We consider the direction-of-arrival (DOA) estimation of much more targets than the number of physical sensors through the exploitation of multi-frequency sparse array design and processing which increase the degrees of freedom as more frequency components are used. A modified sensor interpolation technique is developed to accurately estimate the signal covariance matrix using very few snapshots, thereby eliminating the requirement of a large number of snapshots as in conventional different coarray-based DOA estimation. Simulation results demonstrate high-resolution gridless DOA estimation capability of more targets than the number of physical sensors.

sparse array; multi-frequency sensing; array interpolation; direction-of-arrival estimation