Radiation characteristics of a double‐layer spherical dielectric lens antenna with a conformal PEC disk fed by on‐axis dipoles

Abstract

Abstract The radiation of a double‐layer spherical dielectric lens equipped with a conformal spherical‐disk PEC reflector and excited by elementary sources located on the antenna axis of rotation is considered. The sources are either a radial electric dipole or a tangential magnetic dipole. Using the analytical inversion of the static part of the homogeneous‐lens problem with the aid of the Abel integral transform, developed earlier for plane‐wave scattering, each of the considered problems are cast to the Fredholm second‐kind infinite matrix equation with elements containing only the elementary functions. This guarantees convergence and enables accurate characterisation of the considered lens antennas in terms of directivity and total radiated power, in wide frequency range. It is demonstrated that the best directivity is provided by the quasi‐Luneburg lens configuration with dielectric constants of the core and the shell being 2 and 1.1, respectively, shell thickness being 0.1 of the outer lens radius, and reflector size around 30°. This performance, however, is spoiled by the whispering‐gallery‐mode resonances that can be effectively alleviated by the introduction of the moderate losses to the shell material.