Beamforming of synthetic target signal acquired by the Atlantis PCL system

The passive coherent location system, Atlantis, is a test bed for digital beamforming at the Norwegian Defence Research Establishment (FFI). The system has functionality for real time direction of arrival (DoA) estimation. An acquisition experiment involving a synthetic target has been conducted for the purpose of investigating the DoA estimation capabilities of polarized signals. Data recorded during the experiment was subsequently processed offline to test the effect of various beam patterns. The offline processing underlying this report made use of Matlab -scripts replacing the beamscan algorithms of Atlantis. Some findings from this experiment are that DoA estimation works fine for target signals that are co-polarized with the receiver antenna, and for signals where the co-polarized component makes a substantial part of the signal. On the other hand, target signals that are mainly cross-polarized with the receiver antenna appear with a diffuse and sometimes incorrect location. In addition to DoA estimations, attempts were made of suppressing an unwanted signal by placing one or more static nulls in the direction of the known synthetic target signal. Suppression attempts were made for target signals that were co-polarized with the receiver antenna as well as for cross-polarized signals. In the co-polarized case a substantial reduction of the signal noise ratio (SNR) at the nulled signal direction occurred when that direction appeared within 20 from the mainlobe direction. When the synthetic target direction appeared further from the mainlobe, placing a null in the target direction had little effect. Even though the reduction close to the mainlobe was substantial for a single null, it was in most cases more profound when three close nulls were placed in the direction of the synthetic target. Nulling a signal cross-polarized with the receiver antenna turned out problematic.