Co-Located Self-Neutralized Handset Antenna Pairs With Complementary Radiation Patterns for 5G MIMO Applications

In this paper, <inline-formula> <tex-math notation="LaTeX">$4\times 4 / 8\times 8 / 10\times 10$ </tex-math></inline-formula> multiple input multiple output (MIMO) antenna systems composed of co-located self-neutralized antenna pairs are proposed to operate at 4.8-5.0 GHz (part of N77 band) for the fifth-generation (5G) communication applications. The proposed antenna pairs consist of a loop antenna and a monopole antenna, co-locating together with a compact size of <inline-formula> <tex-math notation="LaTeX">$6.7\times 15.5\times 3.08$ </tex-math></inline-formula> mm³. Meanwhile, the co-located design can miniaturize 50% of the antenna size, which is quite significant for practical mobile applications with limited space environment. In addition, the adoption of the self-neutralization technique between the co-located loop antenna and the monopole antenna contributes to a satisfactory isolation with better than 25 / 20 / 16.5 dB for the <inline-formula> <tex-math notation="LaTeX">$4\times 4 / 8\times 8 / 10\times 10$ </tex-math></inline-formula> MIMO systems respectively. Analysis of the isolation improvement is also discussed in this study. Moreover, the antenna pairs are able to generate complementary radiation patterns, enabling the envelope correlation coefficients (ECC) between the antennas to be less than 0.1. Also, efficiencies of the MIMO antenna system achieve up to 60% as there is no external decoupling structure deteriorating the radiation performance of the proposed antenna pairs. Finally, a <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> MIMO antenna system prototype is fabricated and measured to verify its prospect for 5G MIMO applications.