曲面阵列结构散射与辐射特性的迭代分析

建立了一种适用于曲面有限阵列结构辐射与散射特性分析的迭代方法。首先根据阵列结构相同单元电流分布的相似性,对曲面有限阵列单元几何形状和表面电流分布作了两个假定,将有阵阵格林函数法推广应用于曲面有限阵列结构的分析;然后给出曲面有限阵列结构迭代分析的一般公式,通过迭代运算来消除两个假定近似的影响;最后迭代运算来消除两个假定近似的影响;最后以有两曲面带栅的散射和线源激励曲面带栅结构的辐射分析为例,验证了方法的有效性,并同逐元法作了比较,给出了有关的数值计算结果。结果表明：这种迭代法不受阵面曲率变化、单元数量和分布情况的限制,对有限周期和非周期阵列的分析都有着较高的计算效率和稳定性。     

耦合激励系数及对称振子阵列天线的有源方向图研究

为了深入探讨相控阵天线单元间的耦合对阵中单元方向图的影响,以阵列天线单元S参数为基础,给出了阵列天线单元的耦合激励系数计算公式,利用阵列天线单元间的耦合激励系数分析计算阵中单元的有源辐射方向图.同时利用矩量法分析由偶极子单元组成的阵列,并把阵列中每个单元的感应电流幅度和相位与耦合激励系数的幅度和相位进行比较,二者数据基本一致.矩量法计算的单元有源方向图与本文提出方法的计算结果吻合良好,验证了本文给出的阵列耦合激励系数及阵列天线阵中单元有源方向图计算方法的可靠性.     

子阵旋转和子阵错位在非周期阵列应用中的对比分析

随着预警探测需求的提升,大单元间距阵列的应用得到了快速发展,阵列栅瓣的有效抑制是大单元间距有限扫描阵列设计中的一项重要内容。文中首先介绍了非周期阵列抑制栅瓣的原理;然后,对子阵旋转和子阵错位两种非周期排布栅瓣抑制形式进行了仿真对比,从栅瓣电平、近区副瓣电平、量化瓣、阵列重构、极化形式五个维度分析了子阵旋转和子阵错位的性能优势,对大单元间距阵列的设计具有一定的工程指导意义。     

任意形状单元有限微带阵列的电磁散射分析

提出一种有限微带阵列电磁散射特性分析的有效方法。该法采用有限阵格林函数与矩量法相结合的方法，有效地解决了矩量法在大型阵列电磁特性分析中的计算效率问题；通过选取RWG基函数，使该法适用于任何单元形状的微带阵列。文中计算了矩形、十字形及圆形单元微带阵列的雷达截面，并与常规矩量法和参考文献的计算结果进行了比对，验证了该方法的有效性。     

大规模有限周期阵列电磁特性高效分析方法

宏块-特征基函数法(MB-CBFM)是一种分析大规模有限周期结构电磁特性的数值方法,其CPU时间和内存需求均为O(N),其中N是周期阵列的总未知量数.该方法中,周期单元被分成P类宏块.最终得到一个有PK个未知数的压缩矩阵方程,其中K为每个单元上的RWG基函数个数.虽然压缩矩阵计算利用了周期性,然而阻抗元素仍采用矩量法计...     

基于NUFFT方法的二维非周期阵列天线方向图计算

相控阵天线应用在有限电扫描角度时,采用大间距体制以减少有源通道数量,降低天线成本。由于单元间距大于波长,在可视空域内会出现栅瓣,常采用非周期排列方法分散栅瓣能量降低栅瓣电平。文中提出了一种变距平移错位抑制大间距阵列栅瓣的方法,并介绍了基于二维NUFFT计算该非周期排列阵列天线方向图的方法。分析了影响该算法精度的因素,并通过在拟合虚拟阵列幅相值时通过采用局部坐标系有效减小计算量。通过一个由300个单元组成的非周期阵列方向图计算,对二维NUFFT方法以及累加法进行对比。前者的计算时间仅为后者的0. 9% ,验证了算法的高效性。计算结果显示全空域方向图吻合度高,方向性系数误差仅0. 05 dB,最高副瓣误差仅0. 12 dB,验证了算法的准确性。     

