Research On Target Focusing Performance Based On Time Reversal

Time Reversal(TR)is an adaptive space-time focusing technology,which essentially performs a reverse order operation on the received signal in the time domain.It corresponds to phase conjugation processing in the frequency domain.The technology originated from the promotion of phase conjugate mirrors in the optical field,and it has been successfully applied to the fields of acoustic waves,electromagnetic waves and water waves.In this thesis,an in-depth study of the characteristics of time reversal technology in target focusing is carried out,and it explores whether it can break through the diffraction limit in traditional optical imaging—about half a wavelength to achieve super-resolution.Moreover,the technology is applied to the angle estimation problem of the far-field target under the multipath effect problem,and the accurate calculation of the target azimuth can be realized even under the low signal-to-noise ratio.The main work includes the following aspects:First,this thesis introduces the basic theory of the time reversal technology.Based on Maxwell’s equations,the time reversal solution of the wave equation is derived,and the space-time focusing characteristics of the time reversal technology for the target are verified with the time reversal field in the closed region.Then,the basic time reversal methods including Time Reversal Mirror(TRM)and Decomposition of the Time Reversal Operator(DORT)are introduced,which lays a theoretical foundation for subsequent research.Second,in order to explore the characteristics of time reversal in target focusing,this thesis uses electromagnetic simulation software to build a time-reversal mirror model composed of dipole antennas and coaxial probes,and simulation verifies whether the time reversal technology has matched filtering characteristics and super-resolution characteristics;On this basis,the physical factors that affect the resolution of time reversal for the target are explored,including the number of time reversal mirror antennas,the size of the metal cavity,the addition of metal scatterers,etc.The numerical results show that time reversal technology not only has the optimal space-time matched filtering characteristics,but also can break through the Rayleigh limit to achieve super-resolution.At the same time,by loading suitable metal scatterers around the target,the resolution of time reversal technology can be greatly improved.Finally,aiming at the attenuation of the radar echo signal-to-noise ratio under the multipath effect,it is proposed to extract and reasonably utilize the multipath information by time reversal technology,so as to realize the estimation of the direction of arrival(DOA)of the radar far-field target and further improve the detection performance of the radar.First,the mathematical model of radar far-field target is introduced.By constructing the far-field target signal of the array antenna,adding noise and clutter to construct the multipath effect,we simulate the radar echo received in the multipath environment.Then,the obtained echo signal is processed by the DORT algorithm,and the accurate calculation of the target angle is obtained by combining the relevant knowledge of the array antenna pattern.Aiming at the problem that the maximum eigenvalue that appears when multiple target signal sources are coherent corresponds to multiple target angle information,which leads to the inability to accurately estimate the DOA of the targets,a method combining DORT algorithm and decoherence algorithm is proposed.The simulation results show that in the low signal-tonoise ratio and multipath environment,the DORT algorithm can selectively achieve selective focusing of multiple targets and achieve accurate estimation of the angles of each target.