基于数字多波束天线的多星测控系统

针对多星测控存在的问题和技术解决途径,提出采用数字波束形成技术实现单站多星测控的方案,简要说明了系统的体系结构和工作原理,指出了系统特点和技术难点。基于数字多波束天线的多星测控系统具有良好的技术基础和应用前景。     

Performance evaluation of digital beamforming strategies for satellite communications

Smart antennas are becoming one of the promising technologies to meet the rapidly increasing demands for more capacity of satellite communication systems. A main component in a smart antenna system is beamforming. Because of the limitations of analog beamforming, digital beamforming will be employed in future satellite communication systems. We evaluate the performance of various digital beamforming strategies proposed in the literature for satellite communications: 1) single fixed beam/single user, 2) single fixed beam/multiple users, 3) single adaptive beam/single user, and 4) single Chebyshev dynamic beam/multiple users. Multiple criteria including coverage, system capacity, signal-to-interference-plus-noise ratio (SINR), and computation complexity are used to evaluate these satellite communication beamforming strategies. In particular, a Ka-band satellite communication system is used to address the various issues of these beamforming strategies. For the adaptive beamforming approach, subarray structure is used to obtain the weights of a large 2D antenna array, and a globally convergent recurrent neural network (RNN) is proposed to realize the adaptive beamforming algorithm in parallel. The new subarray-based neural beamforming algorithm can reduce the computation complexity greatly, and is more effective than the conventional least mean square (LMS) beamforming approach. It is shown that the single adaptive beam/single user approach has the highest system capacity.     

新型星载多波束相控阵天线分布式数字波束成形网络设计与实现

 针对16波束61阵元数字波束成形（DBF）星载相控阵天线的高速信号处理要求,提出以实信号处理为主体的分布式DBF网络架构,较复信号处理模式节省了一半的资源和数据传输量。通过时域Hilbert变换和分布式算法对波束成形网络各单元进行合理设计,降低了算法的运算量,也减少了硬件资源开销;同时通过单音闭环校正回路设计,改善了射频通道一致性。研制了DBF网络硬件平台和半实物仿真系统,验证了算法设计的正确性。本文提出的算法对资源有限的阵列信号处理有一定的借鉴意义。     

星载DBF接收天线误差校正算法

 提出了一种改进的基于子空间的星载数字波束形成（DBF）接收天线的误差校正方法。根据阵列互耦效应主要取决于阵元间的几何距离这一特点,利用阵元空间排布的对称性简化了天线的互耦模型,将天线的互耦效应及射频(RF)通道失配统一为通道间的幅相不一致。通过在基带注入特定的阵内相位差降低了子空间算法的计算复杂度。在建立7单元正六边形平面阵仿真模型的基础上,分析不同信噪比(SNR)环境下校正算法的性能,经比较得出可以通过提高发射信号功率改善误差估计的精度,验证了算法的有效性。仿真分析结果表明该算法在卫星通信系统中有一定的工程应用价值。     

Electronic Search Beam Stabilization

Compensating for ship's motion (roll and pitch) is a problem fundamental to shipboard radars. The more traditional aproach has been to mechanically stabilize the antenna structure. The alternative approach of stabilizing only the antenna beam is far from being new conceptually, but is more realizable with today's technology. The basic elements are a planar array with an elevation scan capability that rotates continuously in azimuth combined with a high speed digital processor. Electronic stabilization of such an antenna is inherently more challenging than that of a two-axis phase-scanned array. An algorithm is derived for surveillance beam positioning as the antenna rotates. The implementation of this algorithm provides hemispheric search beam stabilization.     

Constrained Least-Squares Synthesis of Coefficients for Arrays of Sensors and FIR Digital Filters

A general method is presented for synthesizing weighting coefficients for arrays of sensors or for finite-impulse-response (FIR) digital filters. The beam pattern of the array or the frequency response of the digital filter is a weighted, least mean-square (LMS) approximation to a desired function, subject to constrained pattern values at specified points. The method is applied to the problem of producing beam patterns of a line array for the rejection of interfering point sources. For this case, we show that adaptive array processing can be based on modification of the roots of the array polynomial.     

