Study On Transmitting Time Diversity And Receiving Robust Beamforming Method

Array radar waveform design and receiving beam forming are key technologies for effective target detection.Compared with traditional phased array radars,MIMO radar has the characteristics of high system freedom,strong anti-interception capability and good Doppler resolution due to its transmit diversity technology.But it also has many limitations such as the difficulty of orthogonal waveforms.In recent years,the new transmit diversity MIMO radar that introduces time stepping into the traditional array configuration has received extensive attention from researchers.In this thesis,further research is carried out on the sub-array division technology of time-diversified arrays,and a sub-array division method based on different arrays and a sub-array division method based on extended Barker codes are proposed.Simulation experiments show that the two methods respectively improve the spatial coverage of the sub-array division and range resolution;in addition,research on robust receive beamforming methods to improve the output signal-to-interference and noise ratio is also the focus of MIMO radar research.This thesis proposes a robust adaptive beamforming method based on structural information under the MIMO radar system with time diversity sub-array division,which can solve the output signal-to-interference-noise ratio loss caused by steering vector mismatch and small number of samples.The content of this thesis is arranged as follows:The first part mainly introduces the signal model and characteristics of the new transmit diversity MIMO radar-time diversity array,describes the space coverage,angle and range resolution of the time diversity array,and analyzes the effects of fixed time shift changes on the time diversity array.On this basis,a method of launching a time diversity array with different time shifts is studied.The launching array element is divided into two parts,and each part of the transmitting array element emits signals with a different time offset.Finally,the simulation verifies that the method can improve the range resolution and reduce the range sidelobe to a certain extent.The second part mainly focuses on the sub-array division of the time-diversity array.Two signal models of the sub-array division are given and the characteristics of the two models under different time shifts are analyzed.Aiming at the problem that the existing sub-array division technology enhances the range resolution but sacrifices the spatial angle coverage,a method of sub-array division time diversity array based on different array intervals is studied.This method is effective in enhancing the distance resolution of the time diversity array.At the same time,the airspace coverage of the sub-array division is improved;then a method of sub-array division of time-diversity matrix based on extended barker code is proposed;the extended barker code is combined with sub-array division,and on this basis,by introducing a different time shift in each sub-array of the waveform-time diversity array to further reduce the distance side lobe.Simulation results show that this method can further improve the range resolution on the basis of sub-array division.The third part focuses on the research on the robust and adaptive beamforming of the time-diversity sub-array.Aiming at the problem of beamforming output performance degradation caused by steering vector mismatch and less training sample data,a robust adaptive beamforming method based on structural information under the time diversity sub-array division MIMO radar system is proposed.The transmitted signals between the sub-arrays are separated,the new covariance matrix is obtained by using the centro-hermitian structure information,and then the steering vector is estimated by the steering vector optimal estimation formula,and finally the optimal weight vector is obtained.The simulation experiment proves the effectiveness of the proposed algorithm.