A Simultaneous Wideband Calibration for Digital Beamforming Arrays at Short Distances [Measurements Corner]

Massive multiple-input, multipleoutput (MIMO) is seen as an enabling technology for 5G communication systems [1]. Future base stations (BSs) featuring massive MIMO technology are expected to be equipped with a large number of antennas with digital beamforming structures, where the signals of all the channels are independently accessible. The array radiation pattern can be controlled via setting proper complex weights to the antenna elements to, e.g., form a beam in a desired direction to overcome the unfavorable propagation loss, or to form a null in an interference signal direction to suppress unwanted signals [2]. In addition, spatial multiplexing can also be utilized to serve multiple users simultaneously over the same time and frequency resource with various precoding schemes, which enlarges the network capacity.