Compact Planar Multistandard MIMO Antenna for IoT Applications

A novel compact single-substrate planar multiband five-element multiple-input multiple-output (MIMO) antenna system is presented in this paper. The tunable two-element folded meandered MIMO antenna covers the long-term evolution frequency bands below 1 GHz (687-813 MHz) and radio frequency identification bands centered around 2.4 and 5.8 GHz. The other two-element compact MIMO antennas operate over 754-971 MHz, 1.65-1.83 GHz, 2-3.66 GHz, and 5.1-5.6 GHz frequency bands. Furthermore, the proposed antenna elements are integrated with a wideband sensing antenna for the spectrum sensing in 0.668-1.94 and 3-4.6 GHz, which also acts as the ground plane for the MIMO elements in the cognitive radio application environment. The antenna is fabricated on a 65 mm x 120 mm x 1.56 mm low-cost FR-4 substrate. The antenna's radiation characteristics are experimentally verified, and the results are in agreement with the full-wave simulation. The 3-D radiation pattern-based envelope correlation coefficient of the MIMO antennas is also experimentally verified which is below the desired value of 0.5. Finally, to show its utility at the Internet-of-Things platform, the antenna is tested in the realistic application environment.