Antennas and Propagation Aspects for Emerging Wireless Communication Technologies

The increasing demand for high data rate applications and the delivery of zero-latency multimedia content drives technological evolutions towards the design and implementation of next-generation broadband wireless networks. In this context, various novel technologies have been introduced, such as millimeter wave (mmWave) transmission, massive multiple input multiple output (MIMO) systems, and non-orthogonal multiple access (NOMA) schemes in order to support the vision of fifth generation (5G) wireless cellular networks. The introduction of these technologies, however, is inextricably connected with a holistic redesign of the current transceiver structures, as well as the network architecture reconfiguration. To this end, ultra-dense network deployment along with distributed massive MIMO technologies and intermediate relay nodes have been proposed, among others, in order to ensure an improved quality of services to all mobile users. In the same framework, the design and evaluation of novel antenna configurations able to support wideband applications is of utmost importance for 5G context support. Furthermore, in order to design reliable 5G systems, the channel characterization in these frequencies and in the complex propagation environments cannot be ignored because it plays a significant role. In this Special Issue, fourteen papers are published, covering various aspects of novel antenna designs for broadband applications, propagation models at mmWave bands, the deployment of NOMA techniques, radio network planning for 5G networks, and multi-beam antenna technologies for 5G wireless communications

Experimental Investigation of the Power Amplifiers’ Nonlinearity using a 3.5 GHz 2×2 RF Front-end Prototype

Next generation communication systems will demand extremely high system capacity. Ap-proaches such as complex digital modulation schemes, widening of the instantaneous band-width and massive multi-input multi-output (MIMO) architectures will need to be employed to realize such high capacity systems. However, these approaches impose stringent requirements on the radio hardware. For instance, in conventional wireless transmitters, isolators/circulators are typically used to immunize the radio hardware and its performance from negative effects of the antenna load variation. However, in massive MIMO transmitters, while the antenna active impedance varies significantly, isolators cannot be used due to their unacceptable overhead in terms of cost and space. Thus, within these transmitters the power amplifiers’ (PA) performance in the aspects of linearity, output power and efficiency are significantly impacted by the load modulation introduced by the finite isolation between the antenna elements. To date, studies in the literature have mainly relied on emulating the load modulation in massive MIMO transmit-ters and have used generic PAs rather than those specifically designed for massive MIMO transmission. This work begins by designing a two-by-two RF front-end for a massive MIMO transmitter, comprised of antenna and PA arrays suitable for use in a base station. The antenna array is formed of multilayered patch antenna elements that achieved an enhanced isolation and ex-tended fractional bandwidth of 19 dB and 14%, respectively. The PA array was built using gal-lium nitride transistors and carefully operated in Class J mode. Under continuous wave meas-urements, the PA array element demonstrated high peak-power efficiency of between 54%-66% over the frequency band ranging from 3.2GHz to 3.8GHz. It also showed excellent linear-izability when driven with modulated signals with 200 MHz instantaneous bandwidth. When both the antenna and PA arrays are connected, they form a front-end that was used to study the effects of the antenna load modulation using realistic modulated signals. This study undertook a large set of measurement configurations specifically devised to investigate the effects of cou-pling due to the PA substrate and finite isolation between the antenna elements, as well as the extent of the nonlinearity of the PA elements. Furthermore, a single-input single-output (SISO) digital pre-distortion (DPD) scheme was applied to attempt to linearize the overall response of the PA array. This study revealed that the coupling attributed to the PA substrate had a minor impact on the array’s performance. Furthermore, it highlighted the necessity of jointly designing for both the PA element linearity and the antenna isolation level, so that SISO DPD can be used and MIMO DPD is avoided

