Design of a four-element multiple-input–multiple-output antenna for compact long-term evolution small-cell base stations

摘要

This study presents a multiple-input–multiple-output (MIMO) antenna for compact small-cell base stations operating in the long-term evolution (LTE) standard. This MIMO antenna comprises four unit antenna elements, targeted at the frequency band of LTE700/850/900 (698–960 MHz). In comparison with the state-of-the-art MIMO antennas covering these frequency bands, the proposed design enables the maximum number of antenna elements, yet it occupies a compact volume of only × 80 × 50 mm ( × 0.18 × 0.11 ), which is the most miniature electrical configuration to date. The unit antenna element consists of a monopole antenna with a sleeve attached to each side, fed by a coaxial cable. Since the spacing between antenna elements is so small (0.24 ), this work uses four miniature and wideband defected ground structures (DGSs) to reduce the mutual coupling; moreover, although the DGSs adversely alter the impedance matching of unit element, the authors applied multi-objective fractional factorial design to achieve isolation enhancement and bandwidth preservation simultaneously. Accordingly, the optimised MIMO antenna shows desired –10 dB impedance bandwidth and sufficient isolation in the targeted frequency band. In addition, the radiation patterns, antenna efficiency, and the signal correlation coefficients are measured and evaluated.