Over the last few years‚ the number of subscribers of wireless services has increased at an explosive rate. This ever growing demand for wireless communications services is constantly increasing the need for better coverage‚ improved capacity and higher quality service. Smart antennas system is an effective technology for the performance improvement of wireless communications. Switching-beam smart antennas use a number of fixed beams at an antenna site. The system provides a beam that offers the best signal enhancement and interference reduction. Using the approach of dynamic switching-beam antenna system‚ an intelligent sector beam synthesis of adjustable sector width can be established. By doing so‚ traffic load balancing can be achieved, and therefore, system capacity is increased. In this thesis, a beam-pattern synthesis algorithm proposed by M.H. Er is applied to shape array patterns with an adjustable mainlobe width and average sidelobe level reduction. Using an established database of weighting for circular arrays, the proposed smart antennas can adjust suitable sectors for the high dense subscribers not uniformly distributed. Simulation results demonstrate the proposed technique can dramatically improve the performance of traditional switching-beam antennas.

Novel broadband designs of planar antenna with an air substrate are proposed in this dissertation, The operating bands considered include the GSM/DCS band and ISM band. Several antenna designs capable of dual- polarized operation, circularly polarized radiation, and diversity operation are also presented.In these antenna designs, prototypes were constructed. The measured input impedance, return loss, radiation pattern, and antenna gain are presented and discussed. The commercially available simulation software are also used in verifying the measured results.As for the broadband planar antenna designs, the impedance bandwidth obtained reaches about 10% (1.5¡G1VSWR). For the circularly polarized designs, we propose a low-cost, broadband circularly polarized patch antenna fed by a coplanar probe feed, and circular polarization (CP) radiation over a wide frequency range (¡Ö10%) can be achieved. High isolation between two feeding ports (S21 less than ¡V30 dB) can be obtained for the constructed prototype of the proposed dual-polarized design. On the other hand, wrapping a planar monopole into a compact box-like structure allows the antenna¡¦s total height less then 5% of the wavelength at 900 MHz. The proposed antennas are suitable for wireless communications applications.

The switched-beam antenna is one type of the smart antennas, which consists of the antenna array and the beamforming network. The four-beam smart antenna generates four beams to cover a 120¢X area, which can be used to improve the carrier-to-interference ratio and the frequency reuse of a cellular system. Due to the attractive features of microstrip antennas such as low profile, easy fabrication, and low cost, we use microstrip antennas as array elements. In this thesis, we propose a novel four-beam beamforming network which consists of a 4¡Ñ4 Butler Matrix and four 180¢X power dividers. This network is able to provide low side-lobe level. A modified Butler Matrix not only simplifies the circuit of the 8¡Ñ8 Butler Matrix, but also meet the requirement of the original Butler Matrix. From the result of measurement, the side-lobe level of each beam of the modified Butler Matrix is less than ¡V10 dB. We also show that this method is applicable to any Butler matrix.

This dissertation presents the investigation of antennas with improved performances at microwave frequencies. It covers the following three topics: the study of the metamaterial with near-zero index of refraction and its application in directive antenna design, the design technique of a wideband circularly polarized patch antenna for 60GHz wireless application and the investigation of a novel direction of arrival (DOA) estimation technique inspired by human auditory system. First, the metamaterial composed of two-dimensional (2-D) metallic wire arrays is investigated as an effective medium with an effective index of refraction less than unity (n(eff) < 1). The effective medium parameters (permittivity ε(eff), permeability μ(eff) and n(eff)) of a wire array are extracted from the finite-element simulated scattering parameters and verified through a 2-D electromagnetic band gap (EBG) structure case study. A simple design methodology for directive monopole antennas is introduced by embedding a monopole within a metallic wire array with n(eff) < 1 at the antenna operating frequencies. The narrow beam effect of the monopole antenna is demonstrated in both simulation and experiment at X-band (8 – 12 GHz). The measured antenna properties including return loss and radiation patterns are in good agreement with simulation results. Parametric studies of the antenna system are performed. The physical principles and interpretations of the directive monopole antenna embedded in the wire array medium are also discussed. Second, a fully packaged wideband circularly polarized patch antenna is designed for 60GHz wireless communication. The patch antenna incorporates a diagonal slot at the center and features a superstrate and an air cavity backing to achieve desired performances including wide bandwidth, high efficiency and low axial ratio. The detailed design procedure of the circularly polarized antenna, including the design of the microstrip-fed patch antenna and the comparison of the performances of the antenna with different feeding interfaces, is described. The experimental results of the final packaged antenna agree reasonably with the simulation results. Third, an improved two-antenna direction of arrival (DOA) estimation technique is explored, which is inspired by the human auditory system. The idea of this work is to utilize a lossy scatter, which emulates the low-pass filtering function of the human head at high frequency, to achieve more accurate DOA estimation. A simple 2-monopole example is studied and the multiple signal classification (MUSIC) algorithm is applied to calculate the DOA. The improved estimation accuracy is demonstrated in both simulation and experiment. Furthermore, inspired by the sound localization capability of human using just a single ear, a novel direction of arrival estimation technique using a single UWB antenna is proposed and studied. The DOA estimation accuracies of the single UWB antenna are studied in the x-y, x-z and y-z planes with different Signal to Noise Ratios (SNR). The proposed single antenna DOA technique is demonstrated in both simulation and experiment, although with reduced accuracy comparing with the case of two antennas with a scatter in between. At the end, the conclusions of this dissertation are drawn and possible future works are discussed.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 173-177).

