Compact linear antenna arrays for MIMO applications

A size reduction technique for linear antenna arrays is introduced. This approach utilizes different orthogonal eigenmodes existing in antenna arrays with highly-coupled elements as individual radiation mechanisms to avoid various undesired effects caused by mutual coupling and spatial correlations. Consequently, very compact linear arrays can be realized by simply having closer inter-element spacing (<; 0.2λ). In this paper, a general theory for this eigenmode technique is presented. Moreover, a prototype three-element linear array operating at 2 GHz is fabricated and tested to validate the concept. For this particular prototype, three identical monopoles separated by 0.2λ are mounted on a PCB of size 1λ × 1λ. They are then connected to a passive multi-port network, which serves as an eigenmode “decoupler”. Measured results indicate that an isolation of more than 16 dB is achieved between any two mode accessing ports of the network/array module, providing three independent radiation channels for typical MIMO applications.