Made available in DSpace on 2014-12-17T14:55:55Z (GMT). No. of bitstreams: 1 TercioLS_DISSERT.pdf: 2173183 bytes, checksum: 0473c9e56e2e2ec2462372a52af84fd3 (MD5) Previous issue date: 2011-12-21 / This work presents a theoretical analysis and numerical and experimental results of the scattering characteristics of frequency selective surfaces, using elements of type patch perfectly conductor. The structures are composed of two frequency selective surfaces on isotropic dielectric substrates cascaded, separated by a layer of air. The analysis is performed using the method of equivalent transmission line in combination with the Galerkin method, to determine the transmission and reflection characteristics of the structures analyzed. Specifically, the analysis uses the impedance method, which models the structure by an equivalent circuit, and applies the theory of transmission lines to determine the dyadic Green's function for the cascade structure. This function relates the incident field and surface current densities. These fields are determined algebraically by means of potential incidents and the imposition of the continuity of the fields in the dielectric interfaces. The Galerkin method is applied to the numerical determination of the unknown weight coefficients and hence the unknown densities of surface currents, which are expanded in terms of known basis functions multiplied by these weight coefficients. From the determination of these functions, it becomes possible to obtain numerical scattered fields at the top and bottom of the structures and characteristics of transmission and reflection of these structures. At work, we present numerical and experimental results for the characteristics of transmission and reflection. Comparisons were made with other results presented in literature, and it was observed a good agreement in the cases presented suggestions continuity of the work are presented / Esse trabalho apresenta uma an?lise te?rica e resultados num?ricos e experimentais das caracter?sticas de espalhamento de superf?cies seletivas em frequ?ncia, que usam elementos do tipo patch perfeitamente condutor. As estruturas s?o compostas por duas superf?cies seletivas em frequ?ncia sobre substratos diel?tricos isotr?picos cascateadas, separadas por uma camada de ar. A an?lise ? efetuada utilizando-se o m?todo da linha de transmiss?o equivalente em combina??o com o m?todo de Galerkin, visando determinar as caracter?sticas de transmiss?o e reflex?o das estruturas analisadas. Especificamente, a an?lise usa o m?todo da imped?ncia, que modela a estrutura por meio de um circuito equivalente e, aplica-se a teoria de linhas de transmiss?o para determinar a fun??o di?dica de Green, para a estrutura em cascata. Esta fun??o relaciona os campos incidentes e as densidades superficiais de corrente. Estes campos s?o determinados algebricamente por meio dos potenciais incidentes e da imposi??o da continuidade dos campos nas interfaces diel?tricas. O m?todo de Galerkin ? aplicado na determina??o num?rica dos coeficientes pesos desconhecidos e, consequentemente, das densidades superficiais de correntes desconhecidas, que s?o expandidas em termos de fun??es de base conhecidas multiplicadas por esses coeficientes peso. A partir da determina??o destas fun??es, torna-se poss?vel a obten??o num?rica dos campos espalhados no topo e na base das estruturas e das caracter?sticas de transmiss?o e de reflex?o destas estruturas. No trabalho, s?o apresentados resultados num?ricos e experimentais para as caracter?sticas de transmiss?o e de reflex?o. Foram efetuadas compara??es com outros resultados apresentados na literatura, tendo-se observado uma boa concord?ncia nos casos analisados Sugest?es de continuidade do trabalho s?o apresentadas

A circular polarised phased array antenna and a frequency selective hybrid radome are designed and evaluated. The antenna system is well suited as a part of a communication link between platforms with a 600 MHz bandwidth and a centre frequency of 5 GHz. A prototype consisting of 8 x 8 patch elements has been designed, manufactured and characterised. The final configuration will be a compact, relatively inexpensive system with single-fed antenna elements. An array antenna with circular polarisation is suitable when the receiver must maintain a strong signal regardless of the relative antenna orientation. The radome protects the antenna and can also reduce both the radar cross section and interference from out-of-band signals. The main focus is to make sure that the phased array antenna and the radome work as one unit and maximise the field of view in which the polarisation is circular. The method to maximise the field of view is to reduce the coupling between antenna elements by using shorting via fences surrounding each element. Following this method results in a total array gain of 18 dBi, 25° half-power beamwidth and a ±35° maximum scan angle with maintained circular polarisation. Prototype measurements agree well with the simulated results. / En cirkulärpolariserad fasstyrd gruppantenn samt en frekvensselektiv hybrid-radom har designats och utvärderats. Antennsystemet lämpar sig väl som en kommunikationslänk mellan plattformar med en 600 MHz bandbredd och centerfrekvens 5 GHz. En prototyp besåtende av 8 × 8 patchelement har designats, tillverkats och karaktäriserats. Den slutgiltiga konfigurationen resulterade i ett kompakt och relativt billigt system med single-matade antennelement. En gruppantenn med cirkulär polarisation är lämplig när mottagaren måste bibehålla en stark signal oavsett antennens relativa orientering. Radomen skyddar antennen från väder och vind och kan även minska både radarmålsarean och störningar från utombandiga signaler. Huvudfokus är att se till att den fasstyrda gruppantennen och radomen fungerar som en enhet och maximerar scan-området i vilket polarisationen är cirkulär. Metoden för att maximera detta område är att minska kopplingen mellan antennelementen genom att använda ett kortslutande viastaket som omsluter varje element. Metoden resulterar i totalt 18 dBi array gain, 25° half-power beamwidth och en maximal utstyrningsvinkel på ±35° med bibehållen cirkulär polarisation. Prototypens mätresultat stämmer väl överens med simulationsresultaten.

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