In the field of antenna design and analysis, often the need arises to numerically extrapolate the far-zone performance of a radiating structure from its known (or assumed known) near-zone electromagnetic field. Mathematical processes developed to accomplish such a task are known in the literature as near-zone to far-zone transformations (NZ-FZTs) as well as near-field far-field (NF-FF) transformations. These processes make use of sampled near-zone field quantities along some virtual surface, viz., the transformation surface, that surrounds the radiating structure of interest. Depending upon the application, samples of the required near-zone field quantities are supplied via analytical, empirical, or computational means. Over the years, a number of NZ-FZT processes have been developed to meet the demands of many applications. In short, their differences include, but are not limited to, the following: (1) the size and shape of the transformation surface, (2) the required near-zone field quantities and how they are sampled, (3) the computational methodology used, and (4) the imbedding of various application-driven features. Each process has its pros and cons depending upon its specific application as well as the type of radiation structure under consideration. In this dissertation we put forth a new and original NZ-FZT process that allows the transformation surface along which the near-zone is sampled to be spheroidal in shape: namely a prolate or oblate spheroid. Naturally, there are benefits gained in doing so. Our approach uses a formulated eigenfunction expansion of spheroidal wave-harmonics to develop two distinct, yet closely related, NZ-FZT algorithms for each type of spheroidal transformation surface. The process only requires knowledge of the E-field along the transformation surface and does not need the corresponding H-field. Given is a systematic exposition of the formulation, implementation, and verification of the newly developed NZ-FZT process. Accordingly, computer software is developed to implement both NZ-FZT algorithms. In the validation process, analytical and empirical radiation structures serve as computational benchmarks. Numerical models of both benchmark structures are created by integrating the software with a field solver, viz., a finite-difference time-domain (FDTD) code. Results of these computer models are compared with theoretical and empirical data to provide additional validation. / Ph. D.

No description available.

In this thesis, we propose a new bandwidth-enhancement method of using a parasitic open slot to achieve a wide lower band for the internal laptop computer antenna with a small size to cover the GSM850/900 operation and a wide upper band to cover the GSM1800/1900/UMTS operation as well. The occupied antenna volume is only 48 ¡Ñ 10 ¡Ñ 3.5 mm^3 above the top edge of the display ground. For practical application, we analyze the effects of the antenna position, nearby metal plate, shielding metal plate, keyboard ground, FR4 substrate, and the size of display ground on the performance of the WWAN antenna. In addition, effects of the user¡¦s whole-body on the proposed antenna are also analyzed. Owing to the user¡¦s whole-body being mainly lossy materials, a decrease in the antenna¡¦s radiation efficiency is observed when the user¡¦s whole-body is in close proximity to the WWAN laptop computer antenna.

This study is focus on the integration and miniaturess of the active circuit and antennas. Recently, the monolithic microwave integrated circuits have been mature in communication markets and the associated handsets are interesting in the quality and profile. The antenna plays a role as a radiator in wireless system. Therefore, the performance dominates the quality of communication. The aspect of the antenna usually occupies the majority communication hardware¡¦s area. Comparing many front end circuit elements, the challenges in the antennas will be more crucial. Therefore, it has well merits in designing high integration and bandwidth antennas. Based on the integration of the active circuits stage and antennas, this work presents the aperture coupled active antenna with harmonic suppression and broadband dual feeds circularly polarized patch antenna. Utilizing the bented aperture and insertion of narrow rectangular slots on excitation edge for shifting the high order harmonic components from the active stage, the harmonic suppression characterization is implemented by the above approach. The other active antenna, braodband dual feeds circularly polarized antenna, is achieved with spatial power combining. The subject aims the different excitated patch structures and replacing the periodic feeding lines as active circuits in the discussion. Relative to the conventional 50 Ohm feeds, the mechanics of the feeds are modified with stepped impedance resonators and stubs at the same physical wave length condition for achieving the integration of the antenna and the circuit. Besides, this antenna can exhibit excellent behavior and compact the size in the effective frequency range.

By employing a low-cost loop antenna of simple structure, a novel antenna design to efficiently make use of the system ground plane of a PDA (personal digital assistant) is proposed. Owing to a small distance of 3 mm between the antenna and the ground plane, the propose antenna has a very low profile. By selecting a proper loop¡¦s length-to-width ratio, two resonant modes close to each other can be excited, which lead to an impedance bandwidth of 17%. In addition, because of the same direction of the surface currents on the radiating metal plate, the antenna peak gain reaches about 4.5 dBi, which is attractive for application in PDAs.

ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California / There are always some intrinsic tradeoffs among the performance characteristics: radiation efficiency, directivity, and bandwidth, of electrically small antennas (ESAs). A non-Foster enhanced, broad bandwidth, metamaterial-inspired, electrically small, Egyptian axe dipole (EAD) antenna has been successfully designed and measured to overcome two of these restrictions. By incorporating a non-Foster circuit internally in the near-field resonant parasitic (NFRP) element, the bandwidth of the resulting electrically small antenna was enhanced significantly. The measured results show that the 10 dB bandwidth (BW10dB) of the non-Foster circuit-augmented EAD antenna is more than 6 times the original BW10dB value of the corresponding passive EAD antenna.

