Thesis (Ph. D.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2005. / Includes bibliographical references (p. 109-116).

Thesis (Ph.D.)--Ohio University, June, 2008. / Abstract only has been uploaded to OhioLINK. Includes bibliographical references (leaves 199-209)

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references and index.

Σκοπός αυτής της διπλωματικής είναι η μελέτη, σχεδίαση και εξομοίωση κεραιών σχισμής τα χαρακτηριστικά των οποίων τις καθιστούν κατάλληλες για φορητές τερματικές συσκευές. Στο πρώτο κεφάλαιο γίνεται μια σύντομη αναφορά σε βασικές έννοιες της θεωρίας κεραιών, στις ηλεκτρικά μικρές κεραίες αλλά και στην αρχή του Babinet. Στόχος αυτού του κεφαλαίου είναι να συμβάλλει στην καλύτερη κατανόηση του περιεχομένου των επόμενων κεφαλαίων. Στο δεύτερο κεφάλαιο παρατίθενται κάποιες από τις πιο ευρέως διαδεδομένες υπάρχουσες γεωμετρίες κεραιών σχισμής, οι οποίες κατηγοριοποιούνται κυρίως ως προς το εύρος του φάσματος λειτουργίας τους. Στο τρίτο κεφάλαιο μελετάται μια βασική κεραία σχισμής, η κεραία ορθογώνιας σχισμής με τροφοδοσία συνεπίπεδου κυματοδηγού αλλά και μια πολύ ενδιαφέρουσα παραλλαγή της η οποία περιλαμβάνει ένα ζεύγος ορθογώνιων παρασιτικών στοιχείων. Στο τέταρτο κεφάλαιο μελετώνται οι κεραίες σχισμής μονής ζώνης λειτουργίας. Στα πλαίσια αυτής της μελέτης παρουσιάζονται συγκριτικά τα αποτελέσματα από τη σχεδίαση και εξομοίωση μιας κεραίας ζεύγους σχισμών σχήματος δακτυλίου και σχήματος κύκλου αντίστοιχα. Στο πέμπτο κεφάλαιο μελετώνται οι κεραίες σχισμής διπλής ζώνης λειτουργίας. Για το σκοπό αυτό σχεδιάστηκαν και εξομοιώθηκαν μια κεραία ζεύγους σχισμών σχήματος μονόπολου και μια κεραία σχισμής σχήματος βρόχου. Το περιεχόμενο του έκτου κεφαλαίου είναι η ανάλυση της συμπεριφοράς των κεραιών σχισμής ευρυζωνικής λειτουργίας. Αυτό επιτυγχάνεται μέσα από την μελέτη μιας κεραίας ρομβοειδούς σχισμής με ζεύγος μεταλλικών παρασιτικών στοιχειών, μια κεραία τοξοτής σχισμής καθώς και μια κεραία τριγωνικής σχισμής με ζεύγος τροφοδοσίας. Στο έβδομο κεφάλαιο μελετώνται οι υπερευρυζωνικές κεραίες σχισμής. Για το σκοπό αυτό σχεδιάστηκαν και εξομοιώθηκαν μια κεραία ελλειπτικής σχισμής με τροφοδοσία συνεπίπεδου κυματοδηγού και μια κεραίας ελλειπτικής σχισμής με στέλεχος προσαρμογής σχήματος U. Το όγδοο κεφάλαιο που έχει ως στόχο την μελέτη των κεραιών σχισμής που χρησιμοποιούνται σε χιλιοστομετρικές εφαρμογές περιλαμβάνει τα αποτελέσματα της σχεδίασης και εξομοίωσης μιας κεραίας κυκλικής σχισμής με τροφοδοσία μικροταινιακής γραμμής μεταφοράς. Τέλος στο ένατο κεφάλαιο γίνεται μια συνοπτική παρουσίαση των αποτελεσμάτων και παρατίθενται συμπεράσματα και προτάσεις για μελλοντική ενασχόληση στην περιοχή των κεραιών σχισμής. / This diploma thesis includes the analysis, design and simulation of slot antennas for portable terminal devices. In this thesis is presented a variety of slot antennas including single and dual band slot antennas, wideband and ultra wideband antennas as well as slot antennas for millimetre-wave applications.

