双基地多输入多输出虚拟阵列的稳健低旁瓣波束优化技术

双基地多输入多输出(MIMO)系统需要对目标的波达角和波离角进行二维估计,针对高分辨算法中阵列协方差矩阵处理运算量大以及估计性能对阵列流形失配敏感的缺陷,提出了一种基于二阶锥规划的抗阵列流形失配的双基地MIMO虚拟阵列波束优化算法.该方法利用MIMO的波形分集技术与双基地的目标定位解算,通过波达角和波离角在双基地定位椭圆上的对应关系,将双基地MIMO的二维合成方向矢量转化为一维的虚拟阵列流形,并证明了双基地MIMO虚拟阵列的波束图等效为发射波束图在接收阵角度域上的响应和接收波束图的合成.在优化波束图旁瓣的同时,该算法兼顾了固定方向上的相干干扰抑制,并提高了双基地MIMO虚拟阵列波束优化抗阵列流形失配的能力.通过波束图和方位谱优化的仿真分析和水池试验,验证了算法的有效性.     

Directional reception of broadband signals by means of ultrasonic transducer arrays

This paper presents a new approach to the theory and technique of ultrasonic transducer arrays, which makes it possible to obtain their directional beam patterns for receiving broadband acoustical signals.The general formulae were derived for the beam pattern of the array, and as an example the beam patterns of the end-fire array have been computed and plotted, for signals of different correlation function.For experimental verification of the theory the simple processor solution is proposed. This technique is based on spatial/temporal signal processing for beamforming of the directional response of an end-fire array.     

Synthesis of frequency-independent directional patterns for hydroacoustic arrays of arbitrary configurations

Synthesis of directional patterns varying only slightly in a wide frequency band is considered for continuous linear arrays of arbitrary configurations. It is assumed that a linear array lies in a plane, has a convex shape, and is described by a single-valued function y(x). It is shown that, for such an array, stabilization of the width of its directional pattern is possible in a frequency band exceeding several octaves, provided that the required directional pattern is broader than the directional pattern of the array with phase compensation.     

Optical beam steering based on the symmetry of resonant modes of nanoparticles

We report a phenomenon that an optical beam transmits in a negative direction when passing through a single array of high-refractive-index dielectric nanorods. The mechanism of the negative directional transmission is believed to be due to the symmetry of resonant modes in the dielectric nanoparticles. It is expected to find applications in designing compact optical components to achieve the on-chip beam steering in photonic circuits.     

Beaming effect in multimode photonic crystal by using coupled waveguides

Beaming effect of a multimode photonic crystal (PC) covered by a waveguide array on the exit plane is investigated theoretically. The simulation results show that the multimode PC can make the incident light split into two beams, which can be regarded as secondary sources radiating light into the waveguide array. As a result, many light beams can be generated in the array by the coupling among the waveguides, and the interference of these light beams after passing the system leads to directional emission. Additionally, the directional emission is greatly affected by the beam distribution on the exit plane of the system. Once the main light beams are formed on the exit plane of the system by modulating the system size, steady beaming effect can be obtained in the horizontal direction.     

一种波束赋形可调的导航天线设计

提供一种新的调节半功率波束宽度的思路,并设计了一款可实现波束宽度变换以应用于不同波束赋形场景的北斗二号B3频段的导航天线。基于四阵元双馈源的微带贴片天线阵列,在HFSS有限元仿真软件中根据理论进行建模仿真并优化。在保持右旋圆极化的基础上,不用改变阵列的结构,只需适当调节各个阵元激励的幅度与相位,就能实时缩小或者扩大半功率波束宽度,分别实现主瓣方向可调的定向波束赋形与宽波束赋形以应对不同的工作环境,并且具有定向抗干扰能力。仿真结果表明:定向波束赋形与宽波束赋形在B3中心频点的最大增益分别约为7.13,3.56 dBi,半功率波束宽度分别为52°,119°,3 dB轴比宽度分别为90°,166°;在整个B3频段内各个馈电端口反射系数低于?11 dB,相邻端口隔离度低于?28 dB。设计的波束赋形方式可调的导航天线适用于在无遮挡的开阔空间与特定的遮挡环境之间经常切换的工作场景,改善传统的机动式导航终端在“城市峡谷”等高遮蔽角环境下增益较低的缺点。     

