正交偶极子的极化特性分析

双极化相控阵天线的极化特性及其对目标极化散射矩阵测量的影响,将决定相控阵体制雷达获取目标极化信息的精度和能力,是相控阵雷达极化技术的基础。以正交偶极子为阵元模型,分析了双极化阵列天线的空域极化特性及其对雷达目标极化散射矩阵测量的影响。由于两阵元辐射电场在偏离视轴方向的非正交性,不可避免地会引起两天线交叉极化之间的相互干扰。根据传统交叉极化评价指标的定义,分析了正交偶极子天线的交叉极化特性,并从目标极化特性测量性能的角度,定义了双极化雷达系统的交叉极化隔离度,将其表示为极化测量系数矩阵条件数的形式,以衡量全极化相控阵雷达天线的交叉极化特性。     

Calibration algorithm using known angles

A new calibration algorithm using known angles is presented that can be used to directly recover the homography matrix between a projective and Euclidean structure using the invariance of angles under the similarity transformation, and can easily deal with varying cameras using the unique homography matrix     

Scattering from periodic arrays of crossed dipoles

An analysis is presented for calculating the scattering from periodic arrays of symmetrical crossed dipoles. It is shown that in general the reflection coefficient versus frequency of symmetrical crossed-dipole arrays exhibits two distinct resonances, which occur when the dipole elements are on the order of a half-wavelength long. The analysis reveals also the presence of an antiresonance, which occurs at a frequency between the two resonances. At the antiresonant frequency the array reflection coefficient is zero. Thus, within a relatively narrow frequency band, the array reflection characteristics traverse the extremes of complete reflection followed by no reflection, and finally by complete reflection again. The anomalous reflection versus frequency behavior in such arrays is shown to be directly attributable to two distinct resonances excited in the crossed elements. For an isolated crossed dipole, it is shown that the total induced current can be approximately represented by two uncoupled current components. The current components induced on the same elements in an array, however, are coupled to one another through interaction with neighboring elements. The coupling results in complete cancellation of the total bistatic array scattering, at a frequency which lies between the two component current resonant frequencies.     

A subspace-based direction finding algorithm using fractional lowerorder statistics

We propose several classes of fractional lower order moment (FLOM)-based matrices that can be used with MUSIC to estimate the DOAs of independent circular signals embedded in additive SαS (symmetric α stable) noise (e.g., sea clutter). We run simulations with different choices of the FLOM parameter p for our FLOM-based matrices and conclude that when the noise is SαS with unknown α≠2, FLOM-multiple signal classification (MUSIC) with p close to unity yields good performance. The performance of FLOM-MUSIC and robust covariation-based (ROC)-MUSIC are similar. Three scenarios that contain circular signals (phase modulation (PM), circularly symmetrical Gaussian, and quaternary phase-shift keying (QPSK)) and one scenario that contains noncircular signals (binary phase-shift keying (BPSK)), all embedded in the same SαS noise, are tested. These simulation results reveal that the scenario containing BPSK signals leads to poor performance, indicating that FLOM-MUSIC is presently limited to circular signals     

Adaptive crossed dipole antennas using a genetic algorithm

Antenna misalignment in a mobile wireless communications system results in a signal loss due to a decrease in antenna directivity and a polarization mismatch. A genetic algorithm (GA) is used to adaptively alter the polarization and directivity of a crossed dipole receive antenna in order to increase the link budget. The three orthogonal dipole configuration works better than only two crossed dipoles, but both improved the link loss as the angular pointing errors increased. A GA with a high mutation rate works best for a noiseless open loop adaptation, while a GA with a low mutation rate works best for noisy fully adaptive system.     

A Monte Carlo simulation algorithm for finding MTBF

Prediction of mean time between failures (MTBF) is an important aspect of the initial stage of system development. It is often difficult to predict system MTBF during a given time since the component failure processes are extremely complex. The authors present a Monte Carlo simulation algorithm to calculate the MTBF during a given time of a binary coherent system. The algorithm requires the lifetime distributions of the components and the minimal path sets of the system. The MTBF for a specific time interval, e.g. a month or a year, can be estimated. If the component lifetime distributions are unknown, then a lower bound of system MTBF can be estimated by using known constant failure rates for each component     

A two-dimensional FFT algorithm for three-phase inverter-fedsystems

A spectrum analyzer for three-phase inverter-fed balanced systems which is capable of calculating up to 24 harmonic components of the line currents every 130 μs is presented. The method is based on a synchronized sampling technique and on a highly efficient fast Fourier transform (FFT) for three-phase systems. The latter consists of a two-dimensional six-point discrete Fourier transform (DFT) followed by a two-dimensional four-point DFT. The total FFT algorithm has been successfully implemented on a TMS32010 digital signal processor     

A new algorithm for high-resolution two-dimensional spectral estimation

In this letter, we present a new method for two-dimensional spectral estimation. This method has a computational requirement similar to that of the Maximum-Likelihood Method (MLM), but has a resolution property which is considerably better than that of the MLM.     

A finite mixtures algorithm for finding proportions in SAR images

This correspondence describes an algorithm for estimating the proportions of classes in an SAR image by first assuming that an image consists of a mixture of a known number of different pixel types. A maximum likelihood estimate of the parameters of the resulting mixture distribution is then evaluated using the EM algorithm. An advantage of the finite mixtures approach is that the quantities of interest, the proportions, are directly estimated. The technique is applied to aircraft synthetic aperture radar (SAR) images of sea ice. In addition to finding the proportions of the classes, knowledge of the mixture components allows image displays tailored to a user's requirements.     

