Dissertations / Theses on the topic 'Antennes Vivaldi'

Ce travail est consacré à la description de l'antenne Vivaldi et l'utilisation de celle-ci dans divers domaines d'applications, aux ressources spectrales du domaine millimétrique : les systèmes de surveillance radar embarqués et les systèmes de transmission à haut débit. Le premier chapitre repose sur la description et la caractérisation de l'antenne Vivaldi dont le concept repose sur la guidabilité du mode fondamental observé sur la microfente. Dans le deuxième chapitre, l'antenne Vivaldi est incluse dans un système de surveillance radar "monopulse" destiné à la détection et à la poursuite d'une cible mobile. Un réseau de deux antennes alimenté simultanément en phase et en opposition de phase doit générer les deux voies "somme" et "différence" utiles à la détection et à la poursuite. Deux architectures différentes sont proposées. Ces nouvelles architectures sont reprises au troisième chapitre dans une application différente de celle du radar "monopulse". Il s'agit d'une part de la conception d'un transpondeur à diversité de polarisation et d'autre part de celle d'un doubleur de fréquence. Dans le dernier chapitre, des antennes très larges bandes sont présentées, destinées aux applications "intra muros" et boucle radio locale.

LA these presente une premiere etude des technologies uniplanaires dans le but de demontrer leur viabilite dans des applications de type communications par satellites. Le premier chapitre est consacre a la modelisation de l'antenne a rayonnement longitudinal de faible longueur. Un modele theorique proche de la configuration pratique est defini. Le probleme revient alors a l'etude d'une discontinuite en guide ouvert par une methode de raccordement de champs. Ayant defini d'une part, le coefficient de reflexion de la discontinuite et d'autre part, le couplage des modes guides aux modes continus, on peut alors en deduire l'impedance d'entree de l'antenne ainsi que son diagramme de rayonnement. La comparaison theorie-experience valide cette approche simple. Le second chapitre est consacre a la caracterisation de la technologie uniplanaire. Des modeles theoriques simples sont proposes pour les lignes de transmission et les principales discontinuites afin de pouvoir utiliser les logiciels de cao commerciaux. Une methodologie de developpement des dispositifs est proposee et testee sur le cas de transitions coplanaire-microfentes large bande. L'ensemble des resultats obtenus est valide par l'experience. Enfin dans la 3eme partie nous presentons l'etude de l'excitation d'une antenne reseau large bande utilisant les technologies precedemment definies. Un reseau bidimensionnel (4x4) est construit et teste montrant la viabilite des technologies uniplanaires dans ce contexte. Une etude specifique sur les filtres et multiplexeurs associes directement realises sur le meme substrat que les antennes vient renforcer cette conclusion.

Cette thèse a été consacrée à la conception d'antennes volumiques reconfigurables pour les produits sans fils du futur. Ces recherches ont été motivées par la tendance actuelle conduisant à une centralisation des services au sein des réseaux locaux sans fil et une miniaturisation des dispositifs. Ceci se traduit par une contrainte d'encombrement pour les antennes qui se doivent également d'apporter des solutions aux problèmes d'affaiblissements dus aux trajets multiples et aux interférences tout en améliorant les capacités (portée, qualité, consommation) du dispositif. Nous présentons ainsi une solution d'antenne multi-secteurs associant plusieurs antennes Vivaldi en réponse aux problèmes de l'application visée à savoir un système embarqué de type caméra haute définition sans fil. Après une étude théorique de l'antenne Vivaldi, un nouveau concept d'antenne multi-secteurs a été introduit et validé. La nécessité d'une réalisation industrielle à grande échelle et à bas coût de formes complexes nous a conduit vers la technologie plastique métallisé pour fabriquer l'antenne. Un système original de report sans soudure a ainsi été développé pour intégrer l'antenne en plastique au reste du système. La caractérisation d'un prototype a permis de valider l'utilisation du plastique pour ce genre d'applications. Cette antenne a ensuite été intégrée à une caméra sans fil puis recouverte d'un radôme protecteur qui permet d'améliorer les performances. Cette intégration simplifiée associée au contrôle des performances et à la flexibilité de l'antenne permet d'envisager des utilisations dans des applications aussi diverses que les réseaux domestiques ou maillés, ou pour la technologie MIMO
This thesis is dedicated to the design of 3D smart antennas for forthcoming wireless devices. Our research work has been motivated by the actual wireless trends leading to service concentration within WLAN and device miniaturisation. Thus, antenna design is nowadays guided by size constraints and their capacity to deal with fading interference, wireless environments while improving the performances of devices in terms of communication quality, power consumption. This thesis presents a multi-sector antenna solution associating many Vivaldi-antennas to provide a solution for the targeted application which is an embedded system constituting of high definition wireless cameras. A theoretical analysis of the Vivaldi antenna is first performed and then a novel concept of multi-sector antenna has been introduced and validated. Then, in order to target consumer market and to reduce the manufacturing costs in high volume production, the metallized molded plastic technology which enables molding 3D complex structures has been retained. An original without-welding transfer system has been developed for integrating the antenna to the rest of the system. The characterization of a prototype has resulted in the validation of the use of plastics for such applications. This antenna has been integrated in a wireless camera ; a protective radome having as additional property to improve the overall performances of the device is finally designed. This simplified integration procedure associated to a monitoring of the performances and the flexibility of the system makes it a good candidate for various applications like domestic WLAN, mesh networks or for MIMO technology

