Un des enjeux majeurs dans l'intégration de nouveaux systèmes de guerre électronique (GE) dans les avions d'armes est notamment la réduction de l'encombrement des antennes. En GE, La bande passante des antennes peut être de l'ordre de la décade et la fréquence basse peut être voisine de la centaine de MHz, ce qui rend l'intégration des antennes difficile voire impossible selon les cas. Les antennes de GE font habituellement appel à des antennes dites "indépendantes de la fréquence" placées au-dessus d'une cavité absorbante. La fabrication des matériaux absorbants est à ce jour encore "artisanale" et donc onéreuse. De plus, ces matériaux sont lourds et ils ne présentent pas les mêmes caractéristiques électriques d'une fabrication à l'autre. Les travaux présentés dans ce manuscrit sont dédiés à la réalisation d'antennes à très large bande passante de très faible épaisseur et sans absorbant. Nous avons proposé et validé une nouvelle structure basée sur les matériaux à bandes interdites électromagnétiques (BIE). Le nouveau dispositif permet de remplacer les matériaux absorbants, de réduire l'épaisseur des antennes large bande et de réduire les coûts de fabrication grâce à un procédé industriel de fabrication. La nouvelle structure présente contrairement à toutes les autres structures BIE l'avantage d'être ultra large bande et compacte (de l'ordre de 1/100ième de longueur d'onde d'épaisseur). Nous avons montré l'intérêt d'utiliser un tel dispositif pour réduire l'épaisseur et améliorer les performances des antennes planaires de forme et de polarisation quelconque.

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This paper proposes two innovative designs for the broadband and high-gain circularly polarized operation, a corner-truncated inverted -L patch antenna and a cylindrical-probe-fed circularly polarized patch antenna using a single probe feed. Next, the broad circularly polarized printed spiral strip antenna for 5 GHz WLAN operation is studied; we also proporse a compact dual-band circularly polarized antenna for GPS/ETC operation on vechicles. In addition, an experimental study of the nearly square circularly polarized microstrip antenna with a rectangular ground plane is presented. The CP antennas are greatly affected by the different side lengths of the rectangular ground plane. To compensate for this effect, the aspect ratio of the nearly square radiating patch should be increased with the increasing aspect ratio of the rectangular ground plane.

This thesis presents an analysis of the behavior of an equiangular spiral antenna using a mixture of numerical and measurement techniques. The antenna is studied as an isolated element and as a part of a spiral-based ground-penetrating radar (GPR) detection system. The numerical modeling was based on the parallelized finite-difference time-domain method and the model was validated by comparison with a prototype antenna and detection system. The intention is to isolate the effect of varying different geometrical parameters that define the spiral element or the spiral GPR system. With some notion of each parameter's effect, systems that use the spiral antenna can be designed more easily. The analysis of the spiral antenna in isolation provides a set of design graphs for the antenna. A set of design graphs are constructed that allow one to better understand the effect of the chosen dielectric substrate on the characteristic impedance of the antennas. A second set of design graphs give very specific data about the lower cut-off frequency possible for the antennas given a requirement on its minimum boresight gain, axial ratio, or voltage standing-wave ratio when matched with an appropriate transmission line. The analysis of the spiral antenna in the context of a detection system provides information on the effect of the ground on the GPR system and to what extent the circular polarization properties of the spiral antenna play a role in GPR. It is shown that a spiral antenna used in a monostatic radar configuration will reject a symmetric scatterer well into the near-field. The importance of a resistive loading to the spiral arms is demonstrated for this rejection to be optimal. In addition, it is shown that increasing the dielectric constant of the ground narrows the pattern and polarization properties, making the antenna more directive towards boresight when the spiral antennas radiate into a flat ground. In addition to this work, a method for reducing the truncation error when calculating the planewave spectrum of an antenna is described.

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No / An experimental study of coupling compensation for AOA estimation using compact low profile antenna arrays with element separations of a quarter wavelength has been conducted. Two circular arrays of low profile miniaturised logarithmic spiral antennas deployed on a circular metal plate were used for data acquisition. Using the MUSIC direction-finding algorithm, the AOA estimation errors in receiving mode were observed before and after compensation: the errors were significantly decreased by coupling compensation.

