Coherent Beamforming And Parameter Estimation Of Multipath Exploitation Radar

In a low-altitude multipath environment,many scholars have developed many conventional beamforming methods and DOA spectrum estimation.However,in the actual application environment,the multipath interference signal environment is often more complicated.At this time,the performance of the conventional adaptive beamforming method is seriously degraded,and the signal subspace and noise subspace of the coherent signal source penetrate each other,resulting in some super-resolution subspace classes.The multipath effect causes the radar signal to noise ratio to decay.By separating and suppressing multipath signals,the problem of performance degradation caused by multipath signals can be improved.However,if you dig deeper and use multipath information,you can improve the performance of the algorithm.Therefore,it is necessary to study coherent beamforming methods and target parameter estimation algorithms for multipath radars.1.A geometric model and a signal model of the echo signal in a multipath environment are established.The specular reflection mechanism and the diffuse reflection mechanism are systematically summarized.The target echo model and the relationship between the amplitude of the echo signal and the radar height and carrier frequency were studied.2.Aiming at the problems of signal-to-noise ratio attenuation and degradation of the performance of the target beamformer caused by multipath effects,by using the echo information of multipath coherent signals,two coherent beamforming methods using multipath information are studied and proposed.The first method improves the energy of the direct wave component and the signal-to-noise ratio of the echo by obliquely projecting the echo signal to the direct wave subspace and the reflected wave subspace,then performing signal filtering,and then performing conventional beamforming.The second method obtains the optimal weighting vector by constraining the multipath attenuation coefficient,and then performs adaptive beamforming,which improves the energy of the direct wave component and the signal-to-noise ratio of the echo.In the case of low-altitude multipath,compared with the existing methods,these two methods have been proved by theory and experiments.They are more effective in solving the problem of multipath coherent signal reception,and improve the signal-to-noise ratio of the echo signal.3.Aiming at the problems of SNR attenuation and target parameter estimation accuracy degradation caused by multipath effects,by using the incoming wave information of multipath coherent signals,two joint estimates of target angle and multipath attenuation coefficient using multipath information are studied and proposed method.The first method first analyzes the available prior information in a multipath environment,and then improves the traditional maximum likelihood estimation method.By combining the multipath prior information and multifrequency point information with the maximum likelihood algorithm,the target angle and multipath attenuation coefficient can be estimated at the same time without knowing the target angle,and the target parameter estimation performance is improved.One-dimensional angle search replaces two-dimensional angle search,which greatly reduces the computational complexity.The second method uses the prior information such as the angle conversion relationship and the multipath attenuation coefficient in the multipath geometric model,and then improves the traditional sparse Bayesian learning DOA estimation method,and can simultaneously estimate the target angle and the multipath attenuation coefficient.This algorithm does not require multi-dimensional angle search,which effectively reduces the computational complexity.Compared with the existing methods,these two methods have been proved by theoretical and experimental simulations,which makes the parameter estimation performance of the radar at low SNR further improved.