  With the rapid development of large-scale integrated photonics, optical
phased array (OPA) is an effective way to realize highly integrated, stable and
low-cost beam control system. Achieving a large field of view (FOV) in the
longitudinal direction without increasing fabrication cost and system
complexity is still a significant challenge in OPA antennas. Here, a high
sensitivity and large scanning range antenna based on subwavelength structure
array is proposed to enhance the longitudinal scanning and free-space radiating
efficiency by using the ridge-waveguide structure and backward-emitting. A
millimeter-long grating antenna with a far-field beam divergence of 0.13{\deg}
and a wavelength sensitivity of 0.237{\deg}/nm is experimentally demonstrated.
Furthermore, by using different sideband periods, we introduce a multi-casting
grating antenna with a large scanning range up to 42.6{\deg}. The proposed
devices show significant improvement in longitudinal wavelength sensitivity
compared with the typical waveguide grating antennas.
