Pattern synthesis in small phased arrays using adaptive arraytheory

A pattern synthesis technique for low sidelobe difference and scanned beams in small phased arrays is presented. The approach is based on adaptive array theory and is a development of a technique used for beam synthesis in an ideal, λ/2 spaced, isotropic array. The method has been applied to measured element pattern data from a five element linear array, which includes the effects of pattern corruption by mutual coupling. The successful synthesis of low sidelobe sum and difference beams are demonstrated, with the look direction on and scanned off boresight     

Pattern synthesis method for arbitrary arrays based on LCMV criterion

A pattern synthesis method for arbitrary arrays based on the linearly constrained minimum variance (LCMV) criterion is presented. Given mainlobe regions and an arbitrary sidelobe envelope, this algorithm searches the pattern with the lowest sidelobe levels. Its iteration coefficient is robust to synthesis conditions, and patterns with a flat top mainlobe can be obtained using phase-independent derivative constraints     

期望主瓣响应下任意阵方向图综合方法

为实现任意阵列天线的方向图综合,特别是考虑到不同空间指向对阵列方向图的影响,提出自适应原理与凸优化理论相结合的方向图综合法.该方法首先利用自适应原理综合法得到所需阵列方向图的旁瓣特性;而后,选择零度角的方向图主瓣作为期望主瓣;最后,在该期望主瓣响应下,将阵列方向图综合问题转化为二阶锥规划问题.采用凸优化循环迭代算法,完成对非凸优化问题的求解,从而保证方向图在满足期望主瓣响应的同时,使旁瓣特性与自适应方向图综合方法得到的结果最接近.理论分析与仿真结果表明,综合后阵列方向图在不同空间指向上具有与期望主瓣一致的主瓣特性,且其旁瓣也能够很好地保持对动态干扰的抑制特性.     

Pencil-beam pattern synthesis for arbitrary arrays

A pencil-beam pattern is synthesised, based on maximisation of the signal-to-interference-plus-noise ratio (SINR). Artificial interference is introduced and is iteratively adjusted to approximate the desired pattern. In particular, a set of linear equations is derived to find an efficient adjustment for the artificial interference which makes the iterations converge quickly     

改进的快速稳健任意阵列天线方向图综合方法

针对任意阵列天线的方向图综合问题,提出了改进的基于线性约束最小方差准则方向图综合方法.该方法充分考虑综合方向图和参考方向图之间的相对幅度对方向图综合的影响,通过对迭代公式增加一比例常数,使得两者之间的相对幅度对干扰功率变化率的影响增强,不仅提高了干扰功率的迭代效率,即降低了迭代的次数,提高了方向图的综合效率,而且使得迭代系数的取值范围得到了扩展,即降低了迭代系数对方向图综合的影响,增强了方向图综合方法的应用范围和适用性.仿真分析验证了理论分析的正确性和所提方法的有效性.     

Capacity enhancement using adaptive arrays in an AMPS system

Adaptive arrays for an advanced mobile phone service (AMPS) system can significantly increase cell capacity, improve signal quality, and reduce transmitter power requirements. In this paper, we investigate the capacity improvement that can potentially be achieved using adaptive arrays at the base station of an AMPS system. For the analysis, we use two types of spatial filters at the base station: an ideal and flat-top beamformer. An ideal beamformer has a flat main lobe and no side lobes, while a flat-top beamformer has flat main and side lobes. Analysis includes calculation of outage probability when a beamformer is used at the base station, and then we calculate the capacity increase that can be offered by practical antenna arrays. In this paper, we show that spatial-division multiple access (SDMA), i.e., all the users in a cell occupying the same frequency, is impossible to achieve in an AMPS system. A cell-reuse factor of four can be easily achieved with a five-element uniform linear array (ULA) with λ/2 spacings, but to achieve a reuse factor of three, a ULA with eight elements is required     

基于自适应遗传算法的方向图综合

提出了一种改进的方向图综合方法.该方法以遗传算法为基础,以正交基函数表示天线口径分布,并且在优化过程中,对交叉概率、变异概率和变异范围同时进行自适应的变化.和原有的遗传算法相比,该算法减少了优化变量的数目,天线激励的相位和幅度曲线更光滑,提高了收敛的速度,并且缩小了幅度的动态变化范围.线阵和面阵的仿真结果均表明,该方法实用、高效.     

