This dissertation details the development of the star spiral antenna and demonstrates the advantages of the star spiral when used in a wideband array with variable element sizes. The wideband array with variable element sizes (WAVES) is a multi-octave array that uses different sized circular Archimedean spirals for each octave of frequency coverage. A two-octave WAVES array has been presented in the literature, but a gap in the two-octave frequency coverage exists along the principal axes. The star spiral antenna was developed to eliminate the performance gap in the WAVES array. The star spiral is a type of slow-wave spiral that also offers array-packing advantages, particularly for the WAVES array. The size reduction that can be achieved with the star spiral is comparable to that of the square spiral, but the star spiral is much more efficient in terms of its expected size reduction compared to its circumference. The far-field patterns, gain, and scan performance of the star spiral are similar to that of the circular Archimedean spiral. The use of the star spiral to eliminate the performance gap in a WAVES array of circular Archimedean spirals is detailed. Furthermore, a three-octave WAVES array of star spirals is built and measured, and the scan performance of the array is investigated via simulation. / Ph. D.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18470号 / 工博第3906号 / 新制||工||1600(附属図書館) / 31348 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 北野 正雄, 教授 和田 修己, 准教授 山田 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The Log-Periodic Loop Antenna with Ground Reflector (LPLA-GR) is investigated as a new type of antenna, which provides wide bandwidth, broad beamwidth, and high gain. This antenna has smaller transverse dimensions (by a factor of 2/pi) than a log-periodic dipole antenna with comparable radiation characteristics. Several geometries with different parameters are analyzed numerically using ESP code, which is based on the method of moments. A LPLA-GR with 6 turns and a cone angle of 30* offers the most promising radiation characteristics. This antenna yields 47.6 % gain bandwidth and 12 dB gain according to the numerical analysis. The LPLA-GR also provides linear polarization and unidirectional patterns. Three prototype antennas were constructed and measured in the Virginia Tech Antenna Laboratory. Far-field patterns and input impedance were measured over a wide range of frequencies. The measured results agree well with the calculated results. Because of its wide bandwidth, high gain, and small size, the LPLA is expected to find applications as feeds for reflector antennas, as detectors in EMC scattering range, and as mobile communication antennas. / Master of Science

No description available.

The Square Kilometer Array radio astronomy telescope will achieve the majority of its extremely large aperture area with thousands of parabolic dishes, each illuminated by a wideband antenna feed, and this thesis introduces a new such antenna. The wide bandwidth of this new antenna is achieved with the development of a directional log periodic antenna. Scaling the log periodic elements into three-dimensional space is the present method used for directional log periodic antennas. We propose confining these often complex log periodic elements into a single plane, while the ground "plane" takes on a three dimensional form, permitting low-cost implementations without requiring the introduction of a complicated scaffolding to support the log periodic elements in 3-D. This low-cost solution would scale well in the implementation of the thousands of antenna feeds that the Square Kilometer Array demands. We also introduce a previously unreported LP design: the log periodic log spiral antenna.

Antenas fractais são estruturas irradiadoras geradas recursivamente a partir da aplicação reiterada de um fator de conjunto gerador, possuindo a característica marcante de ser auto semelhante. São baseadas na teoria dos fractais desenvolvida por Mandelbrot e cuja aplicação se encontra presente em quase todos os ramos da ciência. Tais antenas possuem hoje inúmeras aplicações, de celulares a antenas de satélites, e têm se mostrado uma alternativa atraente para aplicações que requeiram característica de multibanda associada a alto ganho e miniaturização. O presente trabalho procura apresentar de forma sistemática a teoria básica envolvendo antenas fractais, tendo-se por base não apenas as contribuições pioneiras de pesquisadores no mundo todo, mas também a teoria básica de antenas, a partir das quais é possível chegar-se a formulações importantes na área. O foco é para antenas de microfita, dada a grande popularidade que têm encontrado nas últimas décadas. Além de vasta bibliografia, contou-se com o auxílio da ferramenta computacional HFSS da Ansoft®, um software que simula estruturas em alta frequência. Este programa é utilizado para simular uma antena fractal de microfita proposta pelo autor, e os resultados são analisados tendo-se um duplo propósito: exemplificar o uso de uma antena fractal, por um lado, e fornecer um protótipo que porventura poderá ser utilizado em aplicações especiais, por algum projetista de antenas. Os principais parâmetros fundamentais de antenas são analisados, como Perda de Retorno, VSWR, Ganho, etc., mas será dada ênfase especial à aplicação de estruturas fractais de microfita em dois tipos de aplicações: antenas eletricamente pequenas e antenas independentes da frequência. / Fractal Antennas are radiating structures generated recursively from the reiterated application of a generating array, having the remarkable feature of being self similar. They are based on the theory of fractal developed by Mandelbrot and whose application is present in almost every branches of science. Such antennas have many applications today, from cell phones to satellite antennas, and have proved to be an attractive alternative for applications that required multiband characteristic associated with high gain and miniaturization. This paper aims do present systematically the basic theory involving fractal antennas, and is based not only on the pioneering contributions of researchers around the world, but also the basic theory of antennas, from which is possible to reach important formulations in the area. Besides the extensive bibliography, was used the computational tool HFSS by Ansoft®, a software that simulates high frequency structures. This program is used to simulate a fractal microstrip antenna proposed by the author, and the results are analyzed, having a dual propose: to exemplify the use of fractal antenna on the one hand, and providing a prototype which could possible be used in special applications, for some designer of antennas. The main fundamental parameters of antennas are analyzed, such as Return Loss, VSWR, Gain, etc., but special emphasis will be given to the application of fractal microstrip structures in two kinds of applications: electrically small antennas and frequency independent antennas. / Dissertação (Mestrado)