An Extremely Low-Profile Wideband MIMO Antenna for 5G Smartphones

A low-profile MIMO antenna is proposed for applications in mobile devices. The antenna is designed by placing multiple inverted-F antennas (IFAs) on an artificial magnetic conductor (AMC) ground. The IFAs excite two distinct modes on the AMC, i.e., the local resonant mode and the TM
₀
surface-wave mode. By combining the two modes, a fractional bandwidth of 12% is realized with a profile of 0.01λ
₀
, where λ
₀
is the free-space wavelength at the center frequency. Within the working band, the radiation efficiencies are higher than 50%, the mutual couplings among antennas lower than -10 dB, and envelope correlation coefficients (ECCs) lower than 0.2. To validate the antenna design, a MIMO antenna with eight elements is fabricated and measured. The antenna can work from 3.4 to 3.8 GHz. The total thickness of the antenna is only 0.97 mm, which can be integrated into smartphones as their back-covers without occupying the inner space of the device. The throughput achieved by the antenna in an outdoor environment is also tested using a fifth-generation (5G) MIMO system. The MIMO performance will be discussed and compared with traditional antennas.