北斗导航接收机旁瓣对消技术研究

北斗导航信号数字化处理技术的研究和发展越来越受到人们的关注,自适应天线旁瓣对消技术在北斗导航接收机中得到了广泛应用。分析了自适应天线旁瓣对消的基本原理,给出了在相对带宽较宽的干扰下按照最小均方(LMS)准则求解最优权值的计算过程以及基于Cholesky分解求取干扰信号自相关矩阵逆阵的方法。最后通过MATLAB对所设计的自适应天线旁瓣对消系统进行仿真分析,其结果表明自适应旁瓣对消技术可有效对抗宽带干扰。     

改进的基于旁瓣对消的单脉冲测角算法

研究了基于自适应广义旁瓣对消技术的单脉冲角度跟踪算法。在自适应广义旁瓣对消器(G enera l s ide lobecance ller,G SC)结构下,当存在指向误差的时候,阻塞矩阵不能完全阻塞期望信号,导致辅助支路上产生期望信号泄露,从而使得单脉冲角度跟踪性能下降。为了解决此问题,提出了一种基于辅助支路子空间投影的算法,该算法利用了期望信号空间和干扰空间正交的特点,减少了泄露的期望信号对波束形成性能的影响,从而保证了单脉冲角度跟踪的性能。理论分析和仿真结果表明了该算法的有效性和优越性。     

抗交串自适应噪声对消系统的算法实现

针对一般的自适应噪声对消系统性能上存在的不足,引入了抗交串自适应噪声对消系统.抗交串自适应噪声对消系统在形式上由两个典型的自适应噪声对消模块串接而成.抗交串自适应噪声对消系统无须预先知道信号和噪声的特征,却能够相当好地抑制噪声的影响,又使有用信号不产生畸变.该文叙述了该系统的算法实现.计算机仿真结果表明,在强噪声环境背景下,该算法将功率信噪比提高了50db左右,而且运算速度快.该算法对某些特定采样信号的分析和处理有重要意义.     

神经网络自适应噪声对消的研究

基于神经网络中自适应线性单元(ADALINE),结合传统自适应噪声对消原理,提出了一种基于ADALINE的改进型自适应噪声对消器。经仿真和实例证明,具有很强的噪声滤除能力和鲁棒性。     

基于辨识新算法的电子对抗系统干扰对消

收发同时的电子对抗系统常存在隔离问题,采用自适应滤波器对干扰耦合通路进行辨识,消除接收端耦合干扰,能够有效实现收发隔离.考虑到实际侦察接收机接收的雷达信号、接收机内部引入的噪声信号、发射机和接收机微波放大部分的非线性,因素严重影响自适应滤波器的性能.针对上述情况,给出一种平滑梯度估计的变步长最小均方(least mean square,LMS)算法.仿真结果表明,改进算法同传统变步长LMS算法相比具有相近的收敛速度,但在对抗接收机复杂信号环境上具有显著的优越性能.     

基于自适应滤波原理的扩频窄带干扰对消技术

本文在介绍了扩频通信的基本原理的基础上,重点研究了用自适应滤波原理对扩频信号中的窄带干扰进行消除的方法,并建立模型进行了仿真分析。结果表明,用两个自适应滤波器组成的双环噪声消除器对扩频信号中的窄带干扰可以起到非常理想的抑制作用。     

基于量子神经网络的无线电引信干扰对消

为了提高无线电引信的抗干扰性,采用量子神经网络构建非线性滤波器,自适应抵消回波信号中包含的干扰噪声。通过自适应干扰对消系统仿真,实现了对目标反射信号的最优恢复,获得了理想的降噪效果。     

残留频差对自适应阵列天线的影响

自适应阵列天线可以通过数字下变频实现信号正交化,把中频数字信号转换到零中频,然后进行加权求和。分析了变频过程中因没有进行载波同步所导致的残留频差对自适应阵列天线算法的影响。通过详细的理论分析表明,只要上、下变频采用相同本振,残留频差对算法并没有影响,即使对带通采样系统,该结论同样成立。对频谱、阵列增益的仿真证明了理论分析的正确性。     

一种精确控制旁瓣的自适应波束形成算法

提出了一种精确控制旁瓣和抑制干扰的自适应波束形成算法。它是通常的最小方差无畸变（MVDR）波束形成算法的改进形式，使阵列输出信号功率最小的同时，保持目标信号方向的无失真响应，并且严格保证旁瓣低于某一给定值，抑制干扰。在仿真过程中，充分应用了二阶锥规划（second—order cone programming）算法，并与MVDR波束形成算法进行比较，验证了方法的正确性，同时研究了该算法的稳健性。     

