Detection Of High Speed Moving Platform-Borne Radar Targets Under Plasma Sheath

When a hypersonic vehicle is flying in close space,the gas molecules in the air ionize at high temperature due to the strong friction between it and the atmosphere,which causes the formation of shock waves on the surface of the vehicle,that is,a plasma sheath.The plasma sheath presents a non-uniform distribution characteristic on the surface of the aircraft,which produces effects such as amplitude attenuation,phase jitter,and spectral dispersion on the radar signal.The distortion of the radar signal will greatly interfere with the detection of the target by the radar,causing the detection result to deviate,or even Lost.In addition to the impact of the plasma sheath,the high-speed and high-maneuverability of the moving platform carried by the radar will also have a huge impact on target detection.Therefore,this paper combines the characteristics of high-speed moving platform and radar signal processing to study the detection of slow-moving ship targets on the sea surface by the radar on high-speed moving platform under the action of plasma sheath.The main work carried out revolves around the following aspects:1.Establish the intra-pulse motion model of the radar echo from the high-speed moving platform under the plasma sheath,and analyze the influence of the steady-state and timevarying plasma sheath on the intra-pulse echo.The transmission characteristics of the steadystate and time-varying plasma sheaths are obtained by the equivalent transmission line method,and the time-frequency analysis of the radar signal under the steady-state and timevarying plasma sheaths is carried out to explore the influence of the plasma sheath on the signal time-frequency distribution.The intra-pulse motion model of radar echoes suitable for high-speed moving platforms is used to act on the plasma sheath to analyze the influence of steady-state and time-varying plasma sheaths on the time domain and frequency domain of the intra-pulse echo.2.Based on the radar in-pulse echo model of the high-speed moving platform under the plasma sheath,a pulse compression model of the echo under the plasma sheath is established,and the influence of different plasma parameters on the one-dimensional range profile of the radar echo is analyzed.The results show that the main lobe energy of the one-dimensional range profile is attenuated by the action of the plasma sheath,which affects the radar ranging results.Under low electron density,high collision frequency and low electromagnetic wave incidence angle,the attenuation effect of the plasma sheath is small,the one-dimensional range image main sidelobe ratio is greater than 1,and the radar ranging is accurate;at high electron density,low collision frequency and high The attenuation effect of the plasma sheath at the incident angle of electromagnetic waves is greater,and the main-sidelobe ratio is less than 1,resulting in ranging errors.3.Based on the pulse compression model under the plasma sheath,establish the coherent accumulation model under the plasma sheath,and analyze the influence of different plasma sheath parameters on the echo coherent accumulation.Considering the clutter interference in the radar target detection process,establish the intrapulse echo model of the coupled sea clutter under the plasma sheath and the multi-pulse coherent accumulation model,and use the Keystone transform to correct the difference caused by the high-speed movement of the radar carrying platform The cross-distance unit movement problem between pulse echoes is analyzed,and the echo coherent accumulation performance under different plasma sheath parameters is analyzed.The results show that the secondary transmission effect of the plasma sheath leads to the attenuation of the accumulated energy of the target echo and clutter echo.As the electron density increases or the collision frequency decreases,false peaks appear in the coherent accumulation,and the number of false peaks increases;the distance extension phenomenon is serious,from several meters to several kilometers;the accumulation performance decreases.4.Aiming at the one-dimensional range profile and coherent accumulation results of radar echoes of high-speed moving platforms under the plasma sheath obtained by simulation,the unit average and ordered statistical constant false alarm detection methods are respectively used for target detection.Analyze the detection performance of the two methods under different plasma parameters.It can be concluded that for the detection of one-dimensional range profile,the performance of the unit averaging algorithm is better than that of the ordered statistical method.For the detection of coherent accumulation results,the detection performance of the unit average algorithm is better than that of the ordered statistical method under the low electron density and the same signal-to-noise ratio.Under high electron density and high signal-to-noise ratio,the detection performance of the ordered statistical method is better than that of the unit average method.And as the electron density increases,the detection probability of the two methods decreases.In summary,the research in this paper takes into account the effects of the characteristics of plasma sheath and radar high-speed moving platform on radar target detection,which is closer to the real situation,and provides some applications for radar target detection on highspeed moving platforms under the action of plasma sheath.