Antenas setoriais para sistemas de localização em redes de sensores sem fios

Doutoramento em Engenharia EletrotécnicaThis work investigates low cost localization systems (LS) based on received signal strength (RSS) and integrated with different types of antennas with main emphasis on sectorial antennas. The last few years have witnessed an outstanding growth in wireless sensor networks (WSN). Among its various possible applications, the localization field became a major area of research. The localization techniques based on RSS are characterized by simplicity and low cost of integration. The integration of LS based on RSS and sectorial antennas (SA) was proven to provide an effective solution for reducing the number of required nodes of the networks and allows the combination of several techniques, such as RSS and angle of arrival (AoA). This PhD thesis focuses on studying techniques, antennas and protocols that best meet the needs of each LS with main focus on low cost systems based on RSS and AoA. Firstly there are studied localization techniques and system that best suit the requirements of the user and the antennas that are most appropriate according to the nature of the signal. In this step it is intended to provide a fundamental understanding of the undertaken work. Then the developed antennas are presented according to the following categories: sectorial and microstrip antennas. Two sectorial antennas are presented: a narrowband antenna operating at 2.4 to 2.5 GHz and a broadband antenna operating at 800MHz-2.4GHz. The low cost printed antennas were designed to operate at 5 GHz, which may be used for vehicular communication. After presenting the various antennas, several prototypes of indoor/outdoor LS are implemented and analyzed. Localization protocols are also proposed, one based on simplicity and low power, and the other on interoperability with different types of antennas and system requirements.O presente trabalho investiga sistemas de localização (SL) de baixo custo baseados na intensidade do sinal (RSS) e integrados com diferentes tipos de antenas com principal destaque para antenas sectoriais. Os últimos anos testemunharam um crescimento surpreendente de redes de sensores sem fios (RSSF), onde entre diversas aplicações possíveis, a localização tornou-se uma das principais áreas de pesquisa. Técnicas baseadas na intensidade do sinal caracterizam-se pela simplicidade e baixo custo de integração. A integração de SL baseados na intensidade do sinal recebido e antenas sectoriais (AS) oferecem uma solução eficaz para reduzir o número de nós necessários e para combinar diversas técnicas de localização. Esta tese de doutoramento foca-se no estudado de técnicas, antenas e protocolos de acordo com os requisitos de cada sistema localização com especial atenção para sistemas de baixo custo baseados na intensidade do sinal e no ângulo de chegada. Inicialmente são estudadas técnicas e SL de acordo com as necessidades do utilizador e as antenas que melhor se enquadram de acordo com a natureza do sinal. Esta etapa tem como objectivo proporcionar a compreensão fundamental do trabalho desenvolvido. Em seguida são apresentadas as antenas desenvolvidas divididas em: antenas sectorias e antenas impressas de baixo custo. Duas antenas sectoriais são apresentadas: uma de banda estreita a operar a 2,4-2,5GHz e outro de banda larga 800MHz-2.4GHz. As antenas impressas foram desenvolvidas para operar a 5 GHz, pelo que podem ser utilizadas para comunicação veicular. Após apresentação das diversas antenas vários protótipos de SL interiores/exteriores são implementados e analisados. Protocolos de localização são também propostos, um baseado na simplicidade e baixo consumo, outro na interoperabilidade com diferentes tipos de antenas e requisitos do sistema

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

Design and development of a low-cost high-performance vehicle mounted UHF RFID system for tracking goods and inventory.

