目标以极高速度在大气层内运动时,周围会因剧烈摩擦产生等离子体绕流场.等离子体绕流场运动速度分布不均匀,而且绕流场电子密度随时间动态变化,导致等离子体绕流场对入射其中的电磁波产生不均匀的频率调制,进而影响雷达的探测性能.为了复现等离子体绕流场在电磁波照射时产生的不均匀频谱调制现象,本文在中国科学院力学研究所JF-10风洞开展了等离子体绕流场回波频谱测量实验,通过信号源、环形器、天线和频谱仪组成的测量系统,以点频发射体制,获取了S和C波段的回波频谱数据,观察到了等离子体绕流场对目标回波频谱的调制现象,对测量现象的形成原因进行了讨论;基于测量数据,仿真分析了等离子体绕流场对目标一维距离像的散焦效应.

When the aircraft moves through the atmosphere at a very high speed, the aircraft will experience intense friction with the surrounding atmosphere, which causes the air to be ionized into plasma, thus producing a plasma flow field around it. Plasma is constantly generated on the windward side of the aircraft and flows backwards. The velocity of plasma is different from that of the aircraft. In addition to the dispersion characteristics of the plasma and the non-uniform distribution around the target, the plasma flow field will produce the effects of amplitude, frequency and phase modulation on the incident radar wave, which will change the electromagnetic scattering characteristics of the target. In order to reproduce the non-uniform Doppler phenomenon in the flow field under electromagnetic wave irradiation, the plasma echo spectrum is measured experimentally in the JF-10 wind tunnel of the Institute of Mechanics, the Chinese Academy of Sciences. The echo spectrum data of S band and C band are obtained by using a measurement system composed of signal source, circulator, antenna and spectrometer, and based on the measured data the one-dimensional range profile of the plasma coated target is simulated, and the results show that the plasma flow field has a spectrum modulation effect on the target. When the speed of the flow field cannot be compensated for accurately, the spectral modulation effect will further cause the one-dimensional range profile to defocus, which will affect the ability of radar to detect and track the object. The preliminary analysis shows that the effect is caused mainly by the inhomogeneous velocity distribution of plasma flow field and the sudden change of medium parameters when the shock wave arrives. This experiment can provide data support for verifying the electromagnetic characteristics modeling method of plasma flow field.