Tapered beamforming for concentric ring arrays

In this paper, some conventional filtering windows are modified and applied to uniform concentric circular antenna arrays (UCCA) for spatial smoothing and sidelobe reduction. The modified windows are applied to individual rings of the array that will taper the corresponding current amplitudes. The resulted sidelobe level, beamwidth and stability for amplitude errors are discussed for the different proposed tapering windows where it shows a sidelobe reduction to about 49 dB as in the case of Binomial UCCA while the Hamming window shows the most immunity to tapered amplitude errors.     

圆阵相位模式空间波束输出的高分辨目标方位估计算法研究

本文推导了均匀圆阵作为接收阵时的相位模式空间,证明圆阵在相位模式空间可以等效为一个虚拟线阵,并把高分辨方位估计算法应用到均匀圆阵相位模式空间虚拟线阵波束输出。计算机仿真结果显示,波束域Root－MUSIC算法应用到虚拟线阵时可以获得良好的解不相关信源的能力,而波束域WSF算法则具有比模式平滑算法更佳的解相干信源性能。     

Design considerations for low sidelobe microstrip arrays

The factors affecting the realizable sidelobe performance of microstrip arrays are discussed and quantified. These include excitation amplitude and phase accuracies, mutual coupling, diffraction effects, positioning errors, and errors due to imperfect element matching and feed network isolation. It is shown that low-sidelobe microstrip arrays require a very tight tolerance on the resonant frequencies of the elements, and the elimination of spurious radiation from the feed network. Cross-polarization and surface wave effects are discussed. An experimental 16-element microstrip array prototype incorporated these considerations into the design, and achieved a -35 dB relative sidelobe level     

Performance analysis of beamforming in two-hop AF relay networks with antenna correlation and interference

This paper investigates the performance of a two-hop amplify-and-forward (AF) relay network with antenna correlation and co-channel interference (CCI) over Rayleigh fading channels. In this network, the relay has multiple antennas while both the source and destination are equipped with a single antenna. By assuming that the statistical channel state information (SCSI) is available at the relay, the maximal output signal-to-interference-plus-noise ratio (SINR) is first obtained. Then, with the help of the specialized functions, the analytical expressions for the outage probability (OP), Ergodic capacity and average symbol error rates (ASERs) of the considered AF relay network are all derived. Moreover, the asymptotic analysis at high signal-to-noise ratio (SNR) is also presented to reveal the diversity order and array gain of the relay system. Finally, computer simulations are given to confirm the validity of the theoretical analysis and indicate the effects of antenna correlation and interference on the system performance.     

Direction-of-arrival and polarization estimation with uniform circular arrays in the presence of mutual coupling

A modified Root-MUSIC algorithm is proposed to estimate the directions-of-arrival (DOAs) and the polarization of plane waves, which impinge at a fixed elevation angle, using a diversely polarized uniform circular array (UCA). Special attention is devoted to the presence of mutual coupling effects in antenna arrays. By describing the electromagnetic characteristics on the basis of a phase-mode expansion for the open-circuit voltages and the mutual coupling matrix, the modified Root-multiple signal classification (MUSIC) algorithm takes mutual coupling effects into account by a limited number of phase modes. Finally, the efficiency of the new algorithm is verified based on synthetic antenna data.     

Optimum quantised low sidelobe phase tapers for arrays

A genetic algorithm is used to find optimum quantised low sidelobe phase tapers for linear arrays of point sources. This method has the advantage that the optimum taper is found in quantised phase space rather than in continuous phase space     

一维线阵唯相位低副瓣技术分析

实现了基于最速下降方法(SDM)的唯相位低副瓣技术,提出了SDM方法的步长公式,对不同阵元分析了唯相位技术的低副瓣性能和能量效率水平,总结了最高副瓣电平同阵元数目的关系,分析了幅相加权对于最高副瓣电平和能量效率水平的影响。     

A HORIZONTAL SMALL SIZED BACKFIRE ANTENNA USING CIRCULAR DIPOLE

In this paper,a horizontal small sized(≈0.5λ)backfire antenna with the circulardipole is described.The antenna structure and experimental results are given.The experimentalresults demonstrate that the antenna has better electrical performances.     