Masters Degree. University of KwaZulu-Natal, Durban.This research work investigates how to design and implement a low-cost high-performance vehicle mounted ultra-high frequency (UHF) radio frequency identification (RFID) system to keep track of cargo whilst in transit. The vehicle mounting include – inside or on cargo vehicle enclosures, the shipping containers, and so forth. In order to achieve a low-cost system, a low cost circularly polarized microstrip patch antenna, which also had a low axial ratio (AR) was designed. Since multiple antennas will be used, the cost factor will be reduced substantially if the cost of each antenna was reduced as compared to reducing the cost of a single RFID reader. The proposed antenna design, measuring 200mm x 200mm x 6.4mm, utilized the corner truncated technology with a thicker substrate and larger ground plane. Two independent simulations were done as well as empirical work. One of the simulations used Computer Simulation Technology (CST) studio suite software and the other used gpr Max simulation software. The investigations aimed at determining how different materials (steel, plastic, and wood) worsen the performance of the UHF RFID system inside a steel container as well as in free space. The investigation involved placing these materials onto the RFID tag and then varying the thickness of the material. The simulation results showed that the proposed antenna has a reflection coefficient of less than -10dB from 886.23 MHz to 924.96 MHz with a bandwidth of 38.73 MHz. The antenna provides the AR less than 3 dB for the frequency range from 915 MHz to 919 MHz. The designed and fabricated antenna has a bandwidth of 57.527 MHz and achieves a minimum reflection coefficient of -27.97 dB at 914.045 MHz. These results were then compared to other similar antenna designs. The antenna designed in this research achieved a lower axial ratio while still offering a respectable amount of gain, directivity and bandwidth. Previous papers showed that there was always a notably trade-off between having a low axial ratio and a high gain, directivity or bandwidth. The results for the simulation tests indicated that wood performs the best, followed by plastic and then steel. Wood and plastic were still detected by the RFID reader’s antenna at their maximum thickness of 20cm and 5cm respectively. It was further found out that the RFID system performs better inside a steel container than in free space. In conclusion the design of a low-cost high-performance circularly polarized microstrip patch antenna allows the cost of the overall UHF RFID system to be reduced, making it a more cost-effective solution for tracking containerized cargo. The antenna also achieved circular polarization which is beneficial to the performance of the UHF RFID system. A circularly polarized antenna allows the UHF RFID reader to detect RFID tags in almost any orientation. The simulation results emulate the data obtained when a horizontally orientated paper RFID tag was used. The results obtained showed the use of steel performed optimally when it is placed directly in line with the receiver. When using plastics, placing them directly in line with the receiver at a distance of 2.36 m, does not offer the best performance. If the plastic material is placed 3 m to the side of the receiver, it is best to use thicker material. The power increased by 3.73 dBm when the thickness of the plastic, increased from 5 mm to 50mm. The system’s performance increased with wood when the RFID tag is in line with the receiver at a distance of 2.36 m, and as the thickness was increased from 20 mm to 200 mm. When the RFID tag was placed 3 m to the side of the receiver, the system’s performance decreased as the thickness was increased from 20 mm to 200 mm.List of Publications on page vii

Wideband and UWB antennas for wireless applications. A comprehensive review

A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems

UWB Technology

Ultra Wide Band (UWB) technology has attracted increasing interest and there is a growing demand for UWB for several applications and scenarios. The unlicensed use of the UWB spectrum has been regulated by the Federal Communications Commission (FCC) since the early 2000s. The main concern in designing UWB circuits is to consider the assigned bandwidth and the low power permitted for transmission. This makes UWB circuit design a challenging mission in today's community. Various circuit designs and system implementations are published in this book to give the reader a glimpse of the state-of-the-art examples in this field. The book starts at the circuit level design of major UWB elements such as filters, antennas, and amplifiers; and ends with the complete system implementation using such modules

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Wideband Microwave Imaging Systems for the Diagnosis of Fluid Accumulation in the Human Torso