Adaptive digital beamforming for angle estimation in jamming

A radar digital beamforming (DBF) architecture and processing algorithm is described for nulling the signal from a mainlobe electronic jammer and multiple sidelobe electronic jammers while maintaining monopulse angle estimation accuracy on the target. The architecture consists of a sidelobe jamming (SLJ) cancelling adaptive array (AA) followed by a mainlobe jamming (MLJ) canceller. A mainlobe maintenance (MLM) technique or constrained adaptation during the sidelobe cancellation process is imposed so that the results of the SLJ cancellation process do not distort the subsequent mainlobe cancellation process. The SLJ signals and the MLJ signals are thus cancelled sequentially in separate processes. This technique was developed for improving radar processing in determining the angular location of a target, and specifically for improving the monopulse technique by maintaining the accuracy of the target echo monopulse ratio in the presence of electronic jamming by adaptive suppression of the jamming signals before forming the monopulse sum and difference beams     

机载共形阵天线阵列信号处理的关键技术分析

机载共形阵是机载有源相控阵天线发展的下一个目标。共形阵天线的阵元具有不同的方向性,空间分辨率算法必须考虑来波的极化问题。本文研究了空间信号波达方向(Direction of Arrival,DOA)估计算法的现状,分析了一种适用于共形阵天线空域自适应波束形成的高速滤波算法。     

Optimal Digital Beam Splitting for Radar Beacon Systems

Beam splitting for a radar beacon system that scans in azimuth is investigated from a theoretical viewpoint. The video output is quantized into two levels corresponding to a detection and no detection. Further, the antenna sensitivity profile is described by sin ?/?. For this system, a digital method of beam splitting that minimizes angular error is developed. Prior information about the probable location of targets can be included. Both Bayesian and minimax approaches are developed. The minimax estimate of the target azimuth is the average of the angles at which beacon signals are detected. The antenna beam can be interpolated by a factor of 10 when the signal power is 3 dB above the noise and without prior azimuth information The interaction of beam splitting and detection is discussed.     

Development of a Digital Array Radar (DAR)

Twenty-first century littoral and open-sea missions present US Navy (USN) shipboard-radar systems with the challenge of detecting small targets in severe clutter and against multiple sources of interference. In Fiscal Year 2000 (FY00), the Office of Naval Research (ONR) sponsored a program to develop an active array radar that includes a digital beamforming (DBF) architecture. The DBF radar system has the potential for improved time-energy management, improved signal-to-clutter (S/C) ratios, improved reliability and reduced life-cycle costs. This paper summarizes the latest developments of the program during FY00     

Adaptive array transient sidelobe levels and remedies

The transient sidelobe level of a sidelobe canceler (SLC) is a function of the external noise environment, the number of adaptive auxiliary antennas, the adaptive algorithm used, auxiliary antenna gain margins, and the number of samples used to calculate the adaptive weights. An analytical result for the adaptive sidelobe level is formulated for the case when the adaptive algorithm is the open-loop, sampled matrix inversion (SMI) algorithm. The result is independent of whether concurrent or nonconcurrent data processing is used in the SMI algorithm's implementation. It is shown that the transient sidelobe level is eigenvalue dependent and increases proportionally to the gain margin of the auxiliary antenna elements with respect to the quiescent main antenna sidelobe level. Techniques that reduce this transient sidelobe level are discussed, and it is theoretically shown that injection independent noise into the auxiliary channels significantly reduces the transient sidelobe level. It is demonstrated that using this same technique reduces the SMI noise power residue settling time     

Proposals for Simplifying Envelope Normalization in Adaptive Antenna Arrays

In adaptive antenna arrays using control loops the processing is determined under certain conditions by the covariance matrix Bmn = E(f(v*m)vn)?n), where ?1,..., ?N are N-complex Gaussian noise video signals and f is some function of the phase of ?m. Half of the storages and real multiplications could be saved by taking only the real part of ?n. It will be shown that this can be done without changing the performance of the adaptive antenna array significantly.     

机载脉冲多普勒雷达DBS技术

 本文从多普勒谱分辨理论出发,分析了DBS成象的基本原理,实现DBS成象的实时信号处理过程,提出了DBS实时数字信号处理方案。通过计算机模拟试验表明,在雷达天线保持匀速扫描状态时,系统的多普勒波束锐化比可达17.4:1左右,并可对载机前方±15°—60°方位范围内提供一幅大面积的,高分辨力的扇形雷达图象。     

