A search and localization algorithm is used to localize a ground based moving target using an Autonomous Air Vehicle (AAV). It is assumed that the target has RF emissions. AAV utilizes Global Search (GS), Approach Target (AT), Locate Target (LT) and Target Reacquisition (TR) modes to search the entire parts of a desired area, approach the detected target, locate it, and even find the target that stop transmitting RF emissions during the localization process. In GS mode, the AAV searches the area to receive signal from a target. In LT mode, the AAV performs a circular motion around the target and uses non-linear Kaiman filters (Extended Kaiman Filter (EKF) and Unscented Kaiman Filter (UKF)) to estimate the target position. The numerical results obtained from localization by UKF and EKF show that in many cases UKF converges faster. Additionally, in certain noisy conditions only UKF converges.