Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

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

Thesis (MEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Balanced loads such as antennas normally require baluns when they are measured. For wide band applications, designing and building a balun complicates the measurement and introduces errors. A simple model for load impedances was developed, together with a novel measurement procedure. The procedure enables the measurement of balanced loads using a network analyzer with no balun. Measured and simulated results are presented. / AFRIKAANSE OPSOMMING: Gebalanseerde laste soos antennas benodig gewoonlik balons om korrek gemeet te word. Die ontwerp van 'n balon vir wye band toepassings bemoeilik die metings en veroorsaak foute. 'n Eenvoudige model vir die lasimpedansies is ontwikkel sowel as 'n eenvoudige meetmetode. Die metode word gebruik om die gebalanseerde laste te meet met 'n netwerk analiseerder sonder die gebruik van 'n balon. Gemete en gesimuleerde resultate word getoon.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The successful operation of a man-pack VHF jamming system requires a compact and efficient antenna operating over a wide bandwidth. The design of such an antenna is the focus of this thesis. The antenna should be of a practical size for a portable system and it must radiate energy efficiently across a frequency bandwidth in excess of a decade. A practical „target‟ specification of such an antenna has been drawn up based on the performance of a commercially available system. Several possible antenna topologies, each with a variety of loading section options, are tested using “Full wave” electromagnetic modelling (FEKO). Each topology/loading-section is numerically optimised for load element values by considering both its gain and reflection coefficient. Results of the „optimally loaded‟ solution for each topology are then compared to each other to arrive at the best overall design. The best result is found to be the traditional monopole whip-type antenna, with four R-L loading sections spread along its length. The simulated results show that the proposed antenna can be expected to meet the target standing wave ratio (SWR) specifications while offering a gain advantage of between 5 and 10 dBi higher than is available commercially. The selected design is constructed and its performance measured. / AFRIKAANSE OPSOMMING: Die suksesvolle werking van ʼn mobiele VHF "jammer‟ benodig ʼn kompakte antenna met ʼn bruikbare benuttingsgraad wat oor ʼn wyeband funksioneer. Die ontwerp van so ʼn antenna is die fokus van hierdie tesis. Die antenna moet kompak genoeg wees om draagbaar te wees en moet ʼn bruikbare benuttingsgraad hê oor ʼn frekwensie-bandwydte van meer as 10:1. ʼn Praktiese spesifikasie is opgestel vir die antenna deur te kyk na die sigblaaie van beskikbare stelsels. “Volgolf” elektromagnetiese modelleringsagteware is daarna gebruik om ʼn parametriese ondersoek te loods van verskillende antennas. Verskillende topologieë is getoets met ʼn verskeidenheid van belaaide seksies waar die topologieë ge-optimaliseer was vir wins en weerkaatskoëffisiënt. Die resultate vir elke optimale oplossing is vergelyk.Opgrond van hierdie resultate is bevind dat die beste topologie die tradisionele monopoolmas "whip-type‟ antenna is met vier RL lading afdelings langs die lengte versprei. Analise word gebruik om te wys dat verwag kan word dat dit aan die aanwins en staande golf verhouding (SGV) spesifikasies sal voldoen met n 10 dB verhoging in aanwins vir n laer SGV. Die geselekteerde ontwerp is gebou en gemeet om te verifieer dat dit aan die spesifikasies voldoen.

Orientadores: Hugo Enrique Hernandez Figueroa, Arismar Cerqueira Sodre Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e Computação / Made available in DSpace on 2018-08-13T10:26:45Z (GMT). No. of bitstreams: 1 Brianeze_JulianoRodrigues_M.pdf: 7661922 bytes, checksum: 0d973e2e61c313de34e1ff70e57df18f (MD5) Previous issue date: 2008 / Resumo: Sistemas embarcados usando Radar de Abertura Sintética (Synthetic Aperture Radar - SAR), em plataformas aerotransportadas ou orbitais, têm sido cada vez mais usados para sensoriamento remoto. Quando estes sistemas são aplicados para estudos de cobertura vegetal e biomassa, sinais com freqüências acima de 1 GHz penetram pouco na vegetação. Já o uso de freqüências na banda P (400 MHz) permite uma maior penetração, possibilitando a detecção da superfície do terreno subjacente. A escolha da antena para esses sistemas é um ponto muito importante, já que vários de seus parâmetros estão diretamente ligados ao desempenho do sistema. O objetivo deste trabalho é propor um novo tipo de antena Yagi que seja eficiente para sistemas SAR aerotransportados: uma combinação das antenas Quasi-Yagi e Yagi-Uda. Da primeira é mantido o balun de microfita, que garante uma grande largura de banda. Já os elementos radiantes (driver e diretores), permanecem semelhantes aos de uma antena Yagi-Uda, ou seja, dipolos cilíndricos de metal. A antena foi projetada para ser fixada ao corpo de uma aeronave, usando a fuselagem para moldar seu padrão de radiação. Após a proposta de um modelo final para a nova antena Yagi, chamado Yagi Tridimensional, suas principais características foral analisadas através de simulações numéricas e experimentos. A antena proposta possui características inovadoras que permitem uma menor radiação para baixo da plataforma, possibilitando o uso simultâneo de duas antenas, uma de cada lado da aeronave, o que diminui consideravelmente os custos operacionais. Finalmente, um protótipo foi projetado e construído para atender os requisitos de um sistema SAR especificado. Além disso, medidas de perda de retorno e padrão de radiação foram realizadas e comparadas com os resultados de simulação. / Abstract: Embedded systems using Synthetic Aperture Radar (SAR), in orbital or airborne platforms, have often been used for remote sensing. When these systems are applied to vegetal cover and biomass studies, signals with frequency above 1 GHz do not properly penetrate in the vegetation. On the other hand, the use of signals with frequencies in P band (400 MHz) allows a deeper penetration, making possible the detection of the underlying terrain surface. The antenna choice for these systems is a very important point, because several of its parameters are directly linked to the system performance. The aim of this work is to develop a new kind of Yagi antenna efficient for airborne SAR systems: a combination of Quasi-Yagi and Yagi-Uda antennas. From the first, the microstrip balun is kept, in order to ensure a large bandwidth. The radiant elements (driver and directors), remain similar to those of Yagi-Uda antenna, in other words, cylindrical metal dipoles. The antenna was designed to be fixed to an aircraft body, using the fuselage to shape its radiation pattern. A novel Yagi antenna was proposed, called Tridimensional Yagi, and its main properties were analyzed by means of numerical simulations and experiments. The proposed antenna provides a lower radiation under the platform, enabling the use of two antennas simultaneously, one at each side of the aircraft. This new feature can considerably decrease the operational costs. Finally, a prototype was designed, and built to meet the requirements of a specified SAR system. Furthermore, experiments on return loss and radiation pattern have been carried out and compared to numerical simulations. / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