Les systèmes électroniques sont au cœur de notre vie quotidienne, ils sont intégrés dans la plupart des objets que nous utilisons chaque jour, et dans des secteurs clés comme l’aéronautique, l’automobile, le spatial, l’électronique grand public... Les techniques d’alimentation classiques (pile ou batterie) restent difficiles à envisager dans certaines applications car, elles sont limitées en autonomie, elles nécessitent des remplacements périodiques et leur recyclage est coûteux. Afin de détourner ces contraintes, le concept de la transmission d’énergie sans fil se présente comme une alternative aux systèmes d’alimentation classiques. La récupération d'énergie électromagnétique a beaucoup attiré l'attention puisque la puissance RF est largement diffusée à partir de nombreuses ressources électromagnétiques fiables. De plus, les circuits électroniques et notamment microondes deviennent de plus en plus rapides à cause des fréquences de travail de plus en plus élevées. L’analyse fréquentielle seule ne peut répondre à un certain nombre d’interrogations dans ces circuits. Une analyse purement temporelle devient nécessaire pour résoudre et répondre à toutes les problématiques. Parmi les problèmes posés dans les circuits microondes, on s’intéresse à deux approches totalement complémentaires:• L’Intégrité du Signal qui représente le dysfonctionnement des circuits du à la distorsion des signaux. • La Compatibilité ElectroMagnétique qui est le résultat de l’encombrement des composants électroniques dans les circuits. La première approche se base sur les modèles de composants et peut prédire parfaitement la qualité des signaux pendant le placement et le routage des cartes électroniques. En revanche, il sera très difficile de mettre en évidence les causes du comportement anormal du circuit en question. La deuxième approche complémentaire de la première, et qui est l’analyse par la compatibilité électromagnétique permettra de couvrir les causes du problème tels que diaphonie (Cross Talk), rayonnement et susceptibilité des systèmes dans le but de corriger le circuit pour qu’il fonctionne correctement.La méthode de travail adoptée dans cette thèse consiste dans un premier temps à identifier les différents problèmes. Ensuite proposer des solutions via des codes de calcul existants (FDTD, FEM, MoM…) et qu’on pourra développer (2D) ou bien via des logiciels adaptés tels que Spice, Matlab, EMPro, ADS…..etc
Electronic systems are integrated into most objects that we use every day, also in different key sectors such as, automotive, railway, spacial, defense and consumer electronics... Conventional feeding techniques remain difficult to envisage in certain applications because they are limited in their autonomy energy, and they require periodic replacements and their recycling is expensive. In this mind, the wireless power transfer is a very interesting solution, less expensive and aesthetic. This solution needs to pick up the RF power transmitted through the free space by a Rectenna and convert it to a DC voltage, to feed one or several wireless devices or to increase the operating life of batteries.The high operating frequencies makes the microwave circuits faster. Frequency analysis can’t answer a number of questions in these circuits. The introduction of the temporal analysis becomes necessary to solve and answer all the problems encountered. In fact, we are interested in two complementary approaches:• Signal integrity, which represents the malfunction of the circuits due to the distortion of the signals• ElectroMagnetic Compatibility, which is the result of the congestion of the electronic components in the circuits.• The first approach is based on component models and can perfectly predict signal quality during placement and routing of electronic boards. On the other hand, it will be difficult to highlight the causes of the abnormal behavior of the circuit. The second approach, is complementary of the first one, which is the analysis by the electromagnetic compatibility, who will allow to cover the causes of the problems such as cross talk, radiation and defined the susceptibility of this systems to work correctly.The working method adopted in this thesis consists in first identifying the various problems. Then propose solutions via existing calculation codes (FDTD, FEM, MoM ...) who can be developed or via the software such as Spice, Matlab, EMPro, ADS …Key words: Wireless power transfer, UWB systems, numerical methods, Rectenna systems, RF/DC converter, EMC analysis

