第五代（5G）网络通信系统主要工作在毫米波波段，预计可以提供数千兆的数据速率，这是目前使用无线服务（包括低于6 GHz的频段）所无法实现的。本文简要综述了几种现有的用于5G应用的毫米波相控阵设计。首先，介绍了低剖面天线阵列设计，包括固定波束和仅在一个平面上扫描波束的两种设计类型。随后，介绍了具有二维（2D）扫描能力的阵列系统，该系统对于大多数5G应用而言具有重要意义。接下来，在本文的主体部分，讨论了两种不同的扫描阵列设计策略，这两种策略都规避了用传统移相器来实现波束扫描。值得注意的是，因为在毫米波波段传统的移相器损耗高且价格昂贵，所以找到一个能替代传统移相器的器件是非常必要的；此外，诸如包括射频放大器在内的有源移相器等替代品也是既昂贵又耗电的。在此背景下，本文提出了两种不同的天线系统，这两种天线系统在毫米波范围内具有理想的2D扫描性能。第一种天线系统是龙伯透镜，该透镜由2D波导阵列或微带贴片天线阵列激励，以实现2D扫描能力。第二种天线系统是相控阵设计，该设计采用可切换的PIN二极管或变容二极管取代传统移相器，并将二极管插入波导中的辐射槽之间，从而为扫描提供所需的相移。最后，讨论了几种通过修改传统阵列配置来提高阵列增益的方法。本文还介绍了通过使用可重构的超表面类型的面板来实现一维（1D）和2D扫描的新技术。

The fifth generation (5G) network communication systems operate in the millimeter waves and are expected to provide a much higher data rate in the multi-gigabit range, which is impossible to achieve using current wireless services, including the sub-6 GHz band. In this work, we briefly review several existing designs of millimeter-wave phased arrays for 5G applications, beginning with the low-profile antenna array designs that either are fixed beam or scan the beam only in one plane. We then move on to array systems that offer two-dimensional (2D) scan capability, which is highly desirable for a majority of 5G applications. Next, in the main body of the paper, we discuss two different strategies for designing scanning arrays, both of which circumvent the use of conventional phase shifters to achieve beam scanning. We note that it is highly desirable to search for alternatives to conventional phase shifters in the millimeter-wave range because legacy phase shifters are both lossy and costly; furthermore, alternatives such as active phase shifters, which include radio frequency amplifiers, are both expensive and power-hungry. Given this backdrop, we propose two different antenna systems with potential for the desired 2D scan performance in the millimeter-wave range. The first of these is a Luneburg lens, which is excited either by a 2D waveguide array or by a microstrip patch antenna array to realize 2D scan capability. Next, for second design, we turn to phased-array designs in which the conventional phase shifter is replaced by switchable PIN diodes or varactor diodes, inserted between radiating slots in a waveguide to provide the desired phase shifts for scanning. Finally, we discuss several approaches to enhance the gain of the array by modifying the conventional array configurations. We describe novel techniques for realizing both one-dimensional (1D) and 2D scans by using a reconfigurable metasurface type of panels.Graphical abstractA number of designs for scanning antennas are presented in this work to realize a one- or two-dimensional scan. The first of these is a Luneburg lens, together with a feed array, designed to realize a wide-angle scan The the second design is based on the use of an electronically reconfigurable phase shifter, which utilizes PIN or varactor diodes inserted between radiating slots in a curved waveguide to provide the desired phase shifts. Next, the paper introduces a novel design to realize both one- and two-dimensional scans, by using reconfigurable metasurface type of panels to provide a wide-angle beam-scanning performance, without compromising either the impedance match or the gain of the array. Additionally, the paper describes several techniques for enhancing the gain of the array to achieve gain levels as high as 30 dB, to render the scanning array competitive with reflectors, for instance.Download : Download high-res image (52KB)Download : Download full-size image