Radar Detection Method Of High-speed Target Based On Coded Pulse System

When the reentry object is flying in the atmosphere at a speed greater than 10 Ma,the air molecules at the stagnation point of the reentry object are ionized due to the aerothermal effect,forming a "plasma sheath" covering the surface of the object.The inside of the plasma sheath contains a lot of charged electricity.Particles are a complex electromagnetic medium.When the reentry object is detected by radar,the plasma sheath produces multi-domain modulation effects on electromagnetic waves such as amplitude,phase,frequency and polarization domain,causing the echo signal to appear amplitude fluctuation,phase disturbance,frequency dispersion and other effects.The fluid characteristics and relative motion characteristics of the plasma sheath result in a large number of reflected signals of different frequencies in the radar echo.The linear frequency modulation pulse signal is used as the transmitting signal,when the radar echo is subjected to pulse compression processing,the one-dimensional range image produces multiple peaks which containing real targets,which seriously affects the reliable radar detection of reentry objects.And because the coded signal has an approximately ambiguous function like pushpin,the coded signal has a better pulse pressure performance.Not only that,its good anti-interference and low interception characteristics also make the phase coded signal have a wide range of applications.Aiming at the "multi-target" phenomenon produced by the chirp signal system and the good characteristics of the phase-encoded signal,this paper adopts the phase-encoded signal system to carry out the research on the reliable detection method of reentry objects,and analyzes the effect of the plasma sheath on the phase-encoding system.This paper also put forward the corresponding reliable detection method.The main research contents of this paper are as follows:(1)Based on the basic theory of plasma sheath and commonly used two-phase coded signal,carry out the research of reliable detection method of target radar covered by plasma sheath,break through the calculation method of radar echo in time domain,and establish the multi-domain characteristics of the echo signal of reentry object model.Analyze the influence of the characteristic parameters of the plasma sheath on the energy distribution characteristics of the radar echo range when the typical two-phase coded signal(Barker code,M sequence code)is used as the radar signal,and reveal the energy ratio of the plasma sheath to the main sidelobe Influence mechanism,and verify the theoretical results through simulation.(2)Under the action of the plasma sheath,the multiple doppler frequencies coupled in the echo of the reentry object greatly reduce the peak ratio of the main and sidelobe in the echo pulse compression result.Through the compensation of the doppler frequency,The peak ratio of the main and sidelobe in the pulse compression can be improved.In response to this problem,this article focuses on two doppler compensation methods,namely:multi-branch compensation method and loop compensation method based on doppler frequency extracting.Simulations have verified the effectiveness of the two compensation methods,the main-sidelobe ratio of pulse compression has improved,and realized effective radar detection of reentry targets covered by the plasma sheath under the coded pulse system.(3)Introduced the hardware implementation platform,FPGA chip selection,hardware implementation schemes and the use of different IP cores in the internal modules,and implemented the time domain pulse compression of the two-phase coded signal on the radar signal processing board,and compared the same parameters under the conditions of MATLAB simulation results,the FPGA processing results are analyzed and summarized.