An Isolation Technique for Closely Stacked MIMO Antennas

In this paper, an isolation technique between two closely stacked conventional Inverted-L antennas (ILAs) is proposed for canceling the induced coupling current between adjacent antenna structures. Two ILAs are sharing the common ground plane and oriented with the same polarization. To improve isolation characteristic, the Ground Well Structure (GWS) is inserted between two ILA layers. The GWS delays the current path up to lambda r/2 which can cancel the coupling effect between two closely placed feeding ports. The isolation characteristic is enhanced while maintaining the radiation characteristics of each ILA in LTE 2300 band (2300 similar to 2400 MHz). The envelope correlation coefficient (ECC) is calculated in a multiple-input-multiple-output (MIMO) antenna system, and the ECC is less than 0.26 in the whole frequency band.