Sidelobe minimisation in active phased arrays

Active Phased Arrays use complex weighted excitations with digitally controlled attenuators and phase shifters with discrete attenuation and phase states to steer the beam In the desired direction with low sidelobe levels. The actual analog phase shifts of the array elements for the desired beam steering is approximated to these discrete levels resulting in quantisation of the actual phase values. This in turn results in a periodic triangular error leading to the generation of parasitic (quantisation) sidelobes. The present paper describes an algorithm to suppress the quantisation sidelobe levels by using a novel phase randomisation method keeping the discretised amplitude distribution constant, The algorithm utilises only the two lower bits of phase shifters to randomise the phase distribution and to achieve quantisation sidelobe minimisation over the complete array scan zone. The method has been successfully employed on a large Active Phased Array and the simulations are reported.