STAP for clutter suppression with sum and difference beams

A unique approach for airborne radar clutter rejection is developed and evaluated. This spatial and temporal adaptive approach employs the sum and difference beams of an antenna, which has significant practical advantages because it can be implemented with no/little change to the front-end electronics of airborne systems where sum and difference beams already exist for other reasons. The low sidelobe implementation of many sum and difference beam systems and the low gain of the difference beam in the direction of the target gives this approach the potential in many radars for a more predictable response pattern. The impact of these factors is shown in an airborne clutter rejection demonstration where the performance of this approach is compared with that of the factored approach (FA) using additional spatial channels and that of conventional pulse-Doppler (PD) processing. Reliable detection of an injected target is only achieved by this approach     

Implementing digital terrain data in knowledge-aided space-time adaptive processing

Many practical problems arise when implementing digital terrain data in airborne knowledge-aided (KA) space-time adaptive processing (STAP). This paper addresses these issues and presents solutions with numerical implementations. In particular, using digital land classification data and digital elevation data, techniques are developed for registering these data with radar return signals, correcting for Doppler and spatial misalignments, adjusting for antenna gain, characterizing clutter patches for secondary data selection, and ensuring independent secondary data samples. These techniques are applied to select secondary data for a single-bin post-Doppler STAP algorithm using multi-channel airborne radar measurement (MCARM) program data. Results with the KA approach are compared with those obtained using the standard sliding window method for choosing secondary data. These results illustrate the benefits of using terrain information, a priori data about the radar, and the importance of statistical independence when selecting secondary data for improving STAP performance     

Digitally Controlled Receiver

Digital computers have evolved to an active role as components in communication systems, performing such functions as data processing, executive and adaptive control, management of waveform, and antenna characteristic selection. At one time, the interface between communication equipment and data processing was clear. At present, however, the computer is capable of accomplishing, by using digital techniques, so many classically analog functions that there is basically no interface. The discussion considers the extent to which this trend toward full utilization of digital techniques can and should be extended.     

Effects of mutual coupling on the performance of STAP antennaarrays

The effect of mutual coupling on the performance of space-time adaptive processing (STAP) antenna arrays is investigated. A signal model that includes the effects of mutual coupling is derived and used to compute the optimum solution for the fully adaptive and a variety of partially adaptive algorithms. The simulations indicate that if the mutual coupling is not properly accounted for there is significant degradation of the signal-to-interference-plus-noise ratio (SINR). In addition, the clutter notch is widened resulting in a larger minimum detectable velocity (MDV) of the target. When the mutual coupling is properly accounted for, the performance can be restored to the ideal level. However, STAP algorithms, in general, are very sensitive to errors in the mutual coupling matrix, requiring a very complete knowledge of this matrix for good performance. Of all the algorithms considered here, beam space algorithms appear to be the most robust with respect to uncertainties in the mutual coupling matrix     

空域数据重排的后多普勒自适应处理方法

传统的后多普勒自适应处理方法,如因子法(FA)和扩展因子法(EFA)虽然能大大降低自适应处理时的运算量和独立同分布样本的需求量,但由于实际中均匀训练样本数目的限制,当天线阵元数进一步增大时,FA和EFA抑制杂波和检测动目标的能力会显著恶化。针对这一问题,提出了一种空域数据重排的后多普勒自适应处理方法。该方法将多普勒滤波后的空域数据重排为一行列数相近的矩阵,空域滤波器权系数也表示成可分离的形式,从而得到一双二次代价函数,利用循环迭代的思想求解权系数。实验表明该方法具有快速收敛,所需训练样本少的优点,尤其在大阵列、小样本条件下该方法抑制杂波的性能明显优于FA和EFA。     

卫星导航接收机空间自适应调零抗干扰技术研究

比较了两种自适应调零抗干扰天线系统方案的优缺点,根据实际应用场合,确定抗干扰天线方案设计为中频输出的数字调零系统.对自适应调零的信号处理进行了理论研究,建立了阵列信号的模型,根据导航卫星信号远小于干扰信号等因素,选用了基于线性约束的功率倒置算法,通过调整权值系数使得天线阵的方向图零点对准干扰信号方向,实现干扰零陷.仿真结果表明:通过零陷处理可达到干信比为77dB的抗干扰能力,验证了算法的有效性.     

定向通信系统天线波束指向误差分析

对影响定向通信系统天线波束指向误差的因素进行了分析,给出了一种特殊情形下波束指向误差与姿态角的关系式,同时给出了一般情形下基于最小二乘估计的波束指向误差与姿态角关系的推导方法.给出的关系式和方法对分析定向通信系统波束指向误差提供了理论依据,有助于评估定向通信系统的波束对准情况.