离散傅里叶变换及变参考阵元特征法在相干信号估计中的应用

本文讨论理想条件下均匀线阵(ULA)对相干入射信号的高分辨测向问题。在分析经典多重信号分类法(MUSIC)对相干信号测向失效原因的基础上提出新算法,它利用1）离散傅里叶变换(DFT)估计入射信号数目;2）变参考阵元重构入射信号功率矩阵估计入射信号方位角。通过与经典MUSIC算法比较验证了该算法对相干入射信号估计的可行性,并经过进一步分析得出如下结论:1）文中介绍的算法在不减少阵列有效口径前提下能够对高度相干信号进行高分辨测向;2）在低信噪比条件下能够精确估计入射信号方位角;3）随着阵列中阵元数目的增加,阵列分辨率逐渐提高。      

基于NC-MUSIC算法的均匀圆阵DOA估计及性能分析

近年来基于非圆信号的DOA估计算法由于其优良的估计性能,受到越来越多的关注。在接收阵列为均匀圆阵的情况下,对入射信号进行方位角和俯仰角的联合估计。依据非圆信号的DOA估计数学模型及阵列模型,采用NC-MUSIC算法完成对均匀圆阵方位角和俯仰角的联合估计。通过计算机仿真,得出该算法对均匀圆阵方位角和俯仰角的估计是比较准确的,并且通过NC-MUSIC与MUSIC算法仿真性能的分析比较,得出在接收阵列为均匀圆阵的情况下,NC-MUSIC算法也优于MUSIC。     

基于虚拟孔径扩展的非均匀稀疏阵无模糊测向算法

针对常规均匀线阵DOA估计中可估计信源数目不足的问题,提出了一种基于虚拟孔径扩展的非均匀稀疏阵无模糊测向算法。该算法在传统MUSIC算法模型基础上,首先对阵列接收信号协方差矩阵进行向量化处理,通过Khatri-Rao积运算实现孔径扩展,提高了阵列自由度。然后利用任意阵列下的空间平滑恢复新协方差矩阵的秩,最后通过MUSIC算法进行DOA估计。仿真实验结果表明,与传统MUSIC算法相比,该算法可以在阵元数目小于信源数目的条件下实现DOA估计,大大增加了可估计信源数目,同时在低信噪比、小快拍条件下仍能得到DOA估计结果。     

基于虚拟孔径扩展的非均匀稀疏阵无模糊测向算法

针对常规均匀线阵DOA估计中可估计信源数目不足的问题,提出了一种基于虚拟孔径扩展的非均匀稀疏阵无模糊测向算法。该算法在传统MUSIC算法模型基础上,首先对阵列接收信号协方差矩阵进行向量化处理,通过Khatri-Rao积运算实现孔径扩展,提高了阵列自由度。然后利用任意阵列下的空间平滑恢复新协方差矩阵的秩,最后通过MUSIC算法进行DOA估计。仿真实验结果表明,与传统MUSIC算法相比,该算法可以在阵元数目小于信源数目的条件下实现DOA估计,大大增加了可估计信源数目,同时在低信噪比、小快拍条件下仍能得到DOA估计结果。     

基于虚拟孔径扩展的非均匀稀疏阵无模糊测向算法

针对常规均匀线阵DOA估计中可估计信源数目不足的问题,提出了一种基于虚拟孔径扩展的非均匀稀疏阵无模糊测向算法。该算法在传统MUSIC算法模型基础上,首先对阵列接收信号协方差矩阵进行向量化处理,通过Khatri-Rao积运算实现孔径扩展,提高了阵列自由度。然后利用任意阵列下的空间平滑恢复新协方差矩阵的秩,最后通过MUSIC算法进行DOA估计。仿真实验结果表明,与传统MUSIC算法相比,该算法可以在阵元数目小于信源数目的条件下实现DOA估计,大大增加了可估计信源数目,同时在低信噪比、小快拍条件下仍能得到DOA估计结果。     

