用神经网络估计到达波方向

本文提出了一种利用神经网络估计到达波方向(DOA)的计算方法.我们将DOA估计问题映射为Hopfield网络的能量函数,利用观测数据的统计量对网络进行编程.由于神经网络的并行集体计算能力,该方法可获得估计问题的实时解。最后,给出了计算机模拟实验结果。     

信源数目欠估计、过估计对DOA估计精度的影响

本文对信源数目估计对波达方向(DOA)估计精度的影响进行了详细分析,得出了过估计对DOA估计没有影响、欠估计使DOA估计有偏的结论.并且简单介绍了基于最小描述长度(MDL)原理的信源数目估计方法以及基于子空间投影技术的MUSIC算法.仿真数据的估计结果证明了该结论的正确性.     

宽带阵列信号波达方向估计的新算法

随着信号处理技术的发展,阵列信号处理的许多领域如雷达、声纳等越来越需要更精确的估计空间宽带信号源的波达方向（direction of arrival,DOA）。CSM（coherent signal subspace method）聚焦类DOA估计算法需要预估计波达方向,预估角偏差会影响聚焦效果,严重时会导致算法失效,本文提出一种基于一致聚焦的DOA估计方法,该方法不需要预先估计到达角,通过聚焦矩阵将宽带信号聚焦到一个中心频率,然后可利用窄带DOA算法进行估计。该算法提高DOA估计的分辨率、估计精度,也增强了算法的实时性,仿真结果验证了此算法的有效性。     

一种矢量阵波束域高分辨估计方法

MUSIC方法在模型准确的前提下,对波达方向(DOA)的估计能够到达足够精度,但对相隔比较近的小信噪比信号源,MUSIC方法不能估计其DOA.提出了一种基于矢量传感器均匀线列阵的密集波束域MUSIC(DBMUSIC)方法.计算机仿真表明,在低信噪比的条件下,DBMUSIC法的高分辨估计性能得到明显改善,应用前景良好.     

用信号方向向量估计到达波方向

由信号方向向量直接估计到达波方向(DOA)可以获得优良的估计性能。本文将ESPRIT技术与信号子空间技术相结合,给出了信号方向向量的完整表达式。模拟实验表明,在低信噪比和短数据的情况下,由该表达式估计DOA可以获得明显优于MUSIC方法的性能。     

增益幅度不一致条件下的SRI算法

阵元增益不一致导致ESPRIT算法的波达方向(DOA)估计性能恶化.本文提出了一种新的利用子空间旋转不变性(SRI)的DOA估计算法,将DOA信息包含于矩阵的特征值估计中,但对增益幅度误差不敏感.由于未利用增益幅度信息,DOA估计结果可能存在模糊性,本文给出了解模糊方法及仿真实验结果.     

信号特征向量分解与到达波方向估计＊

本文提出了到达波方向(DOA)估计的一种新算法。基于信号特征向量分解的一种唯一形式,我们提出了用递推算法来实现由一个或几个信号特征向量进行DOA估计。与一般的特征结构法相比,该方法不但可以解决相干源问题而且改善了在低信噪比情况下的估计性能,并具有使用灵活的特点。计算机仿真证实了上述结论。     

宽带接收机的窄带信号频率 和二维角度估计新方法

 针对宽带接收机对窄带信号进行频率和二维到达角(DOA)估计问题,本文提出了一种新的快速频率和角度估计方法,该方法首先利用参考频率进行DOA预估计,然后利用空域滤波有效地将频率和预估计DOA进行匹配,并根据天线阵列的结构特点利用信号的相应频率进行预估计DOA校准,获得了信号的准确频率和DOA估计值.最后的仿真分析验证了所提出方法的正确性和有效性.     

基于MUSIC及其改进算法的DOA估计研究

在阵列信号处理领域,波达方向(DOA)估计一直是研究的重点之一。在波达方向(DOA)估计中,利用多重分类算法(MUSIC)对来波方向进行估计是最常用的方法。本文概述了经典MUSIC算法,针对现代通信中常用的BPSK和MASK信号都是实信号的特点,结合Eular公式对MUSIC算法进行了改进,使用matlab进行了仿真及对比。     

车载雷达架设控制系统集成设计

针对强相干干扰背景中弱信号的波达方向(DOA)估计问题,提出了一种基于迭代算法的弱信号DOA估计新算法。首先估计强相干干扰的波达方向,然后将阵列划分成两个子阵,进行子阵波束形成来抑制干扰并提高待估计的弱信号的信干噪比,最后利用子阵相位中心偏移进行DOA估计,为提高弱信号的DOA估计精度对以上过程进行迭代运算。该算法在强相干干扰环境下能有效进行弱信号DOA估计,而且估计精度较高。理论分析和计算机仿真结果验证了算法的正确性和有效性。     

Two-dimensional angle-of-arrival estimation in the presence offinite distance sources

When sources are a finite distance away from an array system, most high-resolution bearing estimation techniques exhibit unsatisfactory performance due to the invalidity of the planar wavefront assumption. This problem has been addressed by a far-field approximation (FFA) method based on a preprocessing scheme. By exploiting favorable characteristics of a uniform linear array, the method constructs a FFA covariance matrix, which is Toeplitz and approximates to the far-field data covariance matrix, from the observed data covariance matrix. Then eigenstructure methods can be applied to perform bearing estimation without revising the planar wavefront assumption. This method is extended to the problem of two-dimensional angle-of-arrival (AOA) estimation using a uniform planar array in the presence of finite distance sources. A procedure is derived for reconstructing the 2-D FFA covariance matrix with block-Toeplitz structure. Using the 2-D FFA covariance matrix, eigenstructure methods can be applied in conjunction with a 2-D AOA search to solve the problem. Simulation results confirm the theoretical work     

