This letter presents an antenna system for mobile devices with an unbroken metal rim. By utilizing the characteristic mode analysis for the unbroken metal rim, efficient multiple-input-multiple-output operation can be achieved. The design is based on an antenna cluster technique that uses several coupled elements that are used to efficiently excite the modes of the rim. Nonresonant antenna elements and matching networks are used to couple to the metal rim. The design has small ground clearance of 5 mm and height of only 4 mm, and can operate in wide bandwidths both in 700-960 MHz low band and 1.56-4 GHz high band. Measurement results confirm that competent performance is achieved.