Direction finding for diversely polarized signals using polynomialrooting

A direction finding algorithm for diversely polarized arrays that is based on polynomial rooting is presented. Using polynomial rooting instead of search reduces significantly the computational requirements of the algorithm and enhances resolution. The basic method is limited to linear uniformly spaced arrays. However, using an interpolation technique, the algorithm is extended to a larger class of arrays. The performance of the proposed algorithm is analyzed. Computer simulations are used to demonstrate the performance of the new technique and to verify the performance analysis     

共形阵列非圆信号波达方向估计算法

受共形载体变曲率结构的影响,各天线单元指向不尽相同,使得共形天线阵列呈现极化多样性。因此,共形天线阵列的建模过程中需考虑不同阵元的极化响应特性。基于柱面共形天线阵列的快拍数据模型,利用非圆信号的特性对阵列输出进行扩展,基于秩亏理论和子空间原理实现信号波达方向（DOA）估计,所提方法估计精度高,不需要参数配对。存在相干信源时,提出对扩展后的虚拟阵列进行划分,对划分出的子阵进行虚拟的空间平滑,实现解相干的预处理操作。仿真结果表明该方法能有效应用于柱面共形阵列非圆信号DOA估计,并提高了空间分辨率。      

Direction finding with an array of antennas having diverse polarizations

The advantages of using diversely polarized antennas to determine bearings of multiple cochannel narrow-band signals are shown. Three bearing estimation algorithms-maximum likelihood (ML), adapted angular response (AAR), and Music (multiple signal classification)-are extended to handle antenna arrays with diverse polarizations; the maximum entropy method does not readily extend. The proposed algorithms are applicable to arbitrary antenna locations and directional characteristics and arbitrary noise correlations between the antenna outputs. The algorithms are compared on the basis of multiple signal resolution and bearing accuracy in the presence of noise. The Music algorithm exhibits superior performance at moderate to low signal-to-noise ratio (SNR).     

基于一致聚焦的宽带信号波达方向估计

MTLS聚焦需要预估计波达方向,预估计偏差会影响聚焦效果,严重时会导致CSM算法失效。基于AMI思想构造了CMTLS一致聚焦变换,该聚焦变换无需预估计波达方向,提高了聚焦性能的同时,增强了算法的实时性。     

基于原子范数最小化的单比特稀疏双极子阵列的波达角估计

现有的单比特稀疏双极子阵列的波达角估计方法为子空间方法,其估计精度依赖于信号的统计特征,并且没有充分利用协方差矩阵的结构,导致其估计精度较低。为了提高该阵列的波达角估计精度,本文提出了一种基于原子范数最小化的无网格稀疏化波达角估计方法。该方法将稀疏双极子阵列的波达角估计转化为标量阵波达角估计,并根据参数空间的连续性构造基于原子集的阵列信号稀疏模型,随后利用单比特采样下噪声的稀疏特征,将该波达角估计问题转化为相似文献   

Direction finding using data-supported optimization

A novel data-supported optimization technique for maximum likelihood (ML) direction-of-arrival estimation is proposed. The essence of our approach is to optimize the likelihood function at certaindata-supported points obtained by a resampled root-MUSIC procedure. These points are shown to comprise a small but representative subset of all possible searching points and contain enough information for solving the ML problem.This work was supported in part by grants from the National Sciences and Engineering Research Council of Canada (NSERC), Ministry of Energy, Science and Technology (MEST) of Ontario, Communications and Information Technology Ontario (CITO), and by the Senior Individual Grant Program of the Swedish Foundation for Strategic Research.     

Focusing filters for wide-band direction finding

A time-domain equivalent of the coherent signal-subspace transformations (CST) is established for wideband direction finding in a possible multipath environment using general arrays. Time-domain equivalents of focusing are derived based on the least squared error approach for general transformations, and the Taylor series expansion approach for closed-form transformations. The preprocessor is realized by a multichannel digital finite impulse response filter. For diagonal transformations, the problem reduces to implementing different delays at each sensor, which in turn leads to computational simplicity. Various tapped delay line filters for realizing an arbitrary delay are proposed and compared. Simulation results reveal that low-order filter structures in the time domain achieve similar performance to the frequency domain approach, even at detection and resolution thresholds     

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.     

Direction finding using noise covariance modeling

We consider the problem of direction finding in the presence of colored noise whose covariance matrix is unknown. We show that the ambient noise covariance matrix can be modeled by a sum of Hermitian matrices known up to a multiplicative scalar. Using this model, we estimate jointly the directions of arrival of the signals and the noise model parameters. We show that under certain conditions, it is possible to obtain unbiased and efficient estimates of the signal direction. The Cramer-Rao bound is used as the principal analysis tool. Computer simulations using the maximum likelihood estimator provide a validation of the analytical results     

Separation of cochannel GSM signals using an adaptive array

The Global System for Mobile communications (GSM) is a digital cellular radio network that employs time division multiple access (TDMA). In such a cellular system, frequencies are reused in different regions for spectral efficiency, and thus, the transmissions in a given cell can interfere with those in distant cells. This cochannel interference can be a major impairment to the signal of interest. In this paper, we describe a beamformer and equalizer system that is capable of separating and demodulating several cochannel GSM signals. The signal model includes intersymbol interference (ISI) induced by the Gaussian transmit filter, and the channel model incorporates multipath propagation and additive white Gaussian noise. The GSM synchronization sequences are used to compute the beamformer weights and achieve frame synchronization simultaneously. Decision-feedback equalization is employed to compensate for the transmit filter ISI and to demodulate the data     

