参考阵元可自适应调整的阵列天线抗干扰方法

针对导航接收机抗干扰阵列天线在某些干扰来向存在抗干扰效果减弱的问题,建立了基于功率倒置算法的阵列信号处理模型,提出一种参考阵元可自适应调整的阵列天线抗干扰方法.以四阵元均匀圆阵为例进行了仿真验证,仿真结果表明,相比于参考阵元固定的功率倒置算法,此方法能够很好地解决部分干扰来向抗干扰效果减弱的问题.     

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.     

等离子体对GPS信号载噪比的影响

飞行器再入过程产生等离子体,等离子体中电子密度的变化对电磁波信号造成幅度衰减和相位偏移,严重时导致通信中断。理论分析了等离子体对GPS信号载噪比的影响;利用实验室环境下的等离子体模拟装置,设计了GPS二键相控(BPSK)调制信号透过等离子体的地面模拟方案,进行了等离子体对GPS接收机性能影响的实验研究,获得了不同电子密度下的衰减和导航信号载噪比的数据。实验结果与理论分析一致,不仅证明了等离子体下衰减与导航信号载噪比的变化是一致的结论,而且验证了实验方法的有效性。     

弹载天线旋转对接收信号多普勒偏差的影响

由弹体自旋产生的弹载天线的旋转是引起地面测控站多普勒测速误差的一个重要因素.根据线极化信号接收原理,对弹载天线旋转条件下接收的左旋和右旋信号多普勒偏差进行了理论推导和分析.分析结果表明：左/右旋接收信号将产生幅度相等、极性相反的多普勒偏差,多普勒偏差的均值与弹载天线旋转速率在数值上相等,多普勒偏差的方差随着目标视线与天线转轴之间夹角的增大而增大.为验证理论分析结果,开展了天线转台模拟实验,实验测量得到的多普勒偏差的均值和方差与理论分析结果基本一致.最后,根据理论分析和模拟实验结果,提出在实际任务中,可采用左旋和右旋多普勒偏差均值差的一半分别对左/右旋信号的多普勒进行补偿,以减小弹载天线旋转对测速精度的影响.     

高灵敏GPS接收机抗干扰特性研究

采用圆环阵列天线,利用最小规范算法和线性约束最小方差算法对弱GPS信号的干扰信号进行了抑制,并分别针对固定和可变天线阵元数目以及固定和可变干扰信号等多种情况进行了仿真和分析.GPS信号的功率电平假设为-175dBW,干扰信号的功率值在-100dBW～-140dBW范围内可变.仿真结果表明,圆环天线阵列能精确地判定干扰信号的来波方向,该方法能很好地改善对来波干扰信号的赋零深度.     

未知互耦条件下混合信号波达方向估计

阵列天线互耦对导向矢量的扰动以及信号相干性对数据协方差矩阵造成的秩损,使得基于子空间正交性原理的超分辨波达方向估计(Direction-of-Arrival,DOA)算法性能恶化,甚至失效。针对这一问题,提出一种在相干与非相干信号混合状态下无需阵列互耦补偿的特征矢量平滑DOA估计算法。该算法对部分阵元接收数据的协方差矩阵特征分解,将得到的特征矢量平滑处理后构造等效协方差矩阵,抑制阵列互耦影响的同时完成混合信号DOA估计。在阵列互耦和信号相干性均未知的条件下,正确估计了信号DOA,无需互耦参数估计或补偿。计算机仿真结果验证了算法的有效性。     

基于载噪比同步变化的北斗欺骗检测方法

欺骗干扰已经成为北斗卫星导航系统安全性的一个严重威胁。针对北斗系统面临的欺骗干扰问题,建立二元假设检验模型。由于施加单一天线发射的欺骗干扰后,当前观测频点下各高俯仰角可见星的载噪比值会产生相同的变化趋势,所以基于此变化规律提出了一种利用K-means聚类算法进行分析的北斗卫星信号欺骗干扰检测方法,并给出了施加欺骗载噪比变化域的定义。最后通过在外场搭建实验环境,对实采数据进行了实验验证。实验结果表明,本方法对于欺骗功率优势≥6 dBm的大功率优势欺骗信号的检测概率可以达到95%以上,为提高接收机抗干扰能力提供了有益参考。     

