This work presents optimization of printed wideband antennas that are backed by High Impedance surfaces using a hybrid of constrained Evolutionary Programming (EP) and a MoM based simulator, This approach is used to arrive at optimized designs for semiconformal bowtie antenna structures of about λ/10 thick with enhanced bandwidth performance, which are superior to previously reported structures. Two different designs are presented, where in each a bowtie antenna is used as radiating element and a mushroom-like EBG structure is used as its High Impedance ground-plane, with vias for one design, and without the vias for the other.