La technologie in-band full-duplex a pour objectif d’augmenter l'efficacité spectrale des liaisons sans-fils en permettant à deux systèmes de communiquer simultanément dans la même bande de fréquence. Dans cette configuration in-band full-duplex, le principal défi consiste à annuler ou réduire les signaux d’auto-interférence, qui se couplent de l'émetteur vers son propre récepteur. Divers circuits d'annulation d'auto-interférence peuvent alors être mis en oeuvre : au niveau de l’antenne, de l'étage analogique et/ou numérique. Les techniques classiques d'annulation d'auto-interférence sont majoritairement dédiées aux systèmes à bande étroite et peu de travaux ont été menés pour étendre leurs performances à un fonctionnement en large-bande et encore moins en ultra-large-bande. Dans ce travail, nous nous focalisons sur l'étude des techniques d'annulation compatibles avec un fonctionnement ultra-large-bande et sur leurs mises en oeuvre. Les systèmes antennaires proposés sont basés sur une technique d'annulation en champ proche qui utilise quatre antennes et deux baluns. Les avantages des systèmes développés sont multiples, ils proposent tous une bande passante extrêmement large tout en maintenant un niveau d'annulation d'auto-interférence au moins supérieur à 55-60 dB sur cette bande avec des configurations permettant soit d'en augmenter la solidité mécanique, soit d'obtenir une double polarisation ou encore avec une alimentation innovante des antennes
In-band full-duplex technology aims to mitigate the scarcity of spectral resources by allowing two radios to communicate simultaneously in the same frequency band. The main challenge for full-duplex radios is to cancel the self-interference signals, which couple from the transmitter of one radio to its own receiver, by implementing various self-interference cancellation circuitry at the antenna, analog, and digital stages of the radio front-end. Conventional self-interference cancellation techniques were dedicated for narrowband systems and little work has been conducted to extend their performance for wideband operation. Thus, in this work, we focus on studying the wideband potential of the available cancellation techniques and implementing wideband full-duplex systems based on those techniques. The implemented systems are based on the near-field cancellation technique which uses four antennas and two baluns. The systems' merits vary from extremely wide bandwidth to higher mechanical solidity and dual-polarization, but they all can maintain a decent amount of cancellation

In this thesis, we have investigated antenna elements that allow broadband operation and are relatively compact, while determining methods by which their geometry may be adapted, or various points in their structure loaded, in order to form reconfigurable antennas that may allow their polarisation or matching characteristics to be electronically altered. Much of the work undertaken has involved evanescent open-ended waveguide antennas, whereby the waveguide is operated below its cutoff frequency. Various novel matching methods have been developed, involving: (i) Using the Imaginary Smith Chart to design a match to the aperture admittance of an open-ended wave guide, and thereby to free space, with the match made reconfigurable through loading of the structure using a varactor diode. (ii) Use of capacitive coupling between an open-ended waveguide antenna's coaxial input feed and capacitive obstacles placed across the aperture of the antenna to obtain a broadband match, with polarisation-agile performance possible through varying the ex citations supplied at the input ports of the antenna. (iii) Application of band-pass filter techniques to design a match to the aperture admittance of an open-ended waveguide, through the use of alternating propagating/evanescent sections or by loading the antenna with capacitive obstacles. Radar cross-section reconfigurability is demonstrated, through a printed obstacle with switch implemented at the aperture of the waveguide. The Vivaldi antenna has also been the subject of investigation in the project, with the most notable result obtained being the design of an antipodal Vivaldi antenna loaded by shorted slotline stubs that have a variable capacitor placed across them; this allows wideband operation but with a tuneable rejection band, which enables rejection of cellular and ISM bands.

Esta tese propõe a síntese e o estudo de uma nova técnica de cavidades de borda aplicada a antenas Vivaldi, com o intuito de melhorar suas características de diretividade. Embora as antenas do tipo Vivaldi possuam características diretivas, elas produzem radiações laterais indesejáveis, o que se reflete nos elevados índices de lóbulos laterais devido a correntes superficiais que fluem ao longo das bordas metalizadas nas laterais da antena. Estas correntes são a origem das radiações laterais que vêm sendo mitigadas pela aplicação de cavidades ressonantes, triangulares ou retangulares, que aprisionam tais correntes e, consequentemente, atenuam os lóbulos laterais, sem o incremento do lóbulo principal, uma vez que toda a energia dos lóbulos laterais é apenas confinada nos ressonadores e por isso literalmente perdida. Ao contrário desses esforços, este trabalho propõe cavidades radiantes tanto na forma de abertura exponencial, como na forma do fractais de Koch, que funcionam como radiadores auxiliares (antenas auxiliares), canalizando as correntes de borda e aproveitando-as para aumentar os níveis do lóbulo principal, mitigando os níveis de lóbulo lateral. A síntese desta nova técnica foi implementada em uma antena Vivaldi antipodal com características de baixa diretividade, como qualquer antena Vivaldi, o que foi corrigido e a aplicação da técnica de cavidades radiantes deu origem a duas novas antenas Vivaldis efetivamente diretivas. Os resultados foram obtidos através de simulações do modelo numérico no CST Microwave Studio e confirmados com medidas de laboratório, o que evidenciou a melhora das características de diretividade da antena pela aplicação da nova técnica de cavidades radiantes.
This work presents a new Slot Edge technique applied to Vivaldi antennas to improve their characteristics of directivity, resulting in two new Vivaldi antennas: the Palm Tree Vivaldi antenna and the Koch Vivaldi antenna. This new technique proposes to add lateral radiators which reduce the side lobe level, increasing the gain of the main lobe in an unprecedented way. This technique is called radiating slot edges, and acts as parasitic antennas, surface currents draining edges of the antenna, and using them to increase the gain in the main lobe. The development was done systematically, starting with an extensive literature review, design and simulation in CST, as well as prototyping and measurements of several antenna designs. All this effort proved the functionality of this technique.

