A simple and planar feeding approach is evaluated for use in wideband Resonant Cavity Antennas (RCAs). Boresight directivity performance of the planar (aperture-coupled dual slot) and a conventional feeding technique (waveguide-fed slot) are investigated by placing each under an unprinted all-dielectric single-layer superstrate with transverse permittivity in lateral dimensions. The well-matched printed feed antenna is shown to achieve a peak directivity of 17 dBi over a wide 3dB directivity bandwidth of 16.2%