DESIGN OF VIRTUAL UNIFORM LINEAR ARRAYS FOR EFFICIENT DIRECTION FINDING

The problem considered in this paper is to interpolate a virtual uniform array froma real two-dimensional array with arbitrary geometry via an interpolation matrix. The key to thisproblem is how to arrange these virtual sensors. It is shown that the virtual uniform linear arrayshould have the same main-lobe beam-pattern as the real array over an angular sector of interest.Simulation results are presented to illustrate the application of virtual array in direction finding.     

综合孔径辐射计同心圆形阵排列优化

使用微粒群优化算法(PSO),对干涉式综合孔径微波辐射计(SAIR)系统中带有多个圆环的同心圆形阵(CCA)进行优化处理,以获得在视场范围内较低的峰值旁瓣电平(PSLL)。优化结果显示,在同样的系统空间分辨率条件下,优化后的CCA比未优化的仅有一个圆环的CCA具有更低的PSLL和更少的天线个数。基于上述理论,给出了一个简单的2环CCA优化设计和相关仿真来进行说明。     

An improved cyclic beamforming method for signal DOA estimation

Modulated signals used in telecommunication are cyclostationary. This property can be exploited to improve the direction of arrival (DOA) estimation performance. In this work, we propose an improved cyclic beamforming algorithm exploiting cyclostationarity. The proposed method exploits the information of both cyclic correlation matrix and cyclic conjugate correlation matrix with different cyclic frequencies. Compared with the existing methods, the simulation results show that proposed method improves substantially the signal selectivity; also it allows an increase in resolution power.     

Synthesis of concentric circular antenna arrays using dragonfly algorithm

Due to the strong non-linear relationship between the array factor and the array elements, concentric circular antenna array (CCAA) synthesis problem is challenging. Nature-inspired optimisation techniques have been playing an important role in solving array synthesis problems. Dragonfly algorithm (DA) is a novel nature-inspired optimisation technique which is based on the static and dynamic swarming behaviours of dragonflies in nature. This paper presents the design of CCAAs to get low sidelobes using DA. The effectiveness of the proposed DA is investigated in two different (with and without centre element) cases of two three-ring (having 4-, 6-, 8-element or 8-, 10-, 12-element) CCAA design. The radiation pattern of each design cases is obtained by finding optimal excitation weights of the array elements using DA. Simulation results show that the proposed algorithm outperforms the other state-of-the-art techniques (symbiotic organisms search, biogeography-based optimisation, sequential quadratic programming, opposition-based gravitational search algorithm, cat swarm optimisation, firefly algorithm, evolutionary programming) for all design cases. DA can be a promising technique for electromagnetic problems.     

Transformations for nonideal uniform circular arrays operating in correlated signal environments

The Davies transformation is a method to transform the steering vector of a uniform circular array (UCA) to one with Vandermonde form. As such, it allows techniques such as spatial smoothing for direction-of-arrival (DOA) estimation in a correlated signal environment, developed originally for uniform linear arrays, to be applied to UCAs. However, the Davies transformation can be highly sensitive to perturbations of the underlying array model. This paper presents a method for deriving a more robust transformation using optimization techniques. The effectiveness of the method is illustrated through a number of DOA estimation examples.     

Mixed microwave-digital and multi-rate approach for wideband beamforming applications using 2-D IIR beam filters and nested uniform linear arrays

The presented work explores novel methods for synthesizing approximately frequency independent array factors at lower hardware complexity for wideband beamforming applications. The proposed approach employs 2-D infinite impulse response (IIR) digital beam filters together with nested uniform linear arrays (ULAs). The array is designed to have multiple levels of nesting. Each level of nesting consists of a ULA covering a temporal subband of the incident wideband signal. The use of nested arrays provides the required aperture size using a smaller number of elements compared to using a single ULA to capture the entire wideband signal. The use of different levels of nesting allows the operation of the digital processor for each sub-band at different clock rates. This is a hierarchical approach that saves both digital VLSI hardware and power consumption. The 2-D IIR digital beam filters that process each subband signal from each of the nested subarray achieves wideband beamforming. Simulations illustrate approximately frequency independent passbands as required in wideband beamforming.     

