Here we look a four possible antenna designs. The classical half wave dipole, the half wave folded dipole, the short dipole and monopole. later these designs will be used to excite the plane and corner reflector antennas.
A half wave dipole often used in Yagi's to increase the drive impeadnce.
This is any dipole of less than one tenth lambda. Approaching zero this becomes an isotropic antenna of free space impedance.
This is a dipole of > half lambda. Beyond half lambda the radiation beam begins to generate lobes which tend to distact from the utility of the dipole..