X wave radiator implemented with 3D printed metamaterials

A radiator is presented, capable of generating paraxial X waves over a 50% fractional bandwidth (7.5 − 12.5 GHz) in its radiative near field. X waves are localized pulses formed by the superposition of Bessel beams with a common cone angle. Quasiconformal transformation optics, a 2D variant of transformation optics, is employed to find the inhomogeneous, isotropic dielectric constant profile needed to convert the radiation of a monopole into a paraxial Bessel beam. An impedance matching layer is applied to reduce reflections at the air-dielectric interface of the device. The transformation and impedance matching regions are implemented using rotationally symmetric metamaterial unit cells that yield a spatially varying effective dielectric constant. The resulting design is fabricated through 3D printing, by combining parts made from three low-loss dielectric filaments. The device is experimentally measured, and shows good agreement with simulations. Its ability to generate paraxial X waves when excited by a broadband pulse is verified.