In this thesis, parametric study and design of Vivaldi antennas and arrays are studied. The parameters of single element antennas and arrays are investigated regarding their effects on the design. The return loss responses and radiation patterns are considered in the parametric study. The results of simulations realized using Ansoft HFSS, a high frequency electromagnetic field simulation program, are shown and discussed. Two different Vivaldi antennas operating in 8.5-10.5 GHz frequency band with return loss responses better than 15 dB are designed based on the results of parametric study. Stripline to slotline transition is used in the feeding section of both antennas. In the same manner, two different 8-element uniform linear arrays operating in 8.5-10.5 GHz with half power beam widths smaller than 12&
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and side lobe levels smaller than 13 dB are designed. Binomial and Dolph-Chebyshev feeding techniques are also investigated in order to improve half power beamwidths and side lobe levels of the designed arrays. The designed single element Vivaldi antennas and a linear array of Vivaldi antennas are fabricated. The return loss response and radiation patterns of the fabricated antennas and the array are measured and compared with the simulation results.

This dissertation investigates the use of the harmonic radar technique for passive wireless sensing applications. Issues of DC power consumption, high RF activation power, large node size, and short communication range associated with the existing passive wireless sensing technologies are addressed by the development of novel, completely passive, high efficiency, compact 3-D harmonic sensor nodes. The node transceiver employs a passive frequency doubler to return the second harmonic of the interrogation signal, and electrically-small 3-D antennas to achieve the compactness and high efficiency. The developed nodes fit inside a sphere with a diameter < 3 cm and achieve communication range > 60 m using a 43 dBm EIRP interrogator. Effective modulation is demonstrated experimentally using low cost commercial vibration sensors. To address major challenges associated with long-range, embedded, passive wireless sensing including sensor node identification and remote channel calibration, a 3-D dual-channel transceiver is developed. To the best of the author's knowledge, the presented dual-channel transceiver is the first completely passive design with built-in passive remote channel calibration and identification capabilities, and the presented nodes have the best overall performance among previously published designs, in terms of conversion efficiency, communication range, and occupied volume. To reduce the cost and weight and improve the manufacturing process of the proposed nodes, the 3-D digital additive manufacturing and conformal direct printing technologies are employed. The harmonic interrogator antenna design is also an underlying focus of this work. Different interrogator antenna candidates are developed based on different design approaches. The first approach is based on the use of dual-channel antenna array, where one channel is used for transmission and the second channel is used for reception. Two dual-channel harmonic interrogator antennas that consist of 4-element circular patch antenna arrays and 2-element quasi-Yagi dipole antenna arrays are implemented. The second approach employs mechanically reconfigurable antennas to reduce the size and maintain persistent radiation properties over wide frequency bandwidth. Two mechanical reconfiguration methods are developed; the first method is based on the use of Hoberman's planar foldable linkage to vary the operating frequency of planar circular patch antennas and the second mechanical reconfiguration method is based on the use of a rack and pinion mechanism to reconfigure dual-band slot antennas. The third approach employs a single channel multi-octave Vivaldi antenna to provide the capability to interrogate a large number of harmonic tags that are widely spaced in frequency. To improve the antenna radiation performance over a broad frequency range, a new method based on the introduction of a parasitic elliptical patch in the flare aperture is proposed. This method enables gain and bandwidth improvement compared to what has been reported for Vivaldi antennas with a compact size. To provide the interrogator the capability to steer the radiation beam for locating and tracking sensor nodes, a topology to develop a miniature, non-dispersive switchable 4-bit phase shifter is proposed on the basis of composite right/left handed transmission line unit cells.

Basic properties and new design principles of ultra wideband Vivaldi antennas are presentedand discussed in this paper. The focus will be on the modeling of Vivaldi antenna design curves, by which it is constructed; its simulation results, realization and the measurements.

According to the aim of this research the discussion starts with the review of the previous researches done for Vivaldi antennas. Introductory part of the report also contains the problem description for the current project and the classification of the goals to be achieved. As a theoretical review, the discussion initiates with the definitions anddescription of basic parameters of the antennas and covers a short presentation of UWBpulse-based radar system. The attention will be focused on UWB signals behavior and characterization, their propagation principles and basic troubles stands nowadays. As anapplication the wall penetrating Radar systems will be considered. The major part of thereport holds on the investigation of the design principles of Vivaldi Antenna andoptimization of the key parameters for achieving the best performance for radar. Theending part of the report shows the simulations and measurement results and theircomparisons following with conclusions/discussions.

The report will be supportive for the antenna designers, who work for UWB systems andparticularly for Vivaldi antennas, as long as there are showing up detailed descriptions ofVivaldi antenna characteristics depending on its shape and substrate properties. The modelfor designing Vivaldi antennas, given in this project, can successfully be applied for almostall the cases used in practice nowadays.

