基于差集的综合孔径圆环天线阵稀疏优化方法

稀疏天线阵列设计是综合孔径微波辐射计的一个重要研究内容.圆环阵因其可实现(u,v)平面基线矢量零冗余、结构简单以及共形、波束旋转对称等特点而备受关注.针对均匀圆环阵(UCA)基线长度(基线矢量的模)冗余量大的问题,提出了两种稀疏优化方法:一种是基于受限差集的半圆环阵稀疏方法;一种是基于循环差集的全圆环阵稀疏方法.这两种方法均可大大减少阵元数,节约硬件成本;且均可解析地求出稀疏阵元位置,运算量极小,适于任意大阵元数的圆环阵稀疏优化.通过阵列旋转和分时测量,这两种圆环稀疏阵可获得与UCA相同的空间频率采样.     

基于微分进化算法的综合孔径辐射计圆阵优化

依据二维综合孔径微波辐射计的反演成像原理及天线阵列分布的基本思想,引入微分进化算法优化设计圆周天线阵列分布.以阵列最小冗余及空间频率采样点均匀分布距离最大化为目标函数,得到了16～40个天线单元二维圆周阵列的优化分布结果.与常用的模拟退火算法相比,该算法的优化结果更优,计算时间更短.     

基于量子微粒群的综合孔径圆环阵排列方法

稀疏天线阵列设计是综合孔径微波辐射计的一个重要研究内容。圆环阵因其可实现(u,v)平面基线零冗余、结构简单以及共形、波束旋转对称等特点而备受关注。针对均匀圆环阵UV覆盖不均匀的问题,提出基于量子微粒群优化(QPSO)的综合孔径圆环阵排列方法,以改善圆环阵的UV覆盖。该方法引入量子行为的搜索机制,并设计一种新的圆环阵优化目标函数;与现有方法相比,该方法在提高全局搜索效率的同时,大大降低计算复杂度,且能更好地度量圆环阵UV覆盖的均匀程度。数值仿真结果验证了本文方法的有效性。     

被动微波遥感技术的新发展——综合孔径微波辐射计和全极化参量微波辐射计

介绍了被动微波遥感的两个新的技术-综合孔径微波辐射计和全极化参量微波辐射计.综合孔径微波辐射计采用干涉测量技术,用小天线的干涉基线组合合成大孔径天线的思想,提高被动微波遥感的空间分辨率,并实现视场范围的数字成像;全极化参量微波辐射计是一种新的微波遥感参数的探测技术,它测量目标微波辐射的全部4个Stokes极化参量,对于表面粗糙度各向异性特性的探测和目标的分类与识别具有很好的前景.     

综合孔径微波辐射计顺轨方向亮温反演算法的研究

本文利用卷积理论对综合孔径微波辐射计在顺轨方向的孔径综合进行了理论分析,给出了在一定条件下的基线设计,并且分别利用矩量法和基于Backus-Gilbert理论的线性算法两种数值方法进行了顺轨方向地物亮温的反演.数值模拟结果表明,在顺轨方向有效稀疏天线阵设计的基础上,亮温反演达到了很高的精度.     

一种低冗余二维综合孔径辐射计天线阵列布局

干涉综合孔径微波辐射计是利用孔径合成技术实现高分辨率的无源微波雷达成像系统,天线阵的优化设计是系统设计中的一个关键问题.文章提出了一种利用一维低冗余线性阵列构造低冗余二维天线阵列的方法,并将其设计阵列的冗余度与常规'U'形、'T'形阵列的冗余度进行了分析比较.分析结果表明,当天线单元数目足够多时,文中提出的阵列布局方式比常规的'U'形、'T'形阵列布局方式可节省11%～19%的通道数目.     

半孔径天线阵的可实现性理论研究

在不影响天线主要性能的前题下,以缩小天线的尺寸为目的,对半孔径天线阵的原理及特性进行了分析和研究,提出了用软件无线电和普通模拟器件构筑半孔径天线阵的两种方案,并对这两种方案的优缺点和可行性进行了讨论.     

迭代傅里叶算法用于六边形稀疏阵列天线

针对迭代傅里叶技术在优化稀疏阵列天线时对阵元激励大规模截断带来的不利影响,提出了一种逐步截断的迭代傅里叶算法.该算法从满阵依次减少数个阵元,从而避免阵列大规模截断陷入局部最优解.将其应用到六边形平面天线阵列的稀疏布阵优化中,以改善最大副瓣电平为目的.为了计算六边形天线阵的方向图,通过在口径中添加虚拟阵元转化为可以实现二维傅里叶变换的矩形阵列.仿真结果表明,改进的迭代傅里叶算法对稀疏天线阵最大旁瓣电平的优化比采用遗传算法的结果更理想,且具有计算量小和速度快等优点.     

