海岸监视高频表面波雷达系统中应用水平振子天线自适应抑制天波干扰

介绍了在高频表面波雷达（ＨＦＳＷＲ）中，采用水平振子天线抑制天波干扰的自适应系统的初步研究结果。四个水平振子，两两正交排列，附加到通常采用垂直极化天线（ＶＰＡ）的ＨＦＳＷＲ系统中。从振子接收的数据与从ＶＰＡ接收的数据相关，以便ＶＰＡ自适应地估算和对消掉干扰。研究结果表明，该项技术对抗所研究的干扰效果很好。干扰加噪声功率我达１３ｄＢ，而Ｂｒａｇｇ对干扰加噪声之比升高多达２１ｄＢ。本文对使用１个、２个     

天波超视距雷达中瞬态干扰定位方法研究

为了对抗天波超视距雷达中的瞬态干扰,现有时域算法一般有干扰定位、干扰剔除与数据恢复3个步骤,其中干扰定位的精度直接决定了后续处理的性能。目前工程中应用的固定门限方法定位精度不够,而现有文献中提出的方法运算量较大,且对参数的选择较为敏感。针对这一问题,该文提出一种迭代剔除平均检测器。此检测器将判决为干扰的样本点剔除出迭代平均的过程,并采用前-后向检测的定位方法,保证了背景估计与干扰定位的可靠性。天波超视距雷达的实测数据处理结果证明了所提方法的有效性。     

基于矩阵补全的天波雷达瞬态干扰抑制算法

瞬态干扰持续时间短、强度大,严重影响天波超视距雷达的性能。传统的瞬态干扰抑制方法需要预先抑制海杂波,且只能抑制强瞬态干扰,不能抑制弱瞬态干扰和噪声,该文提出一种基于矩阵补全的瞬态干扰抑制算法,该方法首先利用Teager-Kaiser算子进行瞬态干扰检测,然后将干扰数据剔除,最后利用海杂波和目标回波构成的Hankel矩阵的低秩性,通过改进的低秩矩阵补全算法进行数据恢复。该算法不仅能够抑制强瞬态干扰,而且能同时抑制弱瞬态干扰和噪声,提高了回波信号的信噪比。实测和仿真数据处理结果证明了算法的有效性。     

一种稀疏重建的天波雷达射频干扰抑制算法

天波雷达工作频段通常有大量的射频干扰,严重影响了雷达探测.目前最有效的射频干扰抑制方法主要是基于相似约束的方法,其本质是在匹配滤波器上叠加一个抑制射频干扰的窄带滤波器.基于窄带滤波器稀疏特性,提出了一种稀疏约束的射频干扰抑制方法,对窄带滤波器施加稀疏性约束并加大对稀疏项的惩罚,在保证匹配滤波器效果的同时更加有效抑制干扰.该方法首先将滤波器分解为匹配滤波滤波器和窄带滤波器,然后对窄带滤波器施加稀疏约束,基于此构建一个稀疏约束的非凸优化问题.最后,提出一种低计算复杂度的交替性自适应迭代算法求解该非凸优化问题.仿真和实测数据处理结果表明,所提方法的输出信干噪比较相似约束算法提高了1 dB以上,有效地提高了射频干扰抑制性能.     

一种天波雷达瞬态干扰抑制方法

瞬态干扰是天波超视距雷达中一类常见的干扰,会降低雷达目标的可检测性,需要加以抑制。文中分析了雷达接收回波的多普勒频率稀疏性,建立了由潜在回波信号构成的过完备字典,使得雷达接收回波在该字典下有稀疏表示形式,同时提出了基于压缩感知的天波雷达瞬态干扰抑制方法。该方法利用压缩感知重构雷达接收回波,由其代替瞬态干扰位置上的原始信号,从而实现瞬态干扰抑制。实测数据处理证明了该文方法的有效性。     

天波雷达欠密度流星余迹干扰抑制算法

针对欠密度流星余迹干扰影响天波超视距雷达目标检测的问题,提出了基于总体最小二乘旋转不变估计信号参数(Total Least Squares-Estimating Signal Parameter via Rotational Invariance Techniques TLS-ESPRIT)的欠密度流星余迹干扰抑制算法.首先应用复数据经验模式分解估算流星余迹干扰的位置,并将该位置的回波数据组成Hankel矩阵,然后采用TLS-ESPRIT方法求解Hankel矩阵,解得流星余迹干扰的时域回波,最后从回波数据中去除流星余迹干扰的时域回波,得到流星余迹干扰抑制后的回波数据.与现有流星余迹抑制算法相比,该方法减少了流星余迹干扰的残余和提高了目标的信杂比(SCNR).     

