Four-Element Reconfigurable Coupled Loop MIMO Antenna Featuring LTE Full-Band Operation for Metallic-Rimmed Smartphone

This paper describes a low-profile 2× 2 multi-input multi-output (MIMO) antenna system that is fully functional over the entire long-term evolution (LTE) spectrum 699-960 MHz (lower frequency spectrum) and 1710-2690 MHz (higher frequency spectrum) that is applicable to real-life metallic smartphone platforms. The presented methodology entails utilizing the longitudinal edges of the ground plane amid an extremely narrow ground clearance of 2 mm. The metallic frame of the smartphone is utilized along with a stub network to devise a reconfigurable coupled loop antenna topology. The proposed 2 × 2 MIMO antenna configuration is measured and confirmed to exhibit efficient envelope correlation coefficient (<;0.5) and one of the highest radiation efficiencies to be reported in the literature across the entire LTE spectrum.