Transmit beamspace design for direction finding in colocated MIMO radarwith arbitrary receive array and even number of waveforms

In this paper, colocated multiple-inputmultiple-output (MIMO) radar is used for direction-of-arrival (DOA) estimation. The case of even but otherwise arbitrary number of transmit waveforms is considered. In order to obtain a virtual array with a large number of virtual antenna elements and at the same time obtain a significant signal-to-noise ratio (SNR) gain, a proper transmit beamspace is designed. Moreover, to allow for simple DOA estimation algorithms at the receive array, it is shown that the rotational invariance property (RIP) for the virtual array can be guaranteed at the transmit array also by a proper beamspace design. The main idea of such beamspace design is to obtain the RIP by imposing a specific structure on the beamspace matrix and then designing the matrix to obtain a desired beampattern and a uniform power distribution across antenna elements. Simulation results demonstrate the advantages of the proposed DOA estimation method based on colocated MIMO radar with beamspace design.