This paper studies the Cramer-Rao Bounds (CRB) for estimating parameters of coherently distributed targets (CDT) using Multi-Input Multi-Output (MIMO) radars. Firstly, the MIMO radar signal model for estimating the CDT parameters is given and the general CRB expression is derived. Then, several CRBs are given in special cases such as a distributed target, a point target and a target with partial information. Thirdly, the CRB properties of MIMO radars are discussed. Finally, the MIMO radar performances are simulated in different conditions through computer simulations. Theoretical analyses and computer simulations show that the MIMO radar is superior to the traditional phased array radar in estimating the CDT parameters because the former has no beam-shape loss. The research conducted in this paper reveals the fundamental performances of the MIMO radars.
