Unimodular Transmit Sequence Design for FDA-MIMO Radar in the Presence of Mismatched Target Steering Vectors

When processing radar signals, the target steering vector is generally only partially known, being subject to various forms of errors and mismatches. In this article, we investigate the design of an unimodular transmit sequence that is robust against steering vector mismatches, with the aim of enhancing the performance of a frequency diverse array multiple-input-multiple-output (FDA-MIMO) radar system in the presence of signal-dependent main-lobe interference. The design is formulated as a max-min problem, constrained by the constant modulus of the transmit waveform, and seeks to maximize the worst case output signal-to-interference-plus-noise ratio (SINR) over the mismatched target steering vector. As the resulting problem is NP-hard, an iterative approximate scheme is proposed to allow for a feasible solution. Specifically, in each iteration, the inner optimization problem, which solves the norm-constrained steering vector mismatch, is addressed using a 1-D search. Subsequently, the unimodular transmit sequence is designed via two distinct algorithms, namely, the CC-SDR (Charnes-Cooper transformation combined with semidefinite relaxation technique) and CD-DIN (Dinkelbach’s procedure embedded in a coordinated decent framework) algorithms. Through numerical simulations, we demonstrate the preferable performance of the proposed approaches in mitigating the adverse effects of steering vector mismatch and signal-dependent main-lobe interference.