Nonuniform Luneburg and two-shell lens antennas: Radiation characteristicsand design optimization

Design optimization of radially nonuniform spherical lens antennas is the f ocus of this paper. In particular, special attention is given to the optima l design of nonuniform Luneburg lens antennas. One of the important enginee ring objectives of designing an optimal Luneburg lens antenna is to use as small number of shells as possible while maintaining an acceptable gain and sidelobe performance. In a typical radially uniform design, by reducing th e number of shells, the gain is decreased and the grating lobes are increas ed. This deficiency in the radiation performance of the uniform lens antenn a can be overcome by designing the nonuniform lens antenna. This necessitat es the optimum selection of each layer thickness and permittivity. A geneti c algorithm (GA) optimizer with adaptive cost function is implemented to ob tain the optimal design. In this manner, the GA optimizer simultaneously de termines the optimal material and its thickness for each shell by controlli ng the gain and sidelobes envelope of the radiation pattern. Various lens g eometries, including air gaps and feed offset from the lens surface, are an alyzed by using the dyadic Green's functions of the multilayered dielectric sphere. Many useful engineering design guidelines have been suggested for the optimum construction of the lens. The results have been satisfactory an d demonstrate the utility of the GA/adaptive cost-function algorithm. Addit ionally, radiation characteristics of a novel two-shell lens antenna have b een studied, and its performance is compared to the Luneburg lens.