A Narrowband Criterion for Arrays of General Geometry

This paper derives the bandwidth that signals should be limited to, by filtration or frequency binning, to ensure that they are narrowband and are processed correctly by array processing algorithms for, e.g., interference nulling and angle of arrival estimation. The narrowband condition is defined as the maximum bandwidth signal that can be fully described by a single significant eigenvalue of the array covariance matrix. A simple closed-form expression for this bandwidth is derived that applies to arrays of arbitrary geometry and that clearly indicates how the maximum bandwidth scales with signal SNR and with array geometry.