This thesis investigates control aspects of the Hartebeeshoek Radio Astronomy Observatory (HartRAO) antenna. The installation of a new 22 GHz receiver has required the pointing accuracy to be improved to less than 4 mdeg. The effect of thermal conditions on the the HartRAO antenna pointing offset is investigated using a variety of modelling techniques including simple geometric modelling, neural networks and Principal Component Analysis (PCA). Convincing results were obtained for the Declination pointing offset, where applying certain model predictions to observations resulted in an improvement in Declination pointing offset from 5.5 mdeg to 3.2 mdeg (≈50%). The Right Ascension pointing model was considerably less convincing with an improvement of approximately from 5.5 mdeg to 4.5 mdeg (≈20%) in the Right Ascension pointing offset. The Declination pointing offset can be modelled sufficiently well to reduce the pointing offset to less than 4 mdeg, however further investigation of the underlying causes is required for the Right Ascension pointing offset.

Approved for public release; distribution is unlimited / The Numerical Electromagnetics Code (NEC) was used to evaluate the admittance, average power gain, and the electric near and far field of a monopole antenna mounted on a cubical box over a perfectly conducting ground plane. Two models of the box, employing surface patches and wire grids, were evaluated. The monopole was positioned at the center, the edge, and at a corner of the box's top surface. Admittance and average power gain of the antenna were calculated. NEC results were examined and compared with experimental data and with results from "PATCH", another independent electromagnetic modeling code. The near electric field was calculated for both models. Computer graphics techniques were presented for plotting NEC near field results using DISSPLA (Display Integrated Software System and Plotting Language), a commercial graphics package. Contour and 3-D amplitude, and phase plots of the near electric fields were presented. Radiation patterns were calculated to relate far field and near field behavior of the antenna. Surface patch and wire grid models are compared and conclusions were presented. / Naval Ocean Systems Center / http://archive.org/details/investigationofn00elli / O&MN, Direct Funding / Lieutenant, Hellenic Navy

In situations where information infrastructure is destroyed or not available, on-demand information infrastructure is pivotal for the success of rescue missions. In this paper, a drone-carried on demand information infrastructure for long-distance WiFi transmission system is developed. It can be used in the areas including emergency response, public event, and battlefield. The WiFi network can be connected to the Internet to extend WiFi access to areas where WiFi and other Internet infrastructures are not available. In order to establish a local area network to propagate WIFI service, directional antennas and wireless routers are used to create it. Due to unstable working condition on the flying drones, a precise heading turning stage is designed to maintain the two directional antennas facing to each other. Even if external interferences change the heading of the drones, the stages will automatically rotate back to where it should be to offset the bias. Also, to maintain the same flying altitude, a ground controller is designed to measure the height of the drones so that the directional antennas can communicate to each other successfully. To verify the design of the whole system, quite a few field experiments were performed. Experiments results indicates the design is reliable, viable and successful. Especially at disaster areas, it’ll help people a lot.

In this thesis, we conduct a preliminary study on the controller design for directional antenna devices carried by drones. The goal of the control system is to ensure the best alignment between two directional antennas so as to enhance the performance of air-to-air communication between the drones. The control system at the current stage relies on the information received from GPS devices. The control system includes two loops: velocity loop and position loop to suppress wind disturbances and to assure the alignment of two directional antennae. The simulation and animation of directional antennae alignment control for two-randomly moving drones was developed using SIMULINK. To facilitate RSSI-based antenna alignment control to be conducted in the future work, a study on initial scanning techniques is also included at the end of this thesis.

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