Novas técnicas para a síntese de antenas duplo-refletoras circularmente simétricas com o controle de iluminação na abertura

Abstract

For high-performance wireless communication systems, the use of shaped dual-reflector antennas can be an attractive option. Reflector shaping allows for the desired redistribution of illumination at the aperture, providing a more efficient radiation pattern. In the last decades, the techniques to synthesize circularly symmetric reflectors have been exhaustively investigated. They are based on the principles of Geometrical Optics (GO) and on the numerical evaluation of differential equations or on the use of conic sections, but with a uniform phase in the aperture. Thus, the development of formulations for the synthesis of reflector antennas with simultaneous control of amplitude and phase at aperture becomes a new class of problems to be investigated. In this context, this thesis presents new techniques to synthesize circularly symmetric dual-reflector antennas based on axis-displaced configurations and those that have omnidirectional coverage. For such, iterative algorithms were developed based on the principles GO, using the continuous concatenation of conic sections to represent two shaped generatrices. Differently from the works available in the literature, here the shaped main-reflector generatrix is always described by ellipses, providing simultaneous control of amplitude and phase of the aperture’s GO field. It is reported that the shaped geometries were analyzed by Method of Moments (MoM), validating the new techniques. Initially, the antennas were shaped with uniform phase over the aperture, successfully illustrating the functionality of the procedures. For each case, a numerical convergence study was carried to evaluate the accuracy of the proposed shaping algorithms. As expected, it was found that error rates decrease when the number of conics increases. Next, new formulations were proposed for the synthesis of non-uniform phase distributions at the aperture in order to provide, according to the GO principles, flat-top, isoflux and cosecant-squared patterns. To validate the non-uniform phase, the electric field in the far-field was obtained using the Aperture Method (Ap-M). Consequently, it was possible to synthesize the present antennas with non-uniform phases, demonstrating that they produced the desired specifications at the aperture.