In recent decades, a large amount of studies have been focusing on target tracking using radar measurements. Radar systems typically measure the position of the target in polar coordinates, but in many applications it is of interest to obtain the target Cartesian coordinates. However, due to measurement noise, the conversion from polar to Cartesian coordinates using the classical trigonometric formulas may lead to inaccurate results. This problem can be mitigated by using an observer/filter, which can attenuate the noise effects and provide a more accurate estimate of the target Cartesian coordinates. Designing a state observer, the main two following phases have to be expected: first identifying a system model from an experimental data set, and then designing an observer based on the identified model.