幅值扰动形成零陷方法的性能分析

提出了一种新型的幅值扰动形成零陷的方法,通过极小化扰动值,达到在形成零陷的同时,对波束方向图改变最小.通过仿真分析了不同控制参量扰动,即复权值扰动、幅值扰动形成零陷对波束方向图的影响以及旁瓣增益、零陷深度等性能.提出的方法能够在保证主瓣畸变很小的前提下,在多个干扰源方向形成零陷.该方法的零陷性能可与控制复权值形成零陷的性能相比,且计算量和硬件复杂度更低.     

利用阵元相位和位置扰动形成零陷的技术

论文提出了一种利用阵元相位和位置扰动相结合形成零陷的方法,该方法假设阵元相位扰动和位置扰动都很小,因而能够利用线性化处理的方法形成零陷,相对于非线性处理方法,计算量大大降低.仿真表明单独使用阵元位置扰动或者相位扰动都不能够形成深度零陷,而采用论文提出的零陷技术,能够在多个干扰源方向形成深度零陷,而不影响主瓣,其零陷性能优于位置扰动非线性化处理方法.在此基础上,为了进一步减少需要控制的阵元数,提高系统鲁棒性,论文仿真分析了阵元位置选择性扰动和相位扰动相结合的零陷性能.仿真表明采用该方法,其性能优于文[4]中选择性非线性处理方法的性能.     

一种新的快速零陷形成技术

分解大型阵列为关于阵列中心对称的两个子阵,对内子阵进行阵元位置微扰形成指定零陷。借助对微扰后方向图的泰勒展开进行线性化,以微扰后方向图形变最小化为目标,将指定方向控零的约束条件分实部、虚部分别约束微扰值,运用方向导数法快速求解出微扰值,实现了在指定方位快速控零,并提出引入小值控制零陷深度。方法不改变阵列孔径,在指定方向控零后能维持原主波束形状、副瓣水平不变,仿真表明本方法的有效性和优越性。     

基于模式转换自适应零点形成的研究

利用模式空间变换算法将均匀圆阵转换为均匀线阵,在虚拟线阵的阵列流形中,比较了Gram-Schmidt正交化算法、自适应旁瓣对消和SMI算法这三种算法形成的方向图。G-S正交化算法可以在干扰方向准确地形成零点,但是没有很深的零陷深度;SMI算法的计算量比较大,因此在零点方向上有稍微的误差,但经过旁瓣对消的虚拟线阵的方向图有很深的零点深度。仿真结果表明,经过旁瓣对消的方向图主瓣增益损失较少,副瓣高度降低,主瓣比副瓣高大约10 dB~12 dB。     

一种基于面阵的旁瓣对消方法

目前基于阵列的旁瓣对消方法,主要是通过自适应算法对各阵元进行幅度和相位加权,使得阵列波束图在于扰方向上形成零陷,即可对该方向上的干扰进行抑制。由于利用了自适应算法,所以随着阵元数的增多,该算法的硬件实现将越来越难,甚至会导致算法失效。以面阵为倒,提出了两种在干扰来波方向上快速形成零陷的方法。这两种方法摒弃了以往方法中的自适应权值求取过程,只需要利用事先求取好的权值对选定的阵元进行加权处理,极大地增强了系统的实时处理能力。另外,两种方法形成的零陷足够深且宽,对主瓣没有影响。     

基于空间响应偏差约束的最小二乘宽带波束形成

针对常规最小二乘宽带波束形成中存在波束响应不满足频率不变特性和干扰方向零陷无法控制的问题,提出了一种基于空间响应偏差约束的最小二乘宽带波束形成方法。该方法通过对阵列空间响应在指定的宽频段和方位范围内施加约束,来控制阵列波束响应的频率不变特性,同时增加一系列的线性约束,可以实现旁瓣电平和干扰零陷的灵活控制。在全方位约束和仅主瓣方位约束两种情况下,均能有效改善宽带波束的频率不变性能,并能在干扰方向上准确形成深零陷。仿真实验结果验证了该方法的有效性。     

