On geometric properties of the decorrelator

We discuss the geometric properties of the multiuser decorrelator receiver. In particular we show that the prevalent geometric interpretation of the correlating vectors comprising the decorrelator receiver in terms of orthogonal projections of the signature vectors is incorrect. The correct interpretation established is that the correlating vectors are oblique projections of the signature vectors onto appropriate spaces. Furthermore, we show that each branch of the decorrelator consists of an oblique projection onto the space spanned by the corresponding user's signature vector along the space spanned by the interferers, followed by a correlator with correlating vector equal to the corresponding user's signature vector     

Theory and performance of acoustical dispersive surface wave delay lines

A summary is given of properties of Love and Rayleigh waves in stratified isotropic media. The study of propagation of such waves in anisotropic and piezoelectric media, carried out in view of obtaining "pure" modes, shows that two modes can be "pure" and only one of them at a time can be piezoelectrically stiffened. The Rayleigh wave is stiffened if the sagittal plane is a plane of symmetry whereas the Love wave is stiffened if the perpendicular to the sagittal plane is a binary axis. The problems in devising dispersive delay lines using these waves are discussed and the pairs of materials which seem to be the most interesting ones are given together with the different excitation methods and expected performance of these delay lines relating to large bandwidths and high compression ratios. The results of experiments carried out with Love and Rayleigh waves excited by ceramic transducers directly bonded onto the layer show that the total untuned insertion losses can be less than 20 dB with a 2.5-MHz bandwidth and less than 50 dB with a 100-MHz bandwidth. Also described is the performance of a delay line whose time delay variation is nearly 8 µs with a 30-MHz bandwidth, the central frequency being 32.5 MHz.     

Guided Waves in Moving Media

This paper contains a theoretical study of the guided waves in a moving isotropic medium. The normal modes which can exist in a circular or rectangular wave guides are found by solving the Maxwell-Minkowski Equations subject to the appropriate boundary conditions. By certain transformations of field vectors, it is possible to change the Maxwell-Minkowski Equations into familiar forms such that the method of vector potentials can be applied to derive complete expressions for the field vectors. The results demonstrate that expressions for the propagation constant and the transverse-wave impedance and admittance in stationary media are modified by terms independent of the guide geometry when the media are moving.     

Rigorous formulation of scattering at a randomly varying impedanceplane: general case of oblique incidence

The problem of scattering of electromagnetic plane waves at one-dimensional surfaces (random gratings) is solved in the general case in which the incident wave vector does not lie on the main section of the cylindrical surface (oblique incidence). The scatterer is simulated by a plane boundary characterized by a coordinate-dependent impedance that varies along one of the two coordinates on the surface. This representation could be regarded as a canonical model of one-dimensional surfaces with height corrugations. A rigorous electromagnetic formalism for calculating the fields scattered at the impedance plane is presented. The fields above the scatterer are represented by spectral domain expansions. It is shown that the wave vectors of the scattered waves lie on the surface of a cone containing the direction of specular reflection and whose axis coincides with the direction of the grooves of the random grating. The theory is exemplified by calculating the angular distribution of the mean intensity scattered from an ensemble of surfaces with similar statistical parameters     

Metaparticles of Pulsed Wave Fields

Properties of elementary particles of pulsed (localized) electromagnetic and acoustic wave fields directionally radiated by aperture sources (antennas, lasers, acoustic diaphragms) in free space and homogeneous isotropic media, for which the term metaparticle is used, are considered. The structure of the wave field and the energy transferred by the metaparticles are presented. The results obtained for the presented scalar theory of metaparticles of pulsed transverse electromagnetic (TEM) waves and longitudinal elastic acoustic waves can be extended to vector pulsed wave modes guided by layered inhomogeneous guiding media and guiding technical devices (waveguides).     

