This paper explores the design of probing signals for multiple-input multiple-output (MIMO) radar systems, aiming to maximize power at target locations and minimize cross-correlation. The authors propose a method to design the covariance matrix of the probing signal vector to achieve these goals. They demonstrate that proper signal design can significantly enhance the performance of adaptive MIMO radar techniques. Additionally, they compare several MIMO transmit beampattern designs, including beampattern matching and minimum sidelobe designs, with their phased-array counterparts, showing the advantages of MIMO designs. The paper also discusses the mathematical formulation of the problem and presents numerical examples to illustrate the effectiveness of the proposed designs.This paper explores the design of probing signals for multiple-input multiple-output (MIMO) radar systems, aiming to maximize power at target locations and minimize cross-correlation. The authors propose a method to design the covariance matrix of the probing signal vector to achieve these goals. They demonstrate that proper signal design can significantly enhance the performance of adaptive MIMO radar techniques. Additionally, they compare several MIMO transmit beampattern designs, including beampattern matching and minimum sidelobe designs, with their phased-array counterparts, showing the advantages of MIMO designs. The paper also discusses the mathematical formulation of the problem and presents numerical examples to illustrate the effectiveness of the proposed designs.