Thesis (M.S.E.E.)--University of Puerto Rico, Mayagüez Campus, 2005. / Tables. Printout. Includes bibliographical references (leaves146-148).

Au cours de ces dernières années, les technologies de télécommunication ont fait d'énormes progrès, notamment dans les communications mobiles et les réseaux de capteurs sans fil (WSN). Pour répondre à l’augmentation de la capacité de transmission et à l’amélioration de la qualité des canaux de communications mobiles, l’élargissement de la bande de fonctionnement est nécessaire par l'utilisation d'antennes reconfigurables en fréquence. En outre, dans les applications WSN, afin de réduire les collisions, d’augmenter la distance de communication et d'optimiser la consommation, l’utilisation d’antennes reconfigurables en directivité est une bonne solution. Dans ce cadre, nos travaux de recherche ont portés sur la conception de différentes structures antennaires reconfigurables. Dans un premier temps nous avons réalisés une antenne reconfigurable à base de nouveaux éléments actifs, les digitally tunable capacitors (DTC). Ces composants sont de très bons candidats en vue d’une intégration d'antennes pour des applications communications mobiles et WSN. Ensuite nous nous sommes attachés à concevoir des structures multibande, MIMO et reconfigurables en fréquence, permettant d’augmenter la bande de fréquence de fonctionnement du système de communication, d'optimiser l'efficacité et la qualité spectrale et d'améliorer la qualité de canal. Enfin, une autre voie a été explorée, l’utilisation d’antennes reconfigurables en directivité pour des applications de WSN. Les résultats de simulation et de mesure sont également présentés dans ce chapitre. Grâce à l'utilisation de ce type de structures, la performance des WSN a été optimisée. / In recent years, telecommunication technologies have enormous progress, especially cellular communications and wireless sensor networks. To meet the demand of increasing transmission capacity, improving quality of cellular communication channels, expanding the operating band of the equipment is necessary. As passive antenna has reached the limit on increasing the operating band with the small size, the use of frequency reconfigurable antenna is a feasible solution. Besides, in the applications of WSN, to reduce collisions, increase communication distance and optimize consumption, directional reconfigurable antenna is a good proposal. In this thesis we present several reconfigurable antenna structures. Firstly, a new component is introduced; digitally tunable capacitor (DTC). Thanks to its advantages, such parts are good candidate to be integrated in the antenna for cellular communication and wireless sensor network applications. After, several antennas are introduced include multiband antenna, MIMO and frequency reconfigurable antenna, which can be used to extend the operating frequency band of the communication system, optimize spectral efficiency and quality improve channel quality. The structures of these antennas are introduced together with the results of simulation and measurement for the purpose of solving the challenges given in the future cellular communications systems. And then, the proposed approach to the design of reconfigurable directional antennas is presented. Several reconfigurable directional antennas, which are used in applications of WSN, are introduced. Thanks to the use of directional antennas reconfigurable, performance of WSN system will be optimized.

When an electrically small antenna is conceived, designed, simulated, and tested, the main emphasis is usually placed immediately on its impedance bandwidth and radiation efficiency. All too often it is assumed that its directivity will only be that of a Hertzian dipole and, hence, its directivity becomes a minor consideration. This is particularly true if such a compact antenna radiates in the presence of a large ground plane. Attention is typically focused on the radiator and its size, while the ground plane is forgotten. This has become a too frequent occurrence when antennas, such as patch antennas that have been augmented with metamaterial structures, are explored. In this paper, it is demonstrated that while the ground plane has little impact on the resonance frequency and impedance bandwidth of patch antennas or metamaterial-inspired three-dimensional magnetic EZ antennas, it has a huge impact on their directivity performance. Moreover, it is demonstrated that with both a metamaterial-inspired two-element array and a related Huygens dipole antenna, one can achieve broadside-radiating electrically small systems that have high directivities. Several common and original designs are used to highlight these issues and to emphasize why a fundamental figure of merit such as directivity should never be overlooked.

Transparent patch antennas are microstrip patch antennas that have a certain level of optical transparency. Highly transparent patch antennas are potentially suitable for integration with solar panels of small satellites, which are becoming increasingly important in space exploration. Traditional patch antennas employed on small satellites compete with solar cells for surface area. However, a transparent patch antenna can be placed directly on top of solar cells and resolve the issue of competing for limited surface real estate. For such an integration, a high optical transparency of the patch antenna is required from the solar cells' point of view. On the other hand, the antenna should possess at least acceptable radiation properties at the same time. This dissertation focuses on some of the most important concerns from the perspective of small satellite applications. For example, an optimization method to simultaneously improve both optical transparency and radiation efficiency of the antenna is studied. Active integrated antenna design method is extended to meshed patch applications in an attempt to improve the overall power efficiency of the front end communication subsystem. As is well known, circular polarization is immune from Faraday rotation effect in the ionosphere and thus can avoid a 3-dB loss in geo-satellite communication. Therefore, this research also aims to present design methods for circularly polarized meshed patch antennas. Moreover, a meshed patch antenna capable of supporting a high communication data rate is investigated. Lastly, other types of transparent patch antennas are also analyzed and compared to meshed patches. In summary, many properties of transparent patch antennas are examined in order to meet different design requirements.