A solution for self-calibrating a large distorted phased arrayusing subarray processing

Two subarray procedures are added to the multiple scatterer algorithm (MSA) for the purpose of self-calibrating a large distorted phased array. Depending on whether or not overlapping between adjacent subarrays exists, they are called the multiple scatterer algorithm with subarray processing (MSA-S) or the multiple scatterer algorithm with overlapping subarray processing (MSA-OS). These are tested using experimental microwave echoes from an industrial site and a housing development area. The data sets are obtained using an X-band (3-cm), 83-m phased array. MSA-OS can synthesize a specular-like beamformer using the echoes from three low-quality beamformers, each of which is incapable of phase-cohering the array by itself. MSA is found to be superior to the more basic dominant scatterer algorithm (DSA), and MSA-OS is found to perform the best     

MIMO-Frequency Diverse Array Radar with Unequal Subarrays for Improved Range-Angle Dependent Beamforming

Frequency diverse array (FDA) radar has been proposed in last decade for joint range and angle beamforming of a target. Multiple input multiple output-frequency diverse array (MIMO-FDA) radar has also been presented recently in literature to steer multiple beams by creating subarrays in transmit array. These beams help to localize the target in range as well as angle dimension. Due to same subarray size, all the beams have same beamwidth and thus exhibit same response for a given target. In this paper, we have proposed an unequal size subarrays structure for the FDA radar (US-MIMO-FDA), which allow us more focusing of the target in range and angle dimension by using beams of variable width. As a result the echoes received at the receiver help in better estimation of target parameters. The effectiveness of proposed scheme has been shown by comparing transmit and received beam patterns of proposed scheme with MIMO-FDA with equal subarrays Performance analysis of proposed scheme has also been done in terms of output signal to interference plus noise ratio, detection probability and cramer-rao lower bound. Simulation and results have verified better focusing of target by proposed design as compared to existing subarrays schemes for MIMO-FDA.     

Applications of RF aperture-array spatially-bandpass 2-D IIR filters in sub-Nyquist spectrum sensing,wideband doppler radar and radio astronomy beamforming

The application of two-dimensional (2-D) infinite impulse response (IIR) spatially-bandpass (SBP) filters as a digital beamformer for a wide spectrum of practical applications spanning wireless cognitive radio communications, doppler radar, and radio astronomy instrumentation is discussed. The paper starts with an introduction of the recently proposed 2-D SBP filter. The first application is a spectrum sensing scheme for dynamic spectrum access based cognitive radios. A 2-D IIR SBP filter is used in conjunction with a sub-Nyquist wideband signal reconstruction technique to achieve aperture-array directional spectrum sensing using sub-Nyquist sparse sampling based on the recently reported Eldar algorithm. The second application is related to wideband pulse and continuous-wave frequency modulated Doppler radar sensing. The SBP filter is integrated with a wideband radar back-end connected to an electronically-steerable aperture antenna. A a low-complexity directional localization algorithm is presented, which estimates the range and angle of a target scatterer with a signal to interference ratio improvement of 10 dB. We also present applications of 2-D IIR SBP in the fields of classification and remote sensing of unmanned aerial vehicles. Finally, a digital aperture-array wideband beamforming model using the 2-D IIR SBP filters is presented for radio telescope systems based on dense aperture arrays and time-domain beamforming. A well-known example is the study of pulsar astrophysics using a highly-directional aperture antenna system. The 2-D IIR SBP beamformer is simulated as the digital backend of the time-domain beamforming system with array signals synthesized using measured time-domain signatures from the Crab pulsar obtained from the GAVRT. The SBP filter shows a gain of 12.3 dB with an order of magnitude lower circuit complexity compared to traditional phased-array digital beamformers. To obtain comparable levels of SINR improvement, the wideband phased-array beamformers require 48-point FFTs per antenna. Assuming the optimum three real-multiplications per complex multiplication for the Gauss algorithm, it is discovered that the proposed 2-D IIR SBP beamformers are more than 97 % lower in digital multiplier complexity compared to traditional FIR phased-array FFT-beamformers.     

