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。     

An optically driven phased array antenna utilizing heterodynetechniques

An optically driven phased array antenna system that utilizes heterodyne techniques to generate the microwave carrier frequency and phases is proposed. The heterodyning at each antenna element requires three injection-locked lasers. The microwave carrier frequency is determined by the order of the modulated sideband used in the injection-locking scheme. A design is also presented for an integrated optical fast Fourier transform (FFT). This device can perform the necessary phase processing for both beam steering and detection-of-arrival angle. Recent results on the noise properties of injection-locked semiconductor lasers are applied to the proposed antenna system. The effect of noise on the gain, signal-to-noise ratio, and the bandwidth of the antenna system is examined. It is shown that the performance degradation of the system, due to the noise in the lasers, is minimal, and therefore the bandwidth promise of optical drive could well be achieved with the use of heterodyne laser locking techniques     

Hybridation des méthodes de recherche taboue et du recuit simulé pour l’optimisation d’une antenne en réseau adaptative

The increasing pollution of the electromagnetic environment has prompted the study of array pattern nulling techniques. These techniques are very important in radar, sonar and communication systems for minimising degradation in signal-to-noise ratio performance due to undesired interferences. Adaptive array antennas backed by strong signal processing algorithms are able to automatically change the beam pattern in accordance with the changing signal environment. It not only directs maximum radiation in the direction of the desired mobile user but also introduces nulls for interfering directions while tracking the desired mobile user at the same time. The adaptation is achieved by multiplying the incoming signals with complex weights and then summing them together to obtain the desired radiation pattern. Adaptive array optimization is an NP-hardproblem. In this paper, a technique based on the coupling between tabu search and simulated annealing methods is presented to solve this problem. Several illustrative examples of patterns with imposed single and multiple null directions are given to show the versatility of the present method.     

一种基于LMS算法的天线阵通道失配校正技术及VLSI实现

天线阵各通道之间的通道失配（幅相特性不一致）会严重影响阵列信号处理的性能[1,2],为此在进行阵列信号处理前必须对各通道的幅相特性进行均衡.本文针对天线阵通道之间与频率无关的恒定通道失配问题,提出了一种基于LMS好地校正与频率无关的通道失配.本算法的易于工程实现的通道校正技术.计算机仿真结果表明,采用这种技术可以很文最后还给出了该算法在VLSI（超大规模集成电路）平台上的实现结构.     

Adaptive beamforming with the generalized sidelobe canceller in the presence of array imperfections

Antenna designers often employ linearly constrained adaptive beamforming as an antijamming measure. With minimal a priori knowledge of the signal environment, this technique nulls out jammers while simultaneously preserving the quality of the main lobe so that a friendly look-direction signal can be received with unity gain. Unfortunately, in the absence of special strategies, linearly constrained adaptive beamforming is hypersensitive to array imperfections when the input signal-to-noise ratio exceeds a certain threshold. This hypersensitivity manifests itself as a nailing of the friendly signal as if it were a jammer. Luckily, the signal nulling problem can be easily remedied by artificial receiver noise injection. A particularly simple and general structure for linearly constrained adaptive beamforming was proposed during the 1970's, and is known as the generalized sidelobe canceller. A detailed analysis of the generalized sidelobe canceller in the presence of array imperfections is discussed, and two new artificial receiver noise injection algorithms are proposed. Computer simulations are included to demonstrate that use of these new algorithms alleviates the signal nailing problem without seriously compromising jammer nulling. For the special case of the Capon maximum-likelihood beamformer, simple approximations are presented for: 1) the Wiener output signal-to-interference-plus-noise ratio (SINR_{0}astr), 2) the antenna element error variance that causes a 3 dB loss ofSINR_{0}astrfrom its value for an ideal array, and 3) the optimal artificial receiver noise that maximizesSINR_{0}astr.     

