The main purpose of this thesis is comparing two non-linear filters in target tracking usingradar measurements. These two filters are Extended Kalman filter (EKF) and SigmaPoint filter (SPF). This task was given by Kongsberg Defence Systems (KDS). KongsbergDefense Systems use radars and recursive filters to track airplanes.Sigma Point filter (SPF), also known as the Unscented Kalman filter (UKF), andthe Extended Kalman filter have been compared to each other, looking at performanceof estimating states and parameters from radar measurements in spherical coordinates.Airplane trajectories with perturbations in the horizontal plane and pertubations in bothhorizontal and vertical plane as sines and cosines respectively have been estimated. Estimatingtrajectories are often related to, including estimating the states, to estimatesystem parameters as well. The filters have been compared using both unknown andknown process models. Three scenarios have been modelled where the airplane is headingtowards the radar from east, from north east and north against east away from the radar.In addition an object falling through the atmosphere straight above the radar have beenlooked into. Matlab have been used for the simulations.A theoretical evaluation of EKF and SPF are presented indicating that SPF willperforme better than EKF. This is later confirmed with simulations. SPF gives betterestimates than EKF estimating the states of the airplane with both linear and non-linearprocess filter models. Parameters related to the airplane motion are heading angle andangular velocity. The angular velocity are estimated using Multiple Signal Classification(MUSIC). This was done mainly because it was found that the filters had problemsestimating the frequancy needed to compute the angular velocity. Heading angle areestimated by use of a relation in the filters measurement equation giving informationneeded for the filters. SPF is concluded being the best choice in target tracking of airplanessimulated in this thesis. The same conclusions have been made for the falling bodyscenario, where SPF performed slightly better than EKF.