Numerical and experimental studies of current distributions on thinmetallic posts inside rectangular waveguides

A fast converging and stable moment method solution for the current distribution on arbitrary size rectangular obstacles mounted transversely inside the rectangular waveguide has been developed. A special arrangement of piecewise sinusoidal and pulse basis functions has been utilized to determine the transverse current distributions on the obstacles and their scatterings in the waveguide. The method has been compared well with the Marcuvitz's results for the inductive and capacitive posts and the experimental data of an arbitrary size rectangular obstacle     

Multiple-Post Inductive Obstacles in Rectangular Waveguide

A complete analysis of multiple-post inductive obstacles in rectangular waveguide is presented. A moment method solution with exponential ( e/sup jnTheta/) expansion and weighting functions is used in a Galerkin solution. Post currents are expressed as a Fourier series. As many Fourier series terms (e/sup jn Theta/) as desired may be included. All higher order (cutoff) mode interactions between posts are taken into account. The solution is rapid and accurate, and errors maybe controlled (specified). Data are given for the triple-post obstacle and for a two-element filter.     

Composite inductive posts in waveguide-a multifilament analysis

A multifilament moment solution for the analysis of composite dielectric posts in rectangular waveguide is presented. This method permits the analysis of inductive posts composed of disparate regions, each with its own homogeneous complex permittivity. The solution uses the fields generated by sets of fixed-amplitude current filaments to simulate both the field scattered by the posts and the field inside every homogeneous region comprising the posts. Point matching the electric and magnetic fields on the boundaries between regions of different permittivity yields the as-yet-unknown amplitudes for the current filaments. These currents can in turn be used to calculate field-related parameters of interest such as the scattering matrix and the equivalent circuit parameters. Inductive posts of any shape, composition, size, location, and number can be handled by this method accurately and with very good numerical efficiency. The results obtained are in good agreement with the few cases for which data are available. They also behave well in the limiting cases studied. The solution is further applied to other situations for which no experimental or calculated results are known     

对矩形波导中任意高度细导体柱的研究

本文利用矩量法对矩形波导中任意高度的细柱体进行了研究。从柱体表面的电场积分方程出发,选用脉冲基函数与点匹配的方法求解。对其中收敛较慢的一些无穷级数,采用了若干数学处理,大大加快了收敛速度。对柱体上的电流分布进行了较详细的讨论,得出了一个新的较为精确的解析表达式,求得的等效阻抗与有关文献中的实验值相当吻合。     

Analysis of Inductive Dielectric Posts in Rectangular Waveguide

A rapidly converging moment solution for the complete analysis of homogeneous dielectric posts of the inductive type in rectangular waveguide is presented. The moment method approach uses filamentary currents to simulate both the field scattered by the post and the field inside the post and in turn point-matches the continuity conditions for the tangential components of the electric and magnetic fields across the post surface. The procedure is simple to execute and is general in that inductive posts of arbitrary smooth shape, size, location, and number, Iossless as well as lossy, can be handled effectively. Data are given and compared with the few cases for which approximate results are available. The technique is further appfied to other situations where no experimental data or other analytic results are available.     

改进的IPO-CBFM 分析电大尺寸腔体的RCS

计算电大尺寸复杂腔体电磁散射时,迭代物理光学法与矩量法的混合方法（IPO-MM）是有效方法之一。为 了提高该算法的效率,在IPO 中使用快速远场近似（FAFFA）技术加速,在腔体复杂部分的MM 中使用特征基函数法 （CBFM）技术加速。在新的IPO/FAFFA-CBFM 混合法中,利用分块技术对求解矩阵进行降秩,使用传统的求解方法 即可求解方程,而不需要预条件处理与低频法的迭代求解方法。结果表明,新的混合方法有更高的计算效率和在单机 平台上解决更大复杂腔体电磁问题的能力。     

高斯随机粗糙表面的电磁散射研究

本文利用数值方法研究高斯随机粗糙表面的电磁散射问题.应用矩量法研究高斯随机粗糙表面的电磁散射可以使我们获得较为精确的数值结果.但是,对于表面散射,应用矩量法时,表面未知变量的数目非常大,即使对于一维表面也需要几千个未知变量.当我们求解矩阵方程时,计算机对求解的问题有几个限制,一个是内存的限制,一个是速度的限制.为了克服内存的限制,发展了许多迭代数值算法.本文发展了一种新的数值迭代方法.利用这一方法,我们对高斯随机粗糙表面的电磁散射问题进行了研究,并与矩阵反演方法进行了比较.所得结果表明,这种新的迭代法具有很好的收敛性.     

