To be honest, we learn about the basic antenna designs, and there are many, and then usually new designs come from altering some idea to fit a new need, until there is nothing of the original idea left. LOL. Usually, we’re asked to size reduce but it’s just not physically possible to do what is often asked of us. There is a running joke in the industry that customers always want an infinitely small antenna with infinite gain. Usually we start with something like a monopole design and change the physical parameters until we can no longer meet the spec. Hopefully the antennas fitsb in the required space. At least that how did it. Necessity is the parent of invention, after all.