The path to antenna design is
- knowing LCR circuits
- knowing basic field properties, material properties (E, H, B, D, potentials, etc) and their relation to lumped components.
- to have excellent understanding of transmission line theory.
- knowing how fields and radiation do originate from current segments and how the form the radiated power.
- knowing about constructive and destructive interference and radiation patterns (for your case also near or transition field patterns, they are more elaborate).
- knowing behavior of structures no longer small w.r.t. wavelength (reflection, refraction, fresnel theory).
- knowing properties of existing antenna types to enable you to make a first selection.
- knowing how to use a suitable software package for your challenge.
It is not easy but when you really want it, are willing to put lots of effort in it, you can master it.