Folded Dipole Antenna
A folded dipole takes an ordinary half-wave dipole and adds a second parallel wire connected at both ends, a few inches away from the first, fed at the center of just one side. That second wire turns the antenna into a folded transmission-line structure that raises the feedpoint impedance from a plain dipole's roughly 70 ohms up to around 300 ohms, and noticeably widens the usable SWR bandwidth compared to a single-wire dipole of the same length. It's the same design used for decades as TV/FM receiving antennas and as the driven element inside most Yagi beams, built here as a standalone HF/VHF transmitting antenna.
A shorted transmission-line stub wrapped around a dipole
The second wire, shorted to the first at both ends, behaves like a folded quarter-wave transmission line stub in parallel with the radiating dipole current. That extra current path is what raises the impedance seen at the feedpoint — for two equal-diameter conductors, the commonly cited multiplication factor is about 4x a plain dipole's feedpoint impedance, landing near 300 ohms at resonance.
Folded dipole (equal conductors): ~4x that, ~280-300 ohms at resonance
Why the bandwidth is wider
The folded structure's transmission-line behavior spreads the antenna's reactance swing across frequency more gently than a single wire does, which is why folded dipoles hold a usable SWR across a noticeably wider slice of a band than an equivalent plain-wire dipole — useful if you want to cover an entire phone or CW segment without retuning.
Why Yagi driven elements are almost always folded dipoles
Mutual coupling from nearby parasitic elements in a Yagi typically drags a plain dipole's driven-element impedance down well below 50 ohms, sometimes below 20 ohms. Using a folded dipole as the driven element pushes that already-low impedance back up into a more practical range for matching — which is exactly why designs like the Quagi and most home-built Yagis on this site use a folded driven element rather than a plain one.
- Standalone folded dipole (this guide): ~300 ohms at the feedpoint, matched down with a 4:1 balun.
- Folded dipole inside a Yagi/Quagi: mutual coupling from parasitic elements pulls that impedance down closer to 50-200 ohms depending on spacing.
Matching 300 ohms down to 50-ohm coax
A 4:1 balun brings the nominal 300-ohm feedpoint down to roughly 75 ohms — a reasonable, though not perfect, match into standard 50-ohm coax, typically giving an SWR in the 1.3-1.5:1 range at resonance. Builders who want a cleaner match, or who are feeding the antenna with 300-ohm twin-lead directly, can skip the balun and run straight into a tuner instead.
Installation options
- Flat-top between two supports: the standard install, identical in footprint to a plain dipole of the same band.
- Inverted-V from a single mast: works the same as with a plain dipole, with the usual modest gain and impedance shift that any inverted-V configuration brings.
- Twin-lead direct to a tuner: skips the balun entirely by feeding the ~300-ohm point with matching twin-lead into a balanced or tuner-matched input, at the cost of needing balanced-line-compatible station equipment.
| Band | Design freq (MHz) | Overall length | Conductor spacing |
|---|---|---|---|
| 40m | 7.15 | ~65.5 ft (20.0 m) | 4-8 in (10-20 cm) |
| 20m | 14.15 | ~33.1 ft (10.1 m) | 2-4 in (5-10 cm) |
| 10m | 28.50 | ~16.4 ft (5.0 m) | 1-2 in (2.5-5 cm) |
| 2m | 146.0 | ~3.2 ft (0.98 m) | 1-2 in (2.5-5 cm) |
Folded Dipole Dimension Calculator
Materials for Folded Dipole
Building the Folded Dipole
This build is a standard dipole with a second parallel wire added — keep the spacing between the two wires consistent along the entire run.
Cut both conductors to length
Use the calculator above to get the overall length, and cut two equal lengths of wire.
Install spacer insulators along the run
Space several insulators evenly along the antenna's length to hold the two wires parallel at your chosen spacing.
Short both wires together at each end
At each end insulator, connect both conductors together with a short jumper — this closes the folded loop at both tips.
Install the center feedpoint on one conductor only
At the center, break only one of the two wires and connect the feedpoint bracket there — the second wire continues through uninterrupted at the center.
Install the 4:1 balun
Connect a 4:1 balun at the feedpoint bracket if you're feeding with 50 or 75-ohm coax.
Raise the antenna
Hoist the antenna flat-top or as an inverted-V between supports, same as any ordinary dipole install.
Connect coax and sweep SWR
Connect your feedline and sweep across the band — expect a noticeably wider low-SWR window than a plain single-wire dipole of the same length.
Trim if needed
If the resonant dip is off target, trim both conductors evenly at each end by the same small amount and re-sweep.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| SWR is higher than expected even at resonance | Feedpoint accidentally breaks both conductors instead of just one | Check that only one wire is broken at the center feedpoint | Re-terminate so only one conductor breaks at center; the second must run through uninterrupted |
| Resonance seems shifted from the calculated frequency | Wire spacing isn't consistent or doesn't match the build target | Check spacing along the entire run against your intended value | Correct the spacing to be consistent end to end and re-sweep |
| End shorting jumpers heating up or failing | Poor, high-resistance connection at the end jumpers | Inspect the end jumper joints connecting both conductors | Re-solder for a solid, low-resistance connection — these carry real current in the folded structure |
Is a folded dipole better than a plain dipole?
Not in gain — they perform about the same. The folded dipole's advantages are wider usable bandwidth and a higher feedpoint impedance, which is useful for certain feed methods and as a Yagi driven element.
Do I need the 4:1 balun?
If you're feeding with 50 or 75-ohm coax, yes — without it you'll see a substantial mismatch. If you're feeding with 300-ohm twin-lead into a tuner, you can skip it.
Why is the driven element on a Yagi almost always folded?
Because nearby parasitic elements pull a plain driven element's impedance down quite low, and the folded structure's inherent impedance boost helps bring it back into a practical matching range.
Does the wire spacing matter a lot?
It affects the exact impedance transformation and bandwidth somewhat, but the design is fairly tolerant — a few inches of spacing at HF, kept reasonably consistent along the run, works well in practice.
Can I build this for VHF/2m as well as HF?
Yes — the same folded structure scales down cleanly to VHF lengths, and it's a common choice there too, including as the driven element in VHF Yagi designs.
What happens if I accidentally break both wires at the feedpoint?
You end up with two parallel plain dipoles instead of a folded dipole, which behaves quite differently and loses the impedance-transformation benefit this design is built around.