Current is shared between the conductors. With equal diameters, theoretical impedance is roughly four times that of a simple dipole.
Antennas · F1SYH
Folded dipole
A folded dipole uses two parallel conductors connected at both ends. It presents higher impedance than a simple dipole.
HF
VHF
Boucle repliée
Operating principle
Main characteristics
Typical gain
≈ 2,15 dBi
Impedance
≈ 280 à 300 Ω
Polarization
Selon orientation
Difficulty
Intermédiaire
Dimensions and design
Total length remains close to half a wavelength. Conductor spacing and diameter affect impedance.
Construction and tuning
Step 1
Cut two similar conductors.
Step 2
Keep them parallel with insulated spacers.
Step 3
Connect both remote ends.
Step 4
Feed the centre of one conductor.
Step 5
Use a 4:1 transformer or suitable line.
Advantages
- Wider bandwidth than a simple dipole.
- Balanced construction.
- Suitable for 300 Ω line.
- Useful as a Yagi driven element.
Limitations
- Matching required for 50 Ω coax.
- More complex mechanically.
- Regular spacing is required.
- Sensitive to conductor diameter.
History and origin
The folded dipole became common in broadcasting, television and antenna arrays because of its higher impedance and bandwidth.
Safety
Both ends carry high RF voltage and must remain insulated.