Tapered wave with dominant polarization state for all angles ofincidence

Typical applications of the method of moments (MoM) to rough surface three-dimensional (3-D) electromagnetic scattering require a truncation of the surface considered and call for a tapered incident wave. It is shown how such a wave can be constructed as a superposition of plane waves, avoiding problems near both normal and grazing incidence and providing clean footprints and clear polarization at all angles of incidence. The proposed special choice of polarization vectors removes an irregularity at the origin of the wavenumber space and leads to a least squared error property of the wave. Issues in the application to 3-D scattering from an object over a rough surface are discussed. Approximate 3-D scalar and vector tapered waves which can be evaluated without resorting to any numerical integrations are derived and important limitations to the accuracy and applicability of these approximations are pointed out     

电磁波极化形式的频域判据

电磁波极化的判定问题是电磁场理论教学中的重点和难点。当电磁波的电场分量和波矢量表达式是坐标基矢量的组合形式时,学生往往难以用右手定则判定其极化形式。本文从电磁波极化定义出发,结合有向曲线绕向的计算方法和复矢量运算法则,给出了极化形式的频域判据。学生直接对电场复矢量进行简单的矢量乘法运算即可完成判定,提高了解决此问题的效率和准确度。     

Digital techniques for ULF wave polarization analysis

Digital power spectral and wave polarization analysis are powerful techniques for studying Ulf waves in the earth’s Magnetosphere. Four different techniques for using the spectral matrix to perform such an analysis have been presented in the literature. Three of these techniques are similar in that they require transformation of the spectral matrix to the principal axis system prior to performing the polarization analysis. The differences in the three techniques lie in the manner in which determine this transformation. A comparative study of these three techniques using both simulated and real data has shown them to be approximately equal in quality of performance. The fourth technique does not require transformation of the spectral matrix. Rather, it uses the measured spectral matrix and state vectors for a desired wave type to design a polarization detector function in the frequency domain. The design of various detector functions and their application to both simulated and real data will be presented.     

Propagation and Scattering in Radially Flowing Media

The first-order (in v/c) vector wave equation for electromagnetic waves in moving media is solved for radially moving media. Two modes of flow are considered, the two-dimensional case of media flowing radially, symmetrically with respect to the z axis, and the three-dimensional case where the flow is symmetrical with respect to the origin. It is shown that the solution differs from the case of media at rest by a scalar multiplicative factor, involving the radius and the velocity. Propagation of a plane wave is discussed, and the local behavior is interpreted in terms of a ray propagating in the moving medium. It is shown that for an outgoing flow, the ray moves away from the origin in the finite domain. At large distances the ray enters and emerges from the medium in the same direction. Scattering by a cylinder and by a sphere, symmetrical with respect to the two-, and three-dimensional flow, respectively, are discussed. It is shown that the scattering amplitude is velocity-independent. This result is contrasted with former cases of scattering in moving media.     

Code construction for the T-user noiseless adder channel

A general method for constructing codes for the T-user noiseless adder channel is proposed which achieves the largest sum rate known. The authors consider a multiple-access communication system. In this system, T statistically independent sources which use binary block codes C₁ ,...,C_T of equal length n, simultaneously transmit information via one common channel, maintaining synchronization with respect to words and bits. The output of the adder channel is the (T+l)-ary vector which is the component-wise arithmetic sum of the transmitted binary vectors. The task of the decoder is to uniquely determine the messages of all users     

Scattering by thin dielectric strips

A plane wave incident on a thin dielectric strip with infinite length is considered, letting the incident electric field vector be parallel with the edges of the strip. The field is expanded in the dielectric region as the sum of three plane waves (the forced wave and two surface waves). Thex-axis andy-axis propagation constants are known for each wave, and Galerkin's method is employed to determine the amplitudes of these waves. Finally, the far-zone scattered field is determined by considering the polarization currents radiating in free space. Numerical data are presented to illustrate the scattering properties of lossless and lossy dielectric strips as a function of the angle of incidence and the width of the strip. The calculations show excellent agreement with an earlier moment method using pulse bases and point matching.     

