Crossing Space, Time And Frequency Domains: Recent Developments of Four-Dimensional Antenna Arrays

Thanks to the time dimension introduced into traditional antenna arrays, 4D antenna arrays break through the boundary of space, time and frequency in array design. In addition to the beampatterns formed in traditional space domain, 4D antenna arrays are also able to be used for the synthesis of beampatterns in time and frequency domains. As typical representatives of 4D antenna arrays, time modulated arrays and frequency diverse array have been receiving much attention in recent years. Due to their powerful beamforming ability, 4D arrays have great potential in the applications to a variety of wireless systems. In this paper, several recent advances on 4D antenna arrays are reviewed and their applications in wireless system are reviewed.