O objetivo deste trabalho é desenvolver um modelo conceitual de um sistema transmissor de pulsos eletromagnéticos de banda ultra-larga, capaz de realizar o controle da formação do feixe irradiado de forma totalmente eletrônica. Para isso, é proposto um sistema formado por quatro canais iguais e independentes, sendo que cada um é formado por um controlador de atraso programável, com o qual se pode ajustar a defasagem temporal entre os pulsos de cada canal, um gerador de pulso, capaz de sintetizar a quinta derivada do pulso Gaussiano a partir de uma nova proposta de topologia, e um arranjo de antenas do tipo planar de abertura exponencial conhecida como antena Vivaldi. O sistema proposto é apoiado por modelos matemáticos e simulações elétricas post-layout com variação dos parâmetros por Monte Carlo com os programas LTSpice 4 e Microwind 2.6, utilizando as regras de processo padrão CMOS 180nm e eletromagnética tridimensional com o uso do programa CST Microwave 2011. Os resultados obtidos nas simulações, comparados com propostas anteriores, indicam que realmente houve o controle da formação do feixe irradiado cujo lóbulo principal teve uma magnitude média de 11dBi com uma largura angular do feixe de 33º x 38º e possibilidade de variar os ângulos azimutal e de elevação de -15º a 9º e -18º a 6º, respectivamente, para uma frequência central de 6GHz. O pulso utilizado para estimular as antenas foi o pulso Gaussiano em sua quinta ordem de derivação, que teve como resultados médios de simulação uma amplitude de 90mVpp, uma largura de pulso de 370ps a uma taxa de repetição de 100MHz e uma frequência central de 6GHz.
This work aims to develop a conceptual model of the new Ultra Wide-band fifth-order derivative Gaussian pulse transmitter with Vivaldi antenna array for beamforming using the technique of timed-array. It is proposed a system formed by four equal and independent channels, each of which is formed by a programmable delay controller in which one can adjust the delay time between pulses of each channel, a pulse generator, capable to synthesize the fifth derivative of a Gaussian pulse using a new topology, and a planar Vivaldi antenna. The proposed system was supported by mathematical models and post-layout electrical simulations with parameters variation by Monte Carlo in programs LTSpice 4 and MicroWind 2.6 using the CMOS 180nm Standard process rules and using three-dimensional electromagnetic program CST Microwave 2011. The simulation results indicated that there was indeed control on the beam formation irradiated whose main lobe has an average magnitude of 11dBi with an angular width of the beam 33 x 38 (degrees square) and possibility of varying the angles of azimuth and elevation from -15 to 9 degrees and -18 to 6 degrees, respectively, at a center frequency of 6GHz. The pulse used to stimulate the antennas was the fifth order Gaussian one, which had the average results of a simulation 90mVpp amplitude, a pulse width 370ps to a 100MHz repetition rate and a center frequency of 6 GHz..

This thesis describes design and experimental verification of three types of the wideband antenna Bow-tie antenna, Vivaldi antenna and Spiral antenna. The tracked parameters are bandwidth, input impedance, gain and directivity patterns. Next step is design of millimeter-wave horn antennas. Attention is turned to the proper construction of a wideband feeder of the horn. For the final antenna structure, a bow-tie dipole and a Vivaldi antenna were chosen. The antenna construction is aimed to provide a wide bandwidth on one hand and a high gain on the other hand.

This master thesis deals with a design of Vivaldi antenna due to its broadband properties suitable for radar applications. The folding of single Vivaldi antenna element into 2D antenna array we achieved required radiation properties. Appropriate design of feeding structure realized by SIW technology we obtained suppression of side lobes and deflection of the main lobe. The work also includes design of 3D Vivaldi antenna array. Modeling, simulation and optimization of antenna array were performed in CST Microwave Studio.

碩士
元智大學
通訊工程學系
105
The research in this thesis is separated into two parts: the design of Vivaldi antenna for 4-G Base Transceiver Station application and compact antenna test range (CATR) feed antenna design At present, most of the antennas in the base station are built using dipole antenna arrays, but the beamwidth of dipole antenna is very narrow. That is the reason why I choose the Vivaldi Antenna instead of dipole antenna to complete the design. The first part of this thesis will mainly focus on the design and characteristics of the high-frequency and low-frequency Vivaldi antenna along with its simulation and measurement results. In the second part, the design of CATR feed antenna will be discussed. In the future, there will be more and more mobile devices using mmWave as the communication band. As the physical sizes of the devices are fixed, the distance required for the antenna measurement will be much longer than before while choosing the mmWave as the operation frequency. However, most of the antenna measurement laboratory cannot handle this kind of measurements. Therefore, CATR will be the mainstream of antenna measurements for mmWaves. Thus, the design of the feed antenna used for the CATR system is presented in this thesis.

