照射雷达发射信号特性的测试

现代照射雷达对其发射信号特性(主要为相位噪声、调幅噪声和调制特性等)提出极其严苛的要求。介绍问题提出的背景,概述国外发展情况指标要求,提出几种典型的测试方案,介绍一个实际测试系统研制概况和水平。这种测试技术同样适用于全主动寻的系统雷达导引头信号源特性的测试。     

基于MATLAB间断照射雷达信号仿真技术

针对间断照射雷达信号质量分析过程中没有实际雷达的问题,根据复杂间断照射雷达信号产生原理,提出了用任意波形发生器和微波信号源模拟雷达波形的方法,基于软件无线电技术,给出了用MATLAB软件仿真复杂基带调制信号并导入任意波形发生器的具体实施方案。采用该方案设计的信号模拟方法,产生的信号涵盖调制副载波参数、脉冲同步信号、编码信息等丰富的内容,可以解决实验室环境中复杂间断照射雷达信号的获取问题。经过试验验证,该仿真信号的方案具有通用性好、易于实现等特点,可以为相同体制复杂调制信号的产生提供方法和手段,减少试验成本。     

一种间断照射雷达信号的调制参数测试方法研究

针对间断照射雷达信号调制参数测量问题,提出了基于FSW频谱分析仪和软件无线电技术测量的方法。通过分析间断照射雷达信号的特性,给出间断照射雷达信号调制参数测试方案,解决现场调制参数、编码特性等快速测试问题。     

基于MATLAB间断照射雷达信号仿真技术

针对间断照射雷达信号质量分析过程中没有实际雷达的问题,根据复杂间断照射雷达信号产生原理,提出了用任意波形发生器和微波信号源模拟雷达波形的方法,基于软件无线电技术,给出了用MATLAB软件仿真复杂基带调制信号并导入任意波形发生器的具体实施方案。采用该方案设计的信号模拟方法,产生的信号涵盖调制副载波参数、脉冲同步信号、编码信息等丰富的内容,可以解决实验室环境中复杂间断照射雷达信号的获取问题。经过试验验证,该仿真信号的方案具有通用性好、易于实现等特点,可以为相同体制复杂调制信号的产生提供方法和手段,减少试验成本。     

8mm照射雷达发射信号相位噪声的测试

简述8mm照射雷达发射信号相位噪声的重要性,相位噪声的测试方法,以及影响相位噪声的因素和改善措施,并在克服电磁干扰振动和供电系统方面作了介绍。     

利用MF雷达对耀斑期间电离层D区电子密度的观测研究

利用MF雷达观测资料对X级别耀斑爆发期间在66—80 km高度之间的电子密度进行了研究,观测到了耀斑爆发期间电子密度的突然增加,在较低高度上的电子密度的时间变化趋势与耀斑的软X射线辐射通量相关.电子密度的变化强度依赖于具体的耀斑参数,有些耀斑引起的电子密度增加高达400 cm^-3,有些仅为100 cm^-3左右.但耀斑期间在这一高度区间增加的总电子含量增量仅占耀斑辐射引起的整个电离层总电子含量增量的千分之一左右.最后,利用恢复阶段电子密度的时间变化过程估算了1997年11月4日耀斑期间部分高度上的有效复合系数.     

8mm波段照射雷达及振动状态下调频噪声测试技术

在中主动寻的系统中，照时雷达在挂飞现场的相位噪声的量值和导引头在振动状态下相噪的变化，是影响挂飞成败的关键。介绍的８ｍｍ中功率源及导引头振动状态调频噪声测试系统，提供了可进行上述两种测试的两台测试仪和测试方法。     

基于海南VHF雷达观测的低纬E区场向不规则体研究

利用海南VHF雷达（19.5°N,109.1°E;磁纬8.1°N）在2011年7月15—22日期间的连续观测数据,对东亚低纬3m尺度电离层场向不规则体（FAI）特性进行了分析. 主要结果表明,在整个观测期间,E区场向不规则体几乎每天发生,既可发生于夜间,也可发生于白天,且存在各种不同结构. 根据E区场向不规则体发生的时间及形态,可将其分为三种结构类型：低部连续型结构、上部下降型结构以及白天连续型结构. 这些低纬E区场向不规则体的回波谱特性与赤道电集流（EEJ）和中纬区E区场向不规则体中的2型回波相类似,但其随时间的变化与后两者存在明显差异,且与其他低纬区E区场向不规则体回波存在不同程度的差异.     

