Direction-of-arrival estimation in partly calibrated subarray-based sensor arrays

The problem of direction-of-arrival (DOA) estimation in partly calibrated arrays is addressed. We assume that an array is composed of multiple well-calibrated subarrays of arbitrary known geometry, but there are imperfections between subarrays. We address the cases of unknown (or known with a certain error) intersubarray displacements, imperfect synchronization of subarrays in time, unknown propagation channel mismatches between subarrays, as well as combinations of these effects. A new subspace-based approach to DOA estimation is proposed, which is applicable to this general class of partly calibrated arrays. DOA identifiability issues for such arrays are discussed, and a relevant Cramer-Rao bound (CRB) is derived. Numerical examples illustrate the performance of the proposed estimators.     

Robust Capon-based direction-of-arrival estimators in partly calibrated sensor array

In this paper a problem of direction-of-arrival (DOA) estimation in partly calibrated sensor arrays is considered. It is assumed that a sensor array consists of subarrays with full inner calibration and unknown intersubarray distortions. Capon-based methods are proposed for DOA estimation as suitable techniques have robustness to intersubarray distortions. These methods are an extension of robust Capon beamformer developed for partly calibrated array to the DOA estimation. The simulations validate efficiency of the proposed algorithms.     

Direction finding with time-varying arrays

This paper considers the problem of finding the directions of narrowband signals using a time-varying array, whose elements move during the observation interval in an arbitrary but known way. Assuming a Gaussian signal model, we derive the Cramer-Rao bound (CRB) and the maximum likelihood estimator for the directions of arrival. The single source case is studied in detail. Time-varying arrays are shown to be more robust to ambiguity errors than static arrays of comparable dimensions     

基于同心圆环的大间距子阵级阵列栅瓣抑制

适当增加单元间距和应用子阵级阵列有利于降低相控阵的设计成本, 但是阵列的稀疏会带来不期望的栅瓣.为解决该问题, 设计了一种无栅瓣阵列:子阵在平面内旋转, 围绕阵列中心呈同心圆环分布.为保证子阵之间不会交叠, 对圆环半径范围进行了分析.利用一种改进的穷举算法, 对每一层圆环上的子阵个数以及圆环半径进行了计算机仿真优化.结果表明, 以4×4子阵共1 024个单元为例, 所提方法可抑制峰值旁瓣电平约-17.48 dB.     

Direction finding of coherent sources with nonlinear arrays

This paper presents an approach to estimate the directions-of-arrival (DOAs) of narrowband coherent (completely corrected) signals by an arbitrary geometry sensor array. The concept of focussing matrices is introduced to estimate the outputs of a virtual uniform linear array from the outputs of the real array in order to use spatial smoothing techniques. Unlike the work presented in [5], the proposed approach avoids multiple singular value decomposition (SVD) computations in the various sectors because it is not necessary to divide the field of view of the array into sectors. Simulation results are given to support the approach.On leave from the Department of Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People's Republic of China.     

Direction finding in phased arrays with a neural network beamformer

Adaptive neural network processing of phased-array antenna received signals promises to decrease antenna manufacturing and maintenance costs while increasing mission uptime and performance between repair actions. We introduce one such neural network which performs aspects of digital beamforming with imperfectly manufactured, degraded, or failed antenna components. This paper presents measured results achieved with an adaptive radial basis function (ARBF) artificial neural network architecture which learned the single source direction finding (DF) function of an eight-element X-band array having multiple, unknown failures and degradations. We compare the single source DF performance of this ARBF neural network, whose internal weights are computed using a modified gradient descent algorithm, with another radial basis function network, Linnet, whose weights are calculated using linear algebra. Both networks are compared to a traditional DF approach using monopulse     

Direction finding with unknown array sensor gains and phases

An eigenstructure-based calibration method is presented for an array with unknown sensor gains and phases. The approach requires only one calibration source and a very roughly measured direction of the source. The method can be applied to arrays of arbitrary geometry, and suitable for low signal-to-noise ratio (SNR) applications. Computer simulations are presented to assess the performance of the proposed method.     

Design of phased arrays in terms of random subarrays

Analysis and systematic design of uniform phased arrays with subarrays of unequal sizes are absent from the literature, in spite of the appeal of such architectures to wide-bandwidth beam steering. Unequally sized subarrays are expected to outperform identical, contiguous subarrays in terms of array grating lobes, A uniform linear array that is divided into contiguous subarrays of random sizes is studied. Each array element is connected to a phase shifter, and each subarray is implemented with a common time delayer. Closed-form expressions for the average array factor and the variance of the array factor are developed. These expressions enable the formulation of a design procedure that includes the estimation of the peak-grating-lobe level in terms of the probability that the grating lobes will exceed a desired level     

Direction finding of coherent signals via spatial smoothing foruniform circular arrays

We present a preprocessing technique that in conjunction with spatial smoothing circumvents the difficulty of direction-of-arrival estimation of coherent signals in the case of uniform circular arrays. Special consideration is given to problems arising in practice, such as mutual coupling and array geometry imperfections. Simulation results illustrating the performance of this scheme in conjunction with the MUSIC method are included     

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     

Sidelobe level and wideband behavior of arrays of random subarrays

We propose an extension to the concept of random antenna arrays. Three new array geometries are introduced which are intended to incorporate the wide bandwidth capability of a random array while having simplified geometry to increase their suitability for lower-cost applications. The behaviors of the periodic array of random subarrays, array of periodically rotated random subarrays, and array of randomly rotated random subarrays are each characterized probabilistically. Results indicate that subarray rotation can lower the sidelobe level of the array factor. An example of the design process is presented with calculated array factors.     