Guided Waves in Inhomogeneous Focusing Media Part I: Formulation, Solution for Quadratic Inhomogeneity

This work is a theoretical study of waves in a circular-cylindrical radially inhomogeneous guiding medium. A vector theory based upon Maxwell's equatious is used to derive linear homogeneous fourth-order equations satisfied by the longitudinal electric and magnetic field components for a medium in which the permittivity decreases monotonically from the propagation axis. The percentage change of permittivity from the guide axis to some radius a is assumed small. For modes with propagation constants approximately equal to the wave number at guide center, all field components are shown to satisfy second-order differential equations. In particular, all transverse field components are proportional to a single scalar function. In a Iossless system with no containing boundary, a new class of polynomial-Gaussian solutions describes the longitudinal fields for the case of a quadratically decreasing permittivity, while the transverse fields are Gaussian-Laguerre. Mode patterns, propagation constants, and orthogonality relations are given. It is shown analytically that the modes tend to TE or TM as the mode order increases. Moreover, the transverse fields become dominant at large wave numbers, and the fields become tightly bound to the guide axis as the wave number and/or inhomogeneity increases. Studies of more general permittivity variations and wall effects will be reported shortly.     

Recovery of image blocks using the method of alternating projections.

A technique for block-loss restoration in block-based image and video coding, dubbed recovery of image blocks using the method of alternating projections (RIBMAP), is developed. The algorithm is based on orthogonal projections onto constraint sets in a Hilbert space. For the recovery of a linear dimension N size block, a total of 8N vectors are extracted from the surrounding area of an N x N missing block. These vectors form a library from which the best matching spatial information for the missing block is extracted. Recovery vectors, including both undamaged and restored damaged pixels, are introduced. The vectors are used to find highly correlated information relating to the lost pixels. To assure continuity with the surrounding undamaged area, three additional convex constraints are formulated. Adherance to these sets is imposed using alternating projections. Simulation results using orthogonal projections demonstrate that RIBMAP recovers spatial structure faithfully. Simulation comparisons with other procedures are presented: Ancis and Giusto's hybrid edge-based average-median interpolation technique, Sun and Kwok's projections onto convex sets-based method, Hemami and Meng's interblock correlation interpolation approach, Shirani et al.'s modified interblock correlation interpolation scheme, and Alkachouh and Bellanger's fast discrete cosine transformation-based spatial domain interpolation algorithm. Characteristic of the results are those of the "Lena" JPEG image when one fourth of periodically spaced blocks in the image have errors. The peak signal-to-noise ratio of the restored image is 28.68, 29.99, 31.86, 31.69, 31.57, and 34.65 dB using that of Ancis and Giusto, Sun and Kwok, Hemami and Meng, Shirani et al., Alkachouh and Bellanger, and RIPMAP, respectively.     

Transformation of the polarization of electromagnetic waves by helical radiators

Transformation of the polarization of an electromagnetic wave by a 2D array of double-turn metal helices is investigated both theoretically and experimentally. Electric and magnetic moments induced in an isolated helix by an incident linearly polarized wave are determined. A universal relationship between the projections of the induced moments onto the axis of a helix is derived. The helix parameters that are optimal for radiation of a circularly polarized wave are calculated. A 2D array composed of double-turn helical radiators with optimum parameters is manufactured. Experimental verification of the obtained theoretical results is performed.     

On the PDF of the sum of random vectors

There are various cases in physics and engineering sciences (especially communications) where one requires the envelope probability density function (PDF) of the sum of several random sinusoidal signals. According to the correspondence between a random sinusoidal signal and a random vector, the sum of random vectors can be considered as an abstract mathematical model for the above sum. Now it is desired to obtain the PDF of the length of the resulting vector. Considering the common and reasonable assumption of uniform distributions for the angles of the vectors, many researchers have obtained the PDF of the length of the resulting vector only for special cases. However in this paper, the PDF is obtained for the most general case in which the lengths of vectors are arbitrary dependent random variables. This PDF is in the form of a definite integral, which may be inappropriate for analytic manipulations and numerical computations. So an appropriate infinite Laguerre expansion is also derived. Finally, the results are applied to solve a typical example in computing the scattering cross section of random scatterers     