Design of Time–Frequency Optimal Three-Band Wavelet Filter Banks with Unit Sobolev Regularity Using Frequency Domain Sampling

In this paper, we design three-band time–frequency-localized orthogonal wavelet filter banks having single vanishing moment. We propose new expressions to compute mean and variances in time and frequency from the samples of the Fourier transform of the asymmetric band-pass compactly supported wavelet functions. We determine discrete-time filter of length eight that generates the time–frequency optimal time-limited scaling and wavelet functions using cascade algorithm. Time–frequency product (TFP) of a function is defined as the product of its time variance and frequency variance. The TFP of the designed functions is close to 0.25 with unit Sobolev regularity. Three-band filter banks are designed by minimizing a weighted combination of TFPs of wavelets and scaling functions. Interestingly, empirical results show that time–frequency optimal, filter banks of length nine, designed with the proposed methodology, have unit Sobolev regularity, which is maximum achievable with single vanishing moment. Design examples for length six and length nine filter banks are given to demonstrate the effectiveness of the proposed design methodology.     

Multiple Dielectric Posts in a Rectangular Waveguide

This paper presents a complete analysis for a system of Iinear, homogeneous, and isotropic dielectric posts in a rectangular waveguide. These posts are assumed uniform along the narrow side of the waveguide, but are otherwise of arbitrary cross section and thickness. The scattering and impedance matrices describing the effect of the posts on the dominant waveguide mode are derived. The latter is then realized as a two-port T-network. A moment procedure is devised and applied to a set of test problems with a wide variety of post configurations to compute the scattering parameters and equivalent network elements. The accuracy and convergence aspects of the numerical solution are also investigated. The branch and network resonances are determined for some post configurations.     

A simple adaptive algorithm for real-time processing in antenna arrays

A new adaptation algorithm designed for real-time data processing in large antenna arrays is presented. The algorithm is used to determine the set of filter coefficients (weights) which minimizes the mean-square error in a multidimensional linear filter. The algorithm forms an estimate of the target signal, which is assumed to be of interest, in the presence of interfering noises. It is assumed that the direction of arrival and spectral density of the target signal are known a priori. No such information is assumed to be available regarding the structure of the interfering noise field. The a priori target information is incorporated directly into the adaptation procedure using a modified gradient descent technique. The mathematical convergence properties of the algorithm are presented and a computer simulation experiment is used as an illustration. It is shown that as the number of iterations becomes large, the expected value of the adaptive solution converges to the minimum mean-square-error solution. It is further shown that the variance of the adapted filter about the optimum solution can be made arbitrarily small by appropriate choice of a scalar constant in the algorithm. These results are based on the assumption that the array signals are Gaussian and that successive time samples are statistically uncorrelated. Thus, the new algorithm is shown to converge to the optimum processor in the limit as the number of adaptations becomes large. Any disadvantage which may arise in the use of such an asymptotically optimum system is offset by the extreme simplicity of the adaptive procedure. This simplicity should prove to be particularly useful in many of the practical array processing problems recently encountered in seismic and sonar data processing.     

A multistrip moment method technique and its application to thepost problem in a circular waveguide

A moment method technique for solving obstacle problems in a waveguide is presented. Instead of using a multifilament current representation, which leads to a slowly converging series, a multistrip representation of the current is proposed. In the procedure, the matrix elements are determined by a series involving integrals of mode functions over the strips and the convergence is improved. The true currents on obstacle surfaces are replaced by equivalent planar currents in a number of waveguide cross sections inside the obstacle. The technique is applied to a pair of metallic posts in the TE₁₁-mode circular waveguide. Numerical results are compared with experimental data     

A waveguide transverse slot for array applications

The characteristics of a radiating rectangular transverse slot in a rectangular waveguide have been studied. A moment method solution is used with entire basis expansion and testing functions (Galerkin) including the effect of wall thickness. The results are presented in terms of normalized resistance and reactance versus slot length and frequency. Excellent agreement with a previous pulse basis solution is found, as well as with measured data. An array of resonantly spaced transverse slots radiates large grating lobes. A spatial filter using baffles to suppress the grating lobes is described, suppressed. The effect of the baffles on the transverse slot impedance is analyzed for the case of baffles with infinite height     

A new class of orthonormal symmetric wavelet bases using a complexallpass filter

This paper considers the design of the whole sample symmetric (WSS) paraunitary filterbanks composed of a single complex allpass filter and gives a new class of real-valued orthonormal symmetric wavelet bases. First, the conditions that the complex allpass filter has to satisfy are derived from the symmetry and orthonormality conditions of wavelets, and its transfer function is given to satisfy these conditions. Second, the paraunitary filter banks are designed by using the derived transfer function from the viewpoints of the regularity and frequency selectivity. A new method for designing the proposed paraunitary filterbanks with a given degrees of flatness is presented. The proposed method is based on the formulation of a generalized eigenvalue problem by using the Remez exchange algorithm. Therefore, the filter coefficients can be easily obtained by solving the eigenvalue problem, and the optimal solution is attained through a few iterations. Furthermore, both the maximally flat and minimax solutions are also included in the proposed method as two specific cases. The maximally flat filters have a closed-form solution without any iteration. Finally, some design examples are presented to demonstrate the effectiveness of the proposed method     