Thesis (MScEng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis discusses the design of a dual circularly polarized single element antenna with special emphasis on achieving a wide bandwidth and high polarization isolation. The aim of the study is to produce an antenna for transmission of colour video signals between a ground station and a low earth orbit satellite. Microstrip patch antennas are suitable for satellite applications because they are light weight, conformal and have a thin profile. However, the antennas' inherent naITOW bandwidth is one of their major drawbacks. The aperture coupled microstrip patch antenna boasts of a much-improved bandwidth over the traditional single layer microstrip antenna and the freedom of using separate substrates for the patch and the feeding network. Hence the designed single element antenna is aperture coupled. To achieve dual circular polarization with good polarization purity, the antenna had a crossed slot aperture with a balanced feed. The feed network was designed on a single layer. The design was executed in two steps using IE3D moment of methods simulation software: design of the radiating part, and design of the feed part. Each part was simulated and optimized on its own before the two were combined, simulated and optimized again. Parameters used in the antenna optimization were: the substrates' thicknesses and dielectric constants, patch and aperture dimensions, and the feed line width and offset. The designed antenna was built and measured. Initial measurements of S-parameters yielded unacceptable results, especially for S22 and S21, and so an investigation into the matter was conducted. That led to the sizes of the feed and reflector planes being extended. Absorbing material was used between the parallel feed and reflector planes because some power was, to a lesser extent, still escaping, due to the fact that the planes were fmite. Measurement results demonstrated reasonable agreement with the simulation. The final antenna had a reflection coefficient of less than -10 dB for the entire operating band of 400 MHz centred on 3 GHz, an isolation of approximately -15 dB in the operating band and a gain of 2 dBi and I dBi for Ports 1 and 2, respectively, at 3 GHz. These results, especially the gain, are influenced by the back radiation and the finite sizes of the feed and reflector planes. It is therefore recommended that an enclosed cavity be used at the back of the antenna and a 'dogbone' aperture be used to minimize back radiation. / AFRIKAANSE OPSOMMING: Die tesis omskryf die ontwerp van 'n tweevoudige sikuler gepolariseerde enkel-element antenne met spesiale klem op wye bandwydte en hoe polariserings isolasie. Die doel van hierdie studie is om 'n antenne vir uitsending van kleur video seine tussen 'n grond stasie en 'n omnentelingsatelliet daar te stel. Mikrostrook plakantennes is gepas vir satelliet toepassings weens hulle ligte gewig en dun profiel. Die antenne se gepaardgaande nou bandwydte is egter een van hulle grootste nadele. Die gleufgekoppelde mikrostrook plakantenne gee egter 'n baie beter bandwydte as die tradisionele enkellaag mikrostrook plakantenne asook die vryheid om verskillende substrate vir die plak en die voernetwerkte gebruik. Vir hierdie redes daar besluit om die enkel-element antenne sleufgekoppeld te maak. Om tweevoudige sikuler gepolariseerde met goeie polarisasie suiwerheid te kry, moes 'n kruisvonnige gleuf met 'n gebalanseerde voer ontwerp word. Die voernetwerk was op 'n enkellaag ontwerp. Die ontwerp was in twee fases in IE3D momentmetode simulasie sagteware gedoen: ontwerp van die stralings gedeelte, en ontwerp van die voer gedeelte. Elke gedeelte word afsonderlik gesimuleer en geoptimiseer voordat die twee saam gesimuleer en geoptimiseer word. Parameters wat gebruik word in die antenne optimiseering is: dikte van substraat en dielektriese konstante, plak en gleuf grootes, en voer lynwydte en afwyking. Die ontwerpde antenne is gebou en gemeet. Aanvanklike metings van S-parameters het onaanvaarbare resultate gel ewer, vera I vir S22 en S21,dus is daar besluit om die redes daarvoor te ondersoek. Dit het daartoe gelei dat die voer- en reflector vlakte groter gemmak is. Absorbeer material is tussen die parallel voer- en reflector vlakke gebruik aangesien steeds drywing verloor is weens die eindige vlakke. Meting resultate het taarnlike goed met die simulasies vertoon. Die finale antenne het 'n weerkaatskoeffisient laer as -10 dB getoon vir die volle bandwydte van 400 MHz gesentreerd rondom 3 GHz, 'n isolasie van ongeveer -15 dB in die bandwydte en 'n aanwins van 2 dBi en I dBi vir onderskeidelik Poorte I en 2 by 3 GHz. Hierdie resultate veral die aanwins is deur die straling na agter beinvloed en die eindige grootes van die voer- en reflector vlakke. Dit word om hierdie rede dus voorgestel dat 'n geslote holte aan die rugkant van die antenne gebruik word en dat 'n "dogbone" gleuf gebruik word om straling na agter te minimeer.