综合孔径微波辐射计天线单元互耦的影响及其校正

本文建立了综合孔径微波辐射计天线单元之间互耦对于综合孔径成像的影响的模型,分析了天线单元之间的互耦对于综合孔径微波辐射计分辨率的影响.给出了校正天线单元互耦作用影响的方法,在此基础上提出了一种综合孔径微波辐射计的定标方法.通过数值模拟,证明了所提出的方法的有效性.     

二维综合孔径微波辐射计成像理论与方法研究

本文在顺轨方向孔径综合技术的理论研究的基础之上,对星载二维成像综合孔径微波辐射计的成像理论进行了分析,讨论了二种不同的基线结构方案,并对相应的可见度函数采样方案和成像反演算法进行了讨论.最后通过数值模拟说明了本文提出的成像理论和基线结构方案具有可行性.     

平面稀疏阵列天线的约束优化设计

针对有阵元数和阵列口径约束的矩形平面稀疏阵天线的综合问题,提出了一种基于整数编码的差分进化算法。该方法以每个阵元的栅格位置编号作为设计变量,使阵列的稀疏率满足约束条件,避免了优化过程中的不可行解,还减少了优化变量的个数。为了加速优化过程,采用快速傅里叶变化计算阵列的方向图。以改善阵列峰值副瓣电平为目的进行仿真试验,结果表明：优化后的稀疏天线阵峰值旁瓣电平比现有方法相比改善了1.2~1.7 dB,且具有收敛性和稳定性好的优点。     

平面六边形稀疏阵列天线的优化

针对标准的差分进化算法只能处理连续空间的优化问题,提出了一种基于取整策略的差分进化算法。该方法只需要对优化变量进行四舍五入取整,就能够把标准差分进化算法用于稀疏阵列天线方向图优化。将取整策略的差分进化算法应用到六边形平面稀疏天线阵的布阵设计。为了计算六边形阵列天线的方向图,提出在口径中添加虚拟单元的计算模型,把六边形阵列转化为可以实现二维快速傅里叶变换的矩形阵列。以改善阵列峰值副瓣电平为目的进行仿真试验,结果表明,优化后的稀疏天线阵峰值旁瓣电平与采用遗传算法相比改善了4.5~5.1 dB,且具有计算速度快、稳定性好的优点。     

Isophoric arrays-massively thinned phased arrays withwell-controlled sidelobes

Traditional filled phased arrays have an element placed in every location of a uniform lattice with half-wavelength spacing between the lattice points. Massively thinned arrays have fewer than half the elements of their filled counterparts. Such drastic thinning is normally accompanied by loss of sidelobe control. This paper describes a class of massively thinned linear and planar arrays that show well-behaved sidelobes in spite of the thinning. The term isophoric is derived from Greek roots to denote uniform weight. In isophoric arrays, element placement based on difference sets forces uniformly weighted spatial coverage. This constraint forces the array power pattern to pass through V uniformly spaced, equal, and constant values that are less than 1/K times the main beam peak, where V is the aperture size in half-wavelengths and K is the number of elements in the array. The net result is reduced peak sidelobes, especially when compared to cut-and-try random-placement approaches. An isophoric array will exhibit this sidelobe control even when the array has been thinned to the extent that K is approximately the square root of V. Where more than one beam must be generated at a time, isophoric array designs may be used to advantage even within a traditional filled array. By “interweaving” two isophoric subarrays within a filled array and by appropriate cyclic shifting of the element assignments over time, two independent antenna power patterns can be generated, each with a sidelobe region that is approximately a constant value of 1/(2K) relative to the main beam, where K is the number of elements in the subarray     

基于整数编码遗传算法的稀疏阵列综合

该文针对稀布阵列综合问题,提出一种基于整数编码遗传算法的优化设计方法。采用整数编码的个体描述方式在保证阵元稀布率恒定的同时,减小了搜索的空间。在优化阵元分布的基础上采用凸优化方法进一步优化阵列权值,显著提高了阵列方向图的主副瓣比。仿真数据结果验证了方法的有效性和优越性。     