一种基于遗传算法的唯相位宽零陷波束赋形方法

传统阵列方向图宽零陷形成技术需要对阵元施加复加权或者阵元位置扰动等复杂操作,实际实现比较困难。提出了一种基于遗传算法的唯相位波束赋形方法,针对宽零陷特点,结合均匀线阵方向图数学模型,设计一种适应度函数,优化阵元相位扰动值,最终获得符合要求的宽零陷阵列方向图。仿真结果表明,该方法可以在唯相位条件下形成较深的宽零陷,且零陷较平坦,收敛速度较快,稳健性较好。     

发射波束部分阵元置零综合分析

针对选择阵列部分单元控制的情况,分析了发射波束零点形成的两种方式,即部分阵元的幅相加权综合和部分阵元的唯相位综合加权方式。通过对这两种置零综合的算法研究和仿真分析,并从形成零陷的深度及对副瓣扰动等方面,比较了这两种发射波束置零综合方法的性能。     

基于约束差分进化的阵列置零

阵列置零的同时,阵列的旁瓣电平升高、主瓣增益降低甚至阵列指向都会发生改变,导致阵列性能降低。针对阵列置零时阵列性能降低问题,提出一种约束优化模型。在约束优化模型中不仅设置了零陷深度约束和近旁瓣电平约束,还设置了阵列期望方向增益约束及阵列指向约束。在满足约束条件下,使得阵列旁瓣电平最低。并且针对标准约束差分进化算法收敛慢,采用自适应约束差分进化(e-SADE)算法,该算法采用多种变异方式相结合、自适应地调节交叉概率和缩放因子。运用自适应约束差分进化分别通过调节阵元相位和阵列功率一定时的阵元权值求解这个约束优化问题,仿真结果表明提出的方法实现了需求的目标方向图,利用自适应约束差分进化算法优化实现阵列置零是有效可行的。     

迭代投影的平顶方向图综合算法

针对现有的平顶波束综合形成算法计算量较大的问题,提出了一种迭代求解平顶波束的快速形成算法。该算法首先设置方向图参数、迭代条件,然后利用方向图与阵元加权系数的变换关系设计投影算法并通过二阶差分运算确定过渡带,最后结合蝶形计算方法快速迭代逼近理想的平顶方向图。实验结果表明,该算法相比凸优化算法运算效率较高,并且可修复阵元失效后的平顶方向图。算法运算次数随着副瓣阈值、主瓣宽度和零陷深度等参数的变化而变化。     

基于虚拟阵叠加原理的阵列抗干扰方法研究

提出了一种基于虚拟阵叠加原理的阵列抗干扰方法。将相控阵列分解成一个主阵列和 N 个虚拟阵列,主阵列采用 Taylor 幅度加权实现低旁瓣电平,并通过相位控制使主波束对准来波方向。虚拟阵列也采用 Taylor 加权,并在主阵列旁瓣上产生 N 个零点,实现阵列的旁瓣对消, 虚拟阵的低旁瓣将减少对阵列主波束的影响,虚拟阵加权后与主阵列叠加最终得到整个阵列抗干扰的幅相权值。文中使用该方法对一个 24 元直线阵进行抗 3 个干扰的设计验证,在 3 个干扰方向实现了小于-100dB 的零点,证实了该方法的有效性。     

遗传算法在天线阵自适应算法中的应用

本文采用一种新的基于遗传算法的天线阵列的自适应算法。根据实际的硬件限制,不改变阵列的幅度加权,而通过遗传算法对相位加权作全局优化。为减小对天线方向图的破坏,并希望在干扰源来波方向实时置零,因而采用只优化搜索数字移相器的最后几位。计算机模拟结果证实了这种方法的有效性。     

