I've had mixed success with Hammerite on aluminium (alloy). It certainly
covers well, but in the longer term it tends to flake off aluminium
surfaces that had not been extremely well cleaned and de-greased before
painting. Since the object in question was a 12-yagi antenna array,
scrupulous cleaning of every square inch was not a practical option.

Why do you want to paint an antenna ?
If it is going to be outside, you may need to check out the airplane paint.