A circularly polarized octave-bandwidth unidirectional antenna using conical dipoles

A unique unidirectional octave-bandwidth reflector type circularly polarized antenna is described which uses crossed parallel connected conical dipoles operated near second resonance. The impedance characteristics of the antennas together with added series reactances gives the desired approximately quadrature current relation between the two dipoles. The axial ratio does not exceed 2 to 1.     

A localized algorithm for finding disjoint paths in wireless sensor networks

This letter presents a localized algorithm that finds multiple node-disjoint paths in wireless sensor networks. The algorithm needs only local topology knowledge and provides automatic path restoration. We describe the algorithm, give the proof of correctness, and evaluate its performance using simulation. We conclude that the proposed algorithm is more suitable for wireless sensor networks than the existing distributed algorithms     

A method for the constructive synthesis of an antenna array of crossed orthogonal electric dipoles located near a perfectly conducting sphere

A method for the constructive synthesis of an antenna array of crossed orthogonal dipoles located over a perfectly conducting sphere is proposed. The method is based on a modification of the genetic algorithm for solving the problem of constructive synthesis of the antenna array. In implementation of this method, specific features of a known electrodynamic model are used with the radial coordinate of the radiator taken into account.     

A two-dimensional placement algorithm for the layout of electronic circuits

A method is developed for the optimal placement of components or subsystems to specific locations on the backboard. The objective is to minimize the number of etches passing through unit space on the board (interconnection density) and the number of holes. This avoids the congested area on the board, makes a proper distribution of wiring and reduces the stray capacitances. X-Y coordinate wiring has been used.     

A new two-dimensional fast cosine transform algorithm

The discrete cosine transform (2-D DCT) is based on a one-dimensional fast cosine transform (1-D FCT) algorithm. Instead of computing the 2-D transform using the row-column method, the 1-D algorithm is extended by means of the vector-radix approach. Derivation based on both the sequence splitting and Kronecker matrix product method are discussed. The sequence splitting approach has the advantage that all the underlying operations are shown clearly, while the matrix product representations are more compact and readily generalized to higher dimensions. The bit reversal operations are placed before the recursive additions so that the recursive operations can be performed in a very regular manner. This greatly simplifies the indexing problem in the software implementation of the algorithms. The vector-radix algorithm saves 25% multiplications as compared with the row-column method     

Details of simulated annealing algorithm to estimate parameters of multiple current dipoles using biomagnetic data

The details of the simulated annealing algorithm proposed to estimate the parameters of multiple current dipoles using biomagnetic data are described. The effects of the choices of such numerical conditions as the amount of estimate transitions, the equilibrium criterion, and the temperature decrement on the algorithm's performance are discussed. Incorrect results from the computer simulation obtained with inappropriate choices of such conditions are presented. The verification of a near-optimum convergence by reheating and reannealing is demonstrated. A modification of this algorithm is proposed for implementation by parallel computer, and the validity of this parallel algorithm is demonstrated by computer simulation.     

一种快速二维相关干涉仪测向算法

针对宽带信道化测向处理中传统二维相关干涉仪测向算法计算量过大的缺点,提出了一种基于引导基线的快速相关干涉仪算法.在阵列中选定引导基线,由引导基线的相位差信息计算出一组可能的来波角度信息;在测向处理时,仅对引导基线确定的角度进行相关度计算.快速算法将传统相关干涉仪中的二维相关峰搜索减小为仅对一个由模糊角度组成的点集进行搜索,计算量不到传统方法的百分之一,且测向性能与传统方法相当.试验验证了该算法的有效性.     

An efficient algorithm for two-dimensional frequency estimation

This paper presents a computationally efficient eigenstructure-based 2D-MODE algorithm for two-dimensional frequency estimation. We derive the theoretical performance of the 2D-MODE estimator and show that it is asymptotically statistically efficient under either the assumption that the number of temporal snapshots is large or the signal-to-noise ratio is high. Numerical examples showing the performance of this algorithm and comparing it with the computationally efficient subspace rotation algorithms are also given. We show that the statistical performance of the 2D-MODE algorithm is better than that of the subspace rotation methods. The amount of computations required by the former is no more than a few times of that needed by the latter for either small numbers of spatial measurements or a single temporal snapshot, which are the cases of interest herein.     

A two-dimensional fast lattice recursive least squares algorithm

This paper is mainly devoted to the derivation of a new two-dimensional fast lattice recursive least squares (2D FLRLS) algorithm. This algorithm updates the filter coefficients in growing-order form with linear computational complexity. After appropriately defining the “order” of 2D data and exploiting the relation with 1D multichannel, “order” recursion relations and shift invariance property are derived. The geometrical approaches of the vector space and the orthogonal projection then can be used for solving this 2D prediction problem. We examine the performances of this new algorithm in comparison with other fast algorithms     

基于SQL的二维统计分析方法研究

面对结核病在高校等人口密集区域多发传染的情况,建立一套关于结核病防治的数据库系统,对结核病的发病情况、影响因素做出正确的统计和分析,有效地防预与控制结核病,将是一件非常重要的事情。文中针对高校结核病发病情况统计分析的问题提出了一种基于SQL的二维统计分析算法,该算法运用关系运算中笛卡尔乘积的原理,并对笛卡尔乘积方法进行改进设计,其优点可以得到二维、非线性统计分析结果。算法通过应用测试,算法执行效率高、统计分析结果准确、直观。