基于改进的NLMP的自适应脉冲噪声对消器

在信号传输系统中,存在自适应算法不能处理的α-稳定脉冲噪声,在算法中将步长更新与系统输出误差e(n)的lp范数联系起来,利用系统的输出误差e(n)来确定自适应系统的步长,提出了一种适用于α-稳定脉冲噪声环境下的改进的NLMP自适应对消算法(MNLMP)。MNLMP很好地解决了NLMP算法收敛速度与稳态误差不能兼顾的缺点。通过计算机仿真,结果显示MNLMP比LMP、NLMP有更好的对消性能。同时,仿真结果显示在不同输入信噪比的情况下,MNLMP算法的输出信噪比其它两种算法有了明显的提高。     

Hybrid probabilistic adaptation mode controller for generalized sidelobe cancellers applied to multi-microphone speech enhancement

In this paper, we propose a new adaptation mode controller (AMC) for a generalized sidelobe canceller (GSC)-based speech enhancement system. Here, a likelihood ratio for target speech presence was first estimated and then utilized to estimate both the local target speech presence probability (SPP) and global SPP. Next, the estimated SPPs were applied to the design of an AMC that controlled the parameters of adaptive filters for an adaptive blocking matrix (ABM) and noise canceller (NC). In particular, the combination of local and global SPPs was applied to the AMC in the ABM, whereas only global SPPs were used for the NC. Finally, a multiple-microphone speech enhancement system was constructed on the basis of a GSC having the proposed AMC. The performance of the speech enhancement system was subsequently evaluated in terms of the perceptual evaluation of speech quality (PESQ) and the cepstral distortion (CD) for car noise conditions. It was shown from this evaluation that a speech enhancement system using the proposed AMC method provided better performance than conventional AMC methods using power ratios between the target and non-target directional signals, the inter-channel normalized cross-correlation, and the local SPPs only.     

Dual‐polarized low sidelobe Fabry‐Perot antenna using tapered partially reflective surface

A novel dual‐polarized Fabry‐Perot (FP) cavity antenna with low sidelobes is proposed. Low sidelobes are obtained by using a tapered partially reflective surface (PRS) in the form of circular lattice instead of the conventional rectangular lattice. As the PRS can be regarded as a 2D leaky wave surface on which cylindrical waves propagate outward radially in the form of concentric rings, so arranging the PRS elements in the form of circular lattice and then applying tapering on it yields low sidelobes in both the E‐ and H‐planes. The performance of the proposed PRS is validated by fabricating a dual‐polarized FP antenna and measuring its radiation patterns. Peak realized gains of 18.6 and 18.5 dBi are obtained for horizontal and vertical polarizations respectively, giving an aperture efficiency of around 42%. Measured sidelobe levels are reduced to lower than ?21.3 dB in both the E‐ and H‐planes for the two orthogonal polarizations.     

Investigations on low sidelobe characteristics of reflectarray antenna for W‐band wireless sensor application

A W‐band low sidelobe level offset‐fed reflectarray antenna is designed, fabricated, and measured. Compared to conventional offset‐fed reflectarray antenna, the sidelobe level of proposed one is decreased significantly when the inclination angle of reflector is half of the incident angle of the feeding. At the same time, a large‐radiation‐area element is used to obtain low sidelobe level for the offset‐fed reflectarray antenna because of its large radiating element area and low specular reflection. A 52 mm× 180 mm offset‐fed reflector antenna have been designed and measured to verify the availability. From 90 to 96 GHz, measured results show that a maximum gain of 36dBi at 93 GHz, and the peak sidelobe level of 18dBc can be obtained with the proposed architecture.     

