1 Introduction
Over the past decades, along with the furious development of unmanned technology, UAV has attracted widespread concern in both civilian and military areas. Among them, small fixed-wing UAVs have been extensively employed in such sceneries like environmental monitoring and military reconnaissance, due to their small size, long-endurance and capability of large load [1]. To accomplish the expected missions, UAVs are demanded to track the reference trajectory or prescribed geometric path precisely. Hence, trajectory tracking and path following are fundamental issues of UAVs’ flight control.