Abstract: A new space-time coding configuration for target direction finding by active arrays called multi-input multi-output(MIMO) arrays is proposed.Multiple mutually uncorrelated(orthogonal) probing signals are transmitted by MIMO arrays whose steering vectors are the convolution of transmit and receive steering vectors of conventional phased arrays,which is essentially equivalent to extending the array aperture by additional virtual sensors.These virtual sensors can be used to form narrower beams with lower sidelobes because the MIMO array beam pattern is the product of the transmit beam pattern and the receive beam pattern.The minimum variance distortionless response(MVDR) method for direction of arrival(DOA) is studied,and simulations and experiments show that the MIMO array can achieve better performance in target detection and angular resolution over the conventional phased arrays.