2D tracking and over-flight of a target by means of a non-linear guidance law for UAV

This work deals with the definition and the analysis of a 2D guidance law, suitable to be implemented on an UAV guidance loop, capable of driving it toward a target, while it is moving or not. The purpose of the guidance law is to track the target by heading to it and then by indefinitely loitering around it at a prescribed distance. The main features of the proposed law are that it is nonlinear, globally stable, it automatically takes into account the flight performances of the aircraft never forcing unsuited commands. Only the knowledge of the target present position is required. The geometric methodology used in deriving the expression of the law is explained and the global stability of the proposed law is demonstrated for a particular, although important, case, by a Lyapunov-based criterion. The performances of the closed loop behavior has been tested by means of numerical simulations.