The principal contributions of this study include the development of a new capacitive feeding mechanism for wideband probe-fed microstrip patch antennas as well as the implementation of a spectral-domain moment-method formulation for the efficient analysis of large, but finite arrays of these elements. Such antenna configurations are very useful in the wireless communications industry, but extremely difficult to analyse with commercially available software. Probe-fed microstrip patch antennas have always been a popular candidate for a variety of antenna systems. Due to their many salient features, they are well suited for modern wireless communication systems. However, these systems often require antennas with wideband properties, while an inherent limitation of probe-fed microstrip patch antennas is its narrow impedance bandwidth. This can be overcome by manufacturing the antenna on a thick low-loss substrate, but at the same time it also complicates things by rendering the input impedance of the antenna very inductive. In this thesis, a new capacitive feeding mechanism is introduced that can be used for probe-fed microstrip patch antennas on thick substrates. It consists of a small probe-fed capacitor patch that is situated next to the resonant patch. The benefits of this configuration include the fact that only one substrate layer is required to support the antenna. It is also very easy to design and optimise. The use of full-wave methods for an accurate analysis of microstrip antennas, has basically become standard practice. These methods can become very demanding in terms of computational resources, especially when large antenna arrays have to be analysed. As such, this thesis includes a spectral-domain moment-method formulation, which was developed for the analysis of probe-fed microstrip patch antennas or antenna arrays that comprise of the new capacitive feeding mechanism. Here, entire-domain and subdomain basis functions are combined in a unique way so as to minimise the computational requirements, most notably computer memory. It is shown that, for general antenna array configurations, memory savings of more than 2500 times can be achieved when compared with typical commercial software packages where only subdomain basis functions are used. Some of the numerical complexities that are dealt with, include various methods to evaluate the spectral integrals as well as special algorithms to eliminate the recalculation of duplicate interactions. The thesis also contains a quantitative comparison of various attachment modes that are often used in the moment-method modelling of probe-to-patch transitions. Various numerical and experimental results are included in order to verify the spectral-domain moment-method formulation, to characterise the new feeding mechanism and to illustrate its use for various applications. These results show that, in terms of accuracy, the spectral-domain moment-method formulation compares well with commercial codes, while by comparison, it demands very little computer memory. The characterisation results show that the input impedance of the antenna can be fully controlled by only adjusting the size of the capacitor patch as well as the width of the gap between the capacitor patch and the resonant patch. In terms of applications, it is shown how the new antenna element can effectively be employed in linear arrays with vertical polarisation, horizontal polarisation or dual slant-polarisation. These represent some widely-used configurations for modern base-station antennas. / Thesis (PhD (Electronic Engineering))--University of Pretoria, 2005. / Electrical, Electronic and Computer Engineering / unrestricted

Yes / Microstrip patch antennas with harmonic suppression are designed and optimised, using a genetic algorithm and applying a novel adaptive meshing program to generate a wire-grid simulation. A coaxially-fed air-dielectric patch antenna design with a folded patch was investigated. It was confirmed that antennas with excellent performances could be designed by this method. / MSCRC

This thesis presents design, fabrication and testing of a number of multi-frequency band microstrip-fed re-configurable microstrip patch antennas. All re-configurable antennas are designed to change from one resonance frequency to another by an electronic control of RF MEMS switches, one at a time. Besides a fixed size slot on the patch, switches are placed in insets for satisfying better input match at each resonance frequency individually. Also some switches are placed into the slot for adding another resonance frequency to change the effective slot-length like effective inset length changing.To actuate the RF MEMS switches in the configured way, DC-stubs are also designed to apply required potential difference between switch ports and the carrier. These stubs exhibit RF-open at switch side to prevent any RF leakage, and DCground on the other side. That RF short-to-open conversion is accomplished together with feed structure / with a taper depending on the feed network selected. All devices introduced here are built by Microwave Research Group in Electrical and Electronics Department, Middle East Technical University. Depending on the sensitivity of structure, some devices are built by RF MEMS group in Microelectronic Production Plant for MEMS (METU &amp / #8211 / MET) during the thesis study. Therefore this study is the continuation of the first national work on fabrication of RF MEMS devices.