Antenna System Design for 5G and Beyond – A Modal Approach

Antennas are one of the key components that empower a new generation of wireless technologies, such as 5G and new radar systems. It has been shown that antenna design strategies based on modal theories represent a powerful systematic approach to design practical antenna systems with high performance. In this thesis, several innovative multi-antenna systems are proposed for wireless applications in different frequency bands: from sub-6 GHz to millimeter-wave (mm-wave) bands. The thesis consists of an overview (Part I) and six scientific papers published in peer-reviewed international journals (Part II). Part I provides the overall framework of the thesis work: It presents the background and motivation for the problems at hand, the fundamental modal theories utilized to address these problems, as well as subject-specific research challenges. Brief conclusions and future outlook are also provided. The included papers of Part II can be divided into two tracks with different 5G and beyond wireless applications, both aiming for higher data rates.In the first track, Papers [I] to [IV] investigate different aspects of antenna system design for smart-phone application. Since Long Term Evolution (LTE) (so-called 3.5G) was deployed in 2009, mobile communication systems have utilized multiple-input multiple-output antenna technology (MIMO) technology to increase the spectral efficiency of the transmission channel and provide higher data rates in existing and new sub-6 GHz bands. However, MIMO requires multi-antennas at both the base stations and the user equipment (mainly smartphones) and it is very challenging to implement sub-6 GHz multi-antennas within the limited space of smartphones. This points to the need for innovative design strategies. The theory of characteristic modes (TCM) is one type of modal theory in the antenna community, which has been shown to be a versatile tool to analyze the inherent resonance properties of an arbitrarily shaped radiating structure. Characteristic modes (CMs) have the useful property of their fields being orthogonal over both the source region and the sphere at infinity. This property makes TCM uniquely suited for electrically compact MIMO antenna design.In the second track, Papers [V]-[VI] investigate new integrated antenna arrays and subarrays for the two wireless applications, which are both implemented in a higher part of the mm-wave frequency range (i.e. E-band). Furthermore, a newly developed high resolution multi-layer “Any-Layer” PCB technology is investigated to realize antenna-in-package solutions for these mmwave antenna system designs. High gain and high efficiency antennas are essential for high-speed wireless point-to-point communication systems. To meet these requirements, Paper [V] proposes directive multilayer substrate integrated waveguide (SIW) cavity-backed slot antenna array and subarray. As a background, the microwave community has already shown the benefits of modal theory in the design and analysis of closed structures like waveguides and cavities. Higher-order cavity modes are used in the antenna array design process to facilitate lower loss, simpler feeding network, and lower sensitivity to fabrication errors, which are favorable for E-band communication systems. However, waveguide/cavity modes are confined to fields within the guided media and can only help to design special types of antennas that contain those structures. As an example of the versatility of TCM, Paper [VI] shows that apart from smartphone antenna designs proposed in Papers [I]-[IV], TCM can alsobe used to find the desirable modes of the linear antenna arrays. Furthermore, apart from E-band communications, the proposed series-fed patch array topology in Paper [VI] is a good candidate for application in 79 GHz MIMO automotive radar due to its low cost, compact size, ability to suppress surface waves, as well as relatively wide impedance and flat-gain bandwidths

Body-centric wireless communications: wearable antennas, channel modelling, and near-field antenna measurements

This thesis provides novel contribution to the field of body-centric wireless communications (BCWC) with the development of a measurement methodology for wearable antenna characterisation on the human body, the implementation of fully-textile wearable antennas and the on-body channel modelling considering different antenna types and user's dynamic effects. More specifically, a measurement methodology is developed for characterising wearable antennas on different locations of the human body. A cylindrical near-field (CNF) technique is employed, which facilitates wearable antenna measurements on a full-body solid anthropomorphic mannequin (SAM) phantom. This technique allows the fast extraction of the full spherical radiation pattern and the corresponding radiation efficiency, which is an important parameter for optimising wearable system design. It appears as a cost- effective and easy to implement solution that does not require expensive positioning systems to rotate the phantom, in contrast to conventional roll-over-azimuth far-field systems. Furthermore, a flexible fully-textile wearable antenna is designed, fabricated and measured at 2.4 GHz that can be easily integrated in smart clothing. It supports surface wave propagation and exhibits an omni-directional radiation pattern that makes it suitable for on-body communications. It is based on a multilayer low-profile higher-mode patch antenna (HMMPA) design with embroidered shorting vias. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that play an important role in generating the optimal mode for on-body radiation. The radiation pattern shape of the proposed fully-textile antenna was found to be similar to a copper rigid antenna, exhibiting a high on-body radiation efficiency of 50 %. The potential of the embroidery technique for creating wearable antennas is also demonstrated with the fabrication of a circularly polarised spiral antenna that achieves a broadband performance from 0.9-3 GHz, which is suitable for off-body communications. By testing the textile spiral antenna on the SAM phantom, the antenna-body interaction is examined in a wide frequency range. Finally, a statistical characterisation of on-body communication channels is undertaken both with EM simulations and channel measurements including user's dynamic movement (walking and running). By using antenna types of different polarisation, the on-body channels are examined for different propagation conditions. Four on-body channels are examined with the one part fixed on the waist of the human body while the other part located on the chest, back, wrist and foot. Channel path gain is derived, while large-scale and small-scale fading are modelled by best-fit statistical distributions

