Two-stage based design for phased-MIMO radar with improved coherent transmit processing gain

We consider the problem of two-dimensional (2D) transmit beamforming design for phased-MIMO Radar with a limited number of transmit power amplifiers. Subarray partitioning is used in MIMO radar where individual subarrays operate in a phased-array mode leading to a reduction in the number of power amplifiers required. However, the use of subarray partitioning results in poor transmit beampattern characteristics due to the reduced physical aperture of the subarrays as compared to the aperture of the full transmit array. To address this problem, we introduce a new method for achieving a desired transmit beampattern while applying the concept of phased-MIMO radar. Our design consists of two cascaded stages where the first stage involves mapping a set of finite number of orthogonal waveforms into another set of cross-correlated waveforms using a linear mixing operator. The second stage involves partitioning the transmit array into a finite number of transmit subarrays where each subarray is used to radiate one of the cross-correlated waveforms in phased-array mode. The mixing matrix used in the first stage is appropriately designed to ensure that the overall transmit beampattern, i.e., the summation of all beampatterns of the individual subarrays, is as close as possible to a desired transmit beampattern. The number of power amplifiers required is finite and equals to the number of subarrays. One of the advantages of the new method is that it can achieve coherent transmit gain that is comparable to the coherent transmit gain of a phased-array radar while implementing the concept of MIMO radar. Simulation examples are used to validate the proposed method capabilities.