According to the World Health Organization (WHO), cardiovascular diseases (CVDs) are the leading causes of death worldwide, with one third of deaths attributed to CVDs in 2012. Pulmonary oedema and pleural effusion are the most apparent symptoms of many diseases categorized under CVDs such as heart failure and lung cancer, at which fluid (mainly with high water content) is accumulated in or around the lungs. Therefore, constant monitoring of fluid levels inside the lungs is one of the most efficient ways of early detection of CVDs. Chest X-Rays and computational tomography (CT)-scans are the most widely used devices for fluid detection; however, they suffer from lack of sensitivity and ionizing radiation, respectively, that makes them unsuitable for long term monitoring purposes. Currently, magnetic resonance imaging (MRI) is the most reliable device that can be utilized for fluid accumulation detection. However, considering the fact that more than 75% of the CVDs occur in countries with low or middle income, it is not widely available. Moreover, due to their bulky structures, the abovementioned devices lack the capability of being used in mobile emergency units such as ambulances or clinics at rural areas. To that end, this thesis is dedicated to design and fabrication of a low cost, portable and non-invasive device that can be used as an initial decision making tool for medical staff to pursue further investigations to define the exact cause of the oedema. First chapter of the thesis is allocated to introduction of the cardiovascular diseases and their effects on the dielectric properties of the tissues inside the lungs. A complete literature review on various alternative methods for replacing the conventional devices is performed. The obtained results by these systems and their advantages as well as their limitations are discussed. Microwave imaging technique is then presented in chapter two as a robust method which can both provide information about the presence and location of the accumulated fluid. This is specifically of great importance for cases where biopsy is required to remove or take sample of the accumulated fluid for saving the life of the patient. Chapter two is also allocated to the introduction of microwave-based medical diagnostic and monitoring systems for different applications such as breast cancer detection and brain imaging. A prospect of the possible realizable systems is investigated and existing scanning approaches are discussed. The main contributions of the thesis that are the design of several complete platforms, design of novel and unidirectional microwave sensors (antennas), promotion of novel scanning and detection methods are clarified in these chapters. In chapter three, firstly the optimum operating frequency for torso imaging is defined. By applying a circuit model that models different layers of torso as circuit elements, it is shown that a wide operating bandwidth at lower ultra-high frequency (UHF) band provides a reasonable compensation between the resolution of the obtained images and signal penetration inside the body. It is explained that due to the limited allowed microwave power for safety considerations unidirectional antennas are required. Then, it is explained that due to the large wavelengths at lower UHF band the sizes of the prospective antennas are expected to be large. To that end, novel miniaturization techniques are proposed to reduce the sizes of the conventional antennas in chapters three and four. These antennas are categorized under three dimensional (3-D) and planar structure. A folding technique is introduced and used in the proposed 3-D structures and it is shown that by using this technique both size and directivity/back radiation suppression is improved. 3-D slot-antenna and cubic monopole-fed antennas are also proposed that wide operating bandwidth is achieved using slot impedance transformer, and multiple resonance-merging techniques, respectively. Regarding the planar structures that are presented in chapter four, it is shown that by combining the loop-dipole modes, both wide-operating bandwidth and directivity enhancement is achievable. Capacitive-loading of a loop antenna is the other proposed technique in which a loop antenna is partially and/or non-uniformly loaded with capacitors in the forms of simple slots and mu-negative (MNG) metamaterial-unitcells that help miniaturizing the size of the antenna by lowering its first resonance frequency. In chapters five and six, several platforms using single and multiple antennas with linear and circular configurations are presented and the utilized imaging technique for data processing is explained. The platforms are presented in a systematic progressive manner in which each system is covering the limitations of its previous prototype. Two final clinical platforms in the shape of clinical bed and doughnut-shaped chamber are proposed and the obtained test results on artificial phantom, animal lungs and human tests are presented. Based on the obtained results on healthy human beings it is shown that the scattered-field from torso of people with different body sizes vary in a reasonably limited range that is a welcoming result for building a global-database to define a threshold for healthy range. Chapter seven concludes the discussions made throughout the thesis and explains future works that can be carried out to further improve the reported systems

Flexible skin-contact antenna with artifical magnetic conductor for health monitoring application

Flexible antenna plays a significant role to ensure efficient wireless communication in wearable devices. The choice of the dielectric substrate material of the antenna is one of the important factors to ensure good antenna performance while being tolerant to mechanical deformation. In addition, the size of the antenna becomes the main issue in designing the antenna for on-body applications. Furthermore, the radiation and transmissions performance of the on-body antenna suffers from performance degradation due to several factors such as dielectric properties of the human body as well as line of sight (LOS) and non line of sight (NLOS) transmission conditions. Therefore, this study presents a flexible Skin-Contact Antenna with Artificial Magnetic Conductor surface (SCA-AMC) made from medical-friendly material. Initially, three different types of medical materials which include transdermal cotton patch, semi-transparent film, and self-adhesive bandage were proposed for investigation as the antenna’s dielectric substrate. The dielectric properties of the proposed materials were measured prior to the antenna design. For preliminary design investigation, a conventional bowtie antenna was designed using the proposed medical materials and optimized to operate at frequency of 2.4 GHz. To achieve the objectives, the feasibility of medical material usage for the antenna’s substrate was explored based on wetness and repeatability test. The proposed SCA is intended for on-body wireless communication devices where there is a significant limitation on the overall size of the antenna. In order to develop a compact flexible antenna, a meandering technique is applied to the conventional bowtie antenna. By employing the meandering technique, the total length of the antenna can be reduced by 20 %. As the body protection against electromagnetic absorption is important, a dipole-like AMC structure was designed at frequency of 2.4 GHz and integrated with the meandered bowtie antenna. The proposed SCA-AMC is made of flexible material for the substrate and conducting parts, making it suitable for wearable applications. Furthermore, the factors that influence the antenna’s radiation and transmission performance have been determined. The experiments have been carried out considering various conditions such as body movements and the presence of either human body or obstacle in between the SCAAMC transmitter and the receiver. The results indicate that the human body introduces an additional 20 dBm power loss when present between the transmitter and receiver. Also, the presence o f the book causes 6 dBm reduction in received power while sweatshirts and cotton polo shirts contribute to a small variation of approximately from 0.5 to 1 dBm. Besides, wetness measurements were also carried out using tap water and sweat-like solution. The sweat-like solution had been developed using a mixture of sodium chloride, sodium bicarbonate, and water. The material characterization of the developed sweat-like solution was then performed. The developed sweat-like solution has a measured permittivity and loss tangent of 75.8 and 0.13, respectively at the frequency of 2.4 GHz. The proposed SCA-AMC was also tested in a real-life situation by merging it with an electrocardiogram (ECG) sensor node. The results obtained show that the wireless ECG pattern is comparable to the ECG pattern measured using a conventional ECG machine. The findings in this research have profound implications for future studies to develop an efficient wireless device, especially for on-body applications

