基于正交编码的高频地波雷达信号的设计

为了避免电离层杂波折叠现象,高频地波雷达信号需要具有较大的不模糊距离,若采用简单的增大脉冲周期的方法就会使得占空比下降,而高频雷达恰恰需要高占空比信号以保证探测距离。针对这一问题,利用遗传算法来设计双脉冲正交编码,使得两个脉冲的互相关峰值低于各自的自相关峰值旁瓣,将不模糊距离推远到两个脉冲周期。为了进一步降低自相关函数旁瓣,采用反相滤波算法进行旁瓣抑制,仿真实验证明:该算法优于窗函数加权法、最小二乘法和递归最小二乘算法等失配滤波算法,且多普勒容限性高。     

无线电窄波束在低电离层中的聚焦和散焦

推导了无线电窄波束在电离层中传输的非线性几何光学方程,分析了无线电窄波束在低电离层中传输的聚焦和散焦原理,推导出了散焦参数和聚焦参数的计算公式,研究了无线电窄波束在低电离层中传输的散焦现象,讨论了电波频率和功率对发散波束宽度的影响。计算结果表明：低电离层主要表现为一种散焦介质,使电波波束发散,当电波频率较低并且功率较大时,波束散焦现象非常明显,使到达目标点的功率密度大幅度降低,而当频率达到数GHz时,波束散焦现象很微弱。     

电离层色散效应对宽带BOC信号的影响

电离层色散特性导致宽带二进制偏移载波(Binary Offset Carrier,BOC)信号的码片时域波形和相关函数曲线产生畸变,影响BOC信号完好性和跟踪性能。为了评估电离层对BOC信号传输的影响,构建了宽带BOC信号的电离层影响分析框架,分析了电离层色散效应对码片时域波形和相关特性的影响,并评估了三类典型BOC信号的带内电离层色散效应在码跟踪环路和载波跟踪环路引入的偏差。研究结果表明,电离层色散效应会导致宽带BOC信号时域码片实部和虚部边缘产生抖动现象,色散信号与标准信号间的互相关函数会产生明显的相关损耗;在电离层活跃期间,电离层色散效应在码跟踪与载波相位跟踪中均引入明显的鉴别误差。该结果对BOC信号的电离层误差的评估与校正有一定的参考意义。     

暴时行星际穿透电场与电离层效应的卫星观测

联合利用Geotail卫星、ROCSAT-1卫星和DMSP卫星等观测数据,分析了2000年7月15-16日超强磁暴期间行星际穿透电场的特征及低纬电离层响应。研究得到以下主要结果:1)磁暴主相期间,位于近地太阳风中的Geotail卫星观测到行星际电场晨昏分量迅速增强达60 mV/m,与此同时,ROCSAT-1卫星在低纬电离层中几乎即时地观测到垂直于磁场的离子向上漂移速度达300 m/s以上,表征行星际电场穿透至低纬电离层。分析表明:在正午和黄昏扇区穿透电场为东向,引起低纬电离层离子向上漂移,穿透效率约为13-19%;而在午夜前扇区,穿透电场极性相反,使离子向下漂移,穿透效率高达30%;行星际电场穿透持续时间达3小时以上。2)磁暴期间,低纬电离层发生剧烈变化。GPS/TEC观测显示美洲扇区黄昏附近的中纬度电离层发生SED现象、同时DMSP卫星观测到纬度范围大大扩展的电子密度深度耗空的赤道区等离子体槽、ROCSAT-1卫星观测到暴时离子密度变化呈现较复杂的图像。     

短波天波通信链路计算模型研究

为建立远程舰艇短波通信可靠通信链路,简化短波通信工程中天线和通信台站设计过程,研究设计了一个完整的短波通信链路计算模型。该模型包含天线辐射特性计算模型、短波通信电路计算模型、短波天线数据库和通信链路地理参数数据库四大部分。在此基础上,使用该模型进行了实例分析,确定了在一定条件下的工作频率、反射模式,预估场强强度,为短波天波通信工程设计提供依据。     

