This paper presents an inter-loop switched-turn strategy to drive a mobile sensory aerial agent to the unknown source of a scalar signal field in planar and 3-D environments. The source may be stationary, moving or maneuvering, but assumed to be of constant signal strength. No range, bearing angle or gradient information is considered to be available. The only available information are the scalar measurements of the signal field taken by the on-board sensor of the UAV at each time-instant, and the signal strength is assumed to lessen with distance from the source. The effectiveness of the presented method in improving estimation of the direction to the source and in approaching closer to the source in each subsequent loop is shown, and verified by simulation results, both in the presence and absence of noise in signal measurement. The time-efficiency of the proposed method for varied initial conditions, and stationary and mobile sources, is shown through simulation results by comparison with two existing methods. © 2019 IEEE.