Optimization of Efficient Dual Band PIFA System for MIMO Half-Duplex 4G/LTE and Full-Duplex 5G Communications

In this paper, a two efficient Planar Inverted-F Antenna (PIFA) system for dual-band functionality on fourth-generation (4G) band (2.5-2.7 GHz) and future fifth-generation (5G) band (3.4-3.8 GHz) is presented. During the optimization process, in order to obtain an efficient system, particular attention has been paid to the antenna system efficiency as well as the isolation between the antennas. Thus, the influence of the antenna slot design used to achieve a dual-band behavior on the antenna efficiency has been particularly studied. Moreover, the antenna positions on the Printed Circuit Board (PCB) have been chosen thanks to the use of characteristic mode analysis to obtain high isolation levels in both bands. The final system is optimized for Multiple Input Multiple Output Half Duplex (MIMO HD) 4G communications and Tx/Rx Full-Duplex (FD) 5G communications. A prototype with 140 mm × 70 mm ground plane was simulated, fabricated and measured. A high isolation level between the two ports of the PIFA elements, better than 35 dB in 5G band and 20 dB in 4G band in simulation and measurement that were done in free space, is obtained. Additionally, the most important diversity metrics are computed to evaluate the potential of this two-antenna system for diversity applications.