Multiple-input multiple-output (MIMO) radar/ sonar systems transmit signals coded in time and space domains and have several advantages upon conventional systems. In this paper, the Barankin bound on target localization errors is used for analysis of the threshold signal-to-noise ratio (SNR) of MIMO radar/sonar systems. It is shown that the threshold SNR of MIMO systems with spatially orthogonal transmit signals, is significantly lower than with coherent transmit signals. Orthogonal signal transmission results in lower threshold SNR, because of the lower sidelobes in the likelihood function. The lower sidelobes are achieved, since MIMO configuration allows to process the signal in both transmit and receive modes. Simulation results show that the threshold SNR obtained by orthogonal signal transmission is lower by more than 10 dB compared to coherent signal transmission.