第五代（5G）移动通信技术将开启“万物互联”的新时代。为了实现高速率、大连接和低时延的移动通信，5G采用了大规模MIMO和毫米波两项新技术，这将大大提高通信天线的设计需求。然而，在手机等移动终端设备中，天线的设计空间十分有限，从而限制了天线的数量和性能。因此，如何在空间受限的环境下设计兼具小尺寸、高集成度、宽频带、高隔离和高效率等特性的5G移动终端天线成为了5G时代天线设计的瓶颈问题之一。为了解决上述问题，本文从“模式”的角度出发，探索了面向5G移动终端天线设计的多模式协同方法，其分为正交模式法和模式抵消法两个部分。其中，正交模式法是在经典正交理论的基础上进行非对称结构下的扩展，模式抵消法则是从天线阵列的共模和差模出发，提出了一种全新的解耦理论体系。基于多模式协同方法，本文实现了高性能的5G移动终端天线设计，主要包括以下三个方面：利用正交模式法设计5G MIMO终端天线。为了提升天线的空间利用率，本论文提出将两个具有正交模式特性的天线单元紧耦合放置，根据模式的正交性实现高隔离（大于20 dB）的窄带集成天线对，并基于此设计八单元5G MIMO终端天线系统。在此基础之上，再通过低频和高频两组正交模式协同工作的方式可以扩展集成天线对的带宽，实现高隔离的宽带集成天线对，覆盖5G N77/N78/N79频段。所设计天线兼具小尺寸、高集成度、宽频带与高隔离等特性。利用模式抵消法设计5G MIMO终端天线。为了进一步减小集成天线对的尺寸并提高集成度，本论文利用模式抵消解耦方法，设计了四款宽带集成双（或多）天线，并应用于八单元5G MIMO终端天线系统。第一款天线为介质边框下设计的π形自解耦集成天线对；第二和第三款天线为金属边框下设计的具有对偶形态的宽带集成天线对；根据对偶原理，第四款天线将两款宽带集成天线对巧妙结合，实现了国际上首款宽带集成四天线，并可以灵活配置集成的天线数量。利用正交模式法设计5G毫米波终端天线。通过激励紧凑型腔体结构中的一组正交极化端射模式，即垂直极化的腔体模式和水平极化的偶极子模式，本论文提出了一款小尺寸的双极化毫米波端射天线单元，并基于此实现了1×4毫米波相控阵天线，可应用于5G毫米波移动终端。所设计天线兼具小尺寸、宽频带、高增益和宽扫描角等优势，推动了5G毫米波技术的发展与应用。
The fifth-generation (5G) mobile communication technology will enable a new era of “Internet-of-Everything”. 5G mobile communication employs two new techniques, massive MIMO and millimeter-wave (mmW), to realize high-throughput, massive-connection, and low-latency mobile communications, which will significantly enhance the requirement of communication antennas. However, in mobile terminal devices, such as mobile phones, the space for antenna design is too limited to achieve multiple high-performance antennas. Therefore, it is a technical bottleneck in the 5G era to design mobile terminal antennas with compact size, high integration level, broad bandwidth, high isolation, and high efficiency in the space-limited environment.To address the above issues, this thesis explores the multi-mode synergy theory for 5G mobile terminal antennas design based on the perspective of antenna modes, which can be divided into two parts: orthogonal mode method and mode cancellation method. The orthogonal mode method in this thesis is an extension of the classical orthogonal theory in asymmetric antenna structures, whereas the mode cancellation method is a new decoupling theory based on the common and differential modes of the antenna array. Based on the multi-mode synergy theory, high-performance 5G mobile terminal antennas are realized as follows:5G MIMO terminal antennas based on the orthogonal mode method. To improve the space utilization of MIMO antennas, we put two closely-spaced antenna elements with orthogonal modes as a building block, yet a high-isolated (better than 20 dB) narrowband antenna pair can be realized based on the mode orthogonality. Based on such antenna pairs, eight-element 5G MIMO terminal antenna system can be readily implemented. Furthermore, by integrating two sets of orthogonal modes in the lower and higher bands together, the operating bandwidth of the integrated antenna pair can be dramatically improved to realize a high-isolated wideband antenna pair, which can cover 5G N77, N78, and N79 bands. The proposed antenna has the characteristics of compact size, high integration level, wide bandwidth, and high isolation.5G MIMO terminal antennas based on the mode cancellation method. To further reduce the antenna size of integrated antenna pairs and enhance the degree of integration, this thesis proposes four small-size and wideband integrated dual (or multiple) antennas based on the mode cancellation decoupling method, which can be used to design eight-element 5G MIMO terminal antenna systems. The first antenna is a π-shaped self-decoupled integrated antenna pair designed under dielectric frames. The second and third antennas are wideband integrated antenna pairs with dual forms designed under metallic frames. Based on the duality theory, the second and third antenna pairs can be ingeniously combined to achieve a wideband integrated quad-antenna module (the forth antenna), which is the first realization in the world to the best of the author’s knowledge. In addition, the number of integrated antennas can be flexibly configured in this design.5G mmW terminal antennas based on the orthogonal mode method. By exciting a set of orthogonally-polarized end-fire modes in a compact cavity structure, that is, the vertically-polarized cavity mode and horizontally-polarized dipole mode, a compact-size dual-polarized mmW end-fire antenna element can be realized. Based on such element, a 1×4 mmW phased array antenna can be implemented, which can be applied to 5G mmW mobile terminals. The proposed antenna possesses the merits of small size, wide bandwidth, high gain, and wide scanning angle, which promotes the development and application of 5G mmW technique.
