The optimal design of aperiodic/irregular clustered phased arrays for base stations (BSs) in multi-user multiple-input multiple-output (MU-MIMO) communication systems is addressed. The paper proposes an ad-hoc synthesis method aimed at maximizing the users traffic capacity within the cell served by the BS, while guaranteeing the sufficient level of signal at the terminals. Towards this end, the search of the optimal aperiodic clustering is carried out through a customized tiling technique able to consider both single and multiple tile shapes as well as to assure the complete coverage of the antenna aperture for the maximization of the directivity. Representative results, from a wide set of numerical examples concerned with realistic antenna models and benchmark 3GPP scenarios, are reported to assess the advantages of the irregular array architectures in comparison with regular/periodic layouts proposed by the standard development organizations, as well.