Robust adaptive beamforming for wide-band, moving, and coherentjammers via uniform linear arrays

The problem of providing robustness to the conventional narrow-band uniform linear array configuration so as to handle wide-band and moving jammers is addressed. This robustness is achieved via the use of derivative constraints in jammer directions. However, since the jammer directions are not known a priori, these constraints are incorporated with a maximum likelihood characterization of the so-called jammer subspace. This formulation does not need to assume the availability of signal-free observations, as stipulated in earlier work. Computer simulation results are presented, which show that the algorithms proposed here yield significantly better performance as compared to the previous algorithms of Gershman et al. (see ibid., vol.44, p.361-6, 1996, and IEEE Trans. Signal Processing, vol.45, p.1878-85, 1997) and Hung and Turner (1983) in a variety of situations required to handle wide-band, moving, and coherent jammers     

An improved woodward method for separate arrays synthesis

Based on the property of sample function, the Woodward synthesis method for separate arrays is improved. The improved method is justified theoretically, and the sample function of the flat-topping and 30 degree cosecant-squared space segment pattern on radar phased array antenna is synthesized using it. Through simulation and analysis, it can be used fewer elements to make the same synthesis effect on the pattern with the traditional Woodward method. And if the same number of elements is used, the synthe-sized pattern using the improved method will have better approach to the sample function, narrower beam width, and higher gain.     

Capacity enhancement by terminal originated beamforming for wireless local area networks

In dense traffic areas, wireless local area networks (WLANs) suffer from interference problems due to the usage of the crowded unlicensed ISM band and the lack of available spectrum. To mitigate these problems, a terminal side beamforming framework is proposed—this beamforming is capable of focusing the transmission and the reception in the relevant direction of the access point to exploit the directivity of the indoor propagation channel. It provides network transparency to achieve the backwards compatibility to the existing WLAN networks, and vendor transparency to ease the system design process and thereby achieve low complexity and costs. The beamforming enabled terminal benefits in terms of capacity, energy efficiency, and security while it does not require any change on the network side costing network providers new investments. It will be an attractive value-added feature as well as low-cost solution for the future WLAN terminal design opening the door for WLAN terminal manufacturers to include the proposed solution into their product line. In this work, a WLAN terminal beamforming demonstrator has been developed to demonstrate the capacity enhancement in real environments. Signal to interference ratio (SIR) improvement as well as array gain were investigated by simulations with IEEE 802.11n cluster channel models and by experiments with the demonstrator in a typical office environment. The comparable results of simulations and experiments show significant array gain and SIR improvement. The significant capacity increase has been demonstrated in the experiments in both an interference free scenario and an interference limited scenario.     

空时编码联合波束形成技术研究现状分析

通过采取适当策略把空时编码和波束形成技术结合起来,可同时获得波束形成增益和分集增益,进一步改善系统性能、提高系统容量.文中分别从不同算法和天线配置结构上,分析介绍了两技术相结合的原理及特点,讨论了几个典型的空时分组码与波束形成的结合技术,分析了它们的内在机理及其优缺点,最后对该结合技术的发展趋势进行了展望.     

大型线阵自适应数字波束形成超低副瓣技术

自适应数字波束形成技术是现代阵列天线系统必须采用的关键技术。为了对付强有源干扰,现代相控阵雷达都必须具有自适应的干扰抑制能力。除了对抗有源干扰外,大部分雷达还要求具有强杂波背景下检测目标的能力,这就需要雷达天线具有低或超低副瓣电平。本文针对大型线阵,结合数字波束形成,讨论了在保证自适应干扰置零的前提下,如何控制自适应波束的副瓣电平,从而实现阵列系统的超低副瓣性能。