用特征散射方向图预估电大平面阵的散射

利用平面照射波在无限大周期阵列上感应电流的周期特性，对无限阵列格林函数加窗的方法得到了有限阵列的格林函数，从而将电大有限阵列的分析缩减到单个的阵元上。进而由矩量法得到单个阵元上的电流分布和散射场，并定义为单元的特征散射方向图。仿照阵列综合理论，整个阵列的散射归结为特征散射方向图和阵因子的乘积，极大的简化了电大有限阵列的散射分析，并通过算例验证了该方法的有效性。     

相位扰动生成陈列零点的MDLS方法

基于矩阵论和可行集分析，本文首先指出在相位扰动生成阵列深零点问题中，不论相位大扰动或小扰动均可利用ＭＤＬＳ方法（修正阻尼最小二乘法）统一地进行求解。然后给出了在均匀分布阵列、泰勒分布阵列中使用ＭＤＬＳ方法生成深零点的计算实例。实例表明该算法快速、有效、稳定性好。最后本文研究了深零点位置变化时各个单元相位的变化规律，其结果已显示了最边侧单元是最关键单元，这一结论可为仅控制部分单元相位生成阵列零点提供单元选择依据。     

相位扰动生成阵列零点的MDLS方法

基于矩阵论和可行集分析，本文首先指出在相位扰动生成阵列深零点问题中，不论相位大扰动或小扰动均可利用ＭＤＬＳ方法统一地进行求解，然后给出了在均匀分布阵列，泰勒分布阵列中使用ＭＤＬＳ方法生成深零点的计算实例。实例表明该算法快速，有效，稳定性好。最后本文研究了深零点位置变化的各个单元相位的变化规律，其结果已显示了最边侧单元是最关键单元，这一结论可为仅控制部分单相位生成阵列零点提供单元选择依据。     

相关处理在干涉测向仪中的应用

介绍和分析相关处理在干涉测向仪中的应用，给出了多单元圆阵列干涉仪的重要特性参数，提供了一种多单元圆阵列干涉仪的设计方法。     

Analysis of finite phase arrays of microstrip patches

A method for the analysis of large phased arrays of microstrip patches is presented. It is based on an infinite array approach where the edge effects are taken into account through the convolution with a proper window function. In the first step, a rigorous Green's function corresponding to a finite array of elementary sources is derived. This Green's function is then used to analyze the finite phased array of microstrip patches. Results are shown for the active impedance and element patterns of several arrays, and compared with measurements or, in the case of small arrays, with results obtained by a rigorous element-by-element approach. It is shown that the method, even if developed for the analysis of large arrays, is able to handle small arrays. Indeed, the results obtained are good even for single patches. Although the method has been developed for the microstrip phased array case, the results are general and are valid for any phased array with a rectangular grid     

Analysis of finite arrays of axially directed printed dipoles on electrically large circular cylinders

Various arrays consisting of finite number of printed dipoles on electrically large dielectric coated circular cylinders are investigated using a hybrid method of moments/Green's function technique in the spatial domain. This is basically an "element by element" approach in which the mutual coupling between dipoles through space as well as surface waves is incorporated. The efficiency of the method comes from the computation of the Green's function, where three types of spatial domain Green's function representations are used interchangeably, based on their computational efficiency and regions where they remain accurate. Numerical results are presented in the form of array current distributions, active reflection coefficient and far-field pattern to indicate the efficiency and accuracy of the method. Furthermore, these results are compared with similar results obtained from finite arrays of printed dipoles on grounded planar dielectric slabs. It is shown that planar approximations, except for small separations, can not be used due to the mutual coupling between the array elements. Consequently, basic performance metrics of printed dipole arrays on coated cylinders show significant discrepancies when compared to their planar counterparts.     