变厚度非平面介质罩发散系数的计算几何光学法

介质共形顶相控阵天线利用变厚度介质透镜改变相控阵波束扫描方向,理论上来说可到达半空域或更大,是一种适用于弹载、机载雷达系统的天线。本文较详细地讨论了介质罩对电磁波的发散系数的计算,给出了分析非平面变厚度分层介质对电磁波反射、折射的两种有效方法,并进行了比较。     

Estimating the bearings of near-field cyclostationary signals

By exploiting favorable characteristics of a uniform linear array (ULA), the far-field approximation (FFA) method reduces the deterioration of most high-resolution bearing estimation techniques due to the invalidity of the planar wavefront assumption when near-field sources exist. We first present a new technique that provides better performance than existing bearing estimation techniques for cyclostationary signals. Then, the proposed technique incorporating with the FFA method is proposed to estimate signal bearings in the presence of near-field sources without revising the planar wavefront assumption. Several simulation examples confirm the theoretical work and show the effectiveness of the proposed technique     

The effect of dielectric loss in FDTD simulations of microstripstructures

The importance of dielectric losses in planar microstrip structures is evaluated with the finite-difference time-domain (FDTD) method. This analysis was previously not possible in many FDTD simulators due to a lack of absorbing boundary conditions (ABCs), which appropriately terminate air/dielectric interfaces for which the dielectric is lossy. The newly proposed lossy two-time derivative Lorentzian material (L2TDLM) model ABC allows for these terminations and is presented and implemented here for three-dimensional FDTD simulations. The effect of dielectric losses on several well-known planar microstrip structures is evaluated. It is shown that the inclusion of these losses in FDTD simulations, which is facilitated by the L2TDLM ABC, is, in fact, important to predict the performance of resonant structure on lossy dielectric substrates     

平面介质光波导的一种矩阵解法

本文将用于多层介质膜堆的矩阵表示方法应用于平面介质光波导中,提出一种简单而适用的获得特征方程的方法。     

A MATRIX METHOD FOR SOLVING PLANAR DIELECTRIC OPTICAL WAVEGUIDES

A matrix method used in multilayer stack of dielectric films is applied-to planar dielectric optical waveguides. A simple and applicable method for obtaining characteristic equation is presented.     

Generalized spectral analysis of planar lines on layered mediaincluding uniaxial and biaxial dielectric substrates

The spectral-domain analysis is generalized to compute the dispersive properties of a wide variety of planar and quasiplanar transmission lines (microstrips and finlines) printed on a stratified dielectric medium. Uniaxial and biaxial dielectric anisotropy can be easily manipulated due to the definition of a transverse propagation matrix characterizing each dielectric layer. The whole boundary value problem is reduced to two simpler problems involving only one or two dielectrics, and the spectral dyadic Green's function is derived by a recurrence algorithm. The dispersion equation is derived by using the Ritz-Galerkin method. The numerical convergence is substantially improved taking into account the asymptotic behavior of the series. A number of illustrative examples are included to emphasize the power of the method     

Spectral Domain Analysis of Frequency Dependent Propagation Characteristics of Planar Structures on Uniaxial Medium

The propagation characteristics of single and multilayered uniaxial dielectric waveguides and planar structures on uniaxial medium can be determined by utilizing Hertzian potentials along the optical axis. The electric and magnetic Hertzian potentials, having components along the optical axis only, lead to TM and TE modes, respectively, with respect to that axis. The dyadic Green's function in Fourier transform domain (immittance matrix) required to solve for the propagation characteristics of planar structures on uniaxial medium are derived for all three orientations of the optical axis. The immittance matrix for all three cases is in the same form as that for the isotropic medium and hence the known Galerkin's method can be used to solve for the propagation characteristics of the structure.     

Coupled canonical grid/discrete dipole approach for computingscattering from objects above or below a rough interface

A numerical model for computing scattering from a three-dimensional (3D) dielectric object above or below a rough interface is described. The model is based on an iterative method of moments solution for equivalent electric and magnetic surface current densities on the rough interface and equivalent volumetric electric currents in the penetrable object. To improve computational efficiency, the canonical grid method and the discrete dipole approach (DDA) are used to compute surface to surface and object to object point couplings, respectively, in O(N log N), where N is the number of surface or object sampling points. Two distinct iterative approaches and a preconditioning method for the resulting matrix equation are discussed, and the solution is verified through comparison with a Sommerfeld integral-based solution in the flat surface limit. Results are illustrated for a sample landmine detection problem and show that a slight surface roughness can modify object backscattering returns     

Improved pentacene growth continuity for enhancing the performance of pentacene-based organic thin-film transistors

This study proposes an alternative planar bottom-contact (pBC) structure to enhance the electrical performance of pentacene-based organic thin-film transistors (OTFTs). This pBC structure uses a bilayer dielectric to control planarization with a precise etch depth and introduces a bilayer photoresist lift-off method to ensure that planarization produces an optimum flatness. Because of the improved growth continuity of pentacene near the edge of the source/drain electrodes, the contact resistance between the source/drain and the pentacene was reduced significantly, thereby enhancing the electrical performance of OTFTs. The mechanism for the enhanced performance was also verified by a physics-based numerical simulation.