Wideband Circularly Polarized Elements and Arrays for Wireless Systems

Circularly polarized (CP) antennas have received increasing interest during recent decades due to their unique features such as the mitigation of multi-path fading, reduction of the "Faraday rotation" effect when signals propagate through the ionosphere and immunity of the polarization mismatching between transmitting and receiving antennas. Due to the requirements of high date rate and large system capacity, CP antennas deployed in various wireless systems are always demanded to have wide bandwidth. Furthermore, other system requirements such as polarization diversity, wide-angle beam scanning and low power consumption impose additional requirements to CP antennas. Therefore, it is becoming a more stringent requirement to design wideband CP antennas with diverse features to fulfil the requirements of various wireless systems. In this thesis, six different types of wideband CP antenna elements and arrays are designed, fabricated and characterized to meet the different demands of wireless systems. Chapters 3-5 investigate three different types of wideband CP antenna elements while Chapters 6-8 investigate three different kinds of wideband CP array antennas. In Chapter 3, an ultra-wideband CP element with a bandwidth of 100% (3:1) is proposed. It over-comes the problem of limited 3 dB axial ratio (AR) bandwidth for single-feed CP antennas and achieves high front-to-back ratio (FBR) by using a novel ground plane with simple configuration, which makes it a good candidate for high-performance Global Navigation Satellite System (GNSS) receivers. Chapter 4 presents a wideband loop antenna with electronically switchable circular polarizations. It solves the issue of narrow overlapped bandwidth under different polarization states for a polarization reconfigurable CP antenna. Because of the available orthogonal polarizations across a wide bandwidth, this antenna can be deployed in wireless communications which implement polarization diversity. The third antenna element investigated in Chapter 5 tackles the difficulty of designing wide-band wide AR beamwidth CP antennas. It achieves wide AR beamwidth within a 42% bandwidth, which is suitable for wideband wide-angle CP beam-scanning applications. The second main part of this thesis focuses on the investigation of wideband CP arrays. In Chapter 6, a dual-CP beam-scanning array is investigated, which can scan its beam independently in right-hand circular polarization (RHCP) and left-hand polarization (LHCP) from 27 GHz to 30 GHz. It tackles the problem of low isolation between the two orthogonally polarized ports across a wide bandwidth at Ka-band. A single-layer high-efficiency CP reflectarray is proposed in the following Chapter. The proposed design solves the issues of bandwidth limitation and low aperture efficiency for single-layer CP reflectarrays. It achieves the widest bandwidth compared with other CP reflectarrays reported in terms of 3 dB AR bandwidth, 3 dB gain bandwidth, larger than 50% aperture efficiency and undistorted radiation pattern bandwidth. In Chapter 8, we investigate the first application of tightly coupled array (TCA) concept into ultra-wideband arrays with CP radiation. Instead of trying to reduce the mutual coupling among the elements, it exploits the strong mutual coupling to improve the bandwidth of a CP array. By using the strong coupling in a constructive way, it overcomes the bandwidth limitation of CP arrays which are constituted by narrow-band elements