Transmit Beampattern Notching And Error Estimation For MIMO Radar

Modern battlefield imposes higher standards on modern electronic radars.Multiple-Input Multipel-Output?MIMO?radar with colocated antennas has received intensive attention in recent years.Compared with traditional radars,colocated MIMO radar has more degrees of freedom through transmitting different waveforms through its transmit antennas.More degrees of freedom brings with more flexible transmit beampattern,capability of suppressing more inactive interferences,a higher angular resolution,better anti-jamming performance and so on.All the advantages are based on good transmit waveforms and waveform optimization is an important issue.Current waveform optimization works concentrate on quiescent scenarios where the waveforms are optimized offline.However,in practice,there may be some hostile electronic counter measurement?ECM?devices that capture radar signals and emit jamming signals to prevent radar from normal operation.In this case,an interesting means of radar is to reduce power emission to the ECM device through transmit beampattern notching.Under the assumption that the direction of the hostile ECM device is known,we present an online transmit beampattern notching technique that can form nulls on the transmit beampattern of a group of MIMO waveforms in use through a linear programing problem.In practice,real beampatterns of transmit antennas may not be exactly known and then the nulling performance may degrade.In this case,we present a transmit beampattern mutual coupling estimation method that can estimate the array errors for a higher nulling performance.The paper is organized as follows:?1?Section 2 introduces basic concept of collocated MIMO radar and main pursuits in MIMO radar optimization.Transmit beampattern with multiple peaks are presented.?2?Section 3 introduces the online transmit beampattern notching method which is a nonconvex programing problem.Under an assumption that the array error is small,we approximate the nonconvex programming algorithm by a linear programming model that has a low computation cost and thus can be implemented online.The basic concept is to add a small phase perturbation to transmit signal matrix such that the result beampattern and sidelobe level will not deteriorate too much but certain degrees of freedom are available for optimization to form the null at interested directions.Numerical results show that this method can effectively form nulls at interested directions,without spoiling original transmit beampattern and the range sidelobe level significantly.?3?The transmit notching method depends greatly on accurate information of transmit beampatterns of transmit antennas,but the information in real application is often inaccurate due to mutual coupling and the interaction with the platform.Therefore,we consider the array error estimation problem at the background of colocated MIMO radar.The mutual coupling matrix is estimated through the LASSO regression model,and the LASSO regression algorithm can be used to solve the solution.Numerical results indicate that the proposed method can reach a normalized error of2.7?10^-3.The method of notching in the presence of mutual coupling is analyzed.Numerical results show that the notching effect is improved after compensating for mutual coupling error.