The sonar beam pattern of a flying bat as it tracks tethered insects

This paper describes measurements of the sonar beam pattern of flying echolocating bats, Eptesicus fuscus, performing various insect capture tasks in a large laboratory flight room. The beam pattern is deduced using the signal intensity across a linear array of microphones. The positions of the bat and insect prey are obtained by stereoscopic reconstruction from two camera views. Results are reported in the form of beam-pattern plots and estimated direction of the beam axis. The bat centers its beam axis on the selected target with a standard deviation (sigma) of 3 degrees. The experimental error is +/- 1.4 degrees. Trials conducted with two targets show that the bat consistently tracks one of the targets with its beam. These findings suggest that the axis of the bat sonar beam is a good index of selective tracking of targets, and in this respect is analogous to gaze in predominantly visual animals.     

Optimization of transmitting beam patterns of a conformal transducer array

A method is presented to calculate the driving-voltage weighting vector of a conformal array of underwater acoustic transmitting transducers to obtain a low-sidelobe beam pattern based on the measured receiving array manifold. The relationship among three quantities is given, which are, respectively, the radiated acoustic field, the measured receiving array manifold matrix and the driving-voltage weighting vector of the transducer array. Then, the driving-voltage weighting vector of the array is calculated using the optimization method to obtain a low-sidelobe transmitting beam pattern. At the frequency of 12.5 kHz, the receiving array manifold matrix of a 27-element conformal array is measured in an anechoic water tank. The driving-voltage weighting vector of the array is calculated using the proposed method. In addition, the computer simulation and experiments are carried out. The results agree well and show that the proposed method can obtain a low-sidelobe transmitting beam pattern and at the same time provide the largest amplitude of pressure in the axial direction when the maximum amplitude of the driving voltages of the array elements keeps unchanged.     

阵列指向性二次型约束稳健波束形成算法

提出了一种基于阵列指向性二次型约束的优化算法,以提高最小方差无畸变响应(MVDR)波束形成对方向矢量的稳健性。通过控制阵列波束指向附近的小区域的自适应波束图与期望波束图的加权平方误差,使波束主瓣区域内的信号畸变最小,同时保持了对约束区间外的干扰信号的抑制能力。数值结果表明:在理想阵形和阵形畸变情况下,无方位失配时,利用本文算法的阵列输出信号与干扰噪声比(SINR)与新近出现的球面约束稳健Capon方法相当,而存在方位失配时,本文算法均优于后者。     

基于矢量水听器阵列空域预滤波处理的多重信号分类算法研究

矢量水听器能同时拾取声压和振速信息,在相同的信噪比、阵元数及阵列孔径下,矢量阵定向性能优于声压阵列。目前,以多重信号分类算法(Multiple signal classification,MUSIC)为代表的高分辨定向算法已经广泛应用于矢量水听器阵列中。但是随着信噪比降低、信号源方位间隔减小,传统MUSIC算法定向精度及分辨概率显著下降。本文采用最小二乘法设计适用于矢量水听器水平阵列的矩阵空域滤波器,用于阵列数据的空间滤波预处理,可以对阻带扇面噪声进行有效抑制。由滤波后的数据协方差矩阵可以得到新的噪声子空间,在传统MUSIC算法基础上修正通带扇面内阵列流型的畸变后即可得到滤波后MUSIC算法的方位谱。仿真结果表明,当信噪比较低时,改进算法有效提高了通带扇面内目标方位分辨性能。最后本文对四基元矢量水平阵列海试数据进行了处理,改进算法对窄带信号定向较常规算法-3 dB束宽减小了13°,旁瓣级降低约8 dB。对有一定带宽的行船辐射噪声定向处理得到了更加精确的航迹图,海试数据处理结果证明了该算法的可行性和有效性。     

A miniaturized adaptive microphone array under directional constraint utilizing aggregated microphones

This paper introduces a miniaturized microphone array using the Directionally Constrained Minimization of Power (DCMP) method, which utilizes the transfer functions of microphones located at the same place, namely aggregated microphones. The phased microphone array realizes a noise reduction and direction of arrival (DOA) estimation system according to differences in the arrival time, phase shift, and/or the level of the sound wave for each microphone. Hence it is difficult to miniaturize the microphone array. The objective of our research is to miniaturize the system size using aggregated microphones. In this paper, we first show that the phased microphone array system and the proposed aggregated microphone system can be described within the same framework. We then apply a microphone array under directional constraint to the aggregated microphones and compare the proposed method with the microphone array. We show the directional pattern of the aggregated microphones. We also show the experimental results regarding DOA estimation.     