基于粒子群优化算法的非均匀子阵波束形成技术

基于粒子群优化算法提出了一种非均匀子阵波束形成方法。首先利用粒子群优化算法实现线阵最优非均匀划分;其次在线阵最优划分的基础上扩展到面阵最优非均匀划分;最后在面阵最优非均匀划分的基础上在期望区域内形成任意指向的波束。该方法既可以在期望区域内形成任意指向波束,又充分发挥了子阵级波束形成的优势。仿真结果表明该方法是有效的。     

On spatial smoothing for two-dimensional direction-of-arrivalestimation of coherent signals

We present an analysis of a spatial smoothing scheme extended for the estimation of two-dimensional (2-D) directions of arrival (DOAs) of coherent signals using a uniform rectangular array. The uniform rectangular array is divided into overlapping rectangular subarrays by the extended scheme, which is referred to as the 2-D spatial smoothing scheme. The analysis shows that when the extended preprocessing scheme is used in conjunction with the eigenstructure technique, the size of the subarrays should be at least (K+1)×(K+1), and the number of the subarrays must be no less than K×K in order to guarantee the “decorrelation” of κ coherent signals for all possible scenarios. The minimum size of the total uniform rectangular array is thus shown to be 2K×2K. Instead of using a uniform rectangular array, a minimal subarray structure incorporated with a minimal subarray grouping is also devised for resolving the 2-D DOAs of K coherent signals. The number of sensor elements of the minimal total array is then (K²+4K-2) instead of 4K²     

A microstrip array feed for land mobile satellite reflectorantennas

A circularly polarized feed array for a spacecraft reflector antenna is described that was constructed by using linearly polarized microstrip elements. The array has seven subarrays which form a single cluster as part of a large overlapping cluster reflector feed array. Each of the seven subarrays consists of four linearly polarized microstrip elements. The array achieved a better than 0.8-dB axial ratio at the array pattern peak and better then 3 dB antenna gain to 20° from the peak, across a 7.5% frequency bandwidth. A teardrop-shaped feed probe was used to achieve wideband input impedance matching for the relatively thick microstrip substrate. The low impedance and axial ratio bandwidths were achieved using a relatively thick honeycomb substrate with the impedance-matching feed probes     

基于改进粒子群算法的分布式频率分集阵栅瓣抑制方法

以均匀线阵（Uniform Linear Array ,ULA）为子阵,结合频率分集阵（Frequency Diverse Array ,FDA）的思想,构建了一种基于分布式子阵的频率分集阵。针对各子阵按等间距布阵将导致严重的栅瓣问题,提出了一种改进粒子群 (Improved Particle Swarm Optimization ,IPSO) 算法来优化分布式FDA中各子阵间的基线距离,以实现高效的栅瓣抑制。同时,从理论上推导了目标距离和角度均未知时参数估计的克拉美罗下界(Cramer-Rao Lower Bound ,CRLB)。仿真结果表明,优化后分布式FDA的栅瓣得到有效抑制,而且阵列角度维分辨率和估计性能亦得到大幅度提升,验证了所提算法的有效性。     

机载雷达极化空时自适应滤波性能分析

该文针对极化空时自适应处理时,目标极化状态未知的瓶颈问题,提出了先预估计目标的极化状态,然后再进行滤波的方法。该方法无需在极化域专门设置滤波器组进行搜索,大大减少了计算量。提出了最小方差无偏估计和正交投影估计两种极化矢量的估计方法,并将估计性能与Cramer-Rao界进行了比较,从理论上证明了最小方差无偏估计性能较好。与之相对应,提出了两种极化空时自适应滤波方法。仿真验证了特别当目标慢速运动时,极化空时自适应滤波明显优于空时自适应滤波。     

Maximum likelihood direction-of-arrival estimation in unknown noise fields using sparse sensor arrays

We address the problem of maximum likelihood (ML) direction-of-arrival (DOA) estimation in unknown spatially correlated noise fields using sparse sensor arrays composed of multiple widely separated subarrays. In such arrays, intersubarray spacings are substantially larger than the signal wavelength, and therefore, sensor noises can be assumed to be uncorrelated between different subarrays. This leads to a block-diagonal structure of the noise covariance matrix which enables a substantial reduction of the number of nuisance noise parameters and ensures the identifiability of the underlying DOA estimation problem. A new deterministic ML DOA estimator is derived for this class of sparse sensor arrays. The proposed approach concentrates the ML estimation problem with respect to all nuisance parameters. In contrast to the analytic concentration used in conventional ML techniques, the implementation of the proposed estimator is based on an iterative procedure, which includes a stepwise concentration of the log-likelihood (LL) function. The proposed algorithm is shown to have a straightforward extension to the case of uncalibrated arrays with unknown sensor gains and phases. It is free of any further structural constraints or parametric model restrictions that are usually imposed on the noise covariance matrix and received signals in most existing ML-based approaches to DOA estimation in spatially correlated noise.     

