A symmetrically crossed-loop antenna featuring very high radiation efficiency across the entire LTE frequency bands for metalrimmed\nsmartphones with only 2mm ground clearance is proposed, analyzed, and verified. The employment of even and odd\nmodes is utilized to achieve wide bandwidth across 698â??960MHz (low-frequency spectrum), 1710â??2170MHz (middle-frequency\nspectrum), and 2300â??2690MHz (high-frequency spectrum). Empirical analysis confirms the crossed-loop topology results in a\n180° phase shift of the electric current distribution on the ground plane, resulting in enhancement of the radiation resistance. As a\nresult, the devised LTE antenna exhibits more than 48% to 75% total system efficiency across the entire band of interest, which is\nthe highest efficiency reported in literature for metal-rimmed smartphones with extremely small ground clearance.
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