An Examination of Bias in SODA Interferometry

Second-order difference array (SODA) interferometry provides unambiguous high-accuracy direction of arrival (DOA) estimation of RF signals. A low-resolution unambiguous DOA estimate is formed by interferometry with a receiver pair having short separation. This is then used to select from a number of high-resolution DOA estimates formed with a receiver pair of large separation. In this study, SODA is applied to DOA estimation of close sources for which the planewave approximation does not hold well. Expressions for bias in SODA estimates are determined. The conditions under which the bias is large enough to prevent successful disambiguation are explored. Implications for the design and deployment of SODA interferometers are inferred.