Isolation in Dual-Sense CP MIMO Antennas and Role of Decoupling Structures

This letter investigates the isolation of a multiple-input-multiple-output (MIMO) antenna system, consisting of two circularly polarized antennas with opposite rotating senses. The challenge in achieving a high isolation for this type of antenna system is analyzed and discussed. Based on this, a low-profile wideband design is proposed and demonstrated, in which the role of the decoupling structure is also explained. As a validation, an antenna prototype is fabricated and measured. The operating bandwidth, in which S 11 and axial ratio are respectively less than -10 and 3 dB, is 8.3% (5.2-5.65 GHz). Within this band, the measured peak realized gain in the broadside direction is 6.2 dBi and the isolation is better than 26 dB. In comparison with other related works, the proposed antenna has one of the smallest spacing while maintaining high isolation characteristics in a relatively wide bandwidth with a low-profile structure.