  Optical antennas are a fundamental element in optical phased arrays (OPA) and
free-space optical interconnects. An outstanding challenge in optical antenna
design lies in achieving high radiation efficiency, ultra-compact footprint and
broad radiation angle simultaneously, as required for dense 2D OPAs with a
broad steering range. Here we demonstrate a fundamentally new concept of a
nanophotonic antenna based on near-field phase-engineering. By introducing a
specific near-field phase factor in the Fraunhofer transformation, the
far-field beam is widened beyond the diffraction limit for a given aperture
size. We use transversally interleaved subwavelength grating nanostructures to
control the near-field phase. The antenna reaches a radiation efficiency of
82%, a compact footprint of 3.1 um * 1.75 um and an ultra-broad far-field beam
width of 52{\deg} and 62{\deg} in the longitudinal and transversal direction,
respectively. This unprecedented design performance is achieved with a
single-etch grating nanostructure in a 300-nm SOI platform.