Thesis (MScEng) -- Stellenbosch University, 2004. / ENGLISH ABSTRACT: The development of a small, cost effective short range FM-CW radar as well as the design and optimization of a double helix antenna is discussed. The FM-CW radar operates at Sband (2450 - 2550 MHz) and is limited at a maximum transmitted power of 5 dBm. The system is required to detect reflections from objects up to a 30 m range. This was made possible largely by the effective high gain antenna design and improved system isolation between the transmitted and received signals. The complete design process from fundamental requirements, through various simulations and system analysis to the final electronic circuit is discussed. The design was also built and measured in the laboratory and initial field measurements were taken. The following aspects were considered: Relation between the beat frequency and various FM-CW radar system parameters based on the theory, preliminary measurements and simulations. Radar component assessment and design. Design of a low cost Lange coupler that isolates the system's transmit and receive signals, which operates as a 90° hybrid and is used to feed a dual-fed circularly polarized patch antenna. A circularly polarized patch antenna and double helix antenna were designed, built and measured in an anechoic chamber. The antennas were implemented in the final radar system and compared on the basis of their contribution to the system's performance. Integrating the final radar system on a circular 60 mm diameter PCB with a double helix antenna mounted on top. The final radar system is able to measure range up to 40 m and meets all the design requirements. The signal processing of the measured beat frequency, however, can be taken further. / AFRIKAANSE OPSOMMING: Die ontwikkeling van 'n klein, koste effektiewe kort-afstand FM-CW radar, sowel as die onwerp en optimalisering van 'n dubbele heliks-antenna word bespreek. Die FM-CW radar werk by S-band (2450 - 2550 MHz) en is beperk tot 'n maksimum uitsaaidrywing van 5 dBm. Van die stelsel word vereis om weerkaatsings van voorwerpe tot op 'n afstand van 30 m waar te neem. Dit is grootliks moontlik gemaak deur die hoë aanwins antenna-ontwerp en verbeterde isolasie tussen die stelsel se uitsaai- en ontvangseine. Die volledige ontwerpsproses van die fundamentele vereistes af tot die finale elektroniese stroombaan word bespreek. Verskeie simulasies andstelselanalises is gebruik om die finale FM-CW radar te realiseer. Die ontwerp is vervolgens in die laboratorium gebou en gemeet en aanvangsveldmetings is geneem. Die volgende aspekte is in nagevors: Verband tussen die puls-frekwensie en verskeie FM-CW radar stelselparameters gebaseer op die teorie, inleidende metings en simulasies. Ontleding van verskeie radarkomponente en -stelselontwerp. Ontwerp van 'n lae koste Lange-koppelaar met die doelom die stelsel se uitsaai- en ontvangseine te isoleer. Die Lange-koppelaar dien as 'n 90° hibriede wat gebruik word om 'n dubbele-voer sirkulêr gepolariseerde mikrostrookantenna aan te dryf. Verder is 'n sirkulêr gepolariseerde mikrostrook-antenna en 'n dubbele heliksantenna ontwerp en opgemeet in 'n anarqoïese kamer. Beide antennas is geïmplimenteer in die finale radarstelsel en is vergelyk op grond van hulle rol in die stelsel se funksionering. Die finale stelsel is geïntegreer en gebou op 'n ronde 60 mm deursnit PCB met 'n dubbele helix-antenna bo-op gemonteer. Die finale radarstelsel kan afstand tot op 40 meter bepaal en voldoen aan al die gestelde vereistes. Seinverwerking van die gemete puls-frekwensie kan nog verder ontwikkel word.

