On the virtual array concept for the fourth-order direction finding problem

For more than a decade, fourth-order (FO) direction finding (DF) methods have been developed for non-Gaussian signals. Recently, it has been shown, through the introduction of the virtual cross-correlation (VCC) concept, that the use of FO cumulants for the DF problem increases the effective aperture of an arbitrary antenna array, which eventually introduces the virtual array concept. The purpose of this correspondence is first to present this virtual array (VA) concept through an alternative way that is easier and more direct to handle than the VCC tool and, second, to present further results associated with this concept, not only for arrays with space diversity but also for arrays with angular and/or polarization diversity.