A novel compact MIMO array based on planar Yagi antennas for multipath fading channels

A novel approach to the design of MIMO arrays exploiting directive antennas is presented. It is well known that pattern orthogonality is a key issue to reach low inter-element correlation, and thus to improve channel capacity. However, in the literature the attention is often focused on reducing mutual coupling instead of optimizing the active element patterns. In this paper a MIMO array of printed Yagi antennas with integrated balun is presented. The end-fire radiation mechanism of the Yagi is exploited to obtain a triangular array of three sectoral antennas. This allows to achieve nearly orthogonal patterns and low mutual coupling between neighbour elements. A properly shaped ground at the antenna feeding points allows to reach small inter-element spacings (well below 0.5 λ) which are typically critical for conventional uniform linear MIMO arrays of omnidirectional radiators. The effectiveness of a planar array made of sectoral-coverage elements to improve MIMO capacity is demonstrated through numerical simulations with IEEE 802.11n channel models.