The thesis deals with the analysis of a microwave Frequency Selective Surface (FSS) on a conical dielectric radome illuminated by a feed hom located at the base. Two approaches have been adopted to solve this problem. The first approach is to calculate the element currents under the assumption that the surface is locally flat. Consequently, the element current at that locality can be determined by employing Floquet modal analysis. The local incidence has been modelled from the radiation pattern of the source or the aperture fields of the feed. Three types of feed model were used to account for the field illumination on the radome. The transmitted fields from the curved surface are obtained from the sum of the radiated fields due to the equivalent magnetic and electric current sources distributed in each local unit cell of the conical surface. This method treats the interaction of neighbouring FSS elements only. In the second approach the curvature is taken into account by dividing the each element into segments which conform to the curved surface. An integral formulation is used to take into account the interaction of all the elements. The current source in each FSS element from the formulation is solved using the method of moments (MOM) technique. A linear system of simultaneous equations is obtained from the MOM and has been solved using elimination method and an iterative method which employs conjugate gradients. The performance of both methods has been compared with regard to the speed of computations and the memory storage capability. New formulations using quasi static approximations have been derived to account for thin dielectric backing in the curved aperture FSS analysis. Computer models have been developed to predict the radiation performance of the curved(conical) FSS. Experiments were performed in an anechoic chamber where the FSS cone was mounted on a jig resting on a turntable. The measuring setup contained a sweep oscillator that supplied power to a transmitting feed placed at the base of the cone. Amplitude and phase values of the far field radiation pattern of the cone were measured with the aid of a vector network analyser. Cones with different dimensions and FSS element geometries were constructed and the measured transmission losses and radiation patterns compared with predictions.

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The research involves the analysis and design of a new band of horn antennas, namely Frequency Selective Horns (FSHs). Folding a Frequency Selective Surface (FSS) into a shape of a cone makes a FSH. The stimulus behind this research emanates from an idea to use the FSH as a microwave camera for medical diagnostic purposes. FSHs with dipole geometries have been modelled using existing software. A quasi-static approximation models the dipole elements with a dielectric backing as dielectrically loaded cylindrical conducting elements.

Made available in DSpace on 2014-10-09T12:27:54Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:48Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:44:43Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:50Z (GMT). No. of bitstreams: 1 07170.pdf: 3547961 bytes, checksum: 2b5adb1189f6eaea8048d92f88627ed4 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:27:54Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:48Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Lasers de estado sólido sintonizáveis com uma estreita largura de linha de emissão na região do vermelho são uma alternativa conveniente aos lasers de corante para aplicações em espectroscopia de alta resolução. Nesse trabalho, foram investigados lasers contínuos de Nd:YLiF4 e Nd:YVO4 operando em frequência única na região de 1,32 - 1,34μm, assim como a geração de segundo harmônico (GSH) desses lasers usando cristais de BiB3O6 (BiBO) e KTiOPO4 com inversão periódica de domínios (ppKTP), para a obtenção da emissão no vermelho (0,65 - 0,67μm). Utilizando um laser de Nd:YVO4 operando em frequência única em uma configuração em anel com um cristal não linear BiBO do tipo I, demonstrou-se o recorde de 680mW no vermelho em 671,1nm, sem a utilizaçãde nenhum elemento seletivo. Uma intonia em todo o ganho (~4 nm) foi obtida atravésda inserção de um etalon com filme refletor (R = 40%) e com 100μm de espessura, o que reduziu a potência de saída no vermelho para 380mW no comprimento de onda de maior ganho (671,15 nm). Em 1342nm foi demonstrada uma potência de saída de 1,5W em frequência única quando utilizado um espelho de saída com transmissão de 2%. Foi demonstrado ainda uma ótima eficiência de conversão de segundo harmônico em um laser em anel de Nd:YLF na polarização π (λ = 1321,5nm) quando usando um cristal de ppKTP. Este laser forneceu 1,4W em frequência única no vermelho em 660,5nm. Essa potência é a máxima que pode ser extraída desse laser no segundo harmônico e no fundamental quando utilizado um espelho com transmissão ótima. Utilizando um etalon com filme refletor (R = 25%), o laser pôde ser sintonizado em Δλ ~ 1,6nm. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP: 06/57945-3