Over the past two decades, Vivaldi antenna arrays have proven to be versatile solutions for wideband, widescan phased array systems, providing 10:1 bandwidth, or more, with 45 degree scan range. The increasing demand for using Vivaldi antenna arrays in diverse, high-performance systems creates the need to explore new concepts under new perspectives, three of which are addressed here: modularity, low-profile and dispersion. Modularity introduces a discontinuity in the E-plane that is disruptive to performance in finite as well as infinite arrays. The effect of this discontinuity is studied in greater detail in infinite arrays with modularity of elements and sub-arrays. Based on the underlying physics the severe resonances observed are characterized, and it is concluded that for very large arrays compartmentalization into large sub-arrays mitigates these detrimental effects while achieving some modularity. Earlier work has shown that dielectric permittivity aids in designing shorter antennas with good bandwidth; here, a new approach utilizing a dielectric cover at the array aperture to improve bandwidth for short antennas is proposed. The technique employs covers of moderate thickness and ensures good match at broadside and scan for an otherwise poorly-matched short Vivaldi element. A framework for analyzing wideband dispersion in antenna arrays is introduced. It is observed that well-matched Vivaldi antenna arrays demonstrate low-dispersion qualities comparable to other well-known wideband arrays, and thus may serve as prime candidates for short pulse transmission systems.

The mobile data market in South Africa is predicted to be a significant revenue contributor for mobile telecommunication operators, such as MTN, over the next five years. In light of the declining revenue from the traditional voice services, most operators worldwide are turning to mobile data as the solution to this problem. However, there is widespread confusion on which is the correct business model to implement in order to maximise the gains from this new market. To add to the complexity, there is also no clear cut technology upgrade path. While it is well understood that the main driver for the mobile data market will be high data throughputs, the industry is still unsure on which is the best route for an operator to follow as it moves from a second generation (2G)to a third generation (3G) network. This dissertation discusses the business model that MTN should implement in order to become the market leader for mobile data in South Africa. A literature survey on the latest market characteristics and forecast for the mobile data industry is presented. The recent developments on mobile data business models is also discussed. The technology upgrades, i.e. GPRS, EDGE and UMTS, available to a mobile telecommunication operator is described in detail. GPRS is the first stage in the evolution from a 2G to a 3G network and offers data rates of 40 Kb/s. EDGE improves on the GPRS technology with data speeds of 59.2 Kb/s per timeslot and utilise the same frequency, radio and switching equipment. UMTS is the final stage and is capable of delivering 2 Mb/s data rates. It operates on a different frequency spectrum, thus, requiring a new licence from the telecommunications regulator. In order to develop a new business model, MTN's current GPRS model is analysed. The poor success rate of this model can be attributed to the high prices being charged for the services and the lack of any "killer applications" to entice the users. The business model focuses on the customer value of service, organisational, technical and pricing models. For the customer value of service, it is shown that MTN must offer cheaper prices for the services, higher data rates and more exciting applications. The pre-paid subscribers should also be allowed access to the mobile data network. The main changes to the organisational arrangement in MTN includes creating sub-departments in marketing, sales and network group to focus solely on mobile data. MTN must develop an integrated services approach and this can only be achieved by developing partnerships with all key players in the mobile data industry, such as content providers and application developers. Due to the high costs, the technology arrangement section proposes that MTN first upgrade the network to be EDGE capable and later implement a UMTS network. The financial arrangement discusses the revenue, pricing and cost model. The revenue model proposes the development of an exciting and attractive mobile portal. New services and applications such as mobile gaming and gambling must be created for the personal consumers. For the corporate consumers, applications and services must be developed for customer relation management, supply chain management and workforce application. A hybrid pricing model must be adopted. A fixed, metered and value based pricing structure should be implemented to make the services more affordable and to gain the maximum revenues. Finally, the various elements that constitute the cost model is examined. The major contributing costs for the operator will be the network upgrade and subscriber acquisition.
Thesis (MBA)-University of KwaZulu-Natal, 2004.

An active, broadband antenna module amenable for use in low cost phased arrays is proposed. The module consists of a Vivaldi antenna integrated with a frequency conversion integrated circuit. A method of orthogonally mounting endfire antennas onto an array motherboard is developed using castellated vias. A castellated active isolated Vivaldi antenna package is designed, fabricated, and measured. An 8x1 phased array of castellated, active Vivaldi antenna packages is designed and assembled. Each element has approximately one octave of bandwidth centered in X-band, and each is mounted onto a coplanar waveguide motherboard. Radiation patterns of the array are measured at several frequencies and scan angles.

碩士
國立成功大學
電腦與通信工程研究所
105
This thesis presents the research of millimeter-wave (MMW) GIPD on-chip antennas. The designed GIPD MMW on-chip antennas are fabricated with AFSC general integrated passive device (GIPD) process. The three-dimensional finite element method (3D FEM) is used to design and analysis. The designed MMW on-chip antennas including: (1) 94-GHz GIPD quasi-Yagi antenna with log-periodic dipole array as driver; (2) 94-GHz GIPD bandpass-filtering planar inverted-F antenna; (3) 94-GHz GIPD on-chip log-periodic dipole array antenna with integrated balun-bandpass filter; (4) 60-GHz GIPD symmetrical two-port Vivaldi monopole antenna with integrated CMOS power amplifier. The measured performances of the designed on-chip antennas are all conducted by the on-wafer measurement setup.

