Near-field focusing with holographic two-dimensional tapered leaky-wave slot antennas

The design of holographic printed-slot leaky-wave microwave lenses is presented in this paper. By properly modulating the radial separation between slots and the width of the slot unit-cell, the surface-to-leaky transformation can be tailored, modulating the leaky-mode pointing angle and leakage rate in order to efficiently synthesize focused near-field patterns, conceiving new planar leaky-wave lenses. Two topologies are proposed: a first one is based on an Archimedean-shaped modulated slot, and a second design uses concentric circularly-shaped modulated slot-rings. The first geometry offers circular transverse polarization of the focused near-fields, while the second one presents linear-axial (vertical) polarized focused fields. Simulation results are reported in this paper, showing high radiation and aperture efficiencies (above 70%), while keeping a flat single-layer low-profile planar design which is simply fed by a vertical coaxial probe. The phenomenon of frequency steering of the focal region is also described. Finally, the design approach is particularized to the synthesis of far-field focused radiation patterns, illustrating the possibility and limitations to obtain high-efficiency broadside-directed antennas. In this way, it is anticipated a new type of low-cost, planar, low-profile, high-gain, simply fed, printed-slot two-dimensional leaky-wave radiator.