Submitted by Marco Antonio Oliveira da Silva (maosilva@ipen.br) on 2017-11-09T11:26:50Z No. of bitstreams: 0 / Made available in DSpace on 2017-11-09T11:26:50Z (GMT). No. of bitstreams: 0 / Os lasers Raman permitem a exploração de novos comprimentos de onda, não comumente acessíveis, graças ao Espalhamento Raman Estimulado. Unidos a processos de conversão não linear, abrem-se campos para emissão de comprimentos de onda na região do visível no espectro eletromagnético. Com uma mesma configuração, diversas combinações de cristais possibilitam a geração de múltiplas frequências, transformando esse tipo de laser em um dispositivo compacto e barato quando comparado com outras tecnologias existentes. Este trabalho apresenta a busca da conversão intracavidade em frequências de lasers Raman, em uma configuração linear. Com dois comprimentos de onda de bombeamento de energia (797 nm e 872 nm), diodos semicondutores foram utilizados para acessar dois picos de absorção do cristal Nd:YLF. O bombeamento em 797 nm levou a emissão fundamental em 908 nm. E através do cristal KGW, com linhas de emissão Stokes, um novo comprimento de onda foi alcançado, em 990 nm. Com o cristal dobrador, BiBO, soma de frequência e segundo harmônico foram gerados, permitindo as emissões em uma região espectral azul bastante larga (450 500 nm). Com o bombeamento em 872 nm, uma emissão de três níveis no cristal Nd:YLF não foi possível, conseguindo apenas a emissão em 1064 nm, linha comum para cristais de neodímio. Uma outra cavidade foi estudada, porém com bombeamento em 880 nm e cristal de Nd:YVO4, conhecido por ser self-Raman. Com uma configuração linear semelhante à anteriormente citada, somente sua linha de emissão fundamental em 914 nm foi obtida, não sendo possível com as condições trabalhadas a emissão Stokes, que permitisse dar continuidade ao estudo. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

The angular location of an acoustic source can be estimated by measuring an acoustic direction of incidence based solely on the noise produced by the source. Methods for determining the direction of incidence based on sound intensity, the phase of cross-spectral functions, and cross-correlation functions are available. In this current work, we implement Dominant Frequency SElection (DFSE) algorithm. Direction of arrival (DOA) estimation usingmicrophone arrays is to use the phase information present in signals from microphones that are spatially separated. DFSE uses the phase difference between the Fourier transformedsignals to estimate the direction ofarrival (DOA)and is implemented using a three-element ’L’ shaped microphone array, linear microphone array, and planar 16-microphone array. This method is based on simply locating the maximum amplitude from each of the Fourier transformed signals and thereby deriving the source location by solving the set of non-linear least squares equations. For any pair of microphones, the surface on whichthe time difference ofarrival (TDOA) is constant is a hyperboloidoftwo sheets. Acoustic source localization algorithms typically exploit this fact by grouping all microphones into pairs, estimating the TDOA of each pair, then finding the point where all associated hyperboloids most nearly intersect. We make use of both closed-form solutions and iterative techniques to solve for the source location.Acoustic source positioned in 2-dimensional plane and 3-dimensional space have been successfully located.

Submitted work engages in suggestion of frequency-selection filters with usage of more active elements of the MCMI (Multi-Output Current Mirror and inverter). The preamble of thesis is applied to theory of frequency-selection filters and possible usage of them. The projected circuit layouts with the active elements are discussed in terms of the impact of parasitic properties of the real models. The part of thesis is numerical suggestion of found solutions, their simulation in suitable program.

<p>With the 1999 introduction of IEEE 802.11b, the 2.4 GHz Wireless Local Area Network (WLAN) standard, the WLAN market finally began to experience the growth levels that had been expected for so long. Now, 5 GHz solutions, with the IEEE 802.11a standard leading the way, offer higher throughput and more efficient use of the spectrum. Just as the 2.4 GHz band, the 5 GHz band is unlicensed. A common concern to all unlicensed bands is interference between devices using the spectrum. Furthermore, in the 5 GHz band, WLAN cells can interfere with radar systems operating at the same frequencies. </p><p>This report describes a software model, WOK, suitable for simulations of IEEE 802.11a WLANs operating in various environments and under various ambient conditions. The WOK model can be configured extensively with respect to topology, traffic behavior, channel models, signal attenuation, interference sources and radar systems. </p><p>Further, the concepts of Dynamic Frequency Selection (DFS) and link adaptation are explored in the context of the IEEE 802.11a standard. DFS aims to avoid channels occupied by radar systems and link adaptation aims to maximize the throughput based on current ambient conditions. A DFS algorithm and a link adaptation algorithm are implemented at the Medium Access Control (MAC) layer and evaluated using the WOK model.</p>