Theory of characteristic modes for conducting bodies

A theory of characteristic modes for conducting bodies is developed starting from the operator formulation for the current. The mode currents form a weighted orthogonal set over the conductor surface, and the mode fields form an orthogonal set over the sphere at infinity. It is shown that the modes are the same ones introduced by Garbacz to diagonalize the scattering matrix of the body. Formulas for the use of these modes in antenna and scatterer problems are given. For electrically small and intermediate size bodies, only a few modes are needed to characterize the electromagnetic behavior of the body.     

Computation of characteristic modes for conducting bodies

A procedure for computing the characteristic modes for conducting bodies of arbitrary shape is developed. The method is applied to conducting bodies of revolution and to wire objects, and general computer programs are discussed. Illustrative examples of the computation of characteristic currents and characteristic fields are given for a cone-sphere, a disk, and a wire arrow. Modal solutions using these modes are computed for representative antenna and scattering problems to illustrate convergence of the solution as the number of modes is increased.     

A high-frequency method for numerical computation of modes and associated losses of arbitrary cross-section hollow waveguides

In order to describe the main features of the first modes of a self-focusing parallel plate waveguide laser, a numerical method based on a high-frequency formal asymptotic expansion has been developed, which is able to give both the shape of the first modes and the associated losses. In the planar and circular geometry, the method was shown to give the same results as the analytic calculation. A good agreement with experimental results was found in the case of a parallel plate self-focusing waveguide. In this case, examples of numerical results are given for various curvature radii and spacings of the plates.     

New method of computation of electrical Y-matrix for arbitrarilyconnected multielement SAW devices

We treat surface-acoustic wave (SAW) devices as an arbitrary multielement system. To describe it, a modified form of the chain matrix (E-matrix) is introduced. The E-matrix has a property of turning the calculation of the transfer matrix of this system into a simple multiplication procedure. This allows one to perform computation of electrical response of almost any type of SAW device since the total transfer matrix could be reduced to a Y-matrix. Examples and simulation results confirming the method described are shown     

A surface formulation for characteristic modes of material bodies

A theory of characteristic modes for material bodies is developed using equivalent surface currents. This is in contrast to the alternative approach using induced volume currents. The mode currents form a weighted orthogonal set over the material body surface, and the mode fields form an orthogonal set over the sphere at infinity. The characteristic modes of material bodies have most of the properties of those for perfectly conducting bodies. Formulas for the use of these modes in electromagnetic scattering problems are given. A procedure for computing the characteristic modes is developed, and applied to two-dimensional bodies. Illustrative examples of file computation of characteristic currents and scattering cross sections are given for cylinders of different material constants.     

Fast computation of wideband RCS using characteristic basis function method and asymptotic waveform evaluation technique

The Asymptotic Waveform Evaluation (AWE) technique is an extrapolation method that provides a reduced-order model of linear system and has already been successfully used to analyze wideband electromagnetic scattering problems. As the number of unknowns increases, the size of Method Of Moments (MOM) impedance matrix grows very rapidly, so it is a prohibitive task for the computation of wideband Radar Cross Section (RCS) from electrically large object or multi-objects using the traditional AWE technique that needs to solve directly matrix inversion. In this paper, an AWE technique based on the Characteristic Basis Function (CBF) method, which can reduce the matrix size to a manageable size for direct matrix inversion, is proposed to analyze electromagnetic scattering from multi-objects over a given frequency band. Numerical examples are presented to illustrate the computational accuracy and efficiency of the proposed method.     

Fast convenient numerical computation of lognormal characteristic functions

No closed-form expression is known for the lognormal characteristic function. Computation of the characteristic function using numerical integration is time consuming and often converges poorly. Alternative published numerical methods for its evaluation are complex and often valid only for particular values of the dB-spread. A novel definite integral form of the lognormal characteristic function is derived. This form lends itself to rapid and convenient computation of the lognormal characteristic function using simple, common methods of numerical integration.     

Small antenna location synthesis using characteristic modes

It is shown that the efficiency of a small antenna can be substantially increased by properly locating it on its support structure. Characteristic modes are used to determine the optimum location and frequency.     

Interpolated histogram method for area optimised median computation

The article describes an area efficient algorithm for real-time approximate median computation on VLSI platforms. The improvement in performance and area optimisation are achieved through linear interpolation within a reduced number of histogram bins. In order to reduce the hardware utilisation further, an approximation technique for interpolation is also proposed. This approach extends the utility of the histogram method to data sets having a large dynamic range. The performance of the proposed algorithm in terms of mean squared error (MSE) and resource utilisation is provided and compared to that of the existing algorithms. This comparison indicates that more than 60% optimisation in resources is achieved with marginal compromise in the accuracy of the median. The proposed algorithm finds applications in the areas of image processing, time series analysis and median absolute deviation (MAD) computation.     