共享孔径同心圆阵稀疏交错优化布阵方法

同心圆阵列天线具有波束对称、360°方位角扫描、抗干扰能力强等优点，被广泛应用于星载、机载、舰载雷达及飞机声呐等领域。在天线孔径有限的情况下，如何进一步提高同心圆阵的孔径利用率，通过孔径的空分复用，设计出子阵稀疏交错分布的多功能同心圆阵列天线，具有较大的研究价值。利用均匀同心圆阵列天线激励与方向图函数存在二维傅里叶-贝塞尔变换关系，基于二维三次插值和密度加权，提出了一种同心圆阵稀疏交错优化布阵的方法。该方法通过对均匀同心圆阵列天线方向图采样值的频谱能量进行分析，采用三次插值的方法，实现了同心圆天线阵列方向图函数到同心圆阵元激励能量的映射转换；基于密度加权的原理，对排序后归一化阵元激励的奇偶交错选取，使得稀疏交错子阵方向图频谱能量均分匹配，实现了同心圆阵的稀疏交错优化布阵设计。仿真结果表明，该方法得到的交错子阵天线具有峰值旁瓣电平低、主瓣宽度窄且方向图性能近似程度高的优点，有效解决了同心圆阵列天线稀疏交错优化布阵的设计难题，实现了两子阵交错的共享孔径多功能同心圆阵列天线设计。     

Numerical annealing of low-redundancy linear arrays

An algorithm is developed that estimates the optimal distribution of antenna elements in a minimum redundancy linear array. These distributions are used in thinned array interferometric imagers to synthesize effective antenna apertures much larger than the physical aperture. The optimal selection of antenna locations is extremely time consuming when large numbers of antennas are involved. This algorithm uses a numerical implementation of the annealing process to guide a random search for the optimal array configuration. Highly thinned low-redundancy arrays are computed for up to 30 array elements. These arrays are equivalent to the optimal solutions that are known for up to 11 elements. The arrays computed for 12-30 elements have the fewest redundancies reported to date     

Synthesis of random antenna array patterns with prescribed nulls

Under study is a method devised to reduce sidelobes of thinned random antenna arrays over specified angular sectors. The thinned array is assumed random in the sense that the nominal location of the elements is known, but their actual position may vary randomly. It is shown that by imposing adequately dense pattern nulls, it is possible to reduce the sidelobes effectively in the region of the nulls. The problem is formulated as a set of points in the radiation pattern, which are constrained to specified values. The unknowns are the excitations, or weights, applied to the array elements. In the general case, the linear system of equations is consistent and has an infinite number of solutions. The solution selected optimizes the pattern in a minimum variance sense. Quantitative relations are derived for the pattern change and the gain cost associated with the imposed pattern nulls. Several examples are included to illustrate the results.     

基于循环特性的均匀圆阵快速空间谱计算

针对在阵元数多、分辨率要求高的情况下,基于均匀圆阵的空间谱直接计算方法存在计算量大、实时性差的缺点,利用循环矩阵、离散傅里叶变换、卷积运算之间的内在联系,提出了一种快速空间谱计算方法.仿真结果表明,在保持测向性能完全一致的情况下,所提快速算法降低空间谱计算过程中角度搜索阶段的计算量随阵元数增加而增加;且在相同计算量条件下,所提快速算方法可以用于更高精度和分辨率的角度搜索.     

Interferometric synthetic aperture microwave radiometry for theremote sensing of the Earth

Interferometric aperture synthesis is presented as an alternative to real aperture measurements of the Earth's brightness temperature from low Earth orbit. The signal-to-noise performance of a single interferometric measurement is considered, and the noise characteristics of the brightness temperature image produced from the interferometer measurements are discussed. The sampling requirements of the measurements and the resulting effects of the noise in the measurements on the image are described. The specific case of the electronically steered thinned array radiometer (ESTAR) currently under construction is examined. The ESTAR prototype is described in detail sufficient to permit a performance evaluation of its spatial and temperature resolution. Critical aspects of an extension of the ESTAR sensor to a larger spaceborne system are considered. Of particular important are the number and placement of antenna elements in the imaging array     

Optimization of thinned aperiodic linear phased arrays using genetic algorithms to reduce grating lobes during scanning

The scan volume of a thinned periodic linear phased array is proportional to the spacing between array elements. As the spacing between elements increases beyond a half wavelength, the scan range of the array will be significantly reduced due to the appearance of grating lobes. This paper investigates a method of creating thinned aperiodic linear phased arrays through the application of genetic algorithms that will suppress the grating lobes with increased steering angles. In addition, the genetic algorithm will place restrictions on the driving-point impedance of each element so that they are well behaved during scanning. A genetic algorithm approach is also introduced for the purpose of evolving an optimal set of matching networks. Finally, an efficient technique for evaluating the directivity of an aperiodic array of half-wave dipoles is developed for use in conjunction with genetic algorithms.