MIMO雷达DOA估计阵列设计

 多输入多输出（MIMO）雷达的关键技术之一是天线阵列的设计。由于MIMO雷达同时增加了收发两端的相位中心,使得系统具有更高的空间分辨率和更多的自由度。论文从接收信号模型出发,对MIMO雷达发射正交信号的等效阵列进行了讨论,以波达方向估计为目标提出了一种MIMO雷达天线阵的设计方法,通过抛物线理论得出了收发组合的唯一性和合理性,然后通过分析各种收发组合给出了发射阵元的最佳间隔设置。推导了几种情景下的MIMO收发阵列最佳设计解析解,最后进行了仿真实验。仿真结果验证了算法的有效性。     

嵌套阵列最大似然估计测向算法

针对在辐射源个数未知的条件下嵌套阵列难以估计多个辐射源角度的问题,提出了基于最大似然估计(MLE)的嵌套阵列角度估计算法。算法在嵌套阵列模型的基础上,首先通过推导阵列截获多辐射源信号的最大似然函数及其梯度,利用最速下降法估计出空域中所有潜在辐射源的角度;然后,通过多元假设检验,利用最大似然比与门限进行比较,确定出空域中所有潜在辐射源中某一时刻发射信号的活跃辐射源角度,排除其余噪声形成的虚假辐射源角度,解决了在辐射源个数未知条件下嵌套阵列对多个辐射源角度估计问题。仿真结果表明:与传统多重信号分类(MUSIC)算法相比,该算法在辐射源数目未知、存在相干信号、低信噪比(SNR)、低快拍数条件下,均具有较好的角度估计精度,并且算法形成的虚拟阵列自由度是空间平滑MUSIC算法的2倍;多元假设检验法比传统信源数目估计算法在低信噪比条件下和处理相干信号方面具有明显优势。     

存在阵列模型误差情况下的宽带DOA估计

 针对工程应用中存在阵列模型误差的任意形状天线阵列的宽带波达方向（DOA）估计问题,提出一种基于信号分离的相关域宽带松弛（RELAX）算法。此算法利用具有记忆与遗忘特征的矩阵算子的投影机理对入射信号进行有效的分离,因此对一定范围内的阵列模型误差较之基于子空间理论的传统宽带测向算法具有较好的鲁棒性与良好的工程应用前景。分析并证明了此算法的信号分离机理及此算法对阵列模型误差稳健的原理。理论分析与仿真结果均表明存在阵列模型误差时此算法宽带DOA估计的有效性和稳健性。     

Results from a Four-Element Adaptive Antenna Experiment

Experimental results from a four-element, linear, half-wavelength spacing, adaptive-array antenna under the control of the least mean square (LMS) algorithm are presented. The array is found to be capable of nulling a 70-MHz signal to -35 dB below a desired signal over a 5-MHz bandwidth. The antenna processing gain is constant over a desired signal-to-jammer signal power ratio range from -20 dB to 5 dB. A sharp reduction in processing gain is observed for angular separations between jammer and desired signal of less than 10°. Antenna patterns taken with weights set in 300 iterations of the LMS algorithm show that the one strong, one weak jammer combination has a longer weight convergence time and reduced processing gain compared with a two strong jammers combination. Contours of constant desired signal-to-jammer signal power ratio, after adaptive antenna processing, reveal a complex shape for communication between air and ground due to the finite angular resolution of the adaptive antenna.     

Effects of finite weight resolution and calibration errors on theperformance of adaptive array antennas

Adaptive antennas are now used to increase the spectral efficiency in mobile telecommunication systems. A model of the received carrier-to-interference plus noise ratio (CINR) in the adaptive antenna beamformer output is derived, assuming that the weighting units are implemented in hardware, The finite resolution of weights and calibration is shown to reduce the CINR. When hardware weights are used, the phase or amplitude step size in the weights can be so large that it affects the maximum achievable CINR. It is shown how these errors makes the interfering signals “leak” through the beamformer and we show how the output CINR is dependent on power of the input signals. The derived model is extended to include the limited dynamic range of the receivers, by using a simulation model. The theoretical and simulated results are compared with measurements on an adaptive array antenna testbed receiver, designed for the GSM-1800 system. The theoretical model was used to find the performance limiting part in the testbed as the 1 dB resolution in the weight magnitude. Furthermore, the derived models are used in illustrative examples and can be used for system designers to balance the phase and magnitude resolution and the calibration requirements of future adaptive array antennas     

