Sufficient conditions for alias-free direction of arrival estimation in periodic spatial spectra

The problem of broadband spatial spectral estimation with a uniform linear array where the interelement spacing is greater than a half-wavelength over the frequency band of interest is addressed. It is shown that by using properly chosen frequencies, ambiguities in the source location estimates can be resolved. The proposed approach is based on the selection of the wavelengths to ensure that aliased versions of the source component occur at different angles, while the source component in the true direction occurs at the same angle at different frequencies