On angle resolution of mono-static multiple-input multiple-output sonar

To study the role of the waveform diversity and the transmitting subarray on the angle resolution of the multiple-input multiple-output (MIMO) sonar, the far-and near-field beampattern derivation model, suitable for both MIMO and traditional active sonars, is proposed; and the sameness on angle resolutions of the two sonars is proved. Firstly, the MIMO and traditional active sonars are set to share the same array con_guration, and the transmitting array is divided into two types: with overlapped and with n-overlapped subarrays. Then the array manifold vectors of the two sonars are proved to be the same, equaling to the Kronecker product of manifold vectors of transmitting and receiving arrays. Finally, the beampatterns (both in the far-and near-fields) of the two sonars are proved to be the same. Furthermore, it is proved that the adoption of overlapped transmitting subarrays can be considered as the amplitude weighting on the transmitting array (where the weights in the array center area are bigger than those in the array marginal area), which reduces the beampattern sidelobe level but not increases the angle resolution. Theoretical analysis and numerical simulations show that the angle resolution of the MIMO sonar is determined by the configurations of transmitting and receiving arrays; the waveform diversity and the transmitting subarrays bring no superior angle resolution for the MIMO sonar.