Frequency diverse array and MIMO hybrid radar transmitter design via Cramér–Rao lower bound minimisation

Frequency diverse array (FDA) produces a range–angle-dependent transmit beampattern and offers a potential solution to localise targets in two dimensions with respect to slant range and azimuth angle. However, it is difficult to unambiguously estimate the target location information by a standard FDA radar via conventional adaptive beamforming due to its coupling range–angle response. In this study, the authors propose two FDA and multiple-input multiple-output (MIMO) hybrid radar transmitter design schemes by minimising the Cramer–Rao lower bound (CRLB) for range-dependent target localisation, namely, FDA–MIMO radar and transmit subarray FDA–MIMO (TS-FDA) radar. The former uses a small frequency increment across the MIMO antennas, whereas the latter divides the FDA elements into multiple subarrays using the same waveform within each subarray and orthogonal waveforms in distinct subarrays. The formulated CRLB minimisation problem is solved by convex optimisation. Furthermore, the targets are localised using the beamspace-based multiple signal classification algorithm. The designed FDA–MIMO and TS-FDA radars are evaluated by comparing their mean square error and cumulative distribution function performance.