The idea of dividing the transmitting array of MIMO radar into unequal subarrays was proposed in the paper. This kind of MIMO radar obtains the coherent processing gain and the waveform diversity gain which the MIMO radar with equal subarrays (called it phased-MIMO radar) enjoys. Furthermore, different sizes of subarrays form multiple beams; the greater apertures of subarrays provide more degree of freedom at the transmitting side. Theoretical analysis shows that compared with the phased-MIMO radar, the MIMO radar with unequal subarrays enjoys higher output signal-to-interference-plus-noise ratio (SINR) at low interference-to-noise ratios (INRs) by nonadaptive beamforming. Simulation results validate the correctness of the above theoretical analysis, and shows that the proposed MIMO radar with unequal subarrays can achieve lower sidelobe levels, deeper null steering, and higher output SINR by minimum variance distortionless response (MVDR), which is contributed to the its ability to reject interference combined with its robustness against sensor noise.
