Compact Reconfigurable Antenna for NB-IoT or LTE-M and MIMO LTE2500 Applications

In this paper, a compact dual-band antenna system for NB-IoT or LTE-M (700-900MHz) and MIMO LTE-2500 dedicated to mobile handsets is presented. The system consists of a dual-band Planar Inverted-F-Antenna (PIFA) for LTE-M and LTE 2500 bands where this designed PIFA is frequency reconfigurable in the LTE-M band.Additionally, another PIFA was designed to cover the LTE2500 band to enable Multiple-Input-Multiple-Output (MIMO) communication for this band. Frequency reconfiguration between 700 MHz and 900 MHz is performed by a varactor diode polarized from the RF port using a decoupling circuit to separate DC and RF signals. The compactness of the system, as well as the good isolation between the two antennas, were obtained thanks to the study of the characteristic modes of the mobile phone chassis, where the ideal positions of the antennas can be easily obtained. A prototype of our system was fabricated where good frequency reconfiguration and good MIMO performance (TARC and envelope correlation) were achieved.