Adaptive angle tracking loop design based on digital phase-locked loop

Angle tracking loop in airborne radar systems is vital in 3D joint tracking loops of range, velocity, and angle. This study concerns two angle tracking issues when an airborne digital array radar system tracks a maneuvering target: slow convergence, and a divergent issue of tracking errors at the final tracking phase. A new angle tracking loop called “constant coefficient angle tracking loop filter” (CCATLF) based on digital phase-locked loop (DPLL) is proposed. To improve tracking performance, a novel algorithm called “adaptive angle tracking loop filter” (AATLF) is also proposed based on CCATLF. In this algorithm, an adaptive equivalent loop noise bandwidth is derived to adjust with the angle by solving an optimization problem that involves angle measuring value and beam pointing. A theoretical error variance formula and stability analysis of the loop are also presented. Experiment results demonstrate that the proposed AATLF algorithm performs better, and is more effective and robust compared with other angle tracking algorithms.