[pt] Os sistemas que operam em banda larga necessitam de radiadores que atendam eletricamente a banda de frequência utilizada. As antenas com características de independência da frequência, em particular as antenas espirais, têm encontrando cada vez mais utilização nesses sistemas, seja em aplicações comercias ou militares. Esta dissertação tem por objetivo a análise de desempenho de antenas espirais do tipo fenda em cavidades, pela aplicação do método dos momentos. Serão consideradas cavidades com a face oposta à antena constituída por um condutor perfeito ou acoplada a uma estrutura de microondas com matriz de espalhamento conhecida. Essa estrutura de microondas, poderá simular, por exemplo, uma ou mais camadas de material absorvente.Um modelo numérico foi desenvolvido, e a partir dele foi elaborado um programa de computador, para determinar as características de radiação de antenas espirais em cavidade. São apresentados e comparados os resultados obtidos para três configurações de antenas espirais de Arquimedes do tipo fenda: sem cavidade, com cavidade condutora e com um material absorvente colocado sobre a face da cavidade oposta a abertura da antena. / [en] Broad band systems need radiators to operate over the entire frequency band. Frequency independent antennas, in particular spiral antennas, are finding increasing application in such systems, for commercial or military purposes. This dissertation has for objective the analysis of performance of cavity-backed slot spiral antenna, by applying the moment method . For this study it will be taken into account cavities with the face opposing to the antenna consisting of a perfect conductor or connected to a structure of microwaves with known scattering matrix. This microwave structure will be able to simulate, for example, one or more layers of absorbing material. A numerical model was developed, and based on it, it was elaborated a computer program to determine the radiation characteristics of cavity-backed spiral antennas. The results surveyed for three configurations of slot Archimedean spiral antenna are presented and compared: without cavity, with conducting cavity, and with an absorbing material placed on the cavity opposite to the antenna.

Ce travail porte sur la conception de réseaux large bande à double polarisation basées sur des antennes spirales d'Archimède. Ces antennes sont connues pour avoir une bande passante très large. Mais, dans un réseau, la bande passante est diminuée du fait de l'apparition de lobes de réseaux. Pour que le réseau fonctionne à double polarisation, il est nécessaire d'utiliser des éléments de polarisations opposées, ce qui accroit encore la distance entre les éléments possédant la même polarisation. Ceci fait ainsi apparaître les lobes de réseaux à des fréquences inférieures par rapport au cas à mono polarisation. Dans ce travail, une méthode analytique a été développée pour estimer la bande passante des réseaux d'antennes spirales. Cette méthode a montré que la bande passante maximale d'un réseau à distribution spatiale uniforme est d'environ une octave pour le cas à mono polarisation et inexistant pour le cas à double polarisation. Pendant la validation de la méthode d'estimation quelques résonances ont été observées. Des explications de ce phénomène sont présentées, ainsi que des possibles solutions. Pour élargir la bande passante du réseau, nous montrons qu'il est possible d'utiliser en même temps les deux tendances actuelles de conception de réseaux d'antennes large bande. En utilisant deux techniques issues de ces deux tendances, nous avons pu réaliser un réseau présentant une bande passante de 6:1. Des perspectives sont aussi présentées. / This work focuses on the design of wideband dual polarized arrays using spiral antennas. These antennas are known for having wideband properties. But, due to the presence of the grating lobes, the bandwidth is decreased when using an array instead of a single antenna. In order to obtain a dual polarized array, it is needed to use elements of opposite polarization, which creates great distances between same polarization elements, meaning an earlier presence of the grating lobes. In this work, an analytic method was developed to estimate the bandwidth of the spiral arrays. This method showed that the maximum bandwidth of uniform spiral arrays is about an octave, for the mono-polarized case, and nonexistent for the dual polarized case. Working on the validation of the method, some resonances were observed. Explanations are presented, as well as possible solutions. Trying to expand the bandwidth of the array, it was found that it is possible and suitable to use at the same time the two current design paradigms for wideband arrays. Using this idea, a 6:1 bandwidth concentric rings array using connected spirals was achieved. Perspectives are also presented.

iv ABSTRACT DESIGN AND CONSTRUCTION OF REDUCED SIZE PLANAR SPIRAL ANTENNA IN THE 0.5-18 GHz FREQUENCY RANGE YILDIZ, 5nan&ccedil / M.S., Department of Electrical and Electronics Engineering Supervisor: Prof. Dr. Altunkan HIZAL October 2004, 106 pages In this thesis, theoretical and practical evaluation of usual spiral antenna is revised. Working principles of both types of planar spiral antennas as Equiangular and Archimedean are introduced. A predesigned microstrip tapered balun used for feeding section of a spiral antenna is simulated on Ansoft HFSS software. Successful simulation results are obtained and measurements of implemented balun structure are made by using an HP 8722 D vector network analyzer. Antenna measurement techniques used in this study are introduced. Measurement set-ups are defined and some preliminary knowledge is given on these. As the main matter of thesis, reduced size planar spiral antennas are designed and implemented. Return loss, gain / radiation and polarization patterns of antennas are measured. Datasets of measurements are compared with each other and with reference spiral antenna. Quite promising results are obtained and size reduction of spiral antenna is achieved in many aspects.