Transmission beam pattern and echolocation signals of a harbor porpoise (Phocoena phocoena)

The transmission beam pattern of an echolocating harbor porpoise (Phocoena phocoena) was measured in both the vertical and horizontal planes. An array of seven Brüel and Kjaer 8103 hydrophones connected to an amplifier-line driver module was used to measure the beam patterns. The porpoise was trained to station in a hoop and echolocate a cylindrical target located at a range between 7 and 9 m while the array was located 2 m in front of the hoop. The 3-dB beamwidth in both the vertical and horizontal planes was the same at approximately 16 degrees and the beam was pointed toward the forward direction. The individual hydrophones in both the vertical and horizontal arrays measured signal waveforms that were similar throughout the 40-degree span of the array. The porpoise emitted signals with intervals that were 20 to 35 ms longer than the round trip travel time between the animal and the target. The average source level, peak frequency, and bandwidth were 157 dB, 128 kHz, and 16 kHz, respectively.     

电离层调制加热产生极低频/甚低频波定向辐射的理论分析

通过低电离层调制加热能够产生极低频/甚低频(ELF/VLF)波. 基于调制加热理论, 并引入相控阵天线思想, 建立了通过双波束幅度调制模式(DAM)和圆形几何调制模式(CGM)产生ELF/VLF波的定向辐射模型, 并通过与实验数据的对比验证了模型的正确性. 据此模型, 采用HARRP加热阵参数, 对比分析了上述两种定向辐射模式与常规幅度调制模式(AM)之间的特性差异, 并研究了调制频率(f_ELF/VLF)和加热波束与垂直方向倾角(ψ)对各模式的影响. 结果表明: 相对AM模式, 通过合理设置初始相位、f_ELF/VLF和ψ, DAM 模式和CGM模式在实现ELF/VLF信号定向辐射的同时还可以提高其辐射强度, 相对AM模式, CGM模式信号强度最大提高约11.3 dB. 关键词： 定向辐射 双波束幅度调制 圆形几何调制     

相控阵天线电磁发射特性的统计分析

相控阵天线波束指向高度动态变化,其电磁发射特性呈现出显著的统计规律,分析和测试所需的资源巨大。采用多项式混沌展开（PCE）探究二维平面相控阵天线发射特性的统计特性,根据方向图乘积定理等确定代表相控阵天线电磁发射特性的目标函数,利用PCE建立目标函数的等效代理模型。从理想点源构成的相控阵天线着手,分别考虑了主波束指向服从均匀分布和正态分布两种典型情况,通过计算机仿真模拟得到等效代理模型的概率密度函数和累积分布函数,并使用传统的蒙特卡罗方法结果作为参照来评估PCE方法的有效性和可靠性,最后对小型偶极子相控阵天线的波束指向服从两种典型分布的情况进行讨论。仿真对比结果表明,PCE方法在保证结果准确度的同时可以大大减少采样样本点数目,大幅提升相控阵天线电磁发射特性分析和测试的效率。     

Theoretical study of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium

The radiation properties of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium are studied. The array factor and far-zone EM-mode and P-mode radiation fields of the array geometry are derived using vector wave function techniques and pattern multiplication approaches. The total field patterns and various characteristics of pattern such as half power beam width (HPBW), first null beam width (FNBW) and direction of maximum radiation are computed for two different values of progressive phase excitation difference between the elements. The results of this array geometry are obtained both in plasma medium and in free space and compared with those of single element equilateral triangular patch microstrip antenna.     