Reduction of sidelobe levels in interrupted phased array antennas by means of a genetic algorithm

Interruptions in the regular lattice of a phased array antenna can lead to elevated sidelobe levels in the resulting antenna pattern. A method for reducing the sidelobe level in such an array is presented, based on the use of a genetic algorithm that modifies the element weights in the array. Results are presented for both scanned and unscanned arrays. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

A new hybridized backtracking search optimization algorithm with differential evolution for sidelobe suppression of uniformly excited concentric circular antenna arrays

In this work, a hybridized combination of backtracking search algorithm (BSA) with differential evolution (DE) is proposed and applied on sidelobe suppression problem of uniformly excited concentric circular antenna arrays (CCAA). Each array is assumed to have isotropic elements and be placed on x‐y plane and has one center element. A search for optimal setting of ring radius and number of elements in each ring is carried out so as to achieve low sidelobe performance on overall azimuth plane. Care has been taken so that directivity does not get degraded as far as possible. Before applying this algorithm to CCAA design problem, BSA and the hybridized algorithm BSA‐DE are tested on five complex benchmark functions. Based on 30‐independent runs for each benchmark function, Wilcoxon's pairwise signed ranks test is utilized to judge the relative search performance of these two algorithms. The hybridized algorithm proves its superiority on almost all the considered benchmark functions. For the CCAA design problem dealt with in this work, BSA‐DE shows its superiority on one or both pattern parameters as well as structural parameters. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:262–268, 2015.     

Planar circularly polarized X‐band array antenna with low sidelobe and high aperture efficiency for small satellites

A planar broadband circularly polarized (CP) X‐band array antenna with low sidelobe and high aperture efficiency is presented for small satellite applications. The array design is composed of 4 × 4 broadband CP stacked patch elements, which are fed by a feeding network consisted of unequal series‐parallel power dividers to achieve the low sidelobe and high aperture efficiency. The final prototype with overall size of 100 mm × 100 mm × 3 mm (2.73λ₀ × 2.73λ₀ × 0.082λ₀ at 8.2 GHz) was fabricated and measured. The antenna has a broadband characteristic with |S₁₁| < ?10 dB bandwidth of 15.9% (7.52‐8.82 GHz) and 3‐dB axial ratio bandwidth of 11.95% (7.63‐8.60 GHz). Also, it achieves an excellent broadside CP radiation with a gain of 17.2‐20.03 dBic, a sidelobe level of <?20 dB, and aperture efficiency of 65% to 97.5%. With these features, the proposed antenna is a good candidate for high‐speed data downlink onboard small satellites (MiniSat, MicroSat, NanoSat, and CubeSat).     

Limits of compensation in a failed antenna array

In large antenna arrays, the possibility of occurrence of faults in some of the radiating elements cannot be precluded at all times. In such situations, the radiation pattern of the array gets distorted, mostly with an increase in sidelobe level and decrease in gain. Although it is not possible to restore the pattern fully by rearranging the excitations of the functioning elements, compensation methods have been reported in the literature for restoring one performance parameter of the array and making a trade‐off on some other parameter. In this article, we have made a study on the tolerance level of this compensation process. One part of the study deals with the thinning in the failed array, that is, to find a limit on the minimum number of functioning elements of the array that can restore the digital beamforming of the failed array. The second part of study deals with finding the maximum number of element failures that can be compensated. The study was carried out by optimizing the amplitude excitations of the failed array. Instead of classical optimization techniques, particle swarm optimization was used for the compensation process. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:635–645, 2014.     

An adaptive large neighborhood search for the discrete and continuous Berth allocation problem

The Berth Allocation Problem (BAP) consists of assigning ships to berthing positions along a quay in a port. The choice of where and when the ships should move is the main decision to be made in this problem. Considering the berthing positions, there are restrictions related to the water depth and the size of the ships among others. There are also restrictions related to the berthing time of the ships which are modeled as time windows. In this work the ships are represented as rectangles to be placed into a space ×time area, avoiding overlaps and satisfying time window constraints. We consider discrete and continuous models for the BAP and we propose an Adaptive Large Neighborhood Search heuristic to solve the problem. Computational experiments indicate that the proposed algorithm is capable of generating high-quality solutions and outperforms competing algorithms for the same problem. In most cases the improvements are statistically significant.     

一种叠双菱形天线的改进设计

在对菱形天线结构和工作原理进行分析的基础上,为缩小天线尺寸结构,提高天线的方向和增益特性,设计了一种以2.4 GHz为中心工作频率的带反射板的叠双菱形天线。设计过程中利用VB软件制作了交互式天线计算器,方便天线尺寸参数的计算和优化调整,并使用4NEC软件搭建天线的模型及仿真优化。在天线测试平台上利用PNA3621网络分析仪对制作的天线进行了测试。测量结果表明,在2.35 GHz～2.45 GHz频率范围内,天线方向图较好,与仿真结果较为吻合,天线输入端电压驻波比和回波损耗较为理想。