Space-time adaptive processing using circular arrays

A direct data-domain (D³) least-squares space-time adaptive-processing (STAP) approach is presented for adaptively enhancing radar signals in a non-homogeneous environment of jammers, clutter, and thermal noise, utilizing a circular antenna array. The non-homogeneous environment may consist of non-stationary clutter. The D ³ approach is applied directly to the data collected by a circular antenna array (utilizing space), and in time (Doppler) diversity. Conventional STAP generally utilizes statistical methodologies, based on estimating a covariance matrix of the interference, using the data from various range cells of the circular array and assuming that it is a uniform linear array. However, for highly transient and inhomogeneous environments, the conventional statistical methodology may be difficult to apply. Moreover, the error in forming the covariance matrix by assuming that the data collected by the circular array is assumed to be a uniform linear array is highly problem dependent. Hence the D³ method is presented, as it analyzes the data in space and time over each range cell separately. However, it treats the antenna array as circular, i.e., it deals with the antenna structure in its proper form. Limited examples are presented to illustrate the application of this approach     

一种对任意线阵天线的主波束赋形方法

基于自适应天线阵理论,给出了一种用于任意线阵天线的主波束赋形算法.该方法通过迭代获得一组最优权值,用来减小加权赋形方向图和期望方向图在主波束上的差别,同时将旁瓣电平降低到期望值.一些算例充分说明了这种算法的有效性.该算法可以有效的控制主波束方向、宽度、形状和旁瓣电平.     

Wavenumber support regions for arbitrary arrays

We set out a procedure for defining the region of wavenumber support relevant for maximum entropy spectral estimation of a noise field incident on a planar array. We consider first linear, nonequispaced arrays, and argue that the problem of defining a region of wavenumber support is only well-posed when either position uncertainty for the array elements is postulated, or phase uncertainty in the measurement of the signals at the array elements is postulated, or one acknowledges that a polar diagram that is almost periodic defines an aliasing frequency in virtually the same way as a polar diagram which is periodic. For planar arrays, the region of wavenumber support can be approximately circular but in general has to be defined with reference to the particular array.Work supported by Australian Department of Defence.     

Robust microphone arrays using subband adaptive filters

A new adaptive beamformer which combines the idea of subband processing and the generalised sidelobe canceller structure is presented. The proposed subband beamformer has a blocking matrix that uses coefficient-constrained subband adaptive filters to limit target cancellation within an allowable range of direction of arrival. Simulations comparing the fullband and subband adaptive beamformers show that the subband beamformer has better performance than the fullband beamformer when the target and/or interfering signals are coloured. In reverberant environments, the proposed subband beamformer also performs better than its fullband counterpart     

Pattern synthesis based on adaptive array theory

Pattern synthesis based on either optimization of signal-to-noise ratio or noise minimization is developed. The connection between adaptive arrays and adapted pattern shape is used in synthesizing linear array patterns with freedom to adjust both amplitude and phase. Phase-only pattern synthesis is described in connection with suppressing interference or clutter in proportions of space. A planar array example applied to a constant-amplitude solid-state phased array is discussed     

Multi-beam synthesis with null constraints by phase control for antenna arrays of arbitrary geometry

A novel synthesis technique for antenna arrays of arbitrary geometry is proposed. Imposing equal excitation amplitudes and modifying only the excitation phases, the method is able to produce patterns endowed with multiple main lobes and nulls in assigned directions. The technique is quite simple and requires low CPU time     

A robust adaptive beamformer for microphone arrays with a blockingmatrix using constrained adaptive filters

