中工程应用方面的能力。