Phase-Mode Processing for Spherical Antenna Arrays With a Finite Number of Antenna Elements and Including Mutual Coupling

Spherical arrays are the answer to obtain an antenna array with isotropic properties. They are capable of receiving an electromagnetic wave with equal strength irrespective of the direction-of-arrival and the polarization. Yet, the construction of an antenna array with spherical symmetry is far from straightforward. In this paper we derive a compact description for the electromagnetic characteristics of a spherical array. Special care is taken to ensure the spherical symmetry of the array when the number of antenna elements is limited and when mutual coupling is present. Besides extra requirements for the individual antenna elements, an appropriate distribution of the antenna elements is required. By means of synthetic antenna data obtained with full-wave simulations we demonstrate that a spherical array provides efficient beam steering relying on the phase-mode excitation principle.