用于分布式目标最优极化求解的Lagrange乘因子法优化

目前拉格朗日乘因子法是求解分布式目标最优极化的主要算法.该算法需要计算一个以拉格朗日乘法因子为自变量的六次多项式方程.针对拉格朗日乘因子法在计算该多项式方程根时存在的问题,提出了一种优化求解法.在理论证明该方程最大根对应天线最大接收功率而最小根对应天线最小接收功率的基础上,该优化求解法通过缩小迭代搜索区间获取方程最大、最小根,然后利用这些根与天线极化之间的关系式求解目标最优极化.为了提高迭代收敛速度,通过理论分析确定了最小初始迭代搜索区间.实验结果表明, 该优化求解法消除了算法对于拉格朗日乘因子初始值的依赖,提高了算法的运算速度.     

分布式发射天线MIMO信号的最优线性检测

 在分布式发射天线多输入多输出(MIMO)系统中,信道传播时延使各个发射天线的符号异步到达接收天线.接收信号符号间干扰的特殊性使分布式发射天线MIMO信号的线性检测算法更加复杂,最优线性检测算法也不能直接由最小均方误差(MMSE)准则得到.针对这一问题,提出了基于MMSE准则的分布式发射天线MIMO信号的最优线性检测算法:先最大比合并,再最小均方误差检测.并且,通过界定误码率上下限,得到其分集阶数.仿真结果验证了最优线性检测接收端信号处理方式的正确性.     

极化信号的优化接收理论:部分极化情形

本文针对部分极化波情形,利用电磁波的Stokes矢量表示法研究了极化信号的优化接收问题;利用Lagrange乘子法,分别推导了以信号干扰功率差(PDSI)和信号干扰噪声比(SINR)作为优化目标函数时接收天线的全局最优极化;并通过数值实例验证了文中结论。     

极化SAR目标相对最优极化研究

极化SAR通过测量地物目标的散射回波得到极化散射矩阵或Stokes矩阵,利用极化合成技术得到任意发射和接收极化组合下的天线接收功率。目标相对最优极化就是选取一种收发极化状态使得研究目标和背景地物的接收功率对比度达到最大。文中首先分析了目标相对最优极化的模型,指出了它们的优缺点,然后提出了一种新的改进模型,并用交替迭代方法进行了模型的解算,最后结合荷兰Flevoland地区全极化数据作了试验,证明了其有效性和正确一陆。     

部分极化电磁波的最佳接收

描述实际散射体散射特性的散射矩阵一般是时间的函数。因此,即使入射电磁波是完全极化电磁波,散射电磁波也不再是完全极化电磁波,而是部分极化电磁波。本文讨论了对部分极化电磁波的最佳接收问题,并给出计算天线接收功率的简化算法。     

极化信号的优化接收理论：部分极化情形

本文针对部分极化波情形，利用电磁波的Ｓｔｏｋｅｓ矢量表示法研究了极化信号的优化接收问题；利用Ｌａｇｒａｎｇｅ乘子法，分别推导了以信号干扰功率差（ＰＤＳＩ）和信号干扰噪声比（ＳＩＮＲ）作为优化目标函数时拉收天线的全局最优极化；并通过数值实例验证了中文结论。     

部分极化电磁波的最佳接收

描述实际散射体散射特性的散射矩阵一般是时间的函数。因此,即使入射电磁波是完全极化电磁波,散电磁波也不再是完全极化电磁波,而是部分极化电磁波。本文讨论了对部分极化电磁波的最佳接收问题,并给出计算天线接收功率的简化算法。     

极化信号的优化接收理论:完全极化情形

本文利用电磁信号的极化特性，研究了多散射源情况下利用变极化接收技术进行信号增强的问题，给出了分别以信号干扰噪声比和信号干扰功率差作为目标函数时接收天线的全局最优极化以及在极化轨道约束下的局部最优极化，并通过数值实例验证了文中的结论。     

一般极化散射矩阵最佳解的简单求解法

讨论了在目标信号和杂波的琼斯极化散射矩阵不一定对称情况下求解天线最佳发射和接收极化状态以使回波信杂比达到最大的问题,提出了一种简单易行的算法,给出了详细的推导过程和相应的仿真数据,结果验证了算法的有效性,并表明了对于天线的最佳发射和接收问题,琼斯极化散射矩阵无须对称。     

一种基于发射极化优化的目标最优估计算法

对于矢量测量极化雷达,针对杂波背景下目标极化散射矢量最优估计问题,以最小化目标散射矢量估计的均方误差为准则,设计了基于发射极化优化的目标散射矢量最优估计问题形式,提出了一种基于序贯估计的发射极化优化算法。数值仿真试验验证了算法的有效性,证明了极化雷达发射极化优化较固定极化设计的性能优势。     

Fully polarimetric bistatic radar scattering behavior of forestedhills

The bistatic radar scattering measurements of forested hills were performed at grazing incidence and at azimuth scattering angles from 28° to 66° from the forward scatter plane. Using pulse-to-pulse switching between orthogonal transmitted polarizations, the radar simultaneously measures two orthogonally polarized components of the scattered wave to obtain full polarimetric information about the scattering process. These are the first fully polarimetric terrain clutter measurements to be conducted at large bistatic angles. The complete Stokes matrix, computed by averaging successive realizations of the polarization scattering matrix, is used to examine the polarization sensitivity of the bistatic clutter. It is found that the polarization state of the EM wave scattered out of the plane of incidence strongly depends on the polarization orientation of the incident electric field. Unlike the monostatic case, these two incident wave polarization states are found to produce substantially different scattered wave behavior when trees are viewed at large bistatic angles. Scattered fields resulting from vertically oriented incident fields are found to be highly polarized and to produce bistatic clutter power levels that are strongly dependent on the polarization of the receiving antenna. In contrast, horizontally oriented incident fields are found to produce weakly polarized scattered waves with bistatic clutter power levels that are insensitive to the polarization of the receiving antenna     