Constrained optimization of the performance indices of arbitrary array antennas

The solution to the optimization of performance indices of array antennas such as directive gain, efficiency index, and signal-to-noise ratio, do not provide information regarding the sidelobe region of the radiation pattern. It is shown that, with proper constraints on the sidelobes, a given performance index can be optimized to give a radiation pattern with desired sidelobe levels. As most of the performance indices of an array antenna can be expressed as a ratio of two Hermitian quadratic forms, an eigenvalue method is used for the constrained optimization. This method gives explicit expressions for the excitation vector and constrained values of the performance indices. An iterative technique is used to ensure that the specified field values occur at the sidelobe peak positions. The element excitations obtained by this technique for maximum gain and uniform sidelobe level are similar to these obtained by the Dolph-Chebyshev technique.     

天线单元存在幅相不一致性时的波束零点合成技术

波束零点对阵列幅相不一致非常敏感,这一点往往降低了利用零点技术抗干扰的性能.为了改善波束零点在实际系统中对干扰的抑制效果,本文通过对理想约束模型进行预畸变处理,大大的降低了天线单元幅相不一致性对波束零点的影响.对该方法的进一步推广,天线单元存在方向性误差和天线单元有缺失情况下的零点合成问题也得到了解决.本文中的仿真结果和实际数据处理结果都进一步证明了该方法的有效性.     

Shaped beam pattern synthesis with desired nulling level and minimum sidelobe level

For the anti-interference/denoise purpose, it usually requires minimizing the sidelobe level (SLL) of a wide-beam pattern with a desired low nulling level (NL) in the nulling region. To realize such an objective, the shaped-beam pattern synthesis (SBPS) is the most commonly used approach. However, since the SBPS problem focuses on synthesizing a predetermined beam shape, the minimum SLL via this approach cannot ensure to obtain the maximum power gain. Conversely, it cannot obtain the lowest SLL with a certain power gain requirement. Based on such consideration, this paper tries to further minimize SLL of a wide-beam pattern with a desired low NL nulling region, by solving the power gain pattern synthesis (PGPS) problem. The PGPS problem selects the array excitation by directly optimizing the power gain. Hence, it has the potential to reduce SLL, when achieving the equal mainlobe power gain constraint via SBPS. An iterative algorithm which converts the primal optimization problem into convex sub-problems is proposed, resulting in an effective problem-solving scheme. Numerical simulations demonstrate the proposed algorithm can obtain about 10-dB lower SLL than the existing algorithms.     

Carrier-to-noise ratio and sidelobe level in a two-laser modeloptically controlled array antenna using Fourier optics

The carrier-to-noise ratio of the microwave signal and the reduction of the antenna sidelobe are discussed for an optically controlled array antenna whose microwave aperture distribution is generated and controlled using Fourier transform and optical/electrical conversion. A two-laser model using two laser diodes whose frequency difference is set to the desired microwave frequency is proposed and compared with a single-laser model using an external modulator. The two-laser model seems to be favorable from the viewpoint of available laser diode output power. The required laser output for the two-laser model can be about 10 dB less than that for the single-laser model. Moreover, relationships between the antenna radiation characteristics and the aperture size of an image mask are investigated. It is clarified that the sidelobe level can be reduced about 20 dB without changing the gain and beamwidth by using a reference optical beam with a tapered amplitude distribution     

Partial adaptive nulling on a monopulse phased array antenna system

A partial phase-only nulling (PPON) algorithm has been developed and evaluated on a 496-element monopulse phased array antenna system which employs five-bit phase shifters. Using this PPON algorithm allows nulls in the far-field pattern to be steered to the desired directions for a phased array equipped with low-resolution phase shifters to perform simultaneous nulling in the sum and two difference patterns in the environment of multiple jammers. Simulated and experimental patterns are illustrated     

The use of optically coherent detection techniques for true-timedelay phased array and systems

