Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This paper presents the implementation of an artificial magnetic ground-plane with a low profile Log-periodic Dipole Array (LPDA) antennas. After the properties of three typical Electromagnetic Bandgap (EBG) structures are investigated and their bandwidth properties are studied, a mechanism is presented to improve the band-width over which the EBG surface acts as a perfect magnetic conductor (PMC). A low profile LPDA is modeled above this surface and the results indicate an improved band-width region. Compared with a LPDA in free space the frequency band is shifted higher by the EBG surface and the gain pattern is shifted from a horizontal orientation to a vertical orientation. / AFRIKAANSE OPSOMMING: Hierdie dokument stel voor die implementering van kunsmatige magnetiese grondvlakke met Logaritmiese Periodiese Dipool Samestelling (LPDS) antennas. Die eienskappe van drie tipiese Elektromagnetiese Bandgaping (EBG) strukture word ondersoek en hul bandwydte eienskappe word bestudeer. ’n Meganisme word voorgestel om die bandwydte te verbeter waar die EBG oppervlakte soos n perfekte magnetiese geleier optree. ’n Lae profiel LPDS word bo hierdie oppervlakte geplaas. Die resultate dui aan ’n verbetering in the bandwydte. In vergelyking met ’n LPDS in vrye ruimte skuif die frekwensie band ho¨er as gevolg van die EBG oppervlakte en die aanwins patroon skuif van ’n horisontale orientasie na ’n vertikale orientasie.

Submitted by camilla martins (camillasmmartins@gmail.com) on 2017-04-27T13:05:18Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnaliseTeoricaFiltros.pdf: 4789588 bytes, checksum: 8e8c2066525cc43ae730dd29a6cdff9d (MD5) / Approved for entry into archive by Edisangela Bastos (edisangela@ufpa.br) on 2017-05-04T12:38:55Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnaliseTeoricaFiltros.pdf: 4789588 bytes, checksum: 8e8c2066525cc43ae730dd29a6cdff9d (MD5) / Made available in DSpace on 2017-05-04T12:38:55Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnaliseTeoricaFiltros.pdf: 4789588 bytes, checksum: 8e8c2066525cc43ae730dd29a6cdff9d (MD5) Previous issue date: 2016-11-25 / Este trabalho apresenta simulações de filtros rejeita-faixa de micro-ondas utilizando estruturas Electromagnetic Bandgap (EBG). Na estrutura de filtro são feitos furos no plano terra e posteriormente esses furos terão o seu diâmetro alterado visando melhorar a qualidade da banda de rejeição e a obtenção de duas bandas de rejeição. Em comparação com filtros convencionais, filtros com estruturas EBG tem melhores características de banda de rejeição na faixa de micro-ondas As referidas simulações foram feitas com o software comercial ANSYS HFSS. Uma estrutura de filtro utilizando guias de ondas fotônicos também é modelada e simulada utilizando o software comercial Comsol. Os efeitos dos parâmetros físicos da estrutura em relação as característica de filtragem são estudados em ambos os filtros. Os resultados do procedimento de criação e de simulação são descritos e possíveis aplicações dessas estruturas de filtro são discutidas neste trabalho. A faixa de rejeição particularmente ampla é alcançada pelos circuitos apresentados neste trabalho bem como duas bandas de rejeição. / This paper presents simulations of a band-stop filter using microwave Electromagnetic Bandgap structures (EBG). In the filter structure are made holes in the ground plane and these holes will subsequently changed its diameter to improve the rejection band of the quality and obtaining two rejection bands. Compared with conventional filters, filters with EBG structures have better rejection bandwidth characteristics in the microwave band. These simulations were performed with commercial software ANSYS HFSS. A filter structure using photonic waveguides is also modeled and simulated using commercial software Comsol. The effects of the physical parameters of the structure in relation to the filter characteristic are studied in both filters. The results of the creation and simulation procedure are described and possible applications of these filter structures are discussed in this paper. The particularly wide stopband is achieved by the circuits presented in this paper as well as two rejection bands.

The main focus of this thesis is placed on high frequency PCB signal Integrity Is-sues and RF/Microwave filters using EBG structures. From the signal Integrity aspect, two topics were mainly discussed. On one hand, the effect of increasing frequency on classical design rules for crosstalk reduction in PCBs was investigated experimentally and by full-wave simulations. An emphasis was placed on the 3×W spacing rule and the use of guard traces. Single-ended and differential transmission lines were considered. S-parameter measurements and simu-lations were carried out at high-frequency (up to 20 GHz). The results emphasize the necessity to reevaluate traditional design rules for their suitability in high frequency applications. Also, the impacts of using guard traces for high frequency crosstalk re-duction were clearly pointed out. On the other hand, the effect of high loss PCB ma-terials on the signal transmission characteristics of microstrip lines at high frequency (up to 20 GHz) was treated. Comparative studies were carried out on different micro-strip configurations using standard FR4 substrate and a high frequency dielectric ma-terial from Rogers, Corporation. The experimental results highlight the dramatic im-pact of high dielectric loss materials (FR4 and solder mask) and magnetic plating metal (nickel) on the high frequency signal attenuation and loss of microstrip trans-mission lines. Besides, the epoxy-based SU8 photoresist was characterized at high frequency (up to 50 GHz) using on-wafer conductor-backed coplanar waveguide transmission lines. A relative dielectric constant of 3.2 was obtained at 30 GHz. Some issues related to the processing of this material, such as cracks, hard-skin, etc, were also discussed. Regarding RF/Microwave filters, the concept of Electromagnetic Band Gap (EBG) was used to design and fabricate novel microstrip bandstop filters using periodically modified substrate. The proposed EBG structures, which don’t suffer conductor backing issues, exhibit interesting frequency response characteristics. The limitations of modeling and simulation tools in terms of speed and accuracy are also examined in this thesis. Experiments and simulations were carried out show-ing the inadequacies of the Spice diode model for the simulations in power electronics. Also, an Artificial Neural Network (ANN) model was proposed as an alternative and a complement to full-wave solvers, for a quick and sufficiently accurate simulation of interconnects. A software implementation of this model using Matlab’s ANN toolbox was shown to considerably reduce (by over 800 times) the simulation time of microstrip lines using full-wave solvers such as Ansoft’s HFSS and CST’s MWS. Finally, a novel cooling structure using a double heatsink for high performance electronics was presented. Methods for optimizing this structure were also discussed. / QC 20100809

This diploma thesis deals with the modeling of planar antennas with special superstrates in the CST Microwave Studio. Attention is given to the electromagnetic bandgap (EBG) substrates. Firstly, the working principle of these special substrates and generally physical phenomena accompanying electromagnetic waves propagation in a periodic medium are analyzed. By modeling of basic EBG structures in CST their dispersion diagrams were obtained and afterwards compared to one another. The object of the second part of this thesis was modeling of a chosen antenna in CST. An Antenna placed first on the conventional and then on the EBG substrate - in both cases with special superstrates - is analyzed and compared to each other. In the third part of this thesis, the particle swarm optimization (PSO) technique was implemented in CST (VBA language), and was applied to the original design of the chosen antenna. In the final part of this thesis, the optimized antenna was modeled and analyzed in ANSOFT HFSS, and the results from both simulation programs are compared to each other.