Extensive numerical simulations and measurements have shown that Balanced Antipodal Vivaldi Antennas (BAVA) are broadband elements when operating as isolated antennas. However, BAVAs behave very differently in large array environments with impedance anomalies limiting the array's most useful bandwidth. Two techniques are developed in this thesis to overcome these performance limiting anomalies. First, a double-mirroring technique is introduced to eliminate one of the anomalies at broadside beam. Second, the antenna depth has been limited < λ highest-frequency/2 in order to move the second anomaly beyond the grating lobe onset frequency, and hence beyond the array's upper frequency bound. The two techniques are used along with metallic crosswalls, metallic poles and magnetic slots to design modular low profile BAVA elements in an array that operates over one-half of a decade of bandwidth and scan up to 60 degrees half angle conical volume. A linearly polarized doubly-mirrored BAVA (DmBAVA) array is fabricated and measured in a parallel plate waveguide simulator. Results from simulations and measurements are in close agreement. Finite arrays of SP- and DP-DmBAVA elements were simulated to explore the active element and array's radiation patterns. The cross-polarized farfield was less than -20dB relative to co-polarized farfield pattern peak at all scan angles. Floquet modes were calculated to prove that no grating lobe problem exists if all the elements are properly excited. The metallic crosswalls in the single-polarized DmBAVA array can be replaced by orthogonal DmBAVA elements to realize a dual-polarized antenna with only a minor degradation in the impedance match. The design methodology presented in this thesis represents a philosophical shift away from traditional design practices. Rather than providing design curves and/or analytical expressions for equivalent circuit models, simple first-order design rules (generated via parametric studies and extensive examinations to the surface currents and electromagnetic fields distribution) provide a framework for reduction of design complexity, and have eliminated the impedance anomalies in BAVA. This will increase the use of BAVA radiating elements in high performance arrays.

Due to high demand for planar structures with low loss, a considerable amount of research has been done to the design of substrate integrated waveguide (SIW) components in the mm-wave and microwave range. SIW has many advantages in comparison to conventional waveguides and microstrip lines, such as compact and planar structure, ease of fabrication, low radiation loss, high power handling ability and low cost which makes it a very promising technology for current and future systems operating in K-band and above. Therefore, all the work presented in this dissertation focuses on SIW technology. Five di erent antenna systems are proposed to verify the advantages of using SIW technology. First, a novel K-band end- re SIW circularly polarized (CP) antenna system on a single layer printed-circuit board is proposed. A high gain SIW H-plane horn and a Vivaldi antenna are developed to produce two orthogonal polarizations in the plane of the substrate. CP antennas have become very popular because of their unique characteristics and their applications in satellites, radars and wireless communications. Second, a K-band front-end system for tracking applications is presented. The circuit comprises an antenna array of two Vivaldi antennas, a frequency-selective power combiner, and two frequency-selective SIW crossovers, which eliminate the need for subsequent ltering. The integration of monopulse systems in planar, printed circuit SIW technology combined with the added bene ts of ltering functions is of great importance to the antennas and propagation community. Third, a phased array antenna system consisting of 24 radiating element is designed as feed system for reflector antennas in radio astronomy applications. A Ku-band antipodal dipole antenna with wide bandwidth, low cross-polarization and wide beamwidth is suggested as the radiating element. Forth, four di erent right-angled power dividers including in-phase and out-of-phase dividers as feed systems for antenna arrays are introduced. TE10 - to - TEq0 mode transducers are used for obtaining two, three, and four output dividers with phase control ability at K- and Ka-band. This feature is practical, for instance, when designing tracking systems since they are employed to obtain controllable phase distributions over the output ports. Fifth, a Ku-band beam steering antenna system which is applicable to use for wireless communications, radar systems, and also 5G applications is proposed. This antenna system uses variable reflection-type phase shifters which electrically steer the beam over a 50-degree scan range. Therefore, the SIW technology's reliability and also promising behavior in the microwave frequency range is proven for di erent applications.
Graduate

