This letter presents a four-element MIMO phone antenna with a metallic rim and 2-mm ground clearance that operates in the low-frequency band. Characteristic mode analysis is used to design the metallic rim so that the structure supports four resonating modes that can be excited separately to obtain MIMO operation in the desired frequency range below 1 GHz. Four exciter elements with matching circuits are designed so that the coupling between the ports is moderate. The prototype is manufactured, and measurement results are shown to corroborate the increased capacity compared to traditional two-element MIMO solutions.
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