基于虚拟孔径扩展的非均匀稀疏阵无模糊测向算法

针对常规均匀线阵DOA估计中可估计信源数目不足的问题,提出了一种基于虚拟孔径扩展的非均匀稀疏阵无模糊测向算法。该算法在传统MUSIC算法模型基础上,首先对阵列接收信号协方差矩阵进行向量化处理,通过Khatri-Rao积运算实现孔径扩展,提高了阵列自由度。然后利用任意阵列下的空间平滑恢复新协方差矩阵的秩,最后通过MUSIC算法进行DOA估计。仿真实验结果表明,与传统MUSIC算法相比,该算法可以在阵元数目小于信源数目的条件下实现DOA估计,大大增加了可估计信源数目,同时在低信噪比、小快拍条件下仍能得到DOA估计结果。     

基于均匀圆阵的循环平稳信号源方位估计

传统的测向算法只利用了信号的空间特性而没有利用其时间特性，而Gardner等人对循环平稳特性用于阵列测向的研究仅限于均匀线阵。文中提出一种利用均匀圆阵列估计循环平稳信号到达角的方法——Cyclic-RMUSIC算法，并与传统MUSIC算法进行了比较。仿真结果表明：该算法具有信号选择能力及抑制干扰、噪声的能力。此外，由于该算法利用了Root—MUSIC技术，在提高分辨性能的同时，极大地提高了计算效率。     

阵元切换时间对单通道阵列测向性能的影响

单通道阵列采用单个通道贯续接入各阵元进行采样,与常规阵列相比,单通道阵列减少了硬件成本以及通道幅相特性不一致问题对估计性能的影响,但现有研究均未考虑单通道阵列的阵元切换时间对系统性能的影响。为填补这一空白,首先参照常规阵列,明确了单通道阵列中窄带信号的带宽限制及其与单通道阵列阵元切换时间的关系;再以单通道阵列MUSIC算法为例,同时考虑信号带宽与单通道阵列阵元切换时间对单通道阵列协方差阵特性的影响,从理论上推导了单通道阵列MUSIC算法关于扩展相对带宽的一阶估计误差。最后对单通道阵列MUSIC算法与单通道阵列空间FFT算法在不同阵元切换时间下进行仿真,对两种算法测向误差与阵元切换时间的关系进行分析,验证了理论推导结果的正确性。      

圆阵二维MUSIC谱快速计算方法研究

针对二维波达方向估计时MUSIC谱的快速计算问题,研究了均匀圆阵变换到虚拟线阵的MUSIC算法(UCA-ULA-MUSIC)、流形分离MUSIC算法(MS-MUSIC)、傅立叶域线性求根MUSIC算法(FD-Line-Search-MUSIC)、基于FFT的 元均匀圆阵MUSIC算法( -UCA-FFT-MUSIC)与基于FFT的任意圆阵MUSIC算法(ACA-FFT-MUSIC)。对各种算法快速计算二维MUSIC谱的实现步骤进行了总结。在此基础上,给出了各算法计算二维MUSIC谱的计算复杂度表达式,并以传统方法为参考,对比了各种快速算法相对于传统方法的计算复杂度比值;同时,针对不同的阵列形式,对适用的快速算法的测向性能进行了仿真对比。根据分析和对比的结果,指出MS-MUSIC算法与ACA-FFT-MUSIC算法具有更高的工程应用价值,由具体的情况单独或分频段联合使用MS-MUSIC算法与ACA-FFT-MUSIC算法,可以使测向系统较好的兼顾测向性能与时效性。      

MUSIC与干涉仪测向算法性能研究

研究了两种阵列信号测向算法的性能：空间谱估计测向算法和干涉仪测向算法。基于均匀圆阵的硬件平台,两种算法均可实现测向功能,为针对不同的实现需要,着重介绍了因测向机理的不同在多种性能方面呈现出的差异。以五元圆阵为例,分别实现干涉仪和空间谱估计测向的仿真实验。仿真结果表明空间谱估计算法在低信噪比情况下测向精度优于干涉仪测向,而后者在测向耗时方面要远优于前者。     

Time-domain array factor for UWB antenna array

A cross-correlation formulation for the computation of time-domain array factor for ultra-wideband (UWB) antenna arrays is presented. In addition, a dual band UWB waveform is proposed for high directivity and high-resolution radar imaging. The dual band UWB waveform is based on a frequency truncated, Gaussian modulated, higher-order sinusoidal UWB pulse.     

