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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 2-D 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 3-D 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. [ABSTRACT FROM AUTHOR]

The authors introduce two flat graded-index (GRIN) lens designs in this study. First of these is a thick lens, which was designed and fabricated by using the three-dimensional (3D)-printing technique. Second, a thin dial-a-dielectric (DaD) lens, which uses state-of-the-art artificially engineered dielectric materials for design and for which they present only the simulated results, with plans to fabricate it in the future. Both designs overcome the difficulties faced in finding desired commercial off-the-shelf materials, either for 3D-printing or for fabricating conventional GRIN lenses. The lenses comprise of several concentric dielectric rings with bespoke relative permittivities for transforming spherical waves into plane waves and vice versa. The 3D-printed thick flat lens is low-cost and light-weight, but provides broadband and high gain performance. Measurement results show that the realised gain of the thick lens is 9-11 dB over the frequency band of 12-18 GHz. The designed DaD lens has the desirable characteristics of low loss, low reflection and broadband properties. [ABSTRACT FROM AUTHOR]