Surface matching of dielectric lenses

Abstract

Two methods of cancelling the surface reflections of dielectric lenses are described. The first utilizes a simulated quarter-wave matching layer, and the second a reactive wall embedded within the dielectric. The reactive wall may take a variety of physical forms, such as arrays of thin conducting discs, which have a capacitive reactance, or arrays of thin wires, which have an inductive reactance. Surface matching is obtained when the discs are placed approximately 3/8 wavelength inside the lens, or the wires 1/8 wave-length Curves are presented that show how the reflections at the air and dielectric boundary are reduced for various angles of incidence and polarization when quarter-wave layer and reactive-wall matching are employed. The reactance of the array of discs for waves incident at various angles and polarizations is computed by means of Bethe's small aperture theory, and Babinet's principle. Measurements in waveguide of the reactance of an array of circular discs for various angles of incidence and for both E- and H-plane polarization show close agreement with the theory.