Focus E-field (energy)

What kind of antenna?
What frequencies?
At what distance do you want to focus?
You are not new here, give more details ?
Anyway, you can use a parabolic dish to focus, all the dish receivers actually do that ?
You can also use dielectric lenses to focus, somewhat similar to optics, but the dimensions are larger
Note that there are physical limits of how small can be the focus, depending on the wavelength.