Direction finding and antenna calibration through analytical inversion of radio measurements performed using a system of two or three electric dipole antennas on a three-axis stabilized spacecraft

International audienceWe present an analytical inversion method to achieve direction-finding (DF) (i.e., retrieve the direction of arrival of an incoming electromagnetic wave, its flux, and its full polarization state) using radio measurements performed using a system of two or three electric dipole antennas on a three-axis stabilized spacecraft. The Radio and Plasma Wave Science (RPWS) radio receiver on board Cassini includes such instantaneous DF capabilities, and so does the Solar Terrestrial Relations Observatory (STEREO) Waves radio receiver. We also present an analytical solution of the inverse problem which consists of calibrating the electric dipole orientations and effective lengths using a known radio source. Error sources (imperfect knowledge of antenna parameters, digitization errors, signal to noise ratio, etc.) and their propagation through the analytical inversion have been studied. The typical expected accuracy of our DF inversion is 1 dB [V2/Hz] for flux measurements, about 1-2° for source position and a few percent for degrees of polarization. For the antenna calibration procedure the expected accuracy is of the order of 2° on antenna direction and of 1% on antenna length. We define the data selection criteria to be used during both DF analysis and antenna calibration. We also discuss the limitations of the methods and the ways to improve their accuracy