Stacked frequency reconfigurable Yagi-like MIMO antenna system

In this work, a 2-layer frequency reconfigurable Yagi-like multiple-input-multiple-output (MIMO) antenna system is proposed based on a closed pentagonal slot-loop excitation. The MIMO system consists of 4 identical active antenna elements reactively loaded with varactor diodes to achieve frequency reconfigurability over a band from 1.5 to 2.1 GHz. The distinguishing feature of the proposed work is achieving Yagi-like directional characteristics over a very wide frequency band. The conventional omni-directional pattern of a slot antenna is made directional by using a parasitic metallic reflector layer below the substrate. By using the reflector element, the back-lobe radiation is highly suppressed and a front-to-back ratio of 5-13 dB is achieved within the entire frequency band of operation. The proposed design is compact with an overall size of 100 × 100 × 20mm³, and a reflector size of 110 × 110mm². A single element has a maximum peak gain of 4 dBi and total measured radiation efficiency of 76%. The antenna system also shows good MIMO performance with high port isolation of 11.3 dB and very low envelope correlation coefficient values within the operational band.