均匀圆阵二维波达角估计的Cramer-Rao界

均匀圆阵(UCA)是一种应用广泛的具有二位波达角估计能力的平面阵列。为了从理论上分析不同阵列参数下到达波方位角(AOA)、仰角估计精度,推导了均匀圆阵二维波达角估计的性能界,以此为基础分析了阵列孔径、阵元个数、快拍数以及来波仰角高低与到达角估计精度的关系,并通过对UCA-MUSIC算法计算机仿真验证了推导结果的正确性。研究结果为波达角估计类算法提供了可供参考的性能下界,圆阵设计时也不再需要大量的Monte Carlo仿真试验确定阵列参数,可直接从估计精度表达式中获得。     

基于均匀圆阵的幅相误差自校正算法

针对实际应用中普遍存在的阵列幅相误差扰动问题,结合子空间类波达方向估计算法,以均匀圆阵为基础,提出了一种幅相误差的自校正算法。先利用均匀圆阵协方差矩阵的结构特点对幅相误差进行初步估计,再通过迭代方法得到更精确的估计值,自校正方法无需任何参数初始值,实现比较简单。仿真实验验证了算法具有良好的误差校正效果,能够比较准确的估计出波达方向角和幅相误差值。     

一种声源波达方向估计方法的性能分析

探讨了环绕在刚性圆柱上均匀圆阵的声源波达方向估计问题.在声场分解理论的基础上,分析了刚性圆柱体对圆阵响应的影响,研究了均匀圆阵对连续圆阵采样所产生的冗余误差及其与阵元数和圆阵半径的定量关系,由声场分解得到的特征波束构成一虚拟线阵,此虚拟线阵具有360.的方位角观察范围,在此基础上利用MUSIC算法实现了声源波达方向估计,在单声源条件下推导了算法的Cramer-Rao界的定量表达式,并进行了计算机仿真验证.     

基于均匀圆阵的相干信源DOA估计算法研究

针对均匀圆阵相干信源的波达方向估计问题,提出了一种去相干的正交预处理方法——阵列移位算法。阵列移位算法改进了抗相干干扰的波束形成方法,通过圆阵移位和MUSIC算法的结合,使相干信源角估计的性能得到改善。与传统的模式空间平滑算法相比,该方法减少了阵列孔径损失,提高了计算速度。     

基于TD-SCDMA无线定位MUSIC算法及其性能的研究

为了实现基于TD-SCDMA智能天线圆-角定位,针对我国TD-SCDMA采用的是非Vandermonde结构的8阵元均匀圆阵智能天线,不能直接采用MUSIC算法对移动台的来波方向(DOA)进行估计的特点,对基于TD-SCDMA智能天线进行了预处理,使MUSIC算法能够用于基于TD-SCDMA智能天线的DOA估计,同时考虑到实际应用分别对理想智能天线和非理想智能天线的MUSIC算法的性能进行了分析。     

基于改进ESPRIT算法的波达方向估计

把经典的波达方向估计算法应用于均匀圆阵智能天线是一个重要的研究课题。通过预处理技术把均匀圆阵转换成虚拟均匀线阵,为了解决噪声造成信号子空间的扰动问题,提出了两种总体最小二乘ESPRIT（TLS—ESPRIT）;为把ESPRIT算法应用于均匀圆阵,引入了模式空间的ESPRIT算法。通过建立恰当的数学模型,对上述各算法的均匀线阵和均匀圆阵上的性能进行仿真和对比分析。仿真结果证明,两种改进的算法性能均好于基本的ESPRIT算法。     

一种基于非一致响应圆阵的DOA估计改进算法

由于传统波达方向(DOA)估计算法对接收天线阵列的阵元一致性要求高,即幅度和相位响应要求一致,在工程应用中受到较大限制。针对该问题,结合均匀圆阵的特点,通过引入阵元幅度和相位不一致因子对传统MUSIC算法的模型加以改进,提出了一种改进的MUSIC算法。该算法降低了阵元的一致性要求,可通过迭代求解的方法来完成对多个信源来波方向进行估计。仿真和分析结果表明,提出的算法可有效地进行多个目标的DOA估计。     

一种均匀圆阵子阵干扰抑制DOA估计算法

常规空间谱估计算法在强干扰背景下往往无法正确估计弱信号的来波方向。针对此问题,本文提出了一种均匀圆阵子阵干扰抑制波达方向估计算法。将整个阵列划分为若干个子阵,利用提出的最小二乘波束形成算法分别对子阵波束加权以抗干扰,加权后的子阵可以看作是一个‘有向阵元’,将它们组成一个新的虚拟阵列,再进行超分辨谱估计。该方法通过子阵波束形成抑制强干扰,子阵输出中消除了强干扰分量,因此能够实现弱信号波达方向的正确估计,同时弱信号到达角估计的成功概率也得到了提高。最后计算机仿真实验验证了本文算法的有效性和正确性。      