No
A compact-size asymmetrical linearly tapered slot antenna required for portable ultra-wideband (UWB) imaging systems is presented. The total antenna size is reduced compared with the conventional linearly tapered slot antenna by using a triangular slot on the left-hand side of the tapered-shaped radiator, whereas introducing a corrugated pattern of cuts on the right side. The antenna operates over a wide bandwidth extending from 3.1 to 10.6 GHz with a maximum gain of 8.5 dBi. Stable radiation patterns are observed across the operational bandwidth, with cross-polarization levels below 20 dB. The realized antenna structure occupies a volume of 35 x 36 x 0.8 mm3, and possesses the essential time domain fidelity needed for UWB imaging applications. (c) 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Wideband, wide-scan antenna arrays are a promising candidate for the future wireless networks and as well as an essential part of experimental radio astrophysics. Understanding the underline physics of the element performance in the array environment is paramount to develop and improve the performance of array systems. The focus of this thesis is to develop novel wideband antenna array technologies and develop new theoretical insights of the fundamental limits of antenna arrays. The developed methodologies have also been extended to include a radio astrophysics application for the global 21cm experiment.   Investigating the fundamental antenna array limits and extracting general performance measures can provide a priori estimates for any application of arrays. In this thesis, a general measure for antenna arrays, the array figure of merit is proposed. This measure couples bandwidth, height from the ground plane and reflection coefficient in a bounded quantity. An extension of the array figure of merit that is able to provide matching, bandwidth and directivity/gain limits is also introduced. The soft Vivaldi array is introduced as a novel wideband, wide-scan angle array technology. Periodic structure loading has been utilized to improve the array's performance and mold the electromagnetic wave behavior to our benefit. The soft condition has been utilized in the same manner as the conventional soft-horn antenna at the Vivaldi element. An integrated matching layer in the form of periodic strip loading is introduced. A single polarized soft Vivaldi array prototype has been developed fabricated and measured. The developed finite array has been loaded with a soft condition in the periphery to mitigate edge effects. The results indicated improved cross-polarization and side-lobe levels. A new class of wideband antenna arrays, the Strongly Coupled Asymmetric Dipole Array (SCADA) was also proposed in this thesis. Exploiting asymmetry in the array element introduces an additional degree of freedom that improves bandwidth and scanning performance. A novel methodology for terminating finite arrays is also proposed. The theory and an experimental antenna array is presented with good agreement between measured and simulated results. An effort to integrate a vertical wide angle matching layer was also addressed and a prototype array with this concept is presented. In the last part of this thesis, a methodology for the detection of the global cosmological 21cm signal from the Epoch of Reionization (EoR) is developed. The main sources of errors in this experiment, the foregrounds and the antenna chromaticity are evaluated. A new algorithmic methodology for extracting the global EoR signal is proposed. The method is based on piecewise polynomial fitting and has successfully been applied and evaluated. An antenna array that is based on the methodologies described in this thesis has been developed and evaluated with the proposed algorithm.
Bredbandiga gruppantenner med stor utstyrningsvinkel är en av de lovande kandidaterna för nästa generations trådlösa kommunikationsnätverk samt en väsentlig del av experimentell radioastrofysik. Att förstå de bakomliggande fysikaliska principerna hos gruppantennens element är avgörande för att kunna utveckla och förbättra prestandan hos ett gruppantennsystem. Denna avhandling är fokuserad på att utveckla nya bredbandstekniker samt nya teoretiska insikter om de grundläggande gränserna för gruppantenner. De här utvecklade metoderna har förutom kommunikationstillämpningar också tillämpats på en radioastrofysik tillämpning i det globala 21cm experimentet. Att undersöka de fundamentala gränserna för gruppantenner och att utröna allmängiltiga mått på deras prestandaegenskaper kan möjliggöra a priori uppskattningar om gruppantenns tillämpbarhet för dess planerade användning. I den här avhandlingen föreslås ett allmänt kvalitetsmått på gruppantenner: gruppantennkvaliten. Detta mått kopplar samman främst bandbredd, reflektionskoefficienten med antennens tjocklek över ett jordplanet. En utvidgning av begreppet gruppantennkvaliten, presenters också i avhandlingen det kopplar samman bandbredd, matchning med antennens direktivitet/förstärkningsfaktor. En Vivaldi-gruppantenn med mjuka ytor introduceras här som en ny sorts bredbandig gruppantenn med stor utstyrningsvinkel. I antennen har en periodisk belastning inkluderats för att förbättra dess egenskaper, och för att forma antennens elektromagnetiska utstrålning till vår fördel. Den mjuka ytan på elementet har används på ett liknande sätt som det välkända korrigerade Vivaldihornets design, och har integrerats direkt i elementets design. Den här utvecklade ändliga gruppantennen har också en mjuk yta på dess yttre delar för att minska kanteffekternas påverkan av antennprestandan. Resultaten indikerade både förbättrad korspolarisations och lägre sidlobsnivåer hos antennen. En ny klass av bredbandiga gruppantenner har utvecklas i denna avhandling, den kallas en Starkt Kopplad Asymmetrisk Dipol-gruppAntennen - SCADA. Genom att utnyttja geometrisk asymmetri i antennelementet introduceras ytterligare en frihetsgrad som möjliggör förbättrad bandbredd och utstyrning. Vidare presenteras här en ny metod för impedansterminering av ändliga gruppantenner. Både SCADA-teorin samt dess verifiering i forma av en experimentell gruppantenn presenteras här. Teori, simulering och experiment visar god överenskommelse, vilket validerar idéerna. En prototyp av ett matchande skikt som stöder stor utstyrbarhet har integrerats med gruppantennprototypen och presenteras i avhandlingen. I den sista delen av avhandling utvecklas också en metod för detektering av den globala kosmologiska 21 cm-signalen från universums rejoniseringsepok - EoR. Huvudkällorna för mätfel i detta experiment utvärderas, de är antennens kromaticiteten och förgrundsstrålningen. En ny algoritmbaserad metod för att extrahera den globala EoR-signalen föreslås. Metoden är baserad på anpassning med multipla polynom och har med framgång tillämpats och utvärderats. En gruppantenn som baseras på de metoder som beskrivs i avhandling har också föreslagits och dess prestanda har utvärderats med den föreslagna metoden.

QC 20171121