Properties of Digital Beamforming with Subarrays

Digital beamforming with array antennas is often applied at subarray outputs. These subarrays can be considered as new array elements; their phase centre is separated by more than half a wavelength. This leads to grating effects when the beam is scanned digitally. We present a mathematical description and properties of digital beamforming and solutions to the grating problem obtained from different optimisation problems. The efficiency of this digital processing is sensitive against the underlying subarray configuration. From this sensitivity it can be derived that partially overlapping subarrays are better suited to reduce grating lobes than non-overlapping (single layer) subarrays or fully overlapping (double layer) subarrays