Design, Modelling, and Characterisation of Millimetre-Wave Antennas for 5G Wireless Applications

PhDFuture 5G systems and beyond are expected to implement compact and versatile antennas in highly densifi ed millimetre-wave (MMW) wireless networks. This research emphasises on the realisation of 5G antennas provided with wide bandwidth, high gain, adaptable performance, preferably conformal implementation, and feasible bulk fabrication. Ka{band (26.5{40 GHz) is selected based on recent 5G standardisation, and novel antenna geometries are developed in this work on both rigid and flexible substrates by implementing advanced techniques of frequency reconfi guration, multiple-input-multiple- output (MIMO) assembly, as well as wideband and multiband antennas and arrays. Nove lMMW wideband antennas are presented for 5G and spatial diversity at the antenna front-ends is substantially improved by deploying wideband antennas in a MIMO topology for simultaneous multiple-channel communication. However, wideband operation is often associated with efficiency degradation, which demands a more versatile approach that allows the adaptable antenna to select the operating frequency. In this research, high performance recon figurable antennas are designed for frequency selection over Ka- {band. Also, an efficient and conformal antenna front-end solution is developed, which integrates both frequency recon guration and MIMO technology. Gain of the antenna is critically important for 5G systems to mitigate high propagation losses. Antenna design with both high gain and bandwidth is challenging as wideband antennas are traditionally gain-limited, while antenna arrays deliver high gain over a narrow bandwidth. An Enhanced Franklin array model is proposed in this thesis, which aggregates multiband response with high gain performance. Furthermore, novel flexible monopole antenna and array con gurations are realised to attain high gain profi le over the complete Ka{band. These proposed 5G antennas are anticipated as potential contribution in the progress towards the realisation of future wireless networks.EECS Fees Waiver Award and National University of Sciences and Technolog

Investigation of reflectarray design techniques for 5.8 GHz Fresnel zone power beaming

Large-scale wireless power transfer using microwaves is a promising technology for power transmission over distances unsuited for physical wire connections, such as between orbit and the Earth. Using large transmitting and receiving apertures, it is possible to focus microwave energy to achieve efficient transfer. This is accomplished by adjusting the phase distribution across the surface of the transmitting array such that it behaves like a Fresnel lens. One method of generating the desired phase distribution is through use of an active reflectarray, comprised of many discrete 2-dimensional unit cells with varying reflection coefficient phases. This thesis investigates the effect of changing the unit cell geometry from square to hexagonal, modifying the individual patch element geometry, and incident pilot signal design for the reflectarray.M.S

Applications of Antenna Technology in Sensors

During the past few decades, information technologies have been evolving at a tremendous rate, causing profound changes to our world and to our ways of living. Emerging applications have opened u[ new routes and set new trends for antenna sensors. With the advent of the Internet of Things (IoT), the adaptation of antenna technologies for sensor and sensing applications has become more important. Now, the antennas must be reconfigurable, flexible, low profile, and low-cost, for applications from airborne and vehicles, to machine-to-machine, IoT, 5G, etc. This reprint aims to introduce and treat a series of advanced and emerging topics in the field of antenna sensors