Optimum polarizations in the bistatic scattering from layeredrandom media

Investigates the polarimetric bistatic scattering characteristics of layered random media. On applying the Born approximation, the authors have calculated the bistatic Mueller matrix of a half-space random medium. The power received by a receiving antenna is the quantity chosen to optimize. The variables of the problem are the polarizations of the transmitting and receiving antennas. For the case when the polarizations of the transmitting and receiving antennas are identical, the authors have calculated the optimum polarizations and they have found that the optimum polarizations include both linear and elliptical polarizations. The conditions for maximum and minimum received power are also obtained. In the backscattering case, they have considered the situation when the transmitting and receiving antennas have independent polarizations. For a two-layer problem, they have observed the influence of the thickness of the layer in the classification of the optimum polarizations     

极化轨道约束下的最优极化（一）

本文针对极化测量过程中干扰和噪声对接收效果的影响，提出一种极化轨道约束下的变极化接收方法，以改卷接收系统的SINR（信号干扰噪声比）。在极化轨道约束下的SINR最大化问题是一个寻求局部最优的问题，本文在任意的信号与干扰极化条件下，解决了任意给定的极化轨道上SINR的最大化问题，并对极化轨迈上最优极化与其他两种最优极化得到的SINR进行了比较。     

一种基于圆偏光的偏振去雾成像优化方法

在经典的偏振成像去雾方法中,后向散射光的偏振度估计值是影响去雾效果的关键。基于圆偏振光在米氏散射介质中良好的保偏特性,提出一种适用于强散射环境下的偏振成像去雾方法。研究不同偏振态的光源照明时,不同散射强度下,CCD接收到的光场偏振度变化规律,在此基础上提出了一种快速简易的散射光偏振度估计方法。该方法在不增加系统复杂度的情况下,提高了偏振成像去雾的效果。实验结果显示,在强散射条件下文中方法获得的去雾图像EME值比传统方法高20.4%。此外,该方法不需要传统偏振去雾方法中对背景区域的判断,降低了算法复杂度。     

W波段数字变极化目标特性测量雷达

提出一种新型的W波段数字变极化目标特性测量雷达.该雷达由两子阵变极化天馈、两通道TR模块与数字处理单元构成, 采用空间波束合成任意极化发射、数字方式实现任意极化接收.通过目标实验结果表明, 该雷达能在多种极化体制下准确提取目标极化散射矩阵, 具备测量目标全极化RCS能力以及可用于目标极化特性分析与研究.     

Observations of insects and birds with a polarimetric radar

The authors present observations of biological scatterers with a polarimetric weather radar. The radar has a pencil beam, a high power, and a wavelength of 10 cm. It transmits horizontally and vertically polarized waves alternately. The available polarimetric variables are differential reflectivity, differential phase, and correlation coefficient between orthogonally polarized returns. Two types of biological scatterers, insects and birds, are contrasted. Observed polarimetric signatures of these are compared and explained with a simple scattering model. Finally, the authors discuss the implications of recognizing the biological scatterers' type and the size of birds     

Poincaré sphere representation of partially polarized fields

The use of points on the surface of the poincaré sphere to represent the polarization state of fully polarized electromagnetic fields is extended to partially polarized fields by representing their polarization by points inside the sphere. The coordinates of a pointbar{W}representing the polarization state are shown to be simply related to the Stokes parameters. The center of the sphere represents a completely unpolarized wave, and the degree of polarization is given by the distance of the pointbar{W}from the center of the sphere. A simple formula is derived for calculating the power received by an antenna illuminated by a partially polarized wave. A method is described for measuring the polarization state by a number of intensity measurements.     

On the basic principles of radar polarimetry: the targetcharacteristic polarization state theory of Kennaugh, Huynen'spolarization fork concept, and its extension to the partially polarizedcase

Basic principles of radar polarimetry are introduced. The target characteristic polarization state theory is developed first for the coherent case using the three stage, the basis transformation, and the power (Mueller) matrix optimization procedures. Kennaugh's and Huynen's theories of radar target polarimetry are verified for the monostatic reciprocal case. It is shown that there exist, in total, five unique pairs of characteristic polarization states for the symmetric scattering matrix of which two pairs, the cross-polarization null and copolarization max pairs, are identical, whereas the cross-pol max and the cross-pol saddlepoint pairs are distinct. The theory is verified by an example for which next to the polarization fork the copolarized and cross-polarized power density plots are also presented. The partially polarized case for completely polarized wave incidence is presented and compared with the results for the coherent and the partially coherent cases, the latter of which is still unresolved     

An analysis of the second moment of fluctuating electromagnetic fields part II: An application to measurement

The theory of the dyadic field spectrum (DFS) of a fluctuating electromagnetic field developed in Part I is applied to the analysis of a particular experiment. The experiment is simply the measurement of the DFS by means of a two-element interferometer. The analysis includes the effect of the polarization and receiving pattern of the interferometer on the measurement and applies to the DFS of a partially polarized, partially coherent radiation field of arbitrary spectral width radiated by an incoherent source. The approach used in this calculation is that described in Section III-C of Part I. It is based on the application of the dyadic Green's function of the electric type for the interferometer. The power at the receiving terminals of the interferometer is expressed in terms of the DFS of the source and the antenna pattern of the interferometer. A method for measuring the distribution of polarization over the source is described.