Near field imaging using microwave in medical applications has gain much attention recently as various researches show its high ability and accuracy in illuminating object comparing to the well-known screening tools such as Magnetic Resonance Imaging (MRI), digital mammography, ultrasound etc. This has encourage and motivate scientists continue to exploit the potential of microwave imaging so that a better and more powerful sensing tools can be developed. This thesis documents the development of antenna design for microwave imaging application such as breast cancer detection. The application is similar to the concept of Ground Penetrating Radar (GPR) but operating at higher frequency band. In these systems a short pulse is transmitted from an antenna to the medium and the backscattered response is investigated for diagnose. In order to accommodate such a short pulse, a very wideband antenna with a minimal internal reflection is required. Printed monopole and planar metal plate antenna is implemented to achieve the necessary operating wide bandwidth. The development of new compact printed planar metal plate ultra wide bandwidth antenna is presented. A generalized parametric study is carried out using two well-known software packages to achieve optimum antenna performance. The Prototype antennas are tested and analysed experimentally, in which a reasonable agreement was achieved with the simulations. The antennas present an excellent relative wide bandwidth of 67% with acceptable range of power gain between 3.5 to 7 dBi. A new compact size air-dielectric microstrip patch-antenna designs proposed for breast cancer detection are presented. The antennas consist of a radiating patch mounted on two vertical plates, fed by coaxial cable. The antennas show a wide bandwidth that were verified by the simulations and also confirmed experimentally. The prototype antennas show excellent performance in terms the input impedance and radiation performance over the target range bandwidth from 4 GHz to 8 GHz. A mono-static model with a homogeneous dielectric box having similar properties to human tissue is used to study the interaction of the antenna with tissue. The numerical results in terms the matching required of new optimised antennas were promising. An experimental setup of sensor array for early-stage breast-cancer detection is developed. The arrangement of two elements separated by short distance that confined equivalent medium of breast tissues were modelled and implemented. The operation performances due to several orientations of the antennas locations were performed to determine the sensitivity limits with and without small size equivalent cancer cells model. In addition, a resistively loaded bow tie antenna, intended for applications in breast cancer detection, is adaptively modified through modelling and genetic optimisation is presented. The required wideband operating characteristic is achieved through manipulating the resistive loading of the antenna structure, the number of wires, and their angular separation within the equivalent wire assembly. The results show an acceptable impedance bandwidth of 100.75 %, with a VSWR < 2, over the interval from 3.3 GHz to 10.0 GHz. Feasibility studies were made on the antenna sensitivity for operation in a tissue equivalent dielectric medium. The simulated and measured results are all in close agreement.

Made available in DSpace on 2014-12-17T14:54:55Z (GMT). No. of bitstreams: 1 RanilsonCF_TESE.pdf: 2036029 bytes, checksum: f7ba8fa789f5420decc75fb98f14f807 (MD5) Previous issue date: 2010-07-27 / The main purpose of this work was the development of ceramic dielectric substrates of bismuth niobate (BiNbO4) doped with vanadium pentoxide (V2O5), with high permittivity, used in the construction of microstrip patch antennas with applications in wireless communications systems. The high electrical permittivity of the ceramic substrate provided a reduction of the antenna dimensions. The numerical results obtained in the simulations and the measurements performed with the microstrip patch antennas showed good agreement. These antennas can be used in wireless communication systems in various frequency bands. Results were satisfactory for antennas operating at frequencies in the S band, in the range between 2.5 GHz and 3.0 GHz. / O objetivo principal deste trabalho foi o desenvolvimento de substratos diel?tricos cer?micos de niobato de bismuto (BiNbO4) dopados com pent?xido de van?dio (V2O5), com alta permissividade el?trica, usados na constru??o de antenas patch de microfita com aplica??es em sistemas de comunica??es sem fio. A alta permissividade el?trica do substrato cer?mico proporcionou uma redu??o no tamanho das antenas. Os resultados num?ricos obtidos nas simula??es e medi??es realizadas com as antenas patch de microfita mostraram boa concord?ncia. Essas antenas podem ser usadas em sistemas de comunica??es sem fio em v?rias faixas de freq??ncias. Foram obtidos resultados satisfat?rios em antenas com freq??ncias de opera??o na banda S, na faixa compreendida entre 2,5 GHz e 3,0 GHz.