基于子阵近场零陷权的联合波达方向估计方法

针对海底长线阵在近场辐射声干扰及空间水平非均匀噪声下的远距离估计目标波达方向 (DoA)问题,该文提出一种基于长线阵分子阵近场零陷权的联合目标方位估计方法。该方法将长线阵分解为多个高重叠子阵,对各个子阵利用零陷抑制技术去除近场强干扰对目标探测的影响,再利用各子阵对远距离目标方位估计结果差异性小、非目标所在频率即噪声对应空间谱最大值随机的特点,空间频率方差加权综合各子阵的目标方位估计结果,从而抑制空间非均匀噪声,实现对远距离目标的探测。仿真结果表明,与长线阵常规波束形成、长线阵近场零陷常规波束形成、长线阵近场零陷传统多重信号分类方法相比,该文方法能够有效降低空间谱背景级60 dB以上,输出信噪比提高15 dB以上,具有较强的提高信噪比能力及较高的空间分辨力,因此具有较好的工程应用价值。     

Design of robust nearfield wideband beamformers with optimum subband constraints

Design of nearfield wideband beamformers robust against microphone mismatches is of great interest in practical applications. The state-of-the-art design approach is based on the fullband processing. In this paper, the over-constraint problem suffered by the fullband design approach is studied, which typically leads to the undesired signal distortion with low-pass filtered characteristics. To combat the over-constraint problem, a new design approach for robust nearfield wideband beamformers with optimum subband constraints is proposed. The performance of the proposed design approach is evaluated and compared with the fullband design counterpart via design examples.     

Velocity filters for multiple interferences in two-dimensionalgeophysical data

A procedure for the velocity filtering of two-dimensional geophysical data is discussed. This procedure involves repeatedly applying multichannel filters to a small number of overlapping subarrays of the input data. The multichannel filters can be chosen so that the resulting velocity filter is capable of suppressing multiple interferences traveling at different velocities. The two-dimensional frequency-wavenumber expression of the velocity filter is derived. With this expression, it becomes possible to implement the filter using two-dimensional fast Fourier transform (FFT) techniques. Two examples which illustrate the performance of the derived filters are presented     

Application of near-field optimum microphone arrays to hands-free mobile telephony

This paper discusses the application of fixed microphone arrays to speech pickup in mobile telephone applications. Array optimization techniques are used to design two broad-band beamformers for speech pickup in the near field. The first beamformer provides optimum gain for spatially incoherent noise while the second beamformer provides optimum gain in spherically isotropic noise. Array performance was measured using vehicular noise recorded under realistic driving conditions. Results obtained are in agreement with theoretical predictions for a spherically isotropic noise field and are comparable to previously reported results obtained using adaptive beamforming algorithms.     

Modified constant modulus algorithm for digital signal processingadaptive antennas with microwave analog beamforming

This paper proposes a novel algorithm, called modified constant modulus algorithm (M-CMA), which is able to give adaptability to microwave beamforming phased array antennas. Since microwave analog beamformers basically require much fewer RF devices than digital beamformers, microwave analog beamformers based on M-CMA, that is, adaptive microwave beamformers, can be cheaply fabricated. Therefore, they are very suitable for mobile communication systems where both miniaturization and low cost are required for the mobile terminals. M-CMA obtains a gradient vector by a combination of analytical calculation and perturbation of the microwave beamforming control voltage. Though M-CMA is implemented with a digital signal processor, M-CMA controls the microwave analog beamformer by utilizing the gradient vector. The microwave analog beamformer based on M-CMA is analyzed to have the following characteristics: (1) the beamformer can point its main beam to the desired direction in additive white Gaussian noise (AWGN) channels; (2) although the beamformer may possibly fail in ill solutions in cochannel interference (CCI) channels, M-CMA can converge to the optimum solution when the desired direction is roughly a priori known     

