Array antennas are used for example in satellites of a satellite system for worldwide navigation (GNSS; GNSS=Global Navigation Satellite System), such as the currently constructed European satellite navigation system, better known under the name “Galileo”, in satellite-based imaging radar systems employing Synthetic-Aperture-Radar (SAR) sensors or in Telecommunication satellites. In order to control the antenna excitation, the characteristics of each branch of the distribution network and array radiator elements of the array antenna must be known. Typical parameters describing the characteristics are the propagation time, the phase and the magnitude of a signal propagating through each branch of the array. The characteristics may be used to calibrate the different paths or branches of an array antenna, thus enabling an improved control of the excitation. Usually, an estimation or determination of the characteristics and a calibration cannot be performed during normal operation of an antenna, since this requires emitting special test or calibration signals, which would interrupt the normal operation. This aspect is particular important in case of a GNSS, where the system requirements of operational continuity are usually mandatory.