Dans le contexte actuel où l’évolution des systèmes sans-fil est jugée importante, il estnécessaire de pouvoir réduire les pollutions électromagnétiques qui limitent l’acceptabilité descommunications et la cohabitation des systèmes. D’une façon générale, les besoins de contrôle durayonnement des antennes miniatures répondent donc à une demande croissante pour améliorer lesportées mais aussi pour limiter les interférences dans les systèmes sans-fil. Ces dernières années,malgré le développement connu dans les domaines des antennes, la question du contrôle durayonnement des antennes miniatures connait plusieurs barrières empêchant leur déploiementtechnologique. L’approche retenue dans le cadre de cette thèse est le développement de nouveauxconcepts de contrôle du rayonnement des antennes miniatures par la mise en oeuvre de différentestechniques. Cette étude a pour objectif de soulever quelques questions concernant un sujet d’étude peuexploré. / In the current context where the evolution of communicating objects is important indifferent growing fields such as: localization, wireless multimedia systems, etc., controlling theradiation pattern of antennas is one of the most important issues for future radio communicationsystems. In recent years, despite the growth experienced in the areas of antennas, the issue of smallantennas radiation control knows several barriers preventing their deployment. This thesis focuses onthe analysis of the problem of controlling the radiation pattern of small antennas and aims to raisesome questions about a little-explored subject of study. This work gives an approach using differenttechniques to develop new concepts of controlling the radiation pattern of antennas.

No description available.

abstract: Global Positioning System (GPS) is a navigation system widely used in civilian and military application, but its accuracy is highly impacted with consequential fading, and possible loss of communication due to multipath propagation and high power interferences. This dissertation proposes alternatives to improve the performance of the GPS receivers to obtain a system that can be reliable in critical situations. The basic performance of the GPS receiver consists of receiving the signal with an antenna array, delaying the signal at each antenna element, weighting the delayed replicas, and finally, combining the weighted replicas to estimate the desired signal. Based on these, three modifications are proposed to improve the performance of the system. The first proposed modification is the use of the Least Mean Squares (LMS) algorithm with two variations to decrease the convergence time of the classic LMS while achieving good system stability. The results obtained by the proposed LMS demonstrate that the algorithm can achieve the same stability as the classic LMS using a small step size, and its convergence rate is better than the classic LMS using a large step size. The second proposed modification is to replace the uniform distribution of the time delays (or taps) by an exponential distribution that decreases the bit-error rate (BER) of the system without impacting the computational efficiency of the uniform taps. The results show that, for a BER of 0.001, the system can operate with a 1 to 2 dB lower signal-to-noise ratio (SNR) when an exponential distribution is used rather than a uniform distribution. Finally, the third modification is implemented in the design of the antenna array. In this case, the gain of each microstrip element is enhanced by embedding ferrite rings in the substrate, creating a hybrid substrate. The ferrite rings generates constructive interference between the incident and reflected fields; consequently, the gain of a single microstrip element is enhanced by up to 4 dB. When hybrid substrates are used in microstrip element arrays, a significant enhancement in angle range is achieved for a given reflection coefficient compared to using a conventional substrate. / Dissertation/Thesis / Ph.D. Electrical Engineering 2013

