ANALYSIS OF ELECTROMAGNETIC-WAVE DIRECTION FINDING PERFORMED BY SPACEBORNE ANTENNAS USING SINGULAR-VALUE DECOMPOSITION TECHNIQUES

By using two rotating noncollinear antennas or three spatially fixed n oncoplanar antennas on a spacecraft, full information on the polarizat ion and the direction of arrival of an electromagnetic wave can be obt ained by measuring the voltages created by the electric field of the i ncident wave. The physical parameters (polarization and direction of a rrival) of the incoming wave are related to the received voltages on t he antenna system by the so-called direction-finding equations. Since the used antennas are generally of small directivity (electrically sho rt monopoles or dipoles), the resulting system of equations is numeric ally close to singular, and generally no unique solution can be obtain ed for the physical parameters of the wave throughout the inversion pr ocess. However, there exists a very powerful tool for dealing with set s of equations that are singular or close to singular, known as singul ar-value decomposition (SVD), which precisely focuses the problem. For illustration, this paper analyzes the direction-finding equations for the Radio and Plasma Wave Science (RPWS) experiment on the Cassini sp acecraft by using SVD techniques. It also compares the expected perfor mances of RPWS with those of the Ulysses Unified Radio and Plasma Wave (URAP) experiment achieved at Jupiter for the kilometer and hectomete r emissions. The RPWS experiment on Cassini, which will be launched in 1997, is supposed to observe wave phenomena between a few hundred Her tz and 16 MHz in the Saturnian magnetosphere.