Made available in DSpace on 2014-12-17T14:55:53Z (GMT). No. of bitstreams: 1 JoseHCM_DISSERT.pdf: 1439414 bytes, checksum: f96f0decdde25078b5110927edf3b75c (MD5) Previous issue date: 2011-12-19 / This work presents techniques used to design and manufacture microstrip patch antennas for applications in portable and mobile devices. To do so, are evaluated several factors that can influence the performance of microstrip patch antennas. Miniaturization techniques are studied and employed in order to apply this type of antenna in mobile and / or mobile. The theories of microstrip patch antennas are addressed by analyzing characteristics such as constitution, kinds of patches, substrates, feeding methods, analysis methods, the main advantages and disadvantages and others. Techniques for obtaining broadband microstrip patch antennas were surveyed in literature and exemplified mainly by means of simulations and measurements. For simulations of the antennas was used the commercial software . In addition, antenna miniaturization techniques have been studied as a main concern the fundamental limits of antennas with special attention to electrically small antennas because they are directly linked to the microstrip patch antennas. Five design antennas are proposed to demonstrate the effectiveness of techniques used to obtain the microstrip patch antennas broadband and miniaturized for use in mobile devices and/or portable. For this, the proposed antennas were simulated, built and measured. The antennas are proposed to be used in modern systems of wireless communications such as DTV, GPS, IEEE 802.16, IEEE 802.11, etc. The simulations of the antennas were made in business and computer programs. The measured results were obtained with a parser Vector of networks of the Rhode and Schwarz model ZVB 14 / Esse trabalho apresenta t?cnicas usadas para projetar e fabricar antenas patch de microfita para aplica??es em dispositivos port?teis e m?veis. Para isso, s?o avaliados diversos fatores que podem influenciar no desempenho das antenas patch de microfita. T?cnicas de miniaturiza??o s?o estudadas e empregadas visando a aplica??o deste tipo de antena em dispositivos port?teis e/ou m?veis. Fundamentos te?ricos sobre as antenas patch de microfita s?o abordados analisandose caracter?sticas como: constitui??o, tipos de patches, substratos, m?todos de alimenta??o, m?todos de an?lises, principais vantagens e desvantagens dentre outros. T?cnicas para obten??o de antenas patch de microfita banda larga foram pesquisadas na literatura e exemplificadas principalmente por meio de simula??es e medi??es. Para as simula??es das antenas foi utilizado o programa computacional comercial . Al?m disso, t?cnicas de miniaturiza??o de antenas foram estudadas tendo como preocupa??o principal os limites fundamentais das antenas com aten??o especial a antenas eletricamente pequenas por estarem diretamente vinculadas ?s antenas patch de microfita. Cinco projetos de antenas s?o propostos para comprovar a efici?ncia das t?cnicas utilizadas para obten??o de antenas patch de microfita banda larga e miniaturizadas, para aplica??o em dispositivos m?veis e/ou port?teis. Para isso, as antenas propostas foram simuladas, constru?das e medidas. As antenas foram propostas para serem utilizadas em sistemas modernos de comunica??es sem fio como: DTV, GPS, IEEE 802.16, IEEE 802.11, etc. As simula??es das antenas foram feitas nos programas computacionais comerciais e . Os resultados medidos foram obtidos com um analisador vetorial de redes da Rhode and Schwarz modelo ZVB 14

