等离子鞘对卫星导航信号的影响与波束形成抑制方法的研究

The plasma sheath will be produced around hypersonic vehicles when it reentry into the earth’s atmosphere. The plasma sheath can affect the radio communication between reentry body and ground control stations or space satellites, which can attenuate control signals such as navigation and guidance rapidly. What’s worse, the communication between reentry body and ground stations or satellites may be interrupted, forming ‘blackout’ phenomenon. However, beam-forming technology can improve the reception gain, in order to weaken the blackout effect. Hence, the study of plasma sheath’s effect on navigation signals and trying to weaken or eliminate the blackout effect are key technologies needed to be solved in hypersonic vehicle’s reentry process. The radio wave propagation characteristics of plasma sheath are analyzed using electromagnetic numerical method of Scattering Matrix Method and Unconditionally Stable For the Finite-Difference Time-Domain. Combining with satellite navigation signal analog technology and mathematical modeling plasma sheath channel, the performance of plasma sheath to satellite navigation is analyzed. In order to utilize beam-forming technology to enhance satellite signal power, weakening the role of the plasma sheath influence, the beam-forming key technologies are studied systematically. Studying the performance and feasibility of beam-forming techniques used in suppressing plasma sheath blackout effect. The experiments about plasma sheath’s impact on wave propagation and satellite navigation’s performance are done. The consistent with measured results and theoretical results verifies the correctness of numerical simulation.

飞行器以高超声速再入大气层时会在飞行器周围产生等离子鞘套，等离子鞘套对再入体与地面控制站以及再入体与空间卫星的无线电通信产生巨大的影响，使导航测控信号功率急剧衰减，严重时会造成再入体与地面站或卫星之间的通信中断，形成“黑障”。研究等离子鞘套对导航测控信号的影响规律并设法减弱或消除“黑障”效应，是高超声速飞行器再入飞行急需解决的技术关键。本项目采用基于解析近似的散射矩阵方法与基于拉盖尔展开的无条件稳定FDTD电磁场数值计算方法分析等离子鞘中的电波传播特性；结合卫星导航信号模拟技术，对等离子鞘信道进行数学建模，分析等离子鞘对卫星导航性能的影响；为了利用波束形成技术增强卫星信号接收功率，达到减弱等离子鞘影响的作用，对波束形成的关键技术进行系统研究。研究波束形成技术用于抑制等离子鞘“黑障”效应的性能及可行性。进行等离子鞘对电波传播及卫星导航性能影响的实验研究，验证数值仿真的正确性。

研究等离子鞘对导航信号的影响规律并设法减弱“黑障”效应，是高超声速飞行器再入飞行急需解决的关键问题。本课题前期研究了等离子体中电波传播理论，针对传统FDTD算法受Courant约束条件的限制导致计算步长较小的问题，首次把基于拉盖尔展开的无条件稳定FDTD（Unconditionally Stable For the Finite-Difference Time-Domain，US-FDTD）用于等离子体中电波传播的计算，该算法在确保计算精度的同时，大幅度减小了计算时间，提高了复杂电子密度分布等离子鞘中电波传播的仿真效率。采用SMM和US-FDTD方法分析均匀等离子鞘套电子密度、厚度及碰撞频率对导航/测控频段信号传播特性影响。建立等离子鞘信道模型，包括频域传递函数和时域单位冲激响应，利用该模型分析等离子鞘对卫星导航接收机伪距测量精度、载噪比和定位精度的影响。应用SMM方法和FDTD算法分别分析了RAMC III飞行器和背景飞行器的等离子鞘对卫星信号传播特性和对卫星导航接收机定位性能的影响。波束形成技术可以提高卫星来波方向的增益，同时抑制多径效应，从而达到减弱等离子体鞘对信号衰减的目的，同时可以提高卫星导航和测控的可靠性。本课题对波束形成的基本准则、算法进行了仿真分析，通过性能及适用条件的比较，选择了适合卫星导航的波束形成算法。通过数值仿真分析等离子鞘对阵列天线的辐射特性、耦合特性及阻抗特性的影响。设计实验系统验证等离子鞘对导航测控信号传播特性的影响及对卫星导航性能的影响。采用西安电子科技大学研发的均匀等离子体发射装置，通过不同电子密度等离子体对信号传播衰减、相位的实验测量，验证数值仿真结果的正确性；实测等离子体对卫星导航接收机性能的影响，并再现“黑障”现象。