Target Detection And Parameters Estimation With Multipath Exploitation Radar Based On Time Reversal

The performance degradation,such as the SNR(signal to noise ratio)attenuation of radar echo,caused by multipath signals can be improved by separating and suppressing multipath signals.Considering that multipath signals also contain part of information about target,if the multipath information can be extracted and explored reasonably,the radar performance can be further improved.TR(Time Reversal)improves the SNR of echo by exploiting multipath signals and achieving adaptive space-time focusing of energy,which provides a new method for solving target detection problems in the multipath environment.Focusing on the detection of targets and parameters estimation in multipath environment,this paper establishes the target distance,angle,velocity and power models of multipath environment.Combined with time reversal algorithm,the method of target detection,distance and angle estimation with time reversal is studied.At the same time,pairing methods about distance and angle for multiple scattering point targets is proposed.The main contents of this paper are organized as follows:1.The geometric relationship,electromagnetic reflection,signal detection and array echo models of sea surface targets in multipath environment are established.Then the TRCACFAR(Time Reversal Cell Averageing Constant False Alarm Rate)detection algorithm is proposed.Radar reverses and normalizes the echo signal in energy to obtain the TR signal after receiving the echo signal.Then the TR signal is retransmitted into environment,and CFAR(Constant False Alarm Rate)target detection performed as soon as the TR echo is received.The TR signal reaches the target through different paths,and achieves energy accumulation at the target,which improves the SNR of TR echo signal and enhances the radar detection performance.2.As for the problem of target ranging accuracy decline caused by multipath effect,a target distance estimation method based on time reversal is proposed.Similar to the time reversal detection method,the echo is retransmitted and received,and the SNR of TR echo is improved by exploring the multipath energy,then the target distance is estimated by the matched filter for the TR echo.Compared with existing method,the time reversal matched filtering method can obtain a smaller ranging root mean square error with higher precision.Finally,for the multi-scattering point target,a distance matching method of multipath target is proposed by exploiting the geometric relationship of multipath.The high-precision distance estimation of the multi-scattering point target is realized by pairing the measured distances with the scattering point paths respectively.3.Aiming at the issue of target angle precision decline caused by multipath effect,a target angle estimation method with time reversal is proposed.Array antennas retransmit and receive the TR echo signals,so that the direct signals and the multipath signals adaptively achieve energy accumulation,which improves the echo signal-to-noise ratio.Considering the correlation between multipath signals and direct signals,the MSS(Modified Spatial Smoothing)decoherence is performed on the TR echo,and the target angle can be estimated by the spatial spectrum estimation of MUSIC(Multiple Signal Classification).The signal propagation process of time reversal is derived in time domain and the physical meaning of time reversal is analyzed.Compared with the traditional method,the DOA(Direction Of Arrival)estimation method of time reversal can obtain smaller angle estimation error with higher precision.Finally,for the multi-scattering point target,an angle matching method of multipath target is proposed according to the geometric relationship of multipath.The highprecision angle estimation of the multi-scattering point target is realized by pairing the measured angles with the scattering point paths respectively.