What is a folded dipole?
A folded dipole is a half-wave dipole with a second, parallel conductor connected at both ends, fed at the center of one conductor. With equal-diameter conductors the current divides equally and the input impedance is stepped up by four, about 4 × 73 ≈ 292 Ω, so it matches 300 Ω twin-lead.[1][2]
Why is the impedance four times higher?
The folded dipole can be analyzed as the superposition of a transmission-line mode (two shorted λ/4 stubs, very high impedance at resonance) and an antenna mode in which both conductors carry the same current. For the same radiated power, the feed current is half that of a simple dipole, so the resistance is (1+a)² times larger, where a is the current ratio set by conductor diameters; a = 1 gives 4.[1]
What are its advantages?
- Higher impedance suits 300 Ω line and Yagi driven elements, where parasitic elements lower the impedance.
- Somewhat broader bandwidth than a thin dipole.
- The center of the unfed conductor is at zero RF voltage, so it can be grounded to the mast for lightning protection.[2]
Where are folded dipoles used?
FM broadcast receiving antennas, driven elements of TV and VHF Yagis, and some base-station arrays. A 4:1 balun converts the ~300 Ω balanced feed to 75 Ω coax.[3]
Frequently asked questions
Does a folded dipole have more gain?
No; its pattern and directivity equal those of a half-wave dipole.
Can the step-up ratio be changed?
Yes, by using conductors of different diameters or spacing.
Is a folded dipole balanced?
Yes; it needs a balun for coax.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.
- “Antennas for All Applications, 3rd ed.”. J. D. Kraus and R. J. Marhefka, McGraw-Hill. 2002.
- “The ARRL Antenna Book for Radio Communications”. ARRL. multiple editions.