A Transmission-Line-Based Decoupling Method for MIMO Antenna Arrays

A transmission-line-based decoupling technique for dual-polarized multiple-input and multiple-output (MIMO) antenna arrays is presented and analyzed. The proposed scheme enables well-canceled coupling for the adjacent elements under co-polarization, without degrading the isolation of the cross-polarized ports. First, a decoupling network based on the presented method for a 2 times 2 MIMO array is provided, along with a comprehensive design procedure. Calculations and simulations are operated to verify decoupling performance. For further verification, a 2 times 2 dual-polarized patch array with the proposed decoupling method is developed. The decoupling network characterizes low profile, compact size, and low insertion loss, which is realized in a single layer. Measurements denote that the isolations between the co-polarized elements are improved from 16 to 20 dB to over 30 dB after decoupling at the center frequency of 2.45 GHz. Subsequently, based on the proposed 2 times 2 decoupling method, a decoupling network for large-scale dual-polarized MIMO arrays is presented. A design example of a 4 times 4 dual-polarized patch antenna array is established. Full-wave simulations indicate that the isolations are enhanced to better than 30 dB with a small insertion loss of less than 0.45 dB and can widely be used for phased array and massive MIMO array systems.