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<p>The development of compact multi-band MIMO antennas for 5G/6G mobile terminals presents significant challenges, primarily due to the trade-off among antenna miniaturization, multi-band operation, and high inter-element isolation. Conventional decoupling techniques often require separate, complex structures for each band, increasing design complexity and layout footprint, which contradicts the stringent space constraints in modern devices. To address these challenges, this paper presents a compact tri-band dual-antenna system for 5G and future 6G mobile terminals. The proposed design consists of two modified inverted-F antennas (IFAs) with extended parasitic feed arms, a multifunctional defected ground structure (DGS) that serves simultaneously as a low-band radiator and a decoupling structure for mid- and high-bands, and a neutralization line for low-band decoupling. The system operates in the 3.3–3.6&#xa0;GHz, 5.1–5.9&#xa0;GHz, and 6.7–7.8&#xa0;GHz bands. With an element spacing of 5&#xa0;mm, the overall antenna size is 6&#xa0;mm × 38&#xa0;mm (approximately 0.07λmin × 0.44λmin, where λmin corresponds to the lowest operational frequency). Independent tri-band tuning is achieved through strategic structural adjustments: DGS dimension controls low-band radiation and decouples mid- and high-bands, IFA arm lengths adjust mid-band performance, and the parasitic feed arm spacing optimizes high-band response. Simulation results show port isolation levels of −16.5&#xa0;dB in the 3.3–3.6&#xa0;GHz band, −18 to −23&#xa0;dB across 5.1–5.9&#xa0;GHz, and −17 to −26&#xa0;dB in the 6.7–7.8&#xa0;GHz band. Measurements show even better performance, with peak isolation values of −23.2&#xa0;dB, −23.7&#xa0;dB, and −48.6&#xa0;dB achieved in their respective operating bands. The operating mechanism of the dual-antenna system is explained using characteristic mode theory and surface current distributions. The proposed tri-band design offers a compact, low-cost structure that can be easily extended to multi-antenna MIMO configurations in mobile terminals.</p>

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A Compact Tri-Band Dual-Antenna System for 5G/6G Mobile Terminals Based on Characteristic Mode Theory and Surface Current Distribution

  • 期刊论文

  • 发表日期：

    2026年2月25日

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  • Zhaozhi Gu,
  • Shibao Li,
  • Wenhan Li

摘要

The development of compact multi-band MIMO antennas for 5G/6G mobile terminals presents significant challenges, primarily due to the trade-off among antenna miniaturization, multi-band operation, and high inter-element isolation. Conventional decoupling techniques often require separate, complex structures for each band, increasing design complexity and layout footprint, which contradicts the stringent space constraints in modern devices. To address these challenges, this paper presents a compact tri-band dual-antenna system for 5G and future 6G mobile terminals. The proposed design consists of two modified inverted-F antennas (IFAs) with extended parasitic feed arms, a multifunctional defected ground structure (DGS) that serves simultaneously as a low-band radiator and a decoupling structure for mid- and high-bands, and a neutralization line for low-band decoupling. The system operates in the 3.3–3.6 GHz, 5.1–5.9 GHz, and 6.7–7.8 GHz bands. With an element spacing of 5 mm, the overall antenna size is 6 mm × 38 mm (approximately 0.07λmin × 0.44λmin, where λmin corresponds to the lowest operational frequency). Independent tri-band tuning is achieved through strategic structural adjustments: DGS dimension controls low-band radiation and decouples mid- and high-bands, IFA arm lengths adjust mid-band performance, and the parasitic feed arm spacing optimizes high-band response. Simulation results show port isolation levels of −16.5 dB in the 3.3–3.6 GHz band, −18 to −23 dB across 5.1–5.9 GHz, and −17 to −26 dB in the 6.7–7.8 GHz band. Measurements show even better performance, with peak isolation values of −23.2 dB, −23.7 dB, and −48.6 dB achieved in their respective operating bands. The operating mechanism of the dual-antenna system is explained using characteristic mode theory and surface current distributions. The proposed tri-band design offers a compact, low-cost structure that can be easily extended to multi-antenna MIMO configurations in mobile terminals.