We analyze a true-time-delay, optically controlled phased array antenna system whereby beam forming is accomplished using a large number of antenna elements that can receive any of several different microwave true-time-delays via the use of coherent optical carriers transmitted through a single fiber. The transmitter and receiver architectures are described in detail. We present calculations for the signal-to-noise ratio (SNR), the signal-to-interchannel interference ratio (SIR) and dynamic range (DR) of one channel for various modulation-demodulation schemes (i.e., AM-heterodyne, FM, PM). We show for an example system that can accommodate 128 antenna elements and provide 128 different delays (7 bits), assuming AM modulation with a bandwidth of 1 MHz, a transmitter power of -5 dBm and a laser linewidth of 10 MHz, we can obtain DR≃50 dB for one channel using a channel separation twelve times of that of the microwave frequency (f_m). For the FM scheme, DR≃60 dB can be obtained for one channel with a laser linewidth of 1 MHz, a FM modulation index of one, and a channel spacing of about 13f_m. With a local oscillator laser tuning range of 100 Å, the system can provide seven-bit resolution for a 128 element antenna array. It is found that coherent optically controlled phased array antennas provide improved controllability over direct detection method, and can have the SNR, SIR and DR that meet the stringent requirements of modern high resolution microwave antenna systems     

A Nulling Performance Comparison Between a Single- and Multiple-Aperture Multiple-Beam Antenna

Discussed in this paper is the nulling performance of a single- and a multiple-aperture multiple-beam antenna (MBA). A linearly constrained minimum power algorithm incorporating both main beam and derivative constraints is formulated and simulated. The nulling resolution of the multiple-aperture MBA is shown to be superior to that of the single-aperture MBA. In addition, a method for illuminating a region in space with constant gain while simultaneously nulling interfering signals within a fractional single element beamwidth of this constant gain region is illustrated. A flat gain pattern is achieved by spacing derivative constraints over the spatial region where the desired signals are known to be transmitting. Derivative constraints are particularly useful when the precise directions of arrival for the desired signals are not available to the beamformer     

A novel adaptive beamforming algorithm for antenna array CDMA systems with strong interferers

Blind beamforming based on the maximum signal-to-noise ratio (MSNR) can improve the performance of an array system only when the processing gain of the given code-division multiple-access (CDMA) system is high enough such that the desired signal can become dominant after despreading (see Choi, S. and Shim, D., IEEE Trans. Veh. Technol., vol.49, p.1793-1806, 2000; Choi, S. and Yun, D., IEEE Trans. Antennas Propagat., vol.45, p.1393-1404, 1997). We consider a maximum signal-to-interference-plus-noise ratio (MSINR) beamforming. The MSINR performance criterion is chosen to deal with strong interferers effectively. It is shown that blind MSINR beamforming is possible by directly utilizing the input and output signals of correlators of the CDMA systems. In addition, we propose an adaptive beamforming algorithm at a lower computational complexity - about O(7.5N) - where N is the number of antenna elements of the array system. Simulation results are presented in various signal environments to show the performance of the proposed adaptive algorithm.     

Circularly polarized dielectric-loaded planar antenna excited bythe parallel feeding waveguide network

A new receiving planar array antenna for DBS (direct broadcasting satellite) is proposed. The element antenna is a short waveguide aperture mounted in the ground plane, loaded with a dielectric and polarizers, and excited through its side wall by another feeding rectangular waveguide. The gain of the element antenna loaded with a dielectric is so high that the grating lobes can be reduced sufficiently even if the element spacing in the array is wider than the wavelength in free space. Therefore we can reduce the number of the array elements, and parallel feeding by the low loss waveguide network can be feasible to provide a planar array antenna. This paper describes the experimental results of several kinds of the circularly polarized dielectric-loaded element antennas and the planar antennas fed by the waveguide network. In the 12 GHz band the planar antenna with 64-element radiators has a maximum gain of 31.9 dBi with an aperture efficiency of 94.7%, the 1 dB-down frequency bandwidth of the gain is about 800 MHz (6.7% for a center frequency of 11.85 GHz), and the frequency bandwidth of the axial ratio is less than 1 dB of 850 MHz (7.2%)     

Evaluation of adaptive phased array antenna, far-field nullingperformance in the near-field region