梁结构的高频响应研究

利用NASTRAN软件得到一简支梁从低频到高频的频响特性,研究了不同有限元网格划分 对结构高频特性的影响,并通过统计能量分析(SEA)法、有限元法以及解析解的对比揭示了S EA法在高频响应 预示中的有效性。然后以耦合梁为例,通过有限元法得到两个梁之间的能量传递,并进而得 到SEA所需的耦合损耗因子;将有限元计算结果和SEA结果对比验证了该方法的有效性,以期 建立一种用有限元法获得SEA参数的新途径。此外,研究了集中质量和不同边界条件对耦合 结构高频能量传递的影响。     

遗传算法在高频区目标二维散射分析中的应用

针对高频区雷达目标的散射特征问题,提出利用联合时频分析--自适应高斯基表示方法(AGR)来简化目前的二维散射中心模型,并将遗传算法(GA)用于二维散射模型参量的估计.该方法充分利用遗传算法的内在并行性,解决了二维等效散射中心的估计问题.仿真结果表明,该简化的二维模型不仅可以区分局域性散射中心,也可以再现具有一定长度的展布式散射结构,利用该简化模型在无噪情况下可以准确估计各散射中心的参数,同时在低信噪比情况下也可以取得很好的估计性能,它对于去除背景噪声起到了很好的作用.通过验证,在简化的散射模型基础上的目标散射特征分析是准确和可行的.     

Analysis of post-sunset F-region vertical plasma drifts during Counter Electrojet days using multi frequency HF Doppler Radar

In this paper, through a case study, an attempt has been made to bring out the relationship between post noon E-region electric field and post sunset F-region vertical plasma drift on quiet time Counter Electrojet (CEJ) days. Study carried out using the data from a multi frequency HF Doppler Radar and Digital Ionosonde located over Trivandrum (8.5° N; 77° E; 0.5° N dip lat.) a geomagnetic dip equatorial station in India during quite time CEJ days of the years 2004 and 2006, revealed some interesting aspects of the E region electrodynamics and post sunset F region electrodynamics. It has been observed that, in contrast to the normal electrojet (EEJ) days, the Pre-Reversal Enhancement (PRE) is either weakened or inhibited on CEJ days and the field reversal takes place much earlier than that on a normal day. It is suggested that even after the effects of the field reversal ceases to show up in the ground magnetic data, the reversed field may persist and shows up as a decrease in the PRE experienced by the F-region. In other words, the study indicates that the EEJ associated electrodynamics have a significant role in controlling the PRE.     

A new inversion algorithm for HF sky-wave backscatter ionograms

HF sky-wave backscatter sounding system is capable of measuring the large-scale, two-dimensional (2-D) distributions of ionospheric electron density. The leading edge (LE) of a backscatter ionogram (BSI) is widely used for ionospheric inversion since it is hardly affected by any factors other than ionospheric electron density. Traditional BSI inversion methods have failed to distinguish LEs associated with different ionospheric layers, and simply utilize the minimum group path of each operating frequency, which generally corresponds to the LE associated with the F₂ layer. Consequently, while the inversion results can provide accurate profiles of the F region below the F₂ peak, the diagnostics may not be so effective for other ionospheric layers. In order to resolve this issue, we present a new BSI inversion method using LEs associated with different layers, which can further improve the accuracy of electron density distribution, especially the profile of the ionospheric layers below the F₂ region. The efficiency of the algorithm is evaluated by computing the mean and the standard deviation of the differences between inverted parameter values and true values obtained from both vertical and oblique incidence sounding. Test results clearly manifest that the method we have developed outputs more accurate electron density profiles due to improvements to acquire the profiles of the layers below the F₂ region. Our study can further improve the current BSI inversion methods on the reconstruction of 2-D electron density distribution in a vertical plane aligned with the direction of sounding.     

A global HF telecommand system for long duration balloon flights

An HF telecommand system for the control of long duration balloon flights at any point on the globe is described. The system proposed consists of a network of low-power transmitters operating at the same carrier frequency. The choice of transmitter frequency, power and location are presented. Control of the transmitters may be performed remotely by means of the public switched telephone network; an assessment of the error-rate in the system as a whole is given.     

高频返回散射回波频谱测量

本文采用脉冲多普勒雷达技术, 测量了电离层高频返回散射回波的时延-功率-多普勒频率的三维频谱图.对典型的频谱图作了分析, 并由谱图推算了电离层等效反射面的垂直运动速度, 它与垂直探测资料推算的结果相符.     