Thesis (Ph. D.)--City University of Hong Kong, 2005. / "Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves 144-153).

Bien que les propriétés optiques des métaux nanostructurés soit connues depuis de nombreuses décennies, ce n'est que dans les dernières années que ce domaine a suscité un grand intérêt. Ceci est en partie dû aux nombreux progrès des techniques de nanofabrication. Le domaine de la plasmonique est souvent présentée comme la support de la prochaine génération de dispositifs de traitement de l'information, mélageant la nanoélectronique et la photonique silicium pour obtenir des disposotifs plus performants. Les systèmes microélectroniques actuels approchant de la saturation en terme de bande passante et de consomation énergétique, la migration vers les systèmes photoniques semble inévitable. La prédiction de la réponse électromagnétique de ces composants nano-photoniques est essentiels au succès de leur intégration réaliste. Les outils numériques de simulation électromagnétiques sont le moyen par excellence de calculer précisement er de manière réaliste les propriétés optiques de composants nanophotoniques, et en particulier ceux utilisant des plasmons de surface. Ce travail de thèse rend compte de l'analyse numérique de la propagation et des caractéristiques de champ proche de composants à base de plasmons pour la photonique en technologie CMOS. Les deux principaux outils de modélisation EM utilisés à cet égard sont la méthode des éléments des moments, ainsi que la FDTD. Deux types principaux de dispositifs actifs plasmoniques actifs ont été étudiés: d'une part les modulateurs électro-optiques intégrés et d'autre part des détecteurs à base de quantum dot de Ge, le tout dans la gamme du proche infrarouge. La question cruciale d'un couplage efficace de la lumière dans un mode très confiné plasmonique a d'abord été étudiée de manière à isoler la part modale des principales contributions. Ensuite, une nouvelle structure de modulateur assisté plasmon a été proposée et une conception optique complète prenant en compte les contraintes technologiques d'une fonderie CMOS est proposée et discutée. Enfin une conception optimisée du couplage radiatif de l'absorption d'un point de Ge, en utilisant une antenne dipolaire plasmonique, est étudiée. En particulier, l'ingénierie radiative du substrat SOI permet de démontrer un effet considérable sur la performance finale du dispositif. / Interest in the field of plasmonics has been primarily driven by the need to guide and confine light in the subwavelength scale. The past few years has witnessed a huge interest in this field largely due to the may advances that have occured in nanofabrication techniques. The field of plasmonics is often touted as the next generation platform that could interface nanoscale electronics and Si photonics. With current electronic systems nearing saturation, the migration to photonic systems would become inevitable. Crucial to achieving this integration is to design reliable plasmonic components within nanophotonics circuits. This however requires an accurate estimation of the electromagnetic response of these components. Numerical modeling tools are one way to gauge this response. By and large the thesis deals with numerically analysing the propagation and near field characteristics of plasmon based components for Si photonics. The two principal EM modelling tools used in this regard are the boundary element method as well as the finite difference time domain.Two main kind of active plasmonic active devices were investigated: integrated modulators, and free space radiation photodetectors. The critical issue of an efficient coupling of light into a very confined guided plasmonic mode was first investigated so as to isolate the main modal governing contributions. Next, a new structure of plasmon assisted modulator was proposed and a complete optical design taking into the technological constraints of a CMOS foundry is provided and discussed. Finally a design optimizing the radiative coupling to the absorption of a Ge dot, using a plasmonic dipolar antenna, is studied. In particular the radiative engineering of the supporting SOI substrate is shown to have a tremendous

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No / A low-profile (λ/43) miniaturized multi-element antenna is presented, which displays vertical polarization with an omni-directional radiation pattern. The antenna uses a logarithmic spiral shape as the main radiating element such that the impedance bandwidth of the antenna is much improved in comparison with both a strip-line square spiral design and a strip-line circular spiral design. The antenna demonstrates stable gain and useful efficiency over the operating frequency band. Significantly, the antenna provides a low profile, omnidirectional pattern in the azimuth plane, polarizes normal to the ground-plane with a 1.2% bandwidth and 0.5 dBi gain.