Les antennes à polarisation circulaire (CP) sont de plus en plus utilisées dans les systèmes de communications spatiaux et terrestres. Le besoin d’intégration est sans cesse plus important, il est donc nécessaire de proposer, de mettre au point des aériens toujours plus compacts et aux performances (adaptation, rayonnement, gain, efficacité, taux d’ellipticité) optimisées. L’objectif de cette thèse est donc de concevoir des antennes planaires, large bande ou multi-bande, à polarisation circulaire et aux performances optimisées. Afin d’atteindre ces objectifs, le travail a été divisée en plusieurs phase, allant de la conception d’une antenne CP à large bande jusqu’à la conception d’une antenne patch à polarisation circulaire tri bandes GNSS. Tout d’abord une étude bibliographique sur les antennes planaires a été faite. Celle-ci a permis de comparer leurs différentes performances, leurs avantages et inconvénients. Ensuite, une antenne patch CP à éléments parasites a été conçue fabriquée et mesurée. On s’est attaché à optimiser sa bande de fonctionnement. En tenant compte des études bibliographiques déjà faites, et en se basant sur la structure de l’antenne CP à large bande validée lors de la phase précédente, une nouvelle antenne plaquée CP GNSS tri bandes a également été conçue réalisée et mesurée. L’essentiel du travail a consisté à minimiser son encombrement tout en conservant des performances électromagnétiques satisfaisantes dans les trois bandes de fréquences objectifs : L2, E6 et L1. On s’est particulièrement attaché à obtenir un bon taux d’ellipticité sur une large ouverture rayonnante. La dernière étape de cette thèse a consisté à aller encore plus loin dans l’amélioration des performances de l’antenne CP GNSS multi bandes particulièrement en améliorant son efficacité. Une excitation par fente a finalement été utilisée après comparaison des performances obtenues via différentes techniques (alimentation coaxiale, fentes, etc…). / Circular polarized antennas (CP) are greatly used in space and terrestrial communication systems. Furthermore, the need for communication systems integration is increasingly important. Therefore, it is necessary to propose and develop more compact antenna design with optimized performance (adaptation, radiation, gain, efficiency, axial ratio).The objective of this thesis is to design planar antennas, broadband or multi-band, with circular polarization and optimized performances. To achieve these objectives, the work was divided into several stages, from the design of a wideband CP antenna to the design of a GNSS tri-band circular polarized patch antenna. Firstly, a literature study of planar antennas has been conducted. Different designs have been examined and contrasted to evaluate their performances. Secondly, a wideband CP patch antenna with parasitic elements has been designed manufactured and measured. It was sought to optimize its operating band. Considering the bibliographical study that was already carried out, and based on the wideband CP antenna structure that was validated during the previous phase, a new GNSS tri-band CP patch antenna was also designed, fabricated and measured. Most of the work was done on minimizing its size while maintaining satisfactory electromagnetic performance in the three required GNSS frequency bands : L2, E6 and L1. Special attention was directed towards getting a good axial ratio over a wide radiating aperture. The last phase of this thesis was to go even further in improving the CP GNSS multi-band antenna's performance, particularly by improving its efficiency. Excitation slots were finally used after a comparison was made between the different performances obtained through the different design techniques (coaxial feed, slots, etc ...).

Near field imaging using microwave in medical applications has gain much attention recently as various researches show its high ability and accuracy in illuminating object comparing to the well-known screening tools such as Magnetic Resonance Imaging (MRI), digital mammography, ultrasound etc. This has encourage and motivate scientists continue to exploit the potential of microwave imaging so that a better and more powerful sensing tools can be developed. This thesis documents the development of antenna design for microwave imaging application such as breast cancer detection. The application is similar to the concept of Ground Penetrating Radar (GPR) but operating at higher frequency band. In these systems a short pulse is transmitted from an antenna to the medium and the backscattered response is investigated for diagnose. In order to accommodate such a short pulse, a very wideband antenna with a minimal internal reflection is required. Printed monopole and planar metal plate antenna is implemented to achieve the necessary operating wide bandwidth. The development of new compact printed planar metal plate ultra wide bandwidth antenna is presented. A generalized parametric study is carried out using two well-known software packages to achieve optimum antenna performance. The Prototype antennas are tested and analysed experimentally, in which a reasonable agreement was achieved with the simulations. The antennas present an excellent relative wide bandwidth of 67% with acceptable range of power gain between 3.5 to 7 dBi. A new compact size air-dielectric microstrip patch-antenna designs proposed for breast cancer detection are presented. The antennas consist of a radiating patch mounted on two vertical plates, fed by coaxial cable. The antennas show a wide bandwidth that were verified by the simulations and also confirmed experimentally. The prototype antennas show excellent performance in terms the input impedance and radiation performance over the target range bandwidth from 4 GHz to 8 GHz. A mono-static model with a homogeneous dielectric box having similar properties to human tissue is used to study the interaction of the antenna with tissue. The numerical results in terms the matching required of new optimised antennas were promising. An experimental setup of sensor array for early-stage breast-cancer detection is developed. The arrangement of two elements separated by short distance that confined equivalent medium of breast tissues were modelled and implemented. The operation performances due to several orientations of the antennas locations were performed to determine the sensitivity limits with and without small size equivalent cancer cells model. In addition, a resistively loaded bow tie antenna, intended for applications in breast cancer detection, is adaptively modified through modelling and genetic optimisation is presented. The required wideband operating characteristic is achieved through manipulating the resistive loading of the antenna structure, the number of wires, and their angular separation within the equivalent wire assembly. The results show an acceptable impedance bandwidth of 100.75 %, with a VSWR < 2, over the interval from 3.3 GHz to 10.0 GHz. Feasibility studies were made on the antenna sensitivity for operation in a tissue equivalent dielectric medium. The simulated and measured results are all in close agreement.

