Wideband MIMO antenna with small ground clearance for mobile terminals

In this study, a compact planar multiple-input-multiple-output (MIMO) antenna is presented for mobile terminal applications. Various dual-element configurations are studied using the theory of characteristic modes. The reason of port isolation is explained from the view of modal weighting coefficients. It is found that by arranging the two elements at the top and bottom sides of the board and placing the feed ports at the corners of the board, not only the bandwidth is enhanced but also the port isolation is improved. To further broaden the bandwidth, three branches are well cooperated to provide three λ/4 modes. The optimised no-ground region (i.e. the ground clearance) of each element only occupies an area of 5 × 30 mm². The measured bandwidth can cover the 1710–2690 MHz band with the criterion of −10 dB reflection coefficient. The measured port isolation achieves 19 dB without using any decoupling structure. The efficiency is >60% in the entire band. In addition, the user effect on MIMO antenna performance is evaluated.