A mode-based technique for compact linear MIMO arrays

In this work, a practical technique for building compact linear antenna arrays based on orthogonal radiations is presented. This approach utilizes passive couplers to separate out different orthogonal eigenmodes of linear arrays with closely-spaced elements as individual radiation mechanisms. In this way, undesired effects due to mutual coupling and spatial correlations can be avoided. Consequently, multiple-input-multiple-output (MIMO) radio front-ends can be made very compact in size by simply using antenna arrays of closely-spaced (<; 0.5λ) elements. An experimental three-element array module of 0.16λ inter-element spacing is fabricated and tested. Good isolation (>; 16 dB) between any two of the three signal transmission/reception ports is obtained, and thus, validating this mode-based technique for realizing compact MIMO terminals.