Compact low-profile four and eight elements Multi-Input Multi-Output (MIMO) antenna arrays are presented for 5G smartphone devices. The proposed antenna systems can operate at two dual-wideband with triple resonance frequencies that cover the extended Personal Communication Purposes (PCS) n25 band and other related applications, the mobile china's band, and the LTE Band-46. The proposed antenna element is designed based on modified Minkowski and Peanocurves fractal geometries. Desirable antenna miniaturization with multi-band capability is obtained by utilizing the space-filling and self-similarity properties of the proposed hybrid fractal geometries where the overall antenna size is (11.47 mm × 7.19 mm). All antennas are printed on the surface layer of the main mobile board. Based on the self-isolated property, good isolation is attained without employing additional decoupling structures and/or isolation techniques, increasing system complexity and reducing antenna efficiency. For evaluating the performance of the proposed antenna systems, the scattering parameters, antenna efficiencies, antenna gains, antenna radiation characteristics, envelope correlation coefficients (ECCs) and mean effective gains (MEGs) are investigated. The performances are evaluated to confirm the suitability of the proposed MIMO antenna systems for 5G mobile terminals. The proposed eight elements MIMO system has been fabricated and tested. The measured and simulated results are in good agreement.
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