Modelagem geométrica de antenas duplo-refletoras para cobertura omnidirecional

Abstract

Based on Geometrical Optics (GO) principles, this work presents a computational tool for the synthesis of dual reflector antennas for omnidirectional coverage. Initially, the algorithm synthesizes one of four omnidirectional classical dual reflector configurations: OADC (Omnidirectional Axially Displaced Cassegrain) OADG (Omnidirectional Axially Displaced Gregorian), OADC (Omnidectional Axially Displaced Ellipse), OADC (Omnidirectional Axially Displaced Hyperbola). Then, by using the classical sub-reflector, the main reflector is shaped to generate a cosecant squared radiation pattern in the elevation plane, according to the principles of GO. To evaluate the synthesized antenna radiation pattern, Method of the Aperture associated with the GO-Fields is employed. This analysis technique is numerically efficient and yields a good approximation for the main radiation pattern. For a comparative study, two types of aperture are employed: the first type is a cylindrical surface in front of main reflector, and the second type is a surface that coincides with the shaped main reflector. As a reference for the radiation pattern, the solution of Electrical Field Integral Equation via Method of Moments is employed. To illustrate the technique, the work presents design examples of omnidirectional antennas where the main reflector is shaped to generate a cosecant square radiation pattern in the elevation plane. These examples consider sub-reflector types derived from the OADE and OADC classical configurations. It also considers two types of ray structure emanating from the main reflector to generate the specified radiation pattern: with a real or virtual caustic.