天波超视距雷达中流星余迹干扰模型

已获得的实测数据表明,天波超视距雷达在3MHz-30MHz的工作频段内存在明显的流星余迹干扰.流星余迹干扰会对天波超视距雷达探测目标的距离和多普勒信息造成负面影响,严重时会影响到天波超视距雷达的正常工作.根据流星余迹的散射特性,结合天波超视距雷达的工作方式,建立了流星余迹干扰模型,为在天波超视距雷达中研究抑制流星余迹干扰技术提供了帮助.仿真结果与实测数据基本一致,验证了模型的有效性.     

基于压缩感知的天波雷达瞬态干扰抑制

瞬态干扰是天波超视距雷达中一种常见的干扰,经常抬高雷达的距离-多普勒二维检测背景,造成目标检测困难,因此需要加以抑制。提出了基于压缩感知的天波雷达瞬态干扰抑制方法。该方法首先确定瞬态干扰的位置,然后利用压缩感知来重构该位置上的杂波和目标信号,从而实现瞬态干扰抑制。为了避免瞬态干扰对信号重构的影响,从单位矩阵中抽取若干行构成压缩感知的观测矩阵。实测数据处理表明,该方法可以有效地抑制瞬态干扰,显著改善雷达的探测性能。     

天波超视距雷达瞬态干扰抑制

天波超视距雷达(OTHR)电波通过电离层折射作下视探测,具有观察距离远,观察范围广的特点.但由于采用HF频段,且电波传播环境复杂,不仅海(地)杂波强,而且有很强的干扰,如电台干扰、工业干扰、冲击噪声、闪电冲击和流星余迹回波等.干扰分长时间干扰和瞬态干扰,瞬态干扰持续时间短、强度大.本文首先讨论OTHR接收到的瞬态干扰的特点;然后讨论了瞬态干扰的滤除方法,即采用特征分解方法滤除海杂波,或在频域直接滤除地杂波,检测出瞬态干扰的位置后,在原始信号中挖除存在瞬态干扰的回波点,并用预测内插的方法,消除瞬态干扰谱对目标掩盖作用,使目标特别是舰船目标能被检测出来;最后通过实测数据的检验.     

短波天波干扰研究

本文首先介绍了利用电离层反射方式进行通信的频率选择问题，然后分析了利用该信道进行远距离干扰的可行性，并地对典型目标计算了所需的干扰功率，最后分析了天波信道可能对干扰效果带来的影响及解决办法。     

利用辅助水平天线对Es层干扰的自适应抑制

基于一个高频双极化雷达系统,给出了一种利用辅助水平天线抑制Es层干扰的自适应系统.水平极化天线接收的数据与垂直极化天线接收的数据进行相关,自适应的估计出垂直天线接收中的干扰,然后对消掉它们.干扰对消在每个相参积累周期后进行.实际数据对消后的信噪比可以提高到25dB.     

Study of compressed log-periodic dipole antennas

The behavior of log-periodic dipole (LPD) antennas, which are compressed along the transmission-line axis, is studied both experimentally and theoretically. Compressed LPD antennas are found to be efficient, of low gain, and frequency independent. With compression, the radiation pattern approaches dipole-like behavior and the bandwidth increases slightly. It is also found that LPD antennas exhibit anomalous frequency-dependent behavior in narrow bands of frequencies (approx 1/8of a log period in width) when a reactive termination is used and when the scaling factortauis below about 0.92-0.93.     

天波超视距雷达海洋回波谱特性研究

根据高频电磁波与海面相互作用产生Bragg谐振散射的特性,首先对一阶和二阶海杂波的产生机理进行了理论分析,然后结合Barrick提出的一阶、二阶散射理论对海洋回波谱进行了模拟。最后详细地研究了洋流、海态、雷达工作参数、电离层等因素对海洋回波谱的影响,并在天波超视距雷达体制下,建立了其海洋回波谱多普勒频率模型,为全面研究海杂波及天波超视距雷达目标检测提供了理论依据。     

