An approach for parameter estimation of combined CPPM and LFM radar signal

In this paper, the problem of parameter estimation of the combined radar signal adopting chaotic pulse position modulation (CPPM) and linear frequency modulation (LFM), which can be widely used in electronic countermeasures, is addressed. An approach is proposed to estimate the initial frequency and chirp rate of the combined signal by exploiting the second-order cyclostationarity of the intra-pulse signal. In addition, under the condition of the equal pulse width, the pulse repetition interval (PRI) of the combined signal is predicted using the low-order Volterra adaptive filter. Simulations demonstrate that the proposed cyclic autocorrelation Hough transform (CHT) algorithm is theoretically tolerant to additive white Gaussian noise. When the value of signal noise to ratio (SNR) is less than 4 dB, it can still estimate the intra-pulse parameters well. When SNR = 3 dB, a good prediction of the PRI sequence can be achieved by the Volterra adaptive filter algorithm, even only 100 training samples.     

Multiple model particle flter track-before-detect for range ambiguous radar

The middle pulse repetition frequency（MPRF）and high pulse repetition frequency（HPRF）modes are widely adopted in airborne pulse Doppler（PD）radar systems,which results in the problem that the range measurement of targets is ambiguous.The existing data processing based range ambiguity resolving methods work well on the condition that the signal-to-noise ratio（SNR）is high enough.In this paper,a multiple model particle flter（MMPF）based track-beforedetect（TBD）method is proposed to address the problem of target detection and tracking with range ambiguous radar in low-SNR environment.By introducing a discrete variable that denotes whether a target is present or not and the discrete pulse interval number（PIN）as components of the target state vector,and modeling the incremental variable of the PIN as a three-state Markov chain,the proposed algorithm converts the problem of range ambiguity resolving into a hybrid state fltering problem.At last,the hybrid fltering problem is implemented by a MMPF-based TBD method in the Bayesian framework.Simulation results demonstrate that the proposed Bayesian approach can estimate target state as well as the PIN simultaneously,and succeeds in detecting and tracking weak targets with the range ambiguous radar.Simulation results also show that the performance of the proposed method is superior to that of the multiple hypothesis（MH）method in low-SNR environment.     

基于北斗/GNSS精密时频量值传递综述

介绍了北斗/GNSS精密时间频率量值传递技术及其应用研究进展,通过对北斗共视比对技术的研究,设计出利用北斗共视与国家授时中心GNSS CV精密时间服务系统进行比对,从而实现用户与标准时间UTC的溯源完成基于GNSS CV技术的时间频率计量服务系统设计,创新性地提出提高北斗共视比对技术以及研制多模多频GNSS CV量值传递设备的研究方向。     

原子钟长期特性测量系统的设计与实现

通过在对各种时频测量硬件的搭建,建立一套多台被测原子钟同时与本地频率标准钟比对的测量系统。该系统以数据库服务做为最底层的数据支持,能够实时的监控测量数据,显示当前被测原子钟的频率准确度,并能够在获得了足够的数据之后,计算和显示被测原子钟的日稳和漂移数据和曲线,方便时频计量人员操作,提高了送检原子钟的计量检定效率。     

基于运动参数估计的高超声速目标检测方法研究

在分析高超声速目标运动对雷达检测影响的基础上,采用参数估计补偿方法进行目标检测。该方法消除了距离走动及多普勒走动的影响,大大提高了高超声速目标的检测性能。在参数估计时,提出一种回波信号分段参数估计方法,分别对前后两段回波信号进行无模糊多普勒频率估计,然后利用两个不同多普勒频率进行多普勒调频率计算。该方法消除了多普勒模糊现象,避免了模糊因子的估计,减少了计算量,同时降低了对输入信噪比的要求。     

一种正交跳频信号动态分选方法

针对复杂电磁环境下正交跳频信号分选时效不高问题,提出了一种正交跳频信号动态分选方法。首先基于滑动窗口的数据流模型,采用构造型神经网络对跳频信号频域数据和方位信息动态聚类,减轻噪声等因素影响,解决方位信息和幅度关联模糊性的问题;再在相应的覆盖簇内运用时频关联方法,实现正交跳频信号的动态分选,实验结果表明该方法是有效的。
     

Study of complex dielectric properties of lunar simulants and comparison with Apollo samples at microwave frequencies

Laboratory characterization of dielectric properties of terrestrial analogues of lunar soil (JSC-1A) and comparison with lunar samples returned from various Apollo missions is made at different as well as normalized bulk density. Here measurements of dielectric constants and losses were made at four microwave frequencies such as 1.7 GHz, 2.5 GHz, 6.6 GHz and 31.6 GHz. Complex permittivity of lunar simulant was measured at temperature ranging from −190 °C to + 200 °C using Wave-Guide cell method. Comparison of permittivity of JSC-1A with Apollo sample also has been done at similar microwave frequencies. The investigations reveal that dielectric constant and loss factor of terrestrial analogues of lunar soil are temperature dependent. As temperature is gradually increased both these parameter (storage factor and loss factor) also gradually increases. These temperatures were chosen because the Moon undergoes at that extremes level of temperature. It is scorching heat at 110 °C during the day and freezing cold at −180 °C during night. The measured value of ε can be useful for designing passive as well as active sensors.     

基于数字信号特征提取的测频方法研究

传统的幂次谱特征能简便有效地提取信号特征并测量参数,但在样本数较少、信噪比较低的情况下,特征就变得不明显了。利用最佳采样点再进行幂次的非线性运算,能够完成特征提取及载频的精确测量。经仿真实验和实际工程验证,在信噪比不大于10dB、样本数不大于1000个符号时,该方法切实、有效。     

基于流动显示的翼尖涡不稳定频率测量

翼尖涡涡核振荡频率的准确测量是翼尖涡控制技术得以有效实施的重要前提。采用流动显示方法,研究了椭圆机翼翼尖涡在低雷诺数条件下的不稳定特性。分别采用单点谱分析和动力学模态分解技术,从流动显示图像序列中提取了涡核振荡的短波不稳定模态的频率,2种方法得到的频率相对误差最大不超过5%。研究结果表明:涡对的空间运动通常展现出长波与短波模态的耦合,涡核的高频短波振荡耦合在低频长波摆动中,以前者为主要含能模态;短波不稳定性的无量纲振荡频率随雷诺数的增大而增大、随机翼攻角的增大而减小。      

基于拉格朗日拟序结构的局部激励流动分离控制有效性分析方法

从流体输运角度提出了用于局部周期激励流动分离控制有效性研究的数值分析方法。基于有限时间不变流形理论建立用于非定常流动的流体输运分析方法,并采用数值方法从非定常流场中提取得到吸引拉格朗日拟序结构（LCSs）和排斥LCSs描述流体输运行为。通过对局部周期激励的流动分离控制规律的研究,结果表明存在三种与激励频率相关的影响翼型气动特性的流体输运模式,其中在锁频激励下吸引LCSs在前缘形成的尖楔结构有效增强主流与分离区流体的物质交换,减小翼面流动分离区的面积,显著提高翼型升力。