Classical axis-displaced dual-reflector antennas for omnidirectional coverage

The aim of this work is to discuss the synthesis and performance of classical dual-reflector antennas suited for an omnidirectional coverage. The reflector arrangements are axially symmetric with surfaces of revolution generated by axis-displaced conic sections, established from geometrical-optics (GO) standpoints to achieve omnidirectional radiation characteristics. Closed-form equations are derived for the design of all possible reflector configurations. The vector GO aperture field is also obtained, yielding an approximate analysis by the aperture method. Some pertinent geometrical characteristics and efficiency curves are then presented and discussed for several antenna configurations fed by transverse electromagnetic coaxial horns (for vertical polarization). A practical antenna design is conducted and analyzed by the method-of-moments technique, demonstrating the accuracy of the efficiency analysis yield by the aperture method for moderately large antenna apertures.