Estimating parameters of multiple wideband polynomial-phase sourcesin sensor arrays

We consider the problem of estimating the parameters of multiple wideband polynomial-phase signal (PPS) sources in sensor arrays. A new maximum likelihood (ML) direction-of-arrival (DOA) estimator is introduced, and the exact Cramer-Rao bound (CRB) is derived for the general case of multiple constant-amplitude polynomial-phase sources. Since the proposed exact ML estimator is computationally intensive, an approximate solution is proposed, originating from the analysis of the log-likelihood (LL) function in the single chirp signal case. As a result, a new form of spatio-temporal matched filter (referred to as the chirp beamformer) is derived, which is applicable to "well-separated" sources that have distinct time-frequency or/and spatial signatures. This beamforming approach requires solving a three-dimensional (3-D) optimization problem and, therefore, enjoys essentially simpler implementation than that entailed by the exact ML. Simulation results are presented, illustrating the performance of the estimators and validating our theoretical CRB analysis     

阵列误差下的多输入多输出雷达测向技术

针对多输入多输出(Multiple-Input Multiple-Output, MIMO)雷达收发阵列同时存在阵元互耦效应和幅相误差时目标测向性能下降的问题,提出了一种基于Capon波束形成的测向算法.该方法利用Toeplitz特性降低了参数空间维数,并结合Kronecker积特性将发射和接收阵列的阵列误差去耦合,从而对收发阵列误差进行迭代补偿,最终获得目标方位角的估计.仿真结果验证了所提算法的有效性和可行性.     

Observability conditions for multiple signal direction finding andarray sensor localization

Three observability issues, which arise in narrowband signal direction-finding in the presence of array sensor location errors are described. Necessary and sufficient conditions for the phase delay ambiguity and the rank-2 ambiguity are presented. However, the characterization of the rank-n ambiguity is still an open problem and only a conjecture is given. Barring these ambiguities, the minimal numbers of known and unknown signals required for uniquely localizing the sources and sensors are determined under the assumption of no measurement noises     

Direction finding in the presence of mutual coupling

An eigenstructure-based method for direction finding in the presence of sensor mutual coupling, gain, and phase uncertainties is presented. The method provides estimates of the directions-of-arrival (DOA) of all the radiating sources as well as calibration of the gain and phase of each sensor and the mutual coupling in the receiving array. The proposed algorithm is able to calibrate the array parameters without prior knowledge of the array manifold, using only signals of opportunity and avoiding the need for deploying auxiliary sources at known locations. The algorithm is described in detail, and its behavior is illustrated by numerical examples     

Polarization-induced fading in fiber-optic sensor arrays

The statistics of polarization-induced visibility fading is studied for fiber-optic interferometric (Michelson or Mach-Zehnder) sensor arrays made of either regular single-mode fibers or polarization-maintaining fibers. Performance is measured in terms of the probability to observe visibilities, all of which exceed a given value, for all members of the array. Very poor performance is obtained for arrays made of nonpolarization maintaining fibers, unless the input state of polarization is dynamically controlled to optimize the visibility of the worst sensor of the array. While the use of the more costly polarization-maintaining fibers could, in principle, solve this polarization-related fading problem, finite extinction ratios of couplers and splices make the performance of such arrays comparable to that of nonpolarization maintaining arrays with optimally controlled input-polarization     

Direction finding in the presence of an intermittent interference

We consider the problem of estimating the direction of arrival (DOA) of a source in the presence of an intermittent jammer, i.e., a jammer that corrupts the signal of interest from time to time. This situation is encountered in slow frequency-hopped spread spectrum systems with partial time or partial band jamming. It has deleterious effects on the receiver performance, at least when a single antenna is used. We consider using an array of sensors to mitigate the effects of such an interference. The influence of the latter on the signal and jammer DOA estimates is studied. A general setup is introduced, and two different models are derived, depending on whether the jammer's presence indicators are considered deterministic or random. In both cases, the Cramer-Rao bounds (CRBs) are derived, and a numerical study of the CRB provides insights into the influence of the jammer's parameters. Additionally, it is shown that conventional methods such as ESPRIT can provide fairly accurate DOA estimates for this type of interference     

DOA and phase error estimation using one calibrated sensor in ULA

A new method is presented to effectively estimate the direction-of-arrival of a source signal and the phase error of a uniform linear array. Assuming that one sensor (except the reference one) has been calibrated, the proposed method appropriately reconstructs the data matrix and establishes a series of linear equations with respect to the unknown parameters through eigenvalue decomposition. The unknown parameters can be determined directly by the least squares method. Unlike the conventional methods, the proposed method only requires one calibrated sensor, which may not be consecutively spaced to the reference one. The computational complexity analysis is given and the effectiveness of the proposed method is validated by simulation results.     

基于遗传算法多子阵平板天线旁瓣电平优化

从理论上分析了多子阵平板天线的方向图特性,指出其旁瓣电平难以通过传统的不等幅馈电技术得以抑制。以降低天线扫描范围内的最高旁瓣电平为目标,采用遗传算法对子阵间距进行优化,并在间距优化的基础上讨论了天线单元方向性与不等幅馈电技术对旁瓣电平的影响。仿真结果证明了理论分析的正确性,表明子阵间距优化可以显著降低天线的旁瓣电平,且在天线口径相同的情况下,所划分的子阵数越多则优化效果越明显。所用方法和分析结果可为多子阵平板天线的设计提供参考。     

Direction finding in multipath environment using method of alternating projection

In a coherent environment the problem of direction finding using arbitrary antenna array geometries always seems to be a multivariate optimisation problem. An estimator derived using suboptimal eigen techniques and optimised using the method of alternating projection (AP) is shown to be superior to the maximum likelihood method.<>