Experimental verification of null steering by element positionperturbations

Null steering in an adaptive array is realized by element position perturbations. Small position perturbations are assumed, which is valid when the number of imposed nulls is small compared to the number of array elements. The null steering has been achieved for an eight-element monopole array over a ground plane. The array illumination function is used solely for pattern formation and can also be used for main beam steering. Single and double nulls are realized in the sidelobe region. The experimental results prove the validity of null steering by controlling the element positions     

Pattern Nulling in Coupled Oscillator Antenna Arrays

An optimization method is presented for constrained beam steering with null formation in linear coupled oscillator arrays. The method is based on a perturbation model of the far field of the array that includes both amplitude and phase perturbations, to accommodate prescribed nulls. Moreover, it takes into account the array nonlinear dynamics through a first-order approximation model of the array steady state. The optimization results are verified by harmonic balance simulations. Also, the stability of the optimized solutions is examined by perturbing the steady state solution and is verified with envelope transient. Design examples are used to demonstrate the validity and limitations of the proposed method     

A proof of the odd-symmetry of the phases for minimum weight perturbation phase-only null synthesis

It is proved that if phase-only weight control is used to impose nulls in a real pattern of a linear array of isotropic equispaced elements while minimizing the sum of the squares of the absolute weight perturbations then the phase perturbations are odd-symmetric with respect to a phase reference at the array center. Equivalently, the perturbed pattern is real.     

Null steering in phased arrays by controlling the element positions

Null steering methods usually involve costly and complicated amplitude and/or phase control systems. A technique is presented for null steering based on the element position perturbations. The technique frees the phase shifters to be used solely for steering the main beam toward the direction of the desired signal. It also removes the limitations of the other techniques by independently steering the main beam and the nulls to arbitrary independent directions. This technique is also capable of obtaining sidelobe cancellation and wideband signal rejection     

Independent null steering in the sum and difference patterns of antenna arrays using real weights

A method for steering nulls in the sum and difference patterns of a phased linear antenna array using only real weights is introduced. The proposed method decouples the weights so that a given jammer is associated with a given weight value. A change in the jammer's direction changes only its corresponding weight value without affecting the other nulls. The main beam is steered independently using a progressive phase shift. This allows the signal-to-jammer power ratio to be maximized with relative ease. The drawback of this method is that the number of jammers that can be nulled will be reduced to about a quarter of the number of array elements.     

Null steering in linear arrays by using amplitude control of signals in the feeder network

A method of steering nulls in linear arrays by using amplitude control, rather than phase shifters, is described. The system is extended to steer all of the independent nulls in an array of any size. The problem of grating nulls is briefly discussed, and it is shown how an automatic null-steering array can be designed.     

Null steering by real-weight control-a method of decoupling theweights

A method for independent steering of each null in the radiation pattern of a linear antenna array using real weight control is introduced. The method depends on decoupling the weights such that each real weight is associated with a given null. It has the capability of tracking the direction of jammers by changing only the weight corresponding to each jammer. Phase shifters are used solely to steer the main beam in the direction of the desired signal. The price for using this method is that the number of steerable nulls is equal to or less than half of the total number of array elements     

Synthesis of antenna patterns with prescribed nulls

The least mean square pattern synthesis method is extended to include constraints such as pattern nulls or pattern-derivative nulls at a given set of angles. The problem is formulated as a constrained approximation problem which is solved exactly, and a clear geometrical interpretation of the solution in a multidimensional vector space is given. The relation of the present method to those of constrained gain maximization and signal-to-noise ratio (SNR) maximization is discussed and conditions for their equivalence stated. For a linear uniformN-element array it is shown that, whenMsingle nulls are imposed on a given "quiescent" pattern, the optimum solution for the constrained pattern is the initial pattern and a set ofM-weighted(sin Nx)/sin x-beams. Each beam is centered exactly at the corresponding pattern null, irrespective of its relative location. For the case of higher order nulls, thenth pattern derivative is similarly canceled by thenth derivative of a(sin Nx)/sin x-beam. In addition, simple quantitative expressions are derived for the pattern change and gain cost associated with the forced pattern nulls. Several illustrative examples are included.