New sparse array for non-circular sources with increased degrees of freedom

Recently, sparse arrays have received considerable attention as they provide larger array aperture and increased degrees-of-freedom (DOFs) compared to uniform linear arrays. These features are essential to enhance the direction-of-arrival estimation performance. However, most of the existing sparse arrays are mainly designed for circular sources and realize limited increment in DOFs for non-circular sources. In this letter, a new sparse array configuration for non-circular sources is presented, which significantly increases the achievable DOFs and improves the direction-of-arrival estimation performance. The proposed geometry comprises two effectively configured uniform linear arrays that exploit the characteristics of non-circular sources and extend the array aperture. For a given number of sensors, its virtual array is advantageously a hole-free uniform linear array. Moreover, the precise sensor locations, achievable DOFs, and optimal distribution of physical sensors are determined analytically by closed-form expressions. Owing to these benefits, the proposed array efficiently resolve multiple sources in under-determined conditions and achieves better direction-of-arrival estimation performance than its counterpart structures. Simulation results validate the superiority of the proposed configuration.