On the properties of small arrays with closely spaced antenna elements

In a multipath-rich environment, increased capacity can be gained by replacing SISO with MIMO communication systems. However, at mobile terminals, the implementation of multiple antenna elements is limited. Hence, a reduction of element spacing significantly below λ/2 becomes of high interest, but the associated system degradation must be traded against the benefit of more antenna elements. Previously, we evaluated pattern distortion and SNR degradation caused by mutual coupling (MC) in dense arrays (Chaloupka, H.J. et al., Proc. WCNC, p.425-30, 2003). Using the same eigenmode representation of the antenna array, new results are provided for the effect of MC on the correlation between the complex valued radiation patterns provided by the different antenna ports of a dense array. It has been shown that MC can help to reduce the correlation between signals received at the different ports. We now provide a rigorous model for a quantitative analysis of this effect. Additionally, the reduction of signal power caused by MC is considered and the use of our decoupling network (Chaloupka et al., 2003) is briefly discussed. To allow for a compact presentation of the basic ideas, we restrict ourselves to the consideration of the most simple case, namely a symmetric 2-element structure and neglect dissipative losses in the antenna. However, a generalization to arrays with a higher number of antenna elements is straightforward.