Near and far-field focusing with holographic two-dimensional tapered leaky-wave spiral antennas

The design of two near and far-field printed-slots spiral antennas working at 10GHz is reported in this work. By properly modulating the radial separation between the slots and its width, it is shown how the TM₀ leaky-mode pointing angle and leakage rate can be adequately tapered to efficiently synthesize focused near and far-field patterns, while keeping a flat single-layer low-profile planar antenna design which is simply fed by a vertical coaxial probe. The far-field operation has been reached using the split condition in which the alpha and beta constants are equal. The two designs are based on an Archimedean-spiral shaped modulated slot to offer circular transverse polarization of the focused fields. An analysis in frequency shows that the near-field antenna has the ability to generate frequency steerable near-field focusing patterns. Simulation results are reported in this paper, showing that high radiation (more than 75%), illumination and focusing efficiency (more than 70% and 25% for near and far-field respectively) can be achieved and agree with the theoretical values.