With the introduction of 5G communication systems operating in the mm-wave frequency range, new opportunities in terms of multimedia services and applications will become available. For this to happen, several technical challenges from an antenna standpoint need to be addressed. The achievements of high-gain characteristics and agile beamforming with wide-scan capabilities are the main targets of the ongoing research on mm-wave antenna arrays. In this paper, an up-to-date overview of antenna array technology for wireless communications at mm-wave frequencies is given. Particular focus is put on the review of the state-of-the art and most advanced antenna array concepts for point-to-point and point-to-multipoint radio links at said frequencies. Various figures of merit are assessed for a comprehensive analysis and bench marking of the technical solutions investigated in the presented survey.
In order to cope with the needs of fifth-generation (5G) cellular networks and beyond, phasedarray antenna systems operating at millimeter-wave (mm-wave) frequencies will be required. This makes the system design very complex. In order to create insight and agility in the design process, we propose a framework that visualises the requirements and trade-offs of 5G-and-beyond systems. Our literature survey uses this framework to compare state-of-the-art papers on Silicon-based beamforming integrated circuits (BFICs) operating in the mm-wave band. Three use-cases are analyzed: Base-stations (BSs), Gateways (GtWs) and User Terminals (UTs). Based on the framework, we explore which implementation fits best with each use-cases. In UT, space and power consumption are the main constraints. For BSs, the main constraint is in output power and noise figure (NF). Finally, in GtW applications there is more flexibility as it has a larger footprint than UT but doesn't necessarily need to cover the same link-budget constraints of BSs. One of the identified limitations throughout all the cases is the heat generation, which is seen as a major bottleneck in mm-wave phased arrays. Only a few of the references show proper modelling and simulations for heat transfer of the realized BFICs. Finally, a limitation in the BFICs is the output power. In order to realize a mm-wave link at least 13 dBm would be required at the input of each antenna element. Only few references meet this criterion, and only at saturation. Further, in order to achieve more than 13 dBm in back-off operation a higher power density would be required. This would imply a further increase of heat generation in the system.
Energy-efficiency is crucial for modern radio-frequency (RF) receivers dedicated to Internet of Things applications. Energy-efficiency enhancements could be achieved by lowering the power consumption of integrated circuits, using antenna diversity or even with an association of both strategies. This paper compares two wideband RF front-end architectures, based on conventional low-noise amplifiers (LNA) and low-noise transconductance amplifiers (LNTA) with N-path filters, operating with three transmission schemes: single antenna, antenna selection and singular value decomposition beamforming. Our results show that the energy-efficiency behavior varies depending on the required communication link conditions, distance between nodes and metrics from the front-end receivers. For short-range scenarios, LNA presents the best performance in terms of energy-efficiency mainly due to its very low power consumption. With the increasing of the communication distance, the very low noise figure provided by N-path LNTA-based architectures outperforms the power consumption issue, yielding higher energy-efficiency for all transmission schemes. In addition, the selected front-end architecture depends on the number of active antennas at the receiver. Hence, we can observe that low noise figure is more important with a few active antennas at the receiver, while low power consumption becomes more important when the number of active RF chains at the receiver increases.
A dual-linear polarised 8-by-8 array of stacked patches is proposed as a flexible, UAV-based, gateway node for Satcom and 5G. The array uses a triangular grid with sequential rotation for a frequency range of 37 GHz to 42 GHz. The scan range extends from −50 • to 50 • on all ϕ-planes while maintaining a scan-loss below cos(θ) 1.1 for most of these scan angles. Moreover, the broadside total active reflection coefficient is below −11.5 dB for the whole frequency range. Circular polarisation is achieved by reconfiguring the two linear polarised ports utilising the beamforming integrated circuits on the phased array to provide the phase difference. The axial ratio is maintained below 3 dB for the whole scan range in the ϕ0 = 0 and ϕ0 = 90 cut. Furthermore, an axial ratio compensation mechanism is presented. This mechanism will use the vector modulators embedded on each antenna port to minimise the axial ratio. The compensation mechanism is experimentally verified on an 8-by-8 active antenna array with similar specifications, where an axial ratio of 0.5 dB is achieved. I. INTRODUCTIONT HE ever-growing market for connected devices has increased the demand for bandwidth and flexibility of communication systems. In order to accommodate the required bandwidth, moving towards millimetre-wave (mm-Wave) frequencies is required. However, mm-Wave frequencies suffer from significant path loss, attenuation, and blockage [1]. Phased-array antennas (PAAs) will be used to compensate these losses, whereas gateway (GtW) nodes [2], a system category between a base station and user terminal, are proposed to prevent blockages by functioning as signal repeaters. Unmanned aerial vehicles (UAVs) have been investigated as flexible GtW nodes in [3] for the fifth generation of mobile communication (5G) and beyond systems.This system, UAV based, is also proposed as a flexible communication interface between satellite communication (Satcom) systems and mobile technologies. A schematic view of this use-case is shown in Fig. 1. In order to serve as a GtW between Satcom and mobile communication systems, UAV based PAAs need to provide both circular-polarised (CP) and linear-polarised (LP) beams -as Satcom uses CP and most mobile communication systems require LP. A possible means to achieve both communication systems is by implementing two separate antenna architectures on a single GtW. However, the system should comply with the stringent swap-c (Size, Weight, Power, and Cost) requirements of . A flexible way to achieve both communication systems is by using a reconfigurable dual-LP antenna element.
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