  We report the first conformal ultra-wide band (UWB) array on a doubly curved
surface for wide angle electronic scanning. We use a quadrilateral mesh as the
basis for systematically arraying UWB radiators on arbitrary surfaces. A
prototype consisting of a 52 element, dual-polarized Vivaldi array arranged
over a 181 mm diameter hemisphere is developed. The antennas and SMP connectors
are 3D printed out of titanium to allow for simple fabrication and assembly. We
derive the theoretical gain of a hemispherical array based on the antenna size
and number of elements. The measured realized gain of the prototype array is
within 2 dB of the theoretical value from 2-18 GHz and scan angles out to
120{\deg} from the z-axis. This field of view is twice that of a planar array
with the same diameter in agreement with theory. This work provides a baseline
performance for larger conformal arrays that have more uniform meshes.
Furthermore, the basic concept can be extended to other UWB radiating elements.