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Neste trabalho, foram investigadas as propriedades estruturais e dielÃtricas da fase monoclÃnica da cerÃmica ferroelÃtrica Na2Nb4O11 com adiÃÃo de Ãxido de bismuto (Bi2O3) nas proporÃÃes de 2, 5 e 10% em massa. Os pÃs Na2Nb4O11 foram produzidos pelo mÃtodo convencional de reaÃÃo em estado sÃlido. ApÃs a calcinaÃÃo, as amostras foram prensadas na forma de pastilhas cilÃndricas e, em seguida, sinterizadas. O estudo da estrutura e da composiÃÃo das amostras foi feito atravÃs de difraÃÃo de raios-X e Refinamento Rieteveld e um estudo da morfologia foi realizado atravÃs de Microscopia EletrÃnica de Varredura onde visualmente, as amostras lembram as medidas de densidade obtidas atravÃs da picnometria. A caracterizaÃÃo dielÃtrica foi realizada na faixa de radiofrequÃncias e de microondas. Em ambos os casos, foi realizado um estudo das propriedades em relaÃÃo à variaÃÃo da temperatura para possÃvel aplicaÃÃo em dispositivos de RF e MW. Nosso interesse foi obter dielÃtricos cerÃmicos com permissividade dielÃtrica alta, baixas perdas dielÃtricas e estabilidade tÃrmica. Nas medidas realizadas em temperatura ambiente de 25ÂC obtivemos um alto valor da permissividade dielÃtrica (εâr = 250,9) com o NN10Bi (10% de Bi2O3) em 10 kHz e um valor da tangente de perda, relativamente baixo (tanδ = 1,80.10-2) com o NN2Bi (2% de Bi2O3) em 1 MHz. Em temperatura variÃvel e numa frequÃncia fixa de 100 kHz, obtivemos um alto valor da permissividade dielÃtrica com εâr = 440,78 a 440ÂC com o NN2Bi e um valor de perda dielÃtrica em torno de 1,81.10-1 a 280ÂC com o NN10Bi. A medida do coeficiente de temperatura da frequÃncia de ressonÃncia mostrou a possibilidade de atingir a estabilidade tÃrmica = 0 com o aumento do nÃvel de adiÃÃo de Bi2O3. Para o NN00 obtivemos um tauf = -3378,42 ppm/ÂC. Com a adiÃÃo do Bi2O3, este valor vai se aproximando do zero e atinge tauf = -250,04 ppm/ÂC para o NN10Bi. As medidas na faixa de microondas foram obtidas utilizando-se o mÃtodo Hakki-Coleman. Uma simulaÃÃo numÃrica foi realizada com cada amostra verificando-se a reciprocidade com os dados experimentais. Neste estudo obtivemos uma cerÃmica NN10Bi, Ãtil para a aplicaÃÃo em dispositivos de antenas omnidirecionais de baixo ganho, em sistemas de comunicaÃÃes via satÃlite, internet sem fio, radar, forno de microondas, recepÃÃo de rÃdio e em projetos de espaÃonaves. / In this present work, Na2Nb4O11, ferroelectric ceramics have been investigated by their monoclinic phase structural and dielectric properties have been enhanced by the addition of 2, 5 and 10 wt% Bismuth. Na2Nb4O11 powders have been produced by conventional solid-state reaction method. Milling process was carried out by using a high energy planetary mill. The calcined powders were thoroughly weighted and pressed using an axial press to make cylinder pellets for sintering. The single-phase Na2Nb4O11 was determined by X-Ray Diffraction (XRD) technique and Rietveld refinement method, while morphology, crystal structure and phase composition were determined via Scattering Electron Microscopy (SEM) where the samplesâ crystal structure micrographs show nearly the density measures obtained by Pycnometry technique. Dielectric characterization was carried out over a radiofrequency (RF) and microwave (MW) range. Both cases, we have studied the properties related to temperature variation for likely applications to RF and MW devices. We have focused on obtaining dielectric ceramics with high dielectric permittivity, low dielectric loss and near-zero temperature coefficient of resonant frequency. Room temperature measures at 25ÂC have had a high permittivity value = 250.9) for NN10Bi (10% of Bi2O3) at 10 kHz and a dielectric loss, relatively low value 1.80 10-2 for NN2Bi (2% of Bi2O3) at 1MHz. Varying temperature and fixed frequency at 100 kHz, we have obtained a high dielectric permittivity value 440.78 at 440ÂC) for NN2Bi and a dielectric loss about 1,81.10-1 at 280ÂC for NN10Bi. Near-zero temperature coefficient of resonant frequency has shown possibility of reaching thermal stability = 0 as increasing Bi2O3 addition level. For NN00 we have obtained = - 3378.42 ppm/oC. More Bi2O3 addition provides = - 250.04 ppm/oC for NN10Bi. Microwave measures were carried out using Hakki Coleman technique. A numerical simulation was also achieved for each sample for verifying the similarity to experimental data. In this study we have obtained NN10Bi ceramics, applicable for low-gain antenna devices, for satellite communication systems, wireless internet, radar, microwave oven, radio frequency receptor and spacecraft designing.