基于MCMC的DOA估计及其在空域滤波中的应用

针对传统算法在进行波达方向角估计时需要进行全空间的谱峰搜索,且依赖初始化迭代和插值的缺陷,设计了一种贝叶斯估计方法。首先,构建基于均匀圆阵的频域信号处理模型,提出了基于马尔科夫链蒙特卡罗进行波达方向角估计的方法,实现了无需初始化和插值的测向算法,且不需要进行全空间的谱峰搜索即可直接估计结果,同时推导了该模型下进行波达方向角估计的克拉美罗下界。在以测向结果为先验信息,同时设计了一种新的空域滤波增益模型。利用马尔科夫链蒙特卡罗算法对信号子空间进行解耦合,然后计算滤波器增益系数,以此实现空域滤波。最后在无线电设备搭建的真实环境中进行实验,验证了基于马尔科夫链蒙特卡罗算法进行阵列波达方向角估计和空域滤波的有效性,并且与其他模型相比要明显优于后者。     

一种实用的多径信号时间平滑二维DOA估计方法

在二维波达方向(DOA)估计领域,均匀圆阵(UCA)应用越来越广泛.针对均匀圆阵,提出了一种可在多径环境下估计二维波达方向的新算法,该算法充分利用了空间和时间上的特性,估计P个多径信号方向仅需P+1个天线阵列.多径信号经过时间平滑处理后,再利用改进的主分量分析(PCA)迭代算法求空间谱,各来波方向可被实时快速地估计出来,整个估计过程中不需要预先知道多径数量,运算复杂度低,系统结构简单.最后给出的仿真试验结果验证了提出方法的有效性.     

有向天线圆阵对椭圆极化信号的测向方法

针对有向天线阵列对椭圆极化信号的测向问题,对椭圆极化信号的瞬时极化矢量做了空间分解,建立了有向天线阵列对信号的接收模型,提出了基于增益比估计的MUSIC算法:筛选接收数据,得到一组含有相近的极化信息的数据;通过参数估计提取出该组数据中所包含的各阵元的增益比信息;应用MUSIC算法测向。就该算法进行了计算机仿真,验证了算法的可行性,并分析了仿真结果,指出了算法的优点与不足。     

An equivalence theory between elliptical and circular arrays

An equivalence relation of a family of arrays defined under a linear transformation is established. By means of this theorem, the far field of an elliptical array can be obtained from that of an equivalent circular array; the theorem can be similarly applied to two- and three-dimensional arrays. A uniformly excited cophasal elliptical array is considered as an example. For nonuniform excitation, the method of symmetrical components may be applied despite the absence of axial symmetry for elliptical arrays. This theory can also be applied to the case of continuous source distribution on an ellipse or in an elliptical aperture. In so doing, solutions can be obtained without use of the complicated wave functions pertaining to the original geometry. As an example, an optimum array in the sense of Dolph-Chebyshev is considered. Similarly, a Taylor distribution for an elliptical aperture can be achieved.     

Angle and time of arrival statistics for circular and ellipticalscattering models

With the introduction of antenna array systems into wireless communication networks comes the need to better understand the spatial characteristics of the channel. Scattering models provide both angle of arrival (AOA) and time of arrival (TOA) statistics of the channel. A number of different scattering models have been proposed in the literature including elliptical and circular models. These models assume that scatterers lie within an elliptical and circular region in space, respectively. In this paper, the joint TOA/AOA, the marginal TOA, and the marginal AOA probability density functions (PDFs) are derived for the elliptical and circular scattering models. These PDFs provide insight into the properties of the spatial wireless channel     

The effect of a finite-distance signal source on a far-fieldsteering Applebaum array-two dimensional array case

Approximate expressions are obtained for the output signal-to-noise ratio (SNR) expressed in terms of the finite signal distance and signal direction for a finite-distance signal source's effect on the performance of a far-field steering two-dimensional Applebaum-type adaptive array. The expression is shown to be consistent with the actual simulated value. Using that expression, a simplified rule is obtained to determine the distance between the signal source and the array center at which the output SNR loss is given by a specific value. The SNR value so obtained varied with two-dimensional signal direction. The analysis for the case of an arbitrarily located array is presented, followed by the cases for rectangular, circular and elliptical arrays. It was found that this distance associated with the given SNR value is always less for a rectangular array than that of a linear array when the total number of array elements for both are equal and the performances of an elliptical array are similar to those of a circular array     