基于改进补零/差分的北斗弱信号捕获算法

北斗信号二次编码调制了速率为1kbps的NH码,频繁的比特跳变导致传统捕获算法的效果受到抑制,并且限制了积分时间的增长。为了实现北斗弱信号的捕获,提出了一种适合北斗弱信号的捕获算法,将补零算法和差分相干积分算法相结合并进行了优化设计。对补零算法和差分相干积分算法进行了改进,将差分延迟时间调整为20ms,有效消除了NH码的影响,并增加了积分时间,提高了信噪比。采用Monte Carlo仿真测试了在载噪比为20dBHz~38dBHz的条件下,此算法与传统算法的检测性能。结果表明,相比传统算法,此算法的捕获灵敏度提高了约10dB。此算法能够有效消除北斗NH码相位变化对信号捕获的影响,并提高信噪比,适用于弱信号条件下的北斗信号捕获。     

An anticipative adaptive array for frequency-hopping communications

To fully utilize the theoretical processing gain achievable when an adaptive array and frequency hopping are combined, frequency compensation is required. Improved versions of an anticipative adaptive array are examined that provide efficient compensation by adapting the complex weights at each antenna element to the appropriate values for a carrier frequency before that frequency is received. The underlying adaptive algorithm used is the maximum algorithm. Computer simulation results are used to compare the different versions of anticipative processing. These results show that an appropriate version ensures the rapid convergence of weights to values that provide wideband nulling of the interference and noise     

Comparison of strapdown inertial navigation algorithm based on rotation vector and dual quaternion

 For the navigation algorithm of the strapdown inertial navigation system, by comparing to the equations of the dual quaternion and quaternion, the superiority of the attitude algorithm based on dual quaternion over the ones based on rotation vector in accuracy is analyzed in the case of the rotation of navigation frame. By comparing the update algorithm of the gravitational velocity in dual quaternion solution with the compensation algorithm of the harmful acceleration in traditional velocity solution, the accuracy advantage of the gravitational velocity based on dual quaternion is addressed. In view of the idea of the attitude and velocity algorithm based on dual quaternion, an improved navigation algorithm is proposed, which is as much as the rotation vector algorithm in computational complexity. According to this method, the attitude quaternion does not require compensating as the navigation frame rotates. In order to verify the correctness of the theoretical analysis, simulations are carried out utilizing the software, and the simulation results show that the accuracy of the improved algorithm is approximately equal to the dual quaternion algorithm.     

利用旋转双天线载波相位双差的欺骗干扰检测技术

有效的欺骗干扰检测是防止卫星导航接收机被欺骗干扰攻击的前提。提出了一种基于旋转双天线载波相位双差的卫星导航接收机欺骗干扰检测技术，在对接收机双天线匀速旋转时输出载波相位测量值进行载波相位双差处理后，利用广义似然比检验实现了对单一发射天线输出欺骗干扰信号的检测。进一步分析了旋转半径和数据长度对检测性能的影响，并与旋转单天线和天线阵载波相位双差欺骗干扰检测方法的性能进行了对比。最后，通过蒙特卡罗方法进行了仿真验证，结果表明了该检测方法和检测性能分析的正确性。     

Convergence Rate of the Extended SMI Algorithm for Narrowband Adaptive Arrays

An extended sample matrix inversion (SMI) algorithm can be used for minimizing the mse (mean-squared error) between the output of an N-element adaptive array and a desired reference signal. This algorithm is shown to yield mse within 3 dB of minimum (on the average) after (2N - 1) observations of the antenna element outputs.     

Ka波段高增益圆极化机载微带天线阵的设计与实现

设计、分析、制作了一种工作在Ka波段的4单元高增益、圆极化机载微带天线阵列。利用顺序旋转阵列和串并馈方式的微带线网络馈电,显著改善了天线的轴比带宽和驻波带宽,减少了馈线损耗,实现了高增益。采用L型微带调配枝节对贴片单元进行匹配,便于组阵,解决了阵列空间布局不合理的难题;馈电网络和天线单元集成在同一介质基板上,易于加工和制作。测试结果表明:该天线阵具有高增益和良好的圆极化特性,从而证实了该方法的正确性和实用性。本文所设计的天线由于具有体积小、质量轻、结构紧凑、易于集成等优点,在机载相控阵雷达以及卫星通信系统中具有很好的应用前景。