Accurate modelling of anti-resonant dipole antennas using themethod of moments

The authors demonstrate that the difficulties encountered when modelling anti-resonant antennas are primarily due to the conventional variable gap source model which is commonly employed in thin-wire moment method codes. An alternative source model is introduced, for use in analysing this class of antennas, where the essential feature is that the gap width of the feed region remains fixed. The fixed gap model is compared to the variable gap model for both a half-wave dipole, where the variable gap is still a valid source model, and for a full-wave anti-resonant dipole, where the fixed gap source is shown to be superior to the variable gap model     

对数周期偶极天线扇形阵的分析

采用矩量法对对数周期偶极天线扇形阵进行理论分析,在计算广义阻抗矩阵元素时,利用矩阵的互易性、天线阵的结构对称性和对数周期天线的工作原理进行了算法简化,从而在保证计算精度的前提下,大大提高了计算速度。     

Analysis of transient responses between coupled dipole antennas by using a simple equivalent circuit

Transient responses between two dipole antennas were analyzed by using a simple equivalent circuit of a dipole antenna. This equivalent circuit is composed of a lossless transmission line and two shunt resistances representing electrical discontinuities at a feed point and tips of the dipole antenna. A closed-form formula for the induced load voltage in the time domain was derived. Since the damping factor due to radiation from antennas is included in this expression, this formulation gives better results than those given by the conventional transmission-line approximation. Measured time histories support the validity of theoretical results.     

Experimental verification of the reduction of coupling between dipole antennas by using a woodpile substrate

In this paper, the mutual coupling between dipole antennas placed on top of a woodpile structure is experimentally investigated. The coupling between dipoles backed by a woodpile substrate is compared with that obtained when the dipole antennas are placed on a dielectric substrate and when they radiate into free space. On average, between 2 and 7 dB reduction of the mutual coupling is achieved with respect to the dielectric substrate case when the woodpile substrate is used. The free space coupling is also reduced in the H-plane configuration case. However, the E-plane coupling slightly increases due to modification of the radiation pattern. Imaging array applications could potentially benefit from the use of EBG substrates due to the improved isolation between pixels.     

On the relationship between fractal dimension and the performance of multi-resonant dipole antennas using Koch curves

This paper relates for the first time, multiple resonant frequencies of fractal element antennas using Koch curves to their fractal dimension. Dipole and monopole antennas based fractal Koch curves studied so far have generally been limited to certain standard configurations of the geometry. It is possible to generalize the geometry by changing its indentation angle, to vary its fractal similarity dimension. This variation results in self-similar geometry which can be generated by a recursive algorithm. Such a variation is found to have a direct influence on the input characteristics of dipole antennas. The primary resonant frequency, the input resistance at this resonance, and the ratio of first two resonant frequencies, have all been directly related to the fractal dimension. Curve-fit expressions can also be obtained for the performance of antennas at their primary resonance, in terms of fractal iteration and fractal dimension. The antenna characteristics have been studied using extensive numerical simulations and are experimentally verified. These findings underscore the significance of fractal dimension as an important mathematical property of fractals that can be used as a design parameter for antennas. The use of these ideas would not only reduce the computational intensity of optimization approaches for design of fractal shaped antennas, but also help antenna designers approach the problem systematically. Design formulation for antennas based on other fractal geometries can be similarly obtained after identifying suitable parameters of variation. This would therefore help analytical design of multiband and multifunctional antennas using fractal geometries.     

利用互模糊函数实现卫星干扰源定位

介绍了双星体制卫星干扰源定位系统工作的原理,对利用信号互模糊函数(CAF-Cross Ambiguity Function)定位参数估计进行了研究,分析了参数估计的时频特性和参数的时变性对估计方法的影响,提出了提高CAF参数估计性能的优化处理方法.通过对实际转发信号的参数估计和定位实验,证实了优化的CAF参数估计和定位方法的有效性.     

一种有效的宽带宽角相控阵接收干扰置零新方法

采用拉伸处理可以在目标方向形成接收主瓣,并能降低宽带宽角相控阵雷达接收信号的带宽,易于工程实现.为了在干扰信号功率远大于目标回波信号功率时获得较大的输出信干比,提出了一种宽带干扰置零新方法.在干扰离目标的空间角度间隔较大时,能在干扰方向准确形成零陷,新方法窄带权系数的零点约束角度会偏离实际干扰方向.偏移方向与信号形式有关,而偏移角度大小与雷达信号相对带宽、干扰离目标的空间角度间隔有关,其值在信号参数给定后可通过离线估计得到.计算机仿真结果验证了新方法的有效性.