Enhanced Transmit–Receive Beamforming for Frequency Diverse Array

Frequency diverse arrays (FDAs) have a more flexible beamforming ability than phased arrays since they provide degrees of freedom (DOFs) in both range and angle domains by applying a tiny frequency offset across adjacent elements. Nevertheless, the beampattern of an FDA is not only range-angle-dependent but also time variant when only considering the transmit procedure. In this article, an enhanced transmit-receive beamforming approach is proposed to achieve the time-invariant and symmetrical beampattern with only a single maximum value in range-angle space. First, two FDAs with symmetric logarithmically increasing frequency offsets (SLFOs) are proposed to achieve a maximum value at the desired range-angle region while exhibiting sidelobe in the region out of interest. Second, the receive procedure is devised to compensate the time-variant terms with multiple mixers corresponding to different frequencies. To maintain the shape of the mainbeam and simultaneously reduce the peak sidelobe level (PSLL) of the pattern, the optimization problem is constructed into a semidefinite programming problem. Numerical results show that both of the two proposed FDAs exhibit fine focused, symmetrically distributed transmit-receive beampatterns in range and angle domains.