A Composite Off-Axis Scan Method for Active Phased Array

Phased Array Seekers (PAS) can be used to achieve longer tracking range in all-weather endo-atmospheric intercep-tors intended to engage long range ballistic targets or highly menuvering aerial targets. The Digital Phase Shifters (DPS) employed in PAS lead to quantization of scan steps which leads to beam pointing errors, off-boresight range losses, or poorer angular accuracies resulting in poorer engagement efficacies. In the classical phased array scanning methods, either an On-Axis target tracking is carried out over narrowly spaced beams, or a pure Off-Axis target LOS estimation is implemented over sparsely spaced ideal beams. Both the classical methods result in lower LOS confidence, the former due to the larger beam pointing errors, and the latter due the poorer off-axis estimation accuracies. This paper proposes a new idea of composite beam-forming and scanning methodology. The proposed method uses a novel composite approach of formation of closely spaced phased array beams and implementation of the off-axis DOA estimation technique. The proposed method gives better accuracy in beam pointing, and better DOA estimation. In addition, the proposed approach has mathematical tractability which will help to avoid need of extensive seeker calibration and result in better angle accuracies as well. The proposed method has been integrated with the guidance algorithm to demonstrate its effectiveness during target homing.