基于HF返回散射和斜向探测的PD变换新方法

提出了基于实测返回散射电离图和斜向探测电离图及三维射线追踪技术综合处理的群路径P到地面距离D变换（简称PD变换）的坐标配准系数（kr）修正方法,采用“归一化”的思想,计算射线追踪技术合成的斜测电离图和实测斜测电离图的归一化频率对应的群路径差值,利用该差值,修正不同距离的合成的群路径,特别是能够对远区没有信标参考地区的坐标配准系数进行修正。仿真分析了临界频率和反射高度估计存在误差时“归一化”方法修正的有效性,从而验证了该方法能够有效地克服电离层参数估计不准对坐标配准系数的影响。     

电离层斜向传播异常信号特性的研究

在对固定电路电离层斜向传播特性的长期连续观测过程中,发现了大量异常斜测电离图.通过对电离层行波扰动情况下电波传播路径的仿真计算,分析了它对电离层斜向传播信号的影响,并利用斜向探测数据,讨论分析了确定行波扰动基本参数的方法.     

地球电离层对短波通信的影响分析

现代通信中,短波通信凭借发射功率小、传输距离远、建站速度快、机动性能好的特点,被广泛用于文电传输、语音电话、低速数据和静态图像业务场景,并在远程通信、应急通信中占据极其重要的地位。本文首先介绍了短波通信的特点,分析了其优势和不足;其次介绍了电离层产生的原因及分层;再次重点分析了电离层对短波通信的影响,并给出了附加电离层影响和最新研究方向;最后对全文进行总结。     

Tethered-Satellite system (TSS): Preliminary results on the active experiment core equipment

Summary The first Tethered-Statellite System (TSS-1) Electrodynamic mission has been launched aboard the Space Shuttle STS-46 on July 31, 1992, as a joint mission between the United States and Italy. A 500 kg spherical Satellite (1.6 m diameter) attached to the Orbiter by a thin (0.24 cm), conducting, insulated wire (Tether), has been reeled upwards from the Orbiter payload bay to a distance of 257 m when the Shuttle was at a projected altitude of 300 km. ASI, the Italian Space Agency, had the responsibility for developing the reusable Satellite, while NASA had the responsibility for developing the Deployer system and the Tether, integrating the payload and providing transportation into space. One of the main scientific goals of this first mission was to demonstrate the possibility of energy conversion from mechanical to electrical by using a long Tether orbiting through the Earth's magnetic field. ASI designed and developed an active experiment, referred to as Core Equipment, in order to carry out this demonstration. The experiment used two Electron Generator Assemblies (EGAs), located on the Orbiter, to re-emit into the ionosphere as an electron beam the electrons collected on the Satellite from the ionosphere. Each EGA had the capability to emit an electron beam with a programmed intensity from 10 mA up to 750 mA with a resolution of 3 mA. The perveance of each EGA was 7.2 microperv, and the beam energy, up to 3 kV, was provided as part of the e.m.f. induced across the TSS due to its motion through the Earth's magnetic field. Other instruments provided current, voltage, and ambient-pressure measurements, and allowed, via a series of switches, different electrical configurations of the TSS. Moreover, the Core Equipment provided a dynamic package, to study the TSS dynamics, as a first goal, and to verify the possibility of using the TSS Satellite as a platform for future experiments in the microgravity field. The expected voltage across the TSS was estimated to be 5 kV for a full Tether deployment of 20 km. During the mission, and due to unforeseenable reasons, the Tether deployment achieved was only of 257 m. Despite this limitation, there is evidence that the experiment was working nominally in the very low-voltage range across the TSS. This result strongly increases the confidence in the possibility of high-voltage operation of the electrodynamic TSS, as the Tether deployment will achieve the 20 km, as expected in the future reflight. The paper describes the experiment, and reports some preliminary results achieved during the first mission. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

掩星观测中电离层延迟对LEO卫星轨道误差的响应

从Haselgrove和Budden方程出发，模拟了GPS信号在电离层中的传播过程，利用GPS/MET实验中5组GPS和LEO卫星的实际轨道，分别模拟了无LEO卫星轨道扰动和有轨道扰动情况下的GPS信号在电离层中的传播，并生成了对应的电离层延迟量，以同步生成的模拟精度序列为参照，就掩星观测中电离层延迟对LEO卫星轨道误差的响应程度进行了估计和分析，初步结果显示：在掩星观测中，电离层延迟对LEO卫星轨道误差的响应比中性层延迟要弱得多，这可能同采用了电离层掩星观测的采样频率比中性层采样频率低两个数量级的技术手段有关。