Finite phased array of microstrip patch antennas: the infinitearray approach

An efficient method of analysis of large infinite arrays based on a convolution technique that allows one to obtain the finite array characteristics from the infinite array results is presented. The edge effects are taken into account by convoluting the infinite array results with the proper current amplitude window on the array. The method is based on the use of Poisson's sum formula in the case of finite arrays applied here to microstrip antennas. It is an approximate technique that can be assimilated into a perturbation method     

Scan blindness phenomenon in conformal finite phased arrays of printed dipoles

Scan blindness phenomenon for finite phased arrays of printed dipoles on material coated, electrically large circular cylinders is investigated. Effects on the scan blindness mechanism of several array and supporting structure parameters, including curvature effects, are observed and discussed. A full-wave solution, based on a hybrid method of moments/Green's function technique in the spatial domain, is used to achieve the aforementioned goals. Numerical results show that the curvature affects the surface waves and hence the mutual coupling between array elements. As a result, the array current distribution of arrays mounted on coated cylinders are considerably different compared to similar arrays on planar platforms. Therefore, finite phased arrays of printed dipoles on coated cylinders show different behavior in terms of scan blindness phenomenon compared to their planar counterparts. Furthermore, this phenomenon is completely different for axially and circumferentially oriented printed dipoles on coated cylinders suggesting that particular element types might be important for cylindrical arrays.     

A flexible array synthesis method using quadratic programming

A highly flexible synthesis method for an arbitrary array is proposed to best approximate a desired array pattern in a minimum-mean-square-error sense. The basic idea of the technique is to form a quadratic program with its cost function given by the mean-square error between the array response and a properly selected pattern described by a known mathematical function. This quadratic program can be a constrained or unconstrained optimization problem depending on the requirements of the desired array pattern. In formulating the quadratic program, no assumption has been made on the gain/phase response or characteristics of the individual array elements. Therefore, one can synthesize an array of arbitrary shape to any appropriate pattern with the characteristic of the array elements taken into consideration as long as one is able to model the array accurately. The proposed method is used to synthesize arrays of different shapes, linear as well as planar arrays (including rectangular and circular planar arrays), using a Chebyshev polynomial or zero function as a design template, to illustrate the feasibility of the proposed method     

Phase-only synthesis of minimum peak sidelobe patterns for linearand planar arrays

Minimization of the maximum sidelobe level for a given array geometry by phase-only adjustment of the element excitations is considered. Optimum phases are obtained by using a numerical search procedure to minimize the expression for the pattern sidelobe level with respect to the element phases. Results for both linear and planar arrays of equispaced elements are presented. The data suggests that optimum sidelobe level is a logarithmic function of array size, and optimum patterns have relative efficiencies that are typically somewhat greater than for comparable-amplitude tapered arrays. An analytic synthesis algorithm is presented for use on very large arrays for which the numerical search technique for the minimization of the sidelobe level is computationally impractical. This method produces patterns with characteristics similar to arrays synthesized using the numerical search method, i.e. relatively uniform angular distribution of energy in the sidelobe region, and generally decreasing maximum sidelobe level as the array size is increased     

Analysis of printed array antennas

A simple but efficient analysis tool for printed antenna arrays is presented. It relies on a perturbation approach, which starts from the infinite periodic array assumption to ultimately take into account effects due to finite size, nonperiodicity, double-periodicity in a multilayer case, complex excitation with nonlinear phase shifts between elements, etc. The technique is an approximation, as are most of the array analysis tools. However, it gives good results for arrays presenting a relatively smooth variation of the antenna characteristics between adjacent cells. Results will be shown for several arrays, including nonperiodic and multilayered cases. The method is validated through the comparison with results obtained by a rigorous element-by-element method     

Edge effects in finite arrays of uniform slits on a ground plane

The results obtained by modeling a linear array as an infinite periodic structure can be used for the analysis of finite arrays as the zero-order approximation of a perturbation technique. This idea is utilized to investigate the edge effects in two arrays of uniform slits fed by parallel-plate waveguides terminated on a ground plane. It is shown that the realized gain pattern of an element depends substantially upon its position in the array. This is true particularly for the deep resonance notches in the patterns which are present for certain element spacings. When the array is excited with uniform magnitude and linear phase, the aperture voltages are the superposition of a term, corresponding to the infinite array model, plus another correction term (a "spatial transient") representing the edge effect. The influence of this term is particularly relevant when the array is scanned at endfire. In such a case, the method introduced here allows the prediction of the element terminal admittances and the array pattern, while according to the infinite array model no radiation would be permitted.