LORA is an ultra-wideband radar system with an array antenna. On ground targets the system produces high resolution synthetic aperture radar images and detect ground moving targets. A system like LORA has high demand on calibration. In this report we investigate the level of accuracy in the calibration. The system is divided in two categories one part for internal calibration and the other part of external calibration. In the radar system there is a calibration signal. If the components are incorporated in the calibration signal the components are internal, otherwise they are external. The internal calibration is dependent on system stability. The stability decides how often the system should be calibrated. For external calibration the transfer function of the external components is measured. The external components have to be stable.