ANALYSIS AND DESIGN OF A WIDEBAND MULTIBEAM ARRAY

Abstract

The geodesic lens is a versatile device that is capable of radiating a beam with omni-directional coverage in azimuth or a directive beam that can be scanned 360 degrees in azimuth. The lens takes the form of a conical coaxial cylinder where the larger end is used to excite a biconical antenna and the smaller end is fed by multiple sectoral waveguides equally distributed around the periphery of the cylinder. These sectoral guides are in turn fed by coaxial probes. To provide matched input ports, the sectoral guides have ridged sections to act as impedance transformer. With the proper amplitude and phase excitations of these probes, power is combined within the lens and radiated out of the bicone antenna. The geodesic lens has five major components - the feed section consisting of sectoral waveguides, a junction between a ring of sectoral guides and a coaxial guide, a conical coaxial cylinder, a transition between a coaxial guide and a radial guide, and a series of stepped radial guides approximating a monocone or a flared biconial antenna. This is a thesis on the theoretical developments carried out for the complete electromagnetic analysis of the geodesic lens antenna. The analytical precedure employed is the field matching method. Within any cross-section of the lens antenna, the electric and magnetic fields are represented by a series of natural eigenmodes. For non-canonical cross-sections, the modes are determined by the transverse resonance technique (TRT). Each discontinuity in the lens is characterized by the Generalized Scattering Matrix (GSM). The GSMs of all the junctions are combined together to give an overall description of the performance of the lens.