Direction finding for wideband source signals via steered effective projection

A direction-of-arrival (DOA) estimation method for wideband source signals is proposed in the paper based on broadside steering. The steered effective noise subspace is constructed for each steering angle by collecting a certain number of subordinate eigenvectors of the steered array output covariance matrix according to the effective rank of its noise free version. The steered effective projection (STEP) based wideband direction finding then is realized as the steered effective noise subspace towards a true DOA of signal is shown to be: 1) orthogonal to a 1-D subspace spanned by an all-one vector with one single signal present and 2) approximately orthogonal to a 1-D subspace spanned by an all-one vector in the presence of multiple uncorrelated signals. The STEP method requires no preliminary DOA estimates for data focusing. It differs from the existing effective subspace based broad-band signal-subspace spatial spectrum (BASS-ALE) technique in three respects: 1) STEP employs the steered array output covariance matrices towards all the scanning angles while BASS-ALE takes into account only the (focused) array output covariance matrix; 2) STEP performs frequency independent effective subspace projections by constructing the steered effective noise subspace towards each scanning angle while BASS-ALE uses frequency dependent effective subspace projection by constructing only one (focused) effective noise subspace; and 3) STEP can be realized by spatial-only processing while BASS-ALE needs spatio-temporal joint processing to avoid ambiguity in frequency-angle pairs. The performance of the STEP method has been evaluated by extensive simulations, and compared with some current popular wideband DOA estimators.