Low-Profile Four-Port MIMO Antenna Module Based 16-Port Closely-Spaced 2 × 2 Module Array for 6G Upper Mid-Band Mobile Devices

The next six-generation (6G) mobile device is expected to support eight MIMO spatial streams to achieve a much larger spectral efficiency than the current fifth-generation (5G) 4×4 MIMO operation in the mid-band such as the 3.5 GHz band. Thus, for the expected 6G higher-order MIMO operation in the new possible upper mid-band of 7.025-8.4 GHz, the mobile device should have at least eight embedded MIMO antennas. However, owing to the limited space inside the mobile device, embedding a large number of MIMO antennas is a great challenge. In this article, we present a 16-port closely-spaced 2×2 module array formed by four low-profile (thickness 0.9 mm) four-port MIMO antenna modules covering 7.025-8.4 GHz for the mobile device to support up to 16×8 MIMO operation (16 receive antennas for 8 spatial streams). With an extreme or a much larger number of the receive antennas than that of the incoming spatial streams, it is denoted here as the extreme receive antennas (ERA)-aided MIMO for enhanced performance. The 16-port 2×2 module array can fit in a mobile device such as in the backcover region of the modern smartphone. The fabricated module array was applied as 16 receive antennas in the 16×8 MIMO system with 8 spatial streams to achieve a high spectral efficiency of about 56 bps/Hz, which is larger than three times that (about 16 bps/Hz) of the 5G 4×4 MIMO operation in the 3.5 GHz band. Also, in term of the obtained spectral efficiency, the 16×8 MIMO system outperforms the 8×8 MIMO system in which about 34 bps/Hz is reported. Details of the proposed 16-port closely-spaced module array and the measured 16×8 MIMO system performance are presented.