In mesh view mode, right click on the object of the helix (at tree folder)
and choose (local) mesh properties - change there the local mesh of the helix antenna...
1) increase the frequency to higher value, it will improve the meshing although not good idea
2) Its better to change the tepmelate u start with, best one is
3) Go to File->select template->Antenna(free space,wavegide)
4) Meshproperties->special->equilibrate mesh