This paper presents a new planar feeding structure for wideband resonant-cavity antennas\n(RCAs). The feeding structure consists of two stacked dielectric slabs with an air-gap in between.\nA U-shaped slot, etched in the top metal-cladding over the upper dielectric slab, is fed by a planar\nstripline printed on the back side of the dielectric slab. The lower dielectric slab backed by a ground\nplane, is used to reduce back radiation. To validate the wideband performance of the new structure,\nin an RCA configuration, it was integrated with a wideband all-dielectric single-layer partially\nreflecting superstructure (PRS) with a transverse permittivity gradient (TPG). The single-layerRCAfed\nby the U-slot feeding structure demonstrated a peak directivity of 18.5 dBi with a 3 dB directivity\nbandwidth of 32%. An RCA prototype was fabricated and experimental results are presented.
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