Constrained feed technique for subarrays of large phased arrays

A technique is presented which combines the subarraying qualities of constrained dual transform beamforming sections and partial overlapping networks to produce arrays of contiguous subarrays. This approach is shown to facilitate wideband scanning or limited field of view coverage with a minimum number of controls and low sidelobes     

Estimation of scale parameters for two exponential distributions[reliability theory]

The scale parameter of the exponential distribution is estimated using conditional specification. When there are two censored samples available for estimating the scale parameter, a preliminary test is usually used to determine whether to pool the samples or to use the individual minimum-variance unbiased estimator. This latter estimator (usual preliminary-test estimator) is studied. The optimum levels of significance and their corresponding critical values for the preliminary test are obtained on the basis of the minimax regret criterion. A preliminary-test shrinkage estimator is proposed, and the optimum values of its shrinkage estimator is proposed, and the optimum values of its shrinkage coefficients are obtained. For a mean-square-error criterion of goodness of estimation, the preliminary-test shrinkage estimator is better than the usual preliminary-test estimator     

On the optimization of the aspect angle windows for the Doppler analysis of the radar return of rotating targets

Optimum resolution in the Doppler spectra of rotating targets is obtained by using an optimum aspect angle window from which the data for the Fourier transforms are taken. The width of the optimum aspect angle window depends on the location, relative to the axis of rotation, of the scattering center to be resolved, so that for optimum resolution a sort of focusing by choosing the appropriate aspect angle window is necessary. Formulae and graphs for optimum width of aspect angle windows and the obtainable resolutions are given. Typical applications of the scheme presented are in the experimental determination of the location, the strength, and the interaction of the scattering centers on a target. These in turn are of major interest, e.g., for the analysis and synthesis of radar cross sections, in glint investigations, and in target imaging.     

On the coherent interference suppression using a spatiallysmoothing adaptive array

The behavior of a spatially smoothing adaptive array is examined. An expression for the weight vector is first derived. Using the array gain on the desired signal and the coherent interference is obtained. Then the expression for output signal-to-noise (SNR) is derived. It shows that the performance of the spatially smoothing array depends on the number of the subarrays, the angle separation, relative power and initial phase difference between the desired signal and the coherent interference. For good interference suppression it is found that the magnitude of the phase difference of the incident and interference signals must be greater than the beamwidths of both the subarray and the equivalent array. There is also a tradeoff between increasing the groups of subarrays and decreasing the number of elements in the subarrays. Computer simulation results are given that validate the analysis     

多光束周视激光引信与定向战斗部的配合

为满足定向战斗部对多光束周视激光引信的延时和方位要求,针对引战配合问题,依据激光探测原理建立了弹目交会过程中最佳起爆延时和最佳起爆方位角的数学模型。仿真结果表明：所建立的最佳起爆延时与方位角模型正确,且与弹目视线角、目标初始方位角、弹目间距、弹目相对速度、破片飞散速度、目标和弹体外型参数等信息有关。根据多光束周视激光引信系统提供的信息参数,可计算出最佳起爆延时与最佳起爆方位角,能够控制战斗部适时定向起爆,实现对目标的有效打击。     

Optimal Design of Nearfield Wideband Beamformers Robust Against Errors in Microphone Array Characteristics

Nearfield wideband beamformers for microphone arrays have wide applications, such as hands-free telephony, hearing aids, and speech input devices to computers. The existing design approaches for nearfield wideband beamformers are highly sensitive to errors in microphone array characteristics, i.e., microphone gain, phase, and position errors, as well as sound speed errors. In this paper, a robust design approach for nearfield wideband beamformers for microphone arrays is proposed. The robust nearfield wideband beamformers are designed based on the minimax criterion with the worst case performance optimization. The design problems can be formulated as second-order cone programming and be solved efficiently using the well-established polynomial time interior-point methods. Several interesting properties of the robust nearfield wideband beamformers are derived. Numerical examples are given to demonstrate the efficacy of the proposed beamformers in the presence of errors in microphone array characteristics.