Dual-Band Antenna Pair With High Isolation Using Multiple Orthogonal Modes for 5G Smartphones

This communication presents a novel decoupling method to design a dual-band closely arranged multiple-input multiple-output (MIMO) antenna pair with high isolation for fifth-generation (5G) smartphones. By combining a bent loop and a T-shaped monopole into a compact space with a miniaturized size of $21.8\times $ 7 mm2, multiple orthogonal in-phase modes and out-of-phase modes are excited at two different bands, respectively, to decrease the mutual coupling. Although the bent loop is closely spaced to the T-shaped monopole, the proposed antenna pair exhibits high isolation of more than 24 dB in dual bands without any decoupling structures. An $8\times $ 8 MIMO system operating at 3.3–3.6 GHz and 4.4–5.0 GHz is developed by arranging four such antenna pairs. The isolation is more than 12.8 dB, the envelope correlation coefficients (ECCs) are lower than 0.18, and the efficiencies are better than 71% and 68% in two bands for the proposed $8\times $ 8 MIMO system. The proposed MIMO system features dual-band operation, compact structure, and excellent isolation, which provides a promising solution for the 5G smartphone antenna design.