What is a folded dipole antenna?

What is a folded dipole antenna?

In a folded dipole antenna, a half-wave length conductor is folded into a longitudinal loop and fed at the centre. It has a higher impedance of around 280 Ohms compared to the 70 Ohms impedance of a horizontal half-wave dipole antenna. Hence while a coaxial cable is suited for a horizontal half-wave dipole antenna, a twin-lead transmission line with about 300 Ohms impedance is used for a folded half-wave dipole antenna.

Half-wave folded dipole is commonly used as the driven element of a Yagi multi-element antenna. Like a half-wave dipole antenna, the folded dipole is also resonant and radiates well at odd integer multiples of half-wave lengths. As mentioned in case of half-wave dipole antenna, it acts as a 3/2 wavelength dipole at three times the fundamental frequency. Folded half-wave dipole antenna is preferred when the impedance has to be higher.