  In order to improve the accuracy and resolution for transmit beamspace
multiple-input multiple-output (MIMO) radar, a search-free direction-of-arrival
(DOA) estimation method based on tensor decomposition and polynomial rooting is
proposed. In the proposed method, a 3-order tensor is firstly designed to model
the received signal of MIMO radar on the basis of the multi-linear property.
Then, the factor matrix with target DOA information is obtained by the tensor
decomposition via alternating least squares (ALS) algorithm, and subsequently
the DOA estimation is converted into the independent minimization problem. By
exploiting the Vandermonde structure of the transmit steering vector, a
polynomial function is constructed to solve the minimization problem via
polynomial rooting. The factor matrix contained in the coefficients of the
polynomial can be regarded as a block matrix in the generalized sidelobe
canceller (GSC), which accordingly forms a unique deep null in the direction of
target in the transmit beampattern. The proposed method can obtain the DOA
estimation without the requirements of spectrum searching or transmit beamspace
matrix design, which is different from the conventional DOA estimation
techniques. The effectiveness of the proposed method is verified by the
simulations.
