Left-Right ambiguity resolution for coprime sparse arrays

Coprime Sparse Arrays (CSA) with two collocated uniform linear arrays are used to estimate O(MN) direction of arrivals for a narrow band source with only O(M+N) sensors. The CSA cannot discriminate the azimuth and its complementary angles due to the symmetry along the array-axis. The bearing ambiguity, also referred to as a Left-Right (LR) ambiguity, is addressed in this paper using CSA. We design Left-Right resolved Coprime Sparse Arrays (LRCSA) to produce a null that is electronically steered to the complementary angle of the desired direction. LRCSA twin array achieves higher spatial resolution than the conventional fully populated LR array with same number of sensors, much like the collocated CSA. Three methods, namely, Null Constrained Beamformer (NCB), two-dimensional Direct Beamformer (2DDB), and LRCSA are studied. The bound on the detection gain is analytically established for the LRCSA under correlated noise scenarios modeled by the first-order autoregressive process. Twin array processing using the LRCSA method results in narrow mainlobe beam width along with a higher rejection ratio (RR) compared to 2DDB and NCB. Data obtained from a sea experiment using a towed array is analyzed. The results confirm that the CSA based cardioid processing resolved LR ambiguity along with a higher RR and narrower beams.