By deploying antenna arrays at the transmitter/receiver to provide additional spatial-domain degrees of freedom (DoFs), multi-antenna technology greatly improves the reliability and efficiency of wireless communication. Meanwhile, the application of multi-antenna technology in the radar field has achieved spatial angle resolution and improved sensing DoF, thus significantly enhancing wireless sensing performance. However, wireless communication and radar sensing have undergone independent development over the past few decades. As a result, although multi-antenna technology has dramatically advanced in these two fields separately, it has not been deeply integrated by exploiting their synergy. A new opportunity to fill up this gap arises as the integration of sensing and communication has been identified as one of the typical usage scenarios of the 6G communication network. Motivated by the above, this article aims to explore the multi-antenna technology for 6G ISAC, with the focus on its future development trends such as continuous expansion of antenna array scale, more diverse array architectures, and more flexible antenna designs. First, we introduce several new and promising antenna architectures, including the centralized antenna architectures based on traditional compact arrays or emerging sparse arrays, the distributed antenna architectures exemplified by the cell-free massive MIMO, and the movable/fluid antennas with flexible positions and/or orientations in a given 3D space. Next, for each antenna architecture mentioned above, we present the corresponding far-field/near-field channel models and analyze the communication and sensing performance. Finally, we summarize the characteristics of different antenna architectures and look forward to new ideas for solving the difficulties in acquiring CSI caused by the continuous expansion of antenna array scale and flexible antenna designs.

翻译：通过在发射端/接收端部署天线阵列以提供额外的空域自由度，多天线技术极大地提高了无线通信的可靠性与效率。与此同时，多天线技术在雷达领域的应用实现了空间角度分辨并提升了感知自由度，从而显著增强了无线感知性能。然而，无线通信与雷达感知在过去几十年间经历了独立发展。因此，尽管多天线技术在这两个领域分别取得了巨大进展，但尚未通过利用其协同效应实现深度融合。随着通感一体化被确立为6G通信网络的典型应用场景之一，填补这一空白的新机遇已然出现。受此驱动，本文旨在探索面向6G通感一体的多天线技术，重点关注其未来发展趋势，例如天线阵列规模的持续扩展、更多样化的阵列架构以及更灵活的天线设计。首先，我们介绍几种新颖且有前景的天线架构，包括基于传统紧凑阵列或新兴稀疏阵列的集中式天线架构、以无蜂窝大规模MIMO为代表的分布式天线架构，以及在给定三维空间中具有灵活位置和/或朝向的可移动/流体天线。接着，针对上述每种天线架构，我们给出了相应的远场/近场信道模型，并分析了其通信与感知性能。最后，我们总结了不同天线架构的特点，并对解决因天线阵列规模持续扩展和天线设计灵活化所带来的信道状态信息获取难题提出了新的展望。