HALF INVERTED NESTED ARRAYS WITH LARGE HOLE-FREE FOURTH-ORDER DIFFERENCE CO-ARRAYS

Sparse arrays with fourth-order cumulant processing can identify up to $\mathcal{O}(N^4)$ source directions with only $N$ physical sensors. To achieve this property, the fourth-order difference co-array is preferable to own a contiguous segment with no holes. However, existing sparse array designs either have holes in the co-array of size $\mathcal{O}(N^4)$ or own fewer than $\mathcal{O}(N^4)$ elements in the hole-free co-array. This paper proposes the half inverted nested array (HINA), which consists of a nested array and an inverted, scaled, and shifted nested array. By maximizing the size of the co-array, it can be shown that HINA with the optimal parameters possesses a hole-free fourth-order difference co-array of size $\mathcal{O}(N^4)$. Numerical examples demonstrate the improved DOA estimation performance of HINA.