The objectives of this research work are to investigate, design and implement circularly-polarized antennas to be used for handheld satellite mobile communication and wireless sensor networks. Several antennas such as Quadrifilar Spiral Antennas (QSAs), two arm Square Spiral and stripline or coaxially-fed microstrip patch antennas are developed and tested. These antennas are investigated and discussed to operate at L band (1.61-1.6214GHz) and ISM band (2.4835-2.5GHz) A substantial size reduction was achieved compared to conventional designs by introducing special modifications to the antenna geometries. Most of the antennas are designed to produce circularly-polarized broadside-beam except for wireless sensor network application a circularly-polarized conical-beam is considered. The polarization purity and Specific Absorption Rate (SAR) of two dual-band antennas for satellite-mobile handsets next to the human head are investigated and discussed, using a hybrid computational method. A small distance between the head and the handset is chosen to highlight the effects of the relatively high-radiated power proposed from this particular antenna. A Genetic Algorithm in cooperation with an electromagnetic simulator has been introduced to provide fast, accurate and reliable solutions for antenna design structures. Circularly-polarized quadrifilar helical antenna handset and two air-dielectric microstrip antennas were studied. The capabilities of GA are shown as an efficient optimisation tool for selecting globally optimal parameters to be used in simulations with an electromagnetic antenna design code, seeking convergence to designated specifications. The results in terms of the antenna size and radiation performance are addressed, and compared to measurements and previously published data.

The objectives of this research work are to investigate, design and implement circularly-polarized antennas to be used for handheld satellite mobile communication and wireless sensor networks. Several antennas such as Quadrifilar Spiral Antennas (QSAs), two arm Square Spiral and stripline or coaxially-fed microstrip patch antennas are developed and tested. These antennas are investigated and discussed to operate at L band (1.61-1.6214GHz) and ISM band (2.4835-2.5GHz) A substantial size reduction was achieved compared to conventional designs by introducing special modifications to the antenna geometries. Most of the antennas are designed to produce circularly-polarized broadside-beam except for wireless sensor network application a circularly-polarized conical-beam is considered. The polarization purity and Specific Absorption Rate (SAR) of two dual-band antennas for satellite-mobile handsets next to the human head are investigated and discussed, using a hybrid computational method. A small distance between the head and the handset is chosen to highlight the effects of the relatively high-radiated power proposed from this particular antenna. A Genetic Algorithm in cooperation with an electromagnetic simulator has been introduced to provide fast, accurate and reliable solutions for antenna design structures. Circularly-polarized quadrifilar helical antenna handset and two air-dielectric microstrip antennas were studied. The capabilities of GA are shown as an efficient optimisation tool for selecting globally optimal parameters to be used in simulations with an electromagnetic antenna design code, seeking convergence to designated specifications. The results in terms of the antenna size and radiation performance are addressed, and compared to measurements and previously published data.