Multifunction wide-band array design

High-performance active arrays operating over C, X, and Ku-band have been demonstrated using newly developed designs of wide-band radiating elements and wide-band monolithic microwave integrated circuits (MMICs). The advanced shared aperture program (ASAP) explored the development of wide-band multifunction arrays capable of simultaneous and time interleaved radar, electronic warfare, and communications functions. Two iterations of radiating element and transmit/receive (T/R) module design were completed during this program. The radiating aperture design approach, overall array concepts, and current design technology and performance are summarized     

宽带方位估计的波束域Root-MUSIC算法

高分辨算法的实现是一个受到普遍重视的问题。为降低运算量,提高估计性能,便于工程应用,该文深入研究宽带波束域Root-MUSIC算法,根据波束域处理的空间滤波特性,将被束域求根多项式的根划分在不同的区域,从而基于子阵分解对求根多项式进行降阶处理,仿真实验讨论了不同波束形成矩阵的估计性能,证明了降阶处理的可行性。     

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     

Gap-coupled microstrip array antenna for wide-band operation

The theoretical and experimental investigations carried out on a gap-coupled microstrip array antenna reveal that there is a significant improvement in VSWR and bandwidth characteristics of the gap-coupled microstrip array antenna as compared with a conventional microstrip array antenna. The input impedance and the resonant frequency of the gap-coupled patch are found to depend heavily on the gap length as well as on the dielectric constant of the substrate material.     

On focusing matrices for wide-band array processing

A general class of transformation matrices for coherent signal-subspace processing is presented. These signal-subspace transformation (SST) matrices are shown to generate a sufficient statistic for maximum-likelihood bearing estimation. Two general forms for calculating SST matrices are presented, and the rotational signal-subspace (RSS) focusing matrices proposed by H. Hung and M. Kaveh (1988) are shown to be a special case of the SST matrices. An efficient procedure for computing a subset of the SST matrices, utilizing Householder transformations, is presented. The procedure reduces the computational load by a factor of 10, compared with that for the RSS matrices. The application of MUSIC to the coherently combined covariance matrix is also discussed, and Monte Carlo simulations comparing the performance of Householder SST matrices and RSS matrices are performed     

2-D SPATIAL-SPECTRUM ESTIMATION FORWIDE-BAND SOURCES BASED ON INTERPOLATED CIRCULAR ARRAYS

In array signal processing, 2-D spatial-spectrum estimation is required to determine DOA of multiple signals. The circular array of sensors is found to possess several nice properties for DOA estimation of wide-band sources. C. U. Padmini, et al.(1994) had suggested that the frequency-direction ambiguity in azimuth estimation of wide-baud signals received by a uniform linear array (ULA) can be avoided by using a circular array, even without the use of any delay elements. In 2-D spatial-spectrum estimation for wide-band signals, the authors find that it is impossible to avoid the ambiguity in source frequency-elevation angle pairs using a circular array. In this paper, interpolated circular arrays are used to perform 2-D spatial-spectrum estimation for wide-band sources. In the estimation, a large aperture circular array (Υ>λmin/2) is found to possess superior resolution capability and robustness.     

A wide-band square-waveguide array polarizer

A stepped-septum polarizer has been designed that is capable of at least 26 dB of isolation over a 20 percent frequency band. The three-port device may be used to excite high purity left or right circular, as well as tilted linear polarizations in a phased array of square waveguides.     

负SNR数字调相信号的干涉仪测向技术

传统意义上的干涉仪测向数学模型与处理流程一般要求目标信号具有正信噪比(SNR),在对负SNR调制信号实施测向时通常会产生较大误差甚至失效。在分析传统方法失效原因的基础上,利用数字调相信号的特点,通过非线性变换对负SNR信号进行高次载波恢复,然后针对恢复后的高次载波进行相位差提取,从而获得被测信号的来波方向。在此基础上对该方法所能达到的精度进行了理论分析,并将其推广至凡是具有可恢复载波分量的测向应用情况。仿真结果验证了该方法的有效性,这对于干涉仪在电子侦察和电磁频谱监测中更加广泛的应用提供了新的参考。     

基于幅相误差阵列的远近场混合信号超分辨测向方法

大多数的超分辨测向方法都需要掌握准确的阵列流型,然而在实际应用当中,各阵元通道对信号的幅度增益和延时往往不一致,使得真正的阵列流型和它的理论模型之间存在一定的误差,最终造成测向性能的下降.针对这个问题,论文提出了一种基于幅相误差阵列的远近场混合信号超分辨测向估计方法.首先对信号的空间谱函数进行变换判断出远场信号方向,接着根据远场信号子空间和噪声子空间的正交性估计出阵列误差并对数据进行校正,在此基础上通过矩阵分解判断出近场信号方向,同时还能够实现近场信号的定位.所提方法直接对信号空间谱函数分母的多项式求根得出信号方向和近场信号距离,回避了谱峰搜索的过程,在保证一定精度的前提下大大提高了计算速度.     

Optical down-sampling of wide-band microwave signals

Phase-encoded optical sampling allows radio-frequency and microwave signals to be directly down-converted and digitized with high linearity and greater than 60-dB (10-effective-bit) signal-to-noise ratio. Wide-band electrical signals can be processed using relatively low optical sampling rates provided that the instantaneous signal bandwidth is less than the Nyquist sampling bandwidth. We demonstrate the capabilities of this technique by using a 60-MS/s system to down-sample two different FM chirp signals: 1) a baseband (0-250 MHz) linear-chirp waveform and 2) a nonlinear-chirp waveform having a 10-GHz center frequency and a frequency excursion of 1 GHz. We characterize the frequency response of the technique and quantify the analog bandwidth limitation due to the optical pulse width. The 3-dB bandwidth imposed by a 30-ps sampling pulse is shown to be 10.4 GHz. We also investigate the impact of the pulse width on the linearity of the phase-encoded optical sampling technique when it is used to sample high-frequency signals.