Radially polarized annular-slot leaky-wave antenna for three-dimensional near-field microwave focusing

Microwave three-dimensional near-field focusing with radial polarization using a holographic annular-slot antenna is demonstrated in this letter. This radial polarization can generate axially polarized focused fields in the near-field regime, which complements the more conventional synthesis of transversally polarized near-field focusing patterns. Moreover, it is shown that more symmetrical focal region is obtained thanks to the radial polarization for similar Fresnel number N and operation frequency. The theory is demonstrated with experiments for a design operating at 10 GHz, with aperture diameter D=6¿ and a Fresnel number N=4. © 2002-2011 IEEE.