Impact of heliogeophysical disturbances on ionospheric HF channels

The article presents the results of the observation of a strong magnetic storm and two X-ray flares during the summer solstice in 2015, and their impact on the HF signals characteristics in ionospheric oblique sounding. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, ultimately causing a long blackout on paths adjacent to subauroral latitudes. On mid-latitude paths, the decrease in 1FMOF reached ～50% relative to the average values for the quiet ionosphere. It is shown that the propagation conditions via the sporadic Es layer during the magnetic storm on a subauroral path are substantially better than those for F-mode propagation via the upper ionosphere. The delay of the sharp decrease in 1FMOF during the main phase of the magnetic storm allowed us to determine the propagation velocity of the negative phase disturbances (～100 m/s) from subauroral to mid-latitude ionosphere along two paths: Lovozero – Yoshkar-Ola and Cyprus – Nizhny Novgorod. It is shown that both the LOF and the signal/noise ratio averaged over the frequency band corresponding to the propagation mode via the sporadic Es layer correlate well with the auroral AE index. Using an over-the-horizon chirp radar with a bistatic configuration on the Cyprus – Rostov-on-Don path, we located small-scale scattering irregularities responsible for abnormal signals in the region of the equatorial boundary of the auroral oval.     

基于X波段雷达海浪监测装置的设计与研究

针对舰船对浪高实时测量的需要,提出了基于x波段雷达海浪监测装置的设计方案,具体介绍了基于X波段雷达海浪监测装置的设计原则、功能设计、硬件设计以及基于VC 的软件实现,并给出基于x波段雷达海浪监测装置系统操作平台功能界面的参考实例,从一定程度上为舰船海浪测量装置的实现与应用提供可行性参考。     

Observations of HF propagation on a path aligned along the mid-latitude trough

Observations of the direction of arrival and time of flight of HF signals propagating on a 1400 km path oriented along the mid-latitude trough are presented. At night, the signal commonly arrives from directions offset from the great circle bearing by up to 80° and these events have been categorised into five main types. Statistics indicating how often these categories of propagation were observed in the period August 2006 to September 2007 are presented. The physical mechanisms which result in the off great circle propagation are also discussed.     

Method of the HF wave absorption evaluation based on GIRO network data

High frequency (HF) communication is strongly dependent on the state of the ionosphere, which specifies the mode structure of the radio wave propagating in ionosphere. Another core factor defining the strength of the HF signal at the receiving site is the ionospheric absorption. Accurate modelling the effect of absorption is an essential part of many studies of the HF propagation in the ionosphere.This paper proposes a method for estimating the absorption. The method is based on analysis of vertical sounding ionograms. The main idea of the approach is to compare the main parameters retrieved from measured and simulated ionograms. The combination of Global Ionospheric Radio Observatory (GIRO, http://giro.uml.edu) data and ionograms modelling allows for developing the empiric absorption model available at near real-time. The ionogram simulation taking into account absorption utilizes the NIM-RT (North Ionospheric Model and Ray Tracing) software. As a result, the proposed technique provides more reliable and accurate evaluation of minimum frequency at which echoes are observed in vertical incidence ionosonde soundings. The values of these frequencies should be used in the following simulation to optimize parameters in the empirical formulae for defining absorption HF wave in ionosphere.The ultimate objective of this work is the designing the method, which allows the simulating of HF radio channel accounting for regular absorption due to UV radiation of the Sun. Eventually it could be considered as some kind of the HF propagation forecasting.     

高频返回散射电离图中的离散源回波的地面距离的确定

本文给出一个从高频返回散射电离图中确定离散散射源回波地面距离的方法.它是假定散射源的描迹是抛物线形式且切于最小时延线来计算固定散射源地面距离的.它仅仅基于单站得到的返回散射电离图的最小时延线和三组散射源回波描迹的时延和频率数据即可完成.实验检验的结果表明,本文方法计算结果的误差不大于3％.     

一种基于被动探测的双机雷达协同定位方法

针对有源探测易被发现及干扰的问题,设计基于被动探测的双机协同射频隐身定位方法。通过测向交叉定位处理获得目标的距离信息,利用属性数据关联消除“鬼影”,从而完成对目标稳定有效的探测。所设计的双机雷达协同定位方法具有目标定位精度高和隐蔽性良好等优点,并通过仿真验证了算法的有效性和实用性。