Virtual array synthesis method for planar array antennas

A new array antenna synthesis method, which we call the virtual array synthesis method, is presented. In this method, the excitation values of a virtual array are synthesized using some known synthesis method. The geometry of the virtual array can be chosen so that there will be a suitable synthesis method for that geometry and the synthesis of the virtual array can be done accurately enough. In the synthesis method presented, the excitation values of the virtual array are transformed into the excitation values of the actual array geometry. Matrix operations are simple and large arrays can be easily synthesized     

Large finite array analysis using infinite array data

The prediction of edge element behavior is a common problem during the design of large array antennas. The performance of the center elements can be approximated by an infinite array model, but the edge element patterns and active reflection coefficients cannot. The full element-by-element analysis of a large finite array is either excessively time consuming or impossible due to the computer power required. A study has recently been carried out to develop and test methods of fully predicting large array performance using infinite array data. The methods devised are presented, together with comparisons of predicted performance and measured data from a 163-element WG-16 array     

阵列天线排阵间距与天线增益的关系探讨

在天线的设计中，为增强天线的方向性、提高天线增益，经常用到天线阵列。阵列天线的增益与排阵间距有关。对于具有某一波束宽度的天线，给出了能使阵列天线获得最大增益的最佳间距。在工程设计应用上，分析了高增益单元天线进行排阵时排阵间距选择问题。     

Adaptive antenna array using real symmetric array covariance matrix

A novel scheme using a real symmetric array covariance matrix for an adaptive antenna array in DS/CDMA is proposed. A real symmetric array covariance matrix is estimated from a complex array covariance matrix using a unitary transformation and Toeplitz matrix approximation methods. The Hermitian Toeplitzation method not only estimates a persymmetric matrix form for a real symmetric array covariance matrix but also enhances the performance of the received signal by removing the undesired effect obtained from a complex array covariance matrix. Simulation results demonstrate the effectiveness of the proposed scheme     

Tree array lasers

Conventional evanescently coupled laser arrays operating in the zero-order supermode are intrinsically unstable. A new type of array that in principle should lase stably in the inphase supermode is proposed. Initial device results are presented.<>     

Microstrip window array

The dichroic microstrip antenna concept is further exploited to create a microstrip antenna array which is also capable of functioning as an electromagnetic window at a higher frequency. Experiments on a planar structure comprised of an expanded polystyrene foam substrate, sandwiched between printed mesh conductors, demonstrate the feasibility for normal incidence. Possible ways of developing the technique further and possible applications are briefly mentioned     

Phased array calibration

Calibration of a phased array antenna while the antenna is in service can be a complex and time-consuming procedure that affects use of the antenna and imposes an unacceptable overhead on the system. The procedure described herein uses a maximum likelihood algorithm to minimize the number of measurements, thus reducing the impact on the system and shifting the overhead to a remote site     

On the virtual array concept for higher order array processing

For about two decades, many fourth order (FO) array processing methods have been developed for both direction finding and blind identification of non-Gaussian signals. One of the main interests in using FO cumulants only instead of second-order (SO) ones in array processing applications relies on the increase of both the effective aperture and the number of sensors of the considered array, which eventually introduces the FO Virtual Array concept presented elsewhere and allows, in particular, a better resolution and the processing of more sources than sensors. To still increase the resolution and the number of sources to be processed from a given array of sensors, new families of blind identification, source separation, and direction finding methods, at an order m=2q (q/spl ges/2) only, have been developed recently. In this context, the purpose of this paper is to provide some important insights into the mechanisms and, more particularly, to both the resolution and the maximal processing capacity, of numerous 2qth order array processing methods, whose previous methods are part of, by extending the Virtual Array concept to an arbitrary even order for several arrangements of the data statistics and for arrays with space, angular and/or polarization diversity.