This paper proposes a new robust adaptive beamformer applicable to microphone arrays. The proposed beamformer is a generalized sidelobe canceller (GSC) with a new adaptive blocking matrix using coefficient-constrained adaptive filters (CCAFs) and a multiple-input canceller with norm-constrained adaptive filters (NCAFs). The CCAFs minimize leakage of the target-signal into the interference path of the GSC. Each coefficient of the CCAFs is constrained to avoid mistracking. The input signal to all the CCAFs is the output of a fixed beamformer. In the multiple-input canceller, the NCAFs prevent undesirable target-signal cancellation when the target-signal minimization at the blocking matrix is incomplete. The proposed beamformer is shown to be robust to target-direction errors as large as 200 with almost no degradation in interference-reduction performance, and it can be implemented with several microphones. The maximum allowable target-direction error can be specified by the user. Simulated anechoic experiments demonstrate that the proposed beamformer cancels interference by over 30 dB. Simulation with real acoustic data captured in a room with 0.3-s reverberation time shows that the noise is suppressed by 19 dB. In subjective evaluation, the proposed beamformer obtains 3.8 on a five-point mean opinion score scale, which is 1.0 point higher than the conventional robust beamformer     

Design of partially adaptive arrays using the singular-valuedecomposition

The objective of partially adaptive array design is to reduce the number of adaptive weights without significantly degrading the performance of the adaptive array. Previous work includes numerical techniques for approximately minimizing the average generalized sidelobe canceller (GSC) output power for a desired number of adaptive weights, where the average is over a range of jammer parameters. Our new “power-space method” also attempts to minimize the average GSC output power, but under a constraint that the reduced-dimensional solutions for all of the scenario trials lie in the same subspace. This constraint allows us to use the singular value decomposition to get the rank-reducing transformation, thereby simplifying the optimization problem. Using computer simulation, we show that our transformation yields lower output power in comparison with a previously reported example that used the numerical methods. The simplicity of the method allows large ranges of jammer parameters to be considered, Using our transformation, we consider how closely the reduced-rank solutions match the full-rank solutions and how the quality of this match relates to the output power of the partially adaptive array     

Signal processing in adaptive arrays using power basis

The development of the theory of adaptive arrays (AAs) is proposed based on the representation of the inverse covariance matrix (CM) of a noise in the AA channels as a finite power series expansion using the direct CM and by representation of a weight vector of the AA as a finite series expansion of the power vectors. The dimension of the power CM basis is equal to the power of the minimum polynomial of the CM. In the case when the number of external interference sources is less than the number of AA channels, such polynomials have the same fundamental role as the characteristic polynomial of the CM in an opposite case. Proofs for the existence of the above mentioned polynomials of the CM are given. A new method for the calculation of the polynomial coefficients is presented, and the physical properties of the power vector basis are studied. It is shown that the power vectors are correlated and that there are two stages of AA signal processing.     

Pattern synthesis of conformal arrays by the simulated annealingtechnique

A design method previously developed for the synthesis of antenna patterns of circular arc arrays is shown to also be applicable to the synthesis of conformal arrays in the 3D case. This method uses the flexibility of the simulated annealing technique to achieve the excitations of the elements for a desired radiation pattern. The algorithm allows the inclusion of constraints in the variability of the excitations in the synthesis procedure, as well the control of the sidelobe level, the beamwidth and any desired design specification     

Pattern synthesis of circular arrays in a moving medium

Based on a modified expression for the radiation field of a circular array in a moving medium, pattern synthesis is performed for medium motion both in the direction of and parallel to the main beam. It is shown that medium motion, even considering only first-order effects, changes the synthesized patterns significantly. The required excitation amplitudes and phases for the proper synthesis of a 21-element circular array to yield a cosine-square pattern in a moving medium are given.     

Computing return loss for arbitrary scan directions using limited scan codes for infinite phased arrays

Analysing infinite phased array antennas using time domain codes is favourable when looking into wideband solutions. Unfortunately, unit cell-based time domain codes using time shifts between cell boundaries have a disadvantage of only being able to analyse phase shifts corresponding to a beam scanned in the visible space. However, to fully characterise the infinite array antenna it is sometimes necessary to compute the active reflection coefficient for scan directions corresponding to invisible space. Presented is a simple new approach on how to do this. By extending the size of the computational domain, and including more than one element, phase shifts corresponding to invisible space are included.