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In direction-of-arrival (DOA) estimation using millimeter waves or ultrasonic, the physical size of the sensors can require inter-element spacing of greater than half wavelength. The accompanied benefits of such spacing are larger array aperture and reduced mutual coupling, but the serious problem of DOA ambiguity arises. This paper proposes a method to suppress grating lobes by employing a MIMO radar array configuration. The resultant virtual array has sufficient half wavelength spacings to significantly suppress grating lobes while the transmit and receive array elements have greater than half wavelength spacing. The grating lobe suppression performance is evaluated by simulation of MIMO-OFDM radar system that also has frequency diversity properties against DOA ambiguity. The simulation results show that the grating lobe suppression performance increases with signal-to-noise ratio (SNR). The effectiveness of the proposed array configuration and frequency diversity for resolving DOA estimation is also demonstrated.