Generalized decomposition of electromagnetic fields inbi-anisotropic media

TE/TM decomposition of electromagnetic fields, with respect to one special direction in space, is well known to be valid for fields in isotropic and uniaxially anisotropic media. The theory was recently generalized to bi-anisotropic media by defining the decomposition for linear combinations of electric and magnetic fields with respect to two vectors. In the present paper, the theory is further generalized by defining the decomposition with respect to four vectors (two six-vectors), which restrict the polarizations of the decomposed electromagnetic fields. It is shown that the class of bi-anisotropic media in which electromagnetic fields can be decomposed into two independent electromagnetic fields (a-field and b-field) is more general than in all previous decomposition theories. It is also shown that the decomposed a- and b-fields see the original bi-anisotropic medium as simpler equivalent ones (aand b-media) for which analytic Green dyadics were previously derived by these authors     

内孤立波环境下稳健降阶自适应匹配场定位方法研究

海洋内孤立波的存在会引起海水混合,温盐结构改变,从而导致声速在时间和空间上的不均匀分布,而在匹配场定位中则表现为声速失配,定位不准确。该文提出一种内孤立波下稳健的降阶自适应匹配场定位方法(RR-AMFP)。在传统自适应匹配场定位算法的基础上,融合了主分量抑制波束形成方法,通过特征分解对拷贝协方差矩阵进行降阶,抑制噪声空间,同时采用抑制系数和权重因子来计算匹配过程中的权向量,监测失配的拷贝向量。因此该算法可以在内孤立波环境下保持更好的稳健性,而且阶数的降低也缩短了计算时间。仿真结果表明:该算法可以实现单个内孤立波下的准确定位,但大振幅的内孤立波波列仍然会造成较大的定位误差。在南海开展了内孤立波环境下的声源定位实验,估计距离误差为3.7%,深度误差为1.6%,验证了该算法在实际海洋内孤立波环境下的有效性。     

EXOS-D (AKEBONO) very low frequency plasma wave instruments (VLF)

The Akebono (EXOS-D) satellite has been successfully observing the Earth's magnetosphere since it was launched on February 21, 1989. The objectives of VLF instruments on board the satellite were to investigate the behavior of plasma waves associated with accelerated auroral particles, wave-particle interaction mechanisms, and propagation characteristics of whistler-mode waves in the magnetosphere. The instruments measured not only the dynamic spectra of VLF waves up to 15 kHz by a wideband receiver, but also their absolute field intensities, wave normal vectors, and Poynting vectors. Two electric and three magnetic components with a bandwidth of about 50 Hz up to 12.5 kHz are sent to measure the wave normal vectors and Poynting vectors. The antenna impedance is measured to determine the correct absolute electric field intensities. The instruments have successfully measured the wave spectra, the wave normal vectors. Poynting vectors, the precise wave intensities, the antenna impedance, etc. The present paper describes the unique features of the instruments, especially the Poynting flux analyzers in more detail. Obtained scientific results are also reviewed     

Propagation of magnetostatic surface waves in a ferrite plate magnetized by a spatially periodic transverse field

Propagation of magnetostatic surface waves (MSSWs) in a ferrite plate magnetized by a spatially periodic transverse field has been considered. The parameters of MSSW propagation have been calculated by the Hamilton-Auld method. It is shown that only noncollinear MSSWs, whose wave-beam trajectories as well as wave numbers and angles, which determine the directions of the vectors of the phase and group velocities, are described by functions that are periodic in the direction of the wave propagation, can exist in this field. The period of these functions is determined by the period of the spatially periodic field. The frequency range of existence of the collinear waves is narrower than that of the waves in a uniformly magnetized plate. The characteristics of wave propagation in a nonuniform spatially periodic field are compared to the characteristics of wave propagation in nonuniform fields of known types.     

Tem study of dark line defect growth from dislocation clusters in (GaAl)As-GaAs double heterostructure lasers

Dark spot defects in (GaAl)As-GaAs double heterostructure lasers are studied by transmission electron microscopy and found to be a cluster of dislocations generated in the first (GaAl)As epitaxial layer during epitaxial growth. Burgers vectors and spatial configuration of dislocation dipoles developing from these dislocations are determined. It is found that Burgers vectors of dislocations in the dislocation cluster obey the Burgers vector sum rule.