Nouvelles antennes à profil bas multi-standards pour application aéronautique

RÉSUMÉ En avionique les antennes sont utilisées pour e˙ectuer l’interface entre le milieu extérieur et les systèmes de Radio-Navigation et Communication installés à bord de l’aéronef. Ces antennes, installées à la surface du fuselage de l’avion, sont opérationnelles pour des fréquences allant de 0.19 MHz à 40 GHz. L’antenne de référence en avionique est l’antenne lame dite ‘blade’ en anglais. Il s’agit le plus souvent d’un monopôle de longueur d’onde) à polarisation verticale encapsulé dans un radôme en forme de lame fixé sur le fuselage de l’avion. La taille de cette antenne est inversement proportionnelle à sa fréquence. Pour les nombreux systèmes basses fréquences opérant dans les bandes VHF et L cette taille devient importante, ce qui est problématique pour l’avion autant au sol qu’en vol. Au sol, l’antenne à la surface du fuselage peut être endommagée lors des opérations de maintenances. En vol, ceci engendre de la traînée aérodynamique et donc une augmentation de la consommation de carburant. Malgré ces défauts d’ordre matériel, les performances de cette antenne blade (notamment en termes de gain et diagramme de rayonnement omnidirectionnel) demeurent les standards fixés par la RTCA que doivent respecter toutes nouvelles antennes installées sur un avion. Dans les enjeux écologiques du XXIe siècle, le nouveau défit des avionneurs est de concevoir l’avion écologique de demain. Des recherches sont menées pour tenter de diminuer le poids et améliorer l’aérodynamisme des aéronefs. Pour allier ces deux axes de recherche, le développement d’architectures compactes multi-systèmes/multi-standards est élaborée. Par exemple, l’utilisation de Radio logiciels SDR (software defined radio) permet de diminuer le nombre de câbles et le nombre de boîtes avions. Le SDR couplé à une antenne multi-standards à profil bas permet de diminuer la traînée de l’avion et le nombre d’antennes en surface. Les antennes multi-standards à profil bas fonctionnant avec un SDR pour les systèmes DME, TCAS, ADS-B et ILS Glideslope seront le sujet de ce mémoire. Une première antenne patch circulaire à profil bas large bande à polarisation verticale fonctionnant en bande L sera présentée. Cette dernière est multi-standards, elle fonctionne pour le système de mesure de distance DME, le système d’alerte de trafic et d’évitement de collision TCAS et le système de surveillance coopératif ADS-B. La conception de cette antenne fut réalisée en respectant les normes de la RTCA (DO-189, DO-144, DO-260) des différents systèmes cités précédemment. La hauteur électrique est de /30, ce qui représente une diminution de plus de 80% par rapport aux antennes actuellement commercialisées.----------ABSTRACT In avionics, the antennas provide the interface between the outside world and the aircraft systems such as Radio-Navigation and Communication systems. These antennas are mounted on the aircraft fuselage and are working for frequencies from 0.19 MHz to 40 GHz. The most common antenna used in avionics is the Blade antenna. Most of the time, this Blade is composed of a vertically polarized quarter-wave monopole encapsulated in a composite radome. It looks like a shark fin located on the upper and bottom of the fuselage. The size of these antennas is inversely proportional to their frequency. For many systems working in the VHF and L frequency band, this height can be very high, which is problematic for the aircraft on the ground and in the air. On the ground, the antenna can be damaged during the maintenance operation. In the air, the size of the antenna is causing some drag resulting in the increase of fuel consumption. In spite of these drawbacks, the performances of Blade antennas are the standard, especially in terms of pattern radiation and gain requirements set by the Radio Technical Commission for Aeronautics RTCA. All the antennas installed on the aircraft have to meet these standards. Regarding the new environmental issues of the XXIst century, the new challenge of the aeronautic industry is to build a greener airplane. Research to reduce the weight and to improve the aerodynamic of aircraft is on-going. To link these two axes of research, the development of multi-standard/multi-system architecture has emerged. For example, the use of Software Defined Radio (SDR) allows a reduction of the number of wires and the number of avionics boxes. SDR, paired with a multi-standard low-profile antenna, allows a diminution of the drag and the number of antennas installed on the fuselage. Multi-standard low-profile antennas for application with an SDR for the DME, TCAS, ADS-B, and ILS Glideslope are the subject of this master’s thesis. A first vertically polarized low-profile circular patch antenna working in the L band is pro-posed. This antenna is multi-standards. It is working for the Distance Measuring Equipment DME, the Trafic Collision Avoidance System TCAS, and the Automatic Dependent Service Broadcast ADS-B. The antenna was designed to comply with the respective RTCAS’s system standards (DO-189, DO-144, DO-260). The electric height of �/30 is making the antenna low-profile and corresponds to an 80% height reduction compared to the current commercial antennas. A bandwidth of 30% was achieved with the use of a resonant cavity and a capac-itive feeding. The radiation pattern is monopole like in the elevation and azimuthal plane. This antenna was fabricated and tested in the laboratory