A practical method to achieve both decoupling and six polarisation states by employing the mode-based approach for a four-element antenna is presented. The eigenmode theory as well as a practical implementation scheme are presented. The resulting approach can operate with vertical, horizontal, slant +45°, slant −45°, right-hand circular polarisation, or left-hand circular polarisation. A prototype has been manufactured and measured results show good agreement with simulations.

In this paper we propose an antenna design procedure based on the eigenmode decomposition technique which avoids the use of the external matching networks that are typically required at the input ports of the mode decomposition network (MDN). We illustrate the technique by examining the properties of a circularly symmetrical 4-port antenna configuration which can achieve four orthogonal radiation patterns or eigenpatterns and that allows both polarization and pattern diversity. We then use the proposed theory to design an actual antenna structure with eigenmodes operating around 2.6 GHz and whose eigenpatterns are directed in one hemisphere. The antenna and an example MDN are manufactured and tested showing that the four eigenmodes can simultaneously operate in 9.5 % of bandwidth (RL > 10 dB) with a worst case total radiation efficiency of 72 %, correlation coefficient of 0.04, and port coupling of-24 dB. Finally, we use the measured results to assess the antenna in a Multiple-Input-Multiple-Output (MIMO) communication system and demonstrate its beam-tilting capability.

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