Study On MIMO Radar Transmit Beampattern Design Methods Based On Priori Information

Transmit beampattern represents the distribution of rader's transmitting power in the space,which is very important for radar. There is some negative influence on radar more or less in radar's work environment,like interference or clutter.If we can obtain them as the priori information in advance and use them reasonably to guide radar's next transmitting,then the performance of radar will be improved. This belongs to the cognitive transmitting, the important direction of modern radar technology.Multiple-Input Multiple-Output(MIMO) radar consists of multiple transmit antennas and multiple receive antennas.As a result, MIMO radar has the advantage of waveform diversity, providing a very good platform for cognitive transmitting. Based on MIMO radar for the realization of the platform, this paper mainly has studied the methods to design transmit beampattern based on the priori information of interference and clutter; The main contents are summarized as the following aspects.The first part introduces three methods to design transmit beampattern of MIMO radar. The first is the traditional matching method to design transmit beampattern based on SDP optimization model, solving the model must depend on the convex optimization toolkit, such as CVX; The second is a mathematical model of unconstrained optimization. Based on the peculiar properties of square root matrix,which belongs to the autocorrelation matrix,putting constraints which are that the autocorrelation matrix is positive semidefinite and all the antenna's power is equal into the parameterized square root matrix,so as to realize that a constrained optimization mathematics model is changed to an unconstrained optimization mathematical model, then using the gradient descent algorithm is be able to solve the unconstrained optimization mathematical model.The third is making the original model's objective function be derived and replaced accordingly,at the same time putting the constraints into the process one by one,then a constrained optimization mathematics model is changed to another unconstrained optimization mathematical model,then we will get a pseudo autocorrelation matrix,in the next step we will use a shrinking method to get the last autocorrelation matrix wanted.The second part introduces three methods to design transmit beampattern of MIMO radar based on the priori information of interference. The first is to use the interference data to estimate the directions of interference based on DOA technology,thses directions are the priori information. On the estimated directions of interference,let the radar to have the minimal energy directly, at the same time,using pth derivative constraint to broaden the null steering.The second is to calculate the correlation matrix of interference at the receiver,then the eigenvalue decomposition method will be used to decompose the correlation matrix to get interference subspace,which is the priori information.When we are designing the transmit beampattern,the interference subspace will be used to lead to the corresponding constraints to get null steering,then pth derivative constraint will be still used to broaden the null steering.The third is to estimate the power of interference plus noise by interference data,which is the objective function to be minimized,at the same time,in the goals' directions there is going to have enough transmission gain,then the Mailloux method is used to broaden the null steering in the end.The third part introduces the method to design transmit beampattern of MIMO radar based on the priori information of clutter,and the method to correct the antenna array position by sparse clutter.Firstly,MIMO radar sends orthogonal waveform signal,then receives echoed data of clutter,which is the priori information.Calculate the autocorrelation matrix by maximizing the signal-clutter-noise ratio based on the priori information,then we will get the transmit beampattern.In the next section, we study the method to correct the antenna array position by sparse clutter.By “sparse reconstruction algorithm” the alternate iteration method is used to estimate clutter scattering coefficient and the error of antenna array position, the former is the priori information to design transmit beampattern, and the latter is going to be used for antenna array position correction.