A theory for analyzing the behavior of adaptive phased array antennas illuminated by a near-field interference test source is presented. Conventional phased array near-field focusing is used to produce an equivalent far-field antenna pattern at a range distance of one to two aperture diameters from the adaptive antenna under test. The antenna is assumed to be a linear array of isotropic receive elements. The interferer is assumed to be a bandlimited noise source radiating from an isotropic antenna. The theory is developed for both partially and fully adaptive arrays. Results are presented for the fully adaptive array case with single and multiple interferers. The results indicate that near-field and far-field adaptive nulling can be equivalent. The adaptive nulling characteristics studied in detail are the array radiation patterns, adaptive cancellation, covariance matrix eigenvalues, and adaptive array weights     

An adaptive array for interference rejection

An adaptive array that rejects undesired or interfering signals is presented. The array pattern is controlled by an adaptive feedback system based on a steepest descent minimization of mean-square error. Error is defined as the difference between the array output and a locally generated reference signal. Minimization of mean-square error is closely related to maximization of signal-to-noise ratio (SNR). A two-element adaptive array has been built, and its experimental performance is discussed. Typical patterns for various desired and interfering signals are shown, as well as measured transient response. Finally, some experiments showing the array behavior with modulated signals are described. The results show that such an antenna system is capable of automatically rejecting interfering signals, subject only to certain basic constraints. No a priori information about the angles of arrival of the signals is required, Detailed knowledge of the waveforms of the desired and interfering signals is also not needed, although the spectral characteristics of the desired signal must be known.     

手持终端波束成形天线阵列的优化设计

设计了一款适用于移动手持终端的低剖面波束成形天线阵列。该天线阵列由八个结构相同的倒F天线组成,可以工作在GSM1900(1880~1920 MHz)、LTE2300(2300~2400 MHz)和LTE2500(2540~2620 MHz)三个频段。通过功率传输效率最大化理论,可以优化出该阵列在所需方向上的最佳激励。通过馈电电路板给8个天线单元提供优化的激励,可以将天线波束偏转到所需方向,并且保证天线在该方向上获得最大可能增益。天线阵列工作在2.45 GHz时,在x、y、z方向上的增益分别为7.80、6.03和7.20 dBi;相应地,在1.9 GHz时分别为6.67、5.27和6.05 dBi。     

GPS自适应调零天线信号处理系统硬件设计

针对GPS抗干扰问题,常用手段是在信号处理系统中采用自适应调零算法来实现抗干扰。结合该算法文中给出了一种信号处理系统的硬件实现方案。首先概述GPS自适应调零天线的系统结构,然后给出信号处理系统的硬件设计思路及其功能模块的实现,最后通过实测数据验证硬件模块可以满足自适应调零算法的要求。     

Maximal-ratio combining architectures and performance with channel estimation based on a training sequence

Maximum-ratio combining (MRC) is a simple and effective combining scheme for adaptive antenna arrays to combat noise, fading, and to a certain degree, cochannel interference. However, it requires estimation of the spatial signature (i.e., the channel gain and phase at each antenna element) of the desired signal across the array. Assuming that this estimate is obtained by correlation using a known training sequence of K symbols embedded in the useful signal, we proceed to develop a fully analytical assessment of the impact of estimation error on the output signal-to-noise ratio (SNR) of the array. The originality of the approach revolves around the derivation of the distribution of the normalized SNR, that is the real SNR normalized to the ideal (i.e., perfect estimation) SNR. The end result is a set of distributions which can potentially reduce or in certain cases eliminate the need for simulation to determine certain design parameters such as array size, training sequence length, etc. These are then applied to find closed-form expressions for the outage probability and the error probability in differential phase-shift keying and quarternary phase-shift keying after training in uncorrelated Rayleigh fading.     

Far-field uncertainty due to random near-field measurement error

Recent planar near-field scanning tests with ultralow-sidelobe antennas have confirmed that random near-field measurement errors will ultimately limit the accuracy of far-field patterns. A formulation is outlined for estimating the spectral signal-to-noise ratio (SNR) arising from noncorrectable near-field random measurement errors. The formulation applies to arbitrarily directive test antennas and probes-even nulling probes. A far-field parameter, called the scan plane coupling factor, may be computed directly from the near-field data, and then used to form the spectral SNR. The accuracy of the spectral SNR is confirmed by simulation and by actual tests with low-sidelobe AWACS array antenna