Dipole antenna is one of the most fundamental antenna that still be widely used today. A single half-wave dipole can work independently, or work as a parabolic antenna's feeder. Several half-wave dipoles can combine to become antenna array.
A dipole antenna with two arms of same length is named symmetrical dipole. If each arm is equal to 1/4 of the wave length and total length is 1/2 of the wave length, such dipole is called half-wave symmetrical dipole (Figure 2a).
In addition, if a full wave length dipole is folded as a rectangular shape, such long, narrow rectangular frame is called folded dipole. Note if a folded dipole is also half wave long, it is called half-wave folded dipole (Figure 2b)