Penalized Gaussian mixture probability hypothesis density filter for multiple target tracking

Bayesian multi-target filter develops a theoretical framework for estimating the full multi-target posterior which is intractable in practice. The probability hypothesis density (PHD) is a practical solution for Bayesian multi-target filter which propagates the first order moment of the multi-target posterior instead of the full version. Recently, the Gaussian Mixture PHD (GM-PHD) has been proposed as an implementation of the PHD filter which provides a close form solution. The performance of this filter degrades when targets are moving near each other such as crossing targets. In this paper, we propose a novel approach called penalized GM-PHD (PGM-PHD) filter to improve this drawback. The simulation results provided for various probabilities of detection, clutter rates, targets velocities and frame rates indicate that the proposed method achieves better performance compared to the GM-PHD filter.     

基于散射中心的风电机叶片散射电场求解

为降低雷达系统的数据处理量及实现风电机实时目标特征识别,必须寻求风电机叶片散射电场的快速求解方法。针对传统电磁求解算法需处理巨量风电机叶片散射电场数据的问题,突破传统以超大电尺寸目标实体为基本单元进行广域空间电磁散射积分计算的思想,提出了一种基于散射中心的风电机叶片散射电场求解方法。基于非衰减指数和散射中心模型,通过距离-多普勒算法构建风电机叶片的雷达逆合成孔径图像,采用CLEAN 算法并结合相关系数提取风电机叶片的散射中心参数集,最终以散射中心产生的散射电场数据等效替代叶片本体的全部散射数据,实现了叶片散射电场的快速求解。以Vestas V82-1.65MW 型风电机为例,以矩量法计算结果为基准,文中所提方法计算准确度为93.20%,数据的压缩比达76.81,计算量的数量级比矩量法降低了106。     

A hybrid technique for combining the moment method treatment of wire antennas with the GTD for curved surfaces

This hybrid technique is a method for solving electromagnetic problems in which an antenna is located near a conducting body. The technique accomplishes this by casting the antenna structure in a moment method (MM) format, then modifying that format to account for the effects of the conducting body via the geometrical theory of diffraction (GTD). The technique extends the moment method to handle problems that cannot be solved by GTD or the moment method alone. Wire antennas are analyzed to find their input impedance when they are located near perfectly conducting circular cylinders, although the methods used are not restricted to circular cylinders. Three orthogonal orientations are identified, and antennas to match them are analyzed. For each case, the hybrid solution is checked with one of three independent solutions: an MM-eigenfunction solution, image theory, or experimental measurement. In almost all cases, excellent agreement is obtained due in large part to the fact that the moment method near fields are, for the first time, cast into a ray optical form.     

Inductive Posts and Diaphragms of Arbitrary Shape and Number in a Rectangular Waveguide

Consider a finite number of posts and/or diaphragms located close to each other in a rectangular waveguide. These are assumed to be perfectly conducting, of arbitrary shape, and uniform in the direction parallel to the narrow side of the waveguide, i.e., of the inductive type, The solution of the problem involves determining the network describing the effect of the posts and diaphragms on the waveguide dominant mode. A moment procedure is devised and applied to a set of test problems. The simplicity and generality of the procedure, together with its excellent performance, as indicated by the results obtained, clearly shows that it is a powerful tool worth using.     

Filtre intégré à transferts récursifs

A new fully integrated mos frequency filter is suggested, using passive charge routing structure. The principle of operation, the synthesis procedure, and the first experimental results are discussed. This new device has to be compared with finite impulse CCD-filters and switched capacitor filters. Large improvements are expected in terms of silicon area and power consumption. Finally, this solution should be of large economical interest for digital communications.     

Nonlinear state estimation for uncertain systems with an integralconstraint

This paper considers a problem of robust filtering for a class of uncertain nonlinear systems. The solution involves a set-valued state estimate that is obtained by solving a Hamilton-Jacobi-Bellman equation. In addition, a less computationally intensive approximate solution to the problem is obtained for filtering problems defined over a large time interval. The paper also presents an approximate solution to the robust filtering problem, which leads to a robust version of the extended Kalman filter     

渐进扩展卡尔曼滤波器

渐进贝叶斯方法将贝叶斯更新步骤等效为伪时间上的连续演化过程,以实现对状态的后验估计.本文基于渐进贝叶斯框架,导出一种新的高斯型非线性滤波算法.在线性高斯条件下推导了渐进贝叶斯方法的精确解;证明了对于由线性高斯解确定的动态系统,其均值和协方差矩阵满足的微分方程与常数状态估计的Kalman-Bucy滤波器是一致的.对于非线性系统,利用一阶Taylor展开推导了近似解表达式,进而导出渐进扩展卡尔曼滤波器.仿真算例表明新滤波器性能较扩展卡尔曼滤波器有大幅提高,且避免了窄形似然函数带来的滤波性能恶化问题.