Review of Recent Phased Arrays for Millimeter-Wave Wireless Communication
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sensors Review Review of Recent Phased Arrays for Millimeter-Wave Wireless Communication Aqeel Hussain Naqvi and Sungjoon Lim * School of Electrical and Electronics Engineering, College of Engineering, Chung-Ang University, 221, Heukseok-Dong, Dongjak-Gu, Seoul 156-756, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-2-820-5827; Fax: +82-2-812-7431 Received: 27 July 2018; Accepted: 18 September 2018; Published: 21 September 2018 Abstract: Owing to the rapid growth in wireless data traffic, millimeter-wave (mm-wave) communications have shown tremendous promise and are considered an attractive technique in fifth-generation (5G) wireless communication systems. However, to design robust communication systems, it is important to understand the channel dynamics with respect to space and time at these frequencies. Millimeter-wave signals are highly susceptible to blocking, and they have communication limitations owing to their poor signal attenuation compared with microwave signals. Therefore, by employing highly directional antennas, co-channel interference to or from other systems can be alleviated using line-of-sight (LOS) propagation. Because of the ability to shape, switch, or scan the propagating beam, phased arrays play an important role in advanced wireless communication systems. Beam-switching, beam-scanning, and multibeam arrays can be realized at mm-wave frequencies using analog or digital system architectures. This review article presents state-of-the-art phased arrays for mm-wave mobile terminals (MSs) and base stations (BSs), with an emphasis on beamforming arrays. We also discuss challenges and strategies used to address unfavorable path loss and blockage issues related to mm-wave applications, which sets future directions. Keywords: beamforming; beam-scanning; millimeter-wave (mm-wave); 5G; line-of-sight (LOS); phased arrays 1. Introduction Of the many fundamental inventions whose histories have been well documented, the origin of the antenna array is not generally known. There has been much focus on Guglielmo Marconi, who was a Nobel Prize-winning scientist, and his famous transatlantic wireless communication in December 1901 [1]. An array of 20 antenna elements was designed for the experiment. Unfortunately, strong winds destroyed the designed array system; therefore, a two-element antenna array was used to successfully transmit a repeated Morse code signal letter “S” from Poldhu, UK to St. John’s in Canada. However, another Nobel Prize-winning scientist, Luis Alvarez, was awarded the recognition globally for the discovery of the electronically scanning phased array. His innovation was initially triggered by the role of the U.S. in World War II, and was the reason for the development of Eagle, which was the first reported radar-based bombing system. Until now, the use of phased arrays has been very common in the defense domain, and the design of warships and military jets focus on phased array radars. 1.1. Phased Array A phased array is defined as a multiple-antenna system that electronically alters or directs the transmission or reception of an electromagnetic (EM) beam [1–3]. These systems can be realized by introducing a time variation or phase delay in every antenna’s signal path to compensate for the path differences in free space. Figure1 shows an illustration of a phased-array receiver with N-channels. 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