Arbitrary footprint patterns from planar arrays with complexexcitations

Elliott and Stern's (1990) method for synthesising shaped patterns using a circular or elliptical planar aperture or array with a complex excitation distribution is generalised to allow the synthesis of footprints of arbitrary shape. The use of complex excitations allows a given footprint to be synthesised using a smaller array than with real excitations. The procedure is illustrated by synthesising a square footprint using an array with a rectangular grid     

Elliptic cylinder geometry for distinguishability analysis in impedance tomography

Electrical impedance tomography (EIT) is a technique that computes the cross-sectional impedance distribution within the body by using current and voltage measurements made on the body surface. It has been reported that the image reconstruction is distorted considerably when the boundary shape is considered to be more elliptical than circular as a more realistic shape for the measurement boundary. This paper describes an alternative framework for determining the distinguishability region with a finite measurement precision for different conductivity distributions in a body modeled by elliptic cylinder geometry. The distinguishable regions are compared in terms of modeling error for predefined inhomogeneities with elliptical and circular approaches for a noncircular measurement boundary at the body surface. Since most objects investigated by EIT are noncircular in shape, the analytical solution for the forward problem for the elliptical cross section approach is shown to be useful in order to reach a better assessment of the distinguishability region defined in a noncircular boundary. This paper is concentrated on centered elliptic inhomogeneity in the elliptical boundary and an analytic solution for this type of forward problem. The distinguishability performance of elliptical cross section with cosine injected current patterns is examined for different parameters of elliptical geometry.     

Efficient modal analysis of arbitrarily shaped waveguides composed of linear, circular, and elliptical arcs using the BI-RME method

This paper deals with the accurate and efficient modal analysis of arbitrarily shaped waveguides whose cross section is defined by a combination of straight, circular, and/or elliptical arcs. A novel technique for considering the presence of circular and/or elliptical segments within the frame of the well-known boundary integral-resonant mode expansion (BI-RME) method is proposed. This new extended BI-RME method will allow a more accurate solution of a wider number of hollow conducting waveguides with arbitrary profiles, which are usually present in most modern passive waveguide components. To show the advantages of this new extended technique, the modal chart of canonical (circular and elliptical) waveguides, as well as of irises with great practical interest (i.e., cross-shaped irises with rounded corners) has been first successfully solved. Next, a computer-aided-design software package based on such a novel modal analysis tool has first been validated with the accurate analysis of a referenced complex dual-mode filter, and then applied to the complete design of a novel twist component for K-band application based on circular and elliptical waveguides. A prototype of this novel device has been manufactured and measured for verification purposes.     

锥形结构超声阵列换能器研究

传统外形构造的换能器难以适应水下高速运动。因此,在头部为圆形或椭圆形的普通阵列式换能器基础上,该文设计了一种锥形结构的超声阵列式换能器,其可适用于水下高速航行器。通过有限元仿真确定了阵元尺寸与阵列构造,分析了换能器整体的声场分布,研制换能器样机并测试其电声性能。样机测试结果与仿真结果呈现出较好的一致性,换能器指向性与发射电压响应满足使用需求。结果表明,此种换能器结构具有实际的可行性。     

High birefringence photonic bandgap fiber with elliptical air holes

In this paper, we proposed a high birefringence photonic bandgap fiber (PBGF) with elliptical air holes in cladding and circular air hole in core. The forbidden gaps of the honeycomb structure are calculated when the circular air holes are deformed to the elliptical shape. And the birefringence of the PBGFs is investigated by using a full-vector finite element method (FEM) and the numerical results are presented.     

Time-Domain Circularly Polarized Antennas

The transient properties of short-pulsed elliptically/ circularly polarized antennas, namely, the transmitting and receiving effective heights, are introduced. Due to the pulsed temporal dependence of the radiation pattern, an instantaneous axial ratio is introduced as a quality measure of the polarization performance. For these antennas, it is shown that the trace of the tip of the electric-field polarization vector in time depends on the pulse-width (bandwidth) regime of the excitation signal. Only for quasi-monochromatic or narrow-band excitations is a “pure” elliptical/circular trace achieved (i.e., axial ratio approaching unity for circular polarization). For short-pulsed excitations, a deformation of the elliptical/circular polarization vector trace is obtained due to a Hilbert-transform dependence in the antenna's effective heights and the finite duration pulsed-envelope. A remedy for that deformation, for circular polarization, is obtained by using an array of sequentially rotated circularly polarized antenna elements, which extends the temporal duration for which an instantaneous axial ratio lower than some prescribed value is obtained beyond that of a single antenna.