Folded quarter-wavelength dual-band 8-element MIMO antenna with high efficiency for 5G smartphones

This paper presents a compact dual-band eight-element MIMO antenna system for sub-6 GHz 5G smartphone applications. The proposed design uses meandered folded quarter-wavelength monopole elements positioned along the side edges of the handset board. Each element is excited by a microstrip feed line on the main substrate, while the radiating strip is printed on the side frame and connected with the common ground plane on the rear side of the board. This configuration provides a compact structure, improved radiation performance, and reduced mutual coupling between adjacent elements. The antenna operates over two important 5G bands, 3.4–3.6 GHz and 4.8–6.2 GHz, covering the n78 and n79 frequency ranges. The fabricated prototype was experimentally tested, and the measured results show good agreement with the simulated response. The antenna achieves reflection coefficients below − 10 dB across the desired bands, with isolation better than 14.5 dB. The measured peak gains are 4.1 dBi in the lower band and 6.86 dBi in the upper band, while the radiation efficiency remains above 80%. The proposed MIMO system also shows strong diversity performance, with an envelope correlation coefficient below 0.01 and a channel capacity of 39.7 bps/Hz. Furthermore, the SAR value remains within the acceptable safety limit, with a maximum value of 1.10 W/kg under typical usage conditions. These results confirm that the proposed eight-element MIMO antenna is a suitable candidate for compact 5G smartphone terminals requiring high gain, low correlation, good isolation, and reliable dual-band operation.