Synthetic aperture radar has become an important technique for generating high-resolution images of the ground, because of its all-weather capabilities. SAR imaging of stationary scenes is nowadays well mastered. If targets are moving, it induces a delocalization and a defocusing effect in the azimuth direction in a SAR image. This last effect can be used to detect moving targets, to image them and to estimate their azimuthal velocity, but the main limitation is the impossibility to estimate the full target velocity vector, because of the Doppler shift dependency on azimuthal position and radial velocity. The purpose of this paper is to use several aspect angles thanks to a circular trajectory acquisition to retrieve the entire velocity and position vector. We first outline the steps of this trajectory reconstruction methodology, then we perform a mathematical analysis of this methodology and finally we present some tracking results on real data, around two French cities.