飞行器参数辨识的一种演化计算方法

将混合遗传算法应用于飞行器气动参数辨识。该方法结合了遗传算法的全局寻优能力和极大似然法的局部寻优能力,使得混合遗传算法不受极大似然法初值选取的影响,同时也解决了遗传算法收敛速度慢和收敛精度较低的问题。在混合遗传算法寻优过程中,仅对最优个体和变异后的个体执行局部寻优操作,从而使得混合遗传算法的计算量维持在一个适当的水平。最后,一个飞行器纵向模型气动参数的辨识仿真表明：混合遗传算法的收敛性和精度都远高于没有采用局部寻优策略的遗传算法。     

New dynamic algorithms for shortest path tree computation

The open shortest path first (OSPF) and IS-IS routing protocols widely used in today's Internet compute a shortest path tree (SPT) from each router to other routers in a routing area. Many existing commercial routers recompute an SPT from scratch following changes in the link states of the network. Such recomputation of an entire SPT is inefficient and may consume a considerable amount of CPU time. Moreover, as there may coexist multiple SPTs in a network with a set of given link states, recomputation from scratch causes frequent unnecessary changes in the topology of an existing SPT and may lead to routing instability. We present new dynamic SPT algorithms that make use of the structure of the previously computed SPT. Besides efficiency, our algorithm design objective is to achieve routing stability by making minimum changes to the topology of an existing SPT (while maintaining shortest path property) when some link states in the network have changed. We establish an algorithmic framework that allows us to characterize a variety of dynamic SPT algorithms including dynamic versions of the well-known Dijkstra, Bellman-Ford, D'Esopo-Pape algorithms, and to establish proofs of correctness for these algorithms in a unified way. The theoretical asymptotic complexity of our new dynamic algorithms matches the best known results in the literature     

New computation approaches for open-loop SSTDMA network synchronization

This paper presents two new open-loop synchronization algorithms for computing the satellite position. One is based on a three-rotational co-ordinate transformation, the other is based on a numerical iteration method. A detailed comparison of these two algorithms with other available algorithms is given with respect to accuracy of the computed separation distances between ground stations and the satellite, sensitivity to measurement and implementation errors, computation speed, and implementation complexity.     

Direct computation of the distribution function from the characteristic function

A simple and exact method to compute the cumulative distribution function directly from the characteristic function is proposed. This method is completely insensitive to errors associated with the divergence of the integral defining the Fourier transform of the distribution function.     

Simple method for obtaining characteristic polarisation states

For a completely polarised wave, a simple method is proposed for obtaining the characteristic polarisation states, in the form of the Stokes vector, showing that the co-polarisation (CO-POL) nulls are the most fundamental characteristic polarisation states, and that the other states can easily be obtained from the expressions of the CO-POL nulls     

A rigorous method for computation of ferrite toroidal phaseshifters

Coupled-wave theory is used to calculate the performance of twin-toroidal phase shifters. Computation results show that this method is effective, rather simple, and easy to handle. In comparison with the single-toroid phase shifter, the twin-toroidal model's phase shift is considerably larger and its production is simpler. The wires carrying magnetizing currents are located in the weak microwave electric field area. Hence, their influence on the performance of the phase shifter is negligible; this also facilitates production. The loss factors of these two kinds of toroid phase shifters are about the same. Experimental results are in good agreement with theoretical analysis. On this basis, it is concluded that coupled-wave theory is a powerful method for treating electromagnetic problems of waveguides loaded with magnetized ferrites     

A fast computation method for time scale signal denoising

This paper presents a novel and fast scheme for signal denoising in the wavelet domain. It exploits the time scale structure of the wavelet coefficients by modeling them as superposition of simple atoms, whose spreading in the time scale plane formally is the solution of a couple of differential equations. In this paper, we will show how the numerical solution of such equations can be avoided leading to a speed up of the scale linking computation. This result is achieved through a suitable projection space of the wavelet local extrema, requiring just least squares and filtering operations. Intensive experimental results show the competitive performances of the proposed approach in terms of signal to noise ratio (SNR), visual quality and computing time.     

一种新的雷达重频模式识别方法

针对雷达重频模式识别中存在的问题,提出了一组新的二维特征向量,对重频固定、重频抖动、重频参差、重频分组和重频滑变5种典型的重频模式进行了识别。仿真结果表明,该方法正确识别率高,为工程应用提供了一种新的思路。     

Biorthonormal-basis method for the vector description ofoptical-fiber modes

This paper gives the theoretical basis for the development of real vector modal methods to describe optical-fiber modes. To this end, the vector wave equations, which determine the electromagnetic fields, are written in terms of a pair of linear, nonself-adjoint operators, whose eigenvectors satisfy biorthogonality relations. The key of our method is to obtain a matrix representation of the vector wave equations in a basis that is defined by the modes of an auxiliary system. Our proposed technique can be applied to fibers with any profile, even those with a complex refractive index. An example is discussed to illustrate our approach     

New formulae for Tate pairing computation on Weierstrass curves

This paper proposes a variation of Miller＇s algorithm for Tate pairing computation on Weierstrass curves. Unlike the original Miller＇s algorithm which consists of two major operations： the doubling operation and the addition operation, this new algorithm replaces the addition with a doubling-addition （DA） operation to take the advantage of the fast point doubling-addition formula. Explicit formulae are given for the new algorithm. We suggest to use the new formulae for Weierstrass curves with general parameters for Tate pairing to gain a better performance.     

差分分析中的特征概率计算问题研究

该文指出了长期以来在差分密码分析中所采用的差分特征概率计算方法与差分分析基本原理不相符合的矛盾，对这一问题进行了深入研究，给出了二者等价的充分条件，力图解决差分分析方法的理论基础问题．