有限波束作用下掩埋球体的散射声场计算

计算并分析了海底掩埋物体的三维散射声场。采用“等效垂直线列阵”方法来进行有限波束的建模,并将浅海波导中点声源散射声场的波数积分计算方法,推广到有限波束作用下海底掩埋物体的散射场计算,本文导出了物体位于沉积层中的散射声场计算公式。计算结果表明,在波导中垂直面内的散射声场,与沉积层中点源形成的声场非常相似;当距离较远时,散射声波呈柱面波衰减。文章还分析利用海面反射以提高散射能量的可能性,表明波束指向性及波束宽度对散射声场有较大影响。     

截断阶梯Legendre函数加权阵列恒定束宽波束特性分析*

连续Legendre函数加权的恒定束宽换能器(CBT)阵列可以在一定频率范围内采用与频率无关的简单阵元权重实现恒定束宽的波束特性。然而常规CBT阵列需要为每个阵元配置相应的阵元权重,当阵元数量较大时会增加复杂度。该文分析了截断阶梯Legendre函数加权的面阵列,包括球面阵、柱面阵和平面阵,并且分别分析了Legendre函数球面加权方法和Legendre函数柱面加权方法应用于上述阵列的性能。结果表明,截断阶梯Legendre函数加权对波束方向的影响可以忽略,而主要影响波束宽度。对于面阵列,当采样阶梯不大于3 dB,截断点不大于-21 dB时,截断阶梯Legendre函数加权能很好近似连续Legendre函数加权。因此截断阶梯Legendre函数加权可以在保证CBT阵列性能的前提下有效减少阵元加权系数的数量。     

Observation of large arrays of plasma filaments in air breakdown by 1.5-MW 110-GHz gyrotron pulses

We report the observation of two-dimensional plasma filamentary arrays with more than 100 elements generated during breakdown of air at atmospheric pressure by a focused Gaussian beam from a 1.5-MW, 110-GHz gyrotron operating in 3-micros pulses. Each element is a plasma filament elongated in the electric field direction and regularly spaced about one-quarter wavelength apart in the plane perpendicular to the electric field. The development of the array is explained as a result of diffraction of the beam around the filaments, leading to the sequential generation of high intensity spots, at which new filaments are created, about a quarter wavelength upstream from each existing filament. Electromagnetic wave simulations corroborate this explanation and show very good correlation to the observed pattern of filaments.     

Beam intensity striations and applications

The single-element spectrogram for a continuous broadband signal, plotted as a function of range, has been shown to exhibit striated bands of intensity maxima and minima. The slope of the striations is an invariant of the modal interference and is described by a waveguide invariant parameter "beta." The striation pattern is analyzed and modeled in this paper for the beam outputs of a horizontal line array obtained by conventional beamforming. Array beamforming makes it possible to measure the waveguide invariant parameter for weak signals due to the enhancement of signal levels by the array gain over that of a single element. It is shown that the signal beam spectrogram as a function of range exhibits the same striation pattern as that (predicted) for a single element. Specifically, for a broadside signal, the beam striation is identical to that of a single-element plus a constant signal gain. For a nonbroadside target, the signal beam intensity will be modified by a frequency-bearing dependent signal gain due to the signal spread over multiple beams, nevertheless the beam spectrogram retains the same striation pattern (slope) as for a single element. The sidelobe beams (outside the canonical cones containing the signal arrivals) exhibit an entirely different striation pattern as a function of frequency and range. For array processing, it is shown that a fast range-rate, close range target and a distant, slow range-rate interference source will have a different striation pattern (slope) in the corresponding beam spectrograms as a function of time, assuming no prior knowledge of the source ranges. The difference in the striations between the beam spectrograms can be used in array processing to suppress the interference contribution. A 5-7 dB interference suppression is demonstrated using simulated data.     

Directional terahertz radiation through groove-assisted hole array

The authors theoretically demonstrate the terahertz beam shaping with metallic subwavelength holes array surrounded by concentric periodic grooves. High transmission and directional radiation can be obtained simultaneously for the resonant excitation of the surface wave in the combined structure. Finite-difference time-domain simulation results shows that the transmission mainly depends on the lattice constant of hole array and the features of incident surface around it, while the far-field angle distribution is dominated by the details of the output surface. This compact beam shaping structure is hoped to serve as a basic device for future terahertz systems.