A 5G smartphone-oriented dual-band dual-antenna system designed via characteristic mode theory and surface current analysis

In this research, a compact dual-band dual-antenna system with mutual coupling reduction based on characteristic mode theory and surface current distribution for 5G mobile terminals is proposed. The edge-to-edge distance between two antennas is only 5 mm. The dimensions of the antenna system are 6 mm × 34 mm (approximately 0.07λmin × 0.41λmin, where λmin corresponds to the lowest operational frequency). The design comprises two modified inverted-F antenna elements with parasitic feeding, which are arranged in a back-to-back configuration. A defected ground structure (DGS) and a neutralization line (NL) are employed for decoupling in the lower (3.3-3.6 GHz) and upper (5.1-5.9 GHz) bands, respectively, achieving isolation levels of |S₂₁|< -25.5 dB and < -23.3 dB. The proposed system demonstrates compact geometry, low-cost fabrication, and scalability for array applications. This study presents a systematic design methodology that integrates characteristic mode analysis with current distribution optimization. The proposed approach enables direct translation of current distributions into physical antenna parameters, effectively eliminating empirical trial-and-error processes while establishing a reproducible design paradigm for future antenna development.