Vertical Antenna Radials: Why the Ground System Decodes Success or Failure
A vertical is only half an antenna
A quarter-wave vertical is a monopole. The upright rod does the radiating, but the return current has to come back through the ground.
In theory, a perfectly conducting earth acts as a mirror: it supplies the image current, completes the monopole into a full dipole, and gives a feedpoint impedance around 36 ohms with efficiency near 100 percent.
Real soil is a lossy dielectric. The return current pushes through dirt with resistance — ground loss resistance, Rg — and that resistance turns your RF into heat. This is why people spend serious money on a vertical and then drive a single ground rod beneath it: they are incinerating most of their output.
The entire purpose of radials is to give that return current a copper path instead of a mud path.
How much difference radials make
For a quarter-wave vertical, the classic comparison runs roughly like this:
- Ground rod only, no radials: Rg about 20 to 40 ohms — the baseline, and a poor one
- 4 buried quarter-wave radials: Rg about 8 to 12 ohms — 3 to 5 dB better than nothing
- 16 buried: Rg about 2 to 4 ohms — 6 to 8 dB better
- 32 buried: Rg about 1 to 2 ohms — 7 to 9 dB better
- 120 buried: Rg about 0.3 to 0.5 ohms — about 10 dB better; the broadcast standard
Now the elevated case:
- 2 resonant elevated radials: Rg about 1 to 3 ohms — 8 to 10 dB better
- 4 elevated: Rg about 0.5 to 1.5 ohms — 9 to 11 dB better
Look hard at that last pair. Four elevated resonant radials deliver performance comparable to well over a hundred buried ones. Modeling by Al Christman, KB8I, showed that 4 to 8 elevated radials perform on par with 120 buried quarter-waves — a result that reshaped portable practice, because a handful of wires in the air buys you the best ground system in the business.
Buried versus elevated radials
These are two different animals with two different rulebooks.
Buried (or on-the-ground) radials lie on the surface or just under it. They work by coupling to the soil, not by resonating. So:
- Count beats length: many short radials outperform a few long ones. For a fixed weight of copper, more wires is the better buy.
- Length is flexible: a quarter wave is the usual target, but precision does not matter.
- More is always better; 30 to 60 or more approaches ideal, and even a dozen makes a visible improvement.
- Multiband-friendly by nature, since nothing depends on resonance.
Elevated radials are held above ground and are themselves resonant elements — current flows in the wire, not the soil. So:
- Few wires: 2 works (with a skewed pattern), 3 is fine, 4 is the practical standard, and beyond that returns diminish.
- Length must be right: every radial is a quarter wave, and each one gets trimmed to resonance after installation.
- Height has a floor: about 0.04 wavelength as a minimum, with modeling suggesting roughly 0.1 wavelength as the sweet spot for a four-radial system. Below the floor, soil loss takes over again.
- Impedance: horizontal elevated radials present roughly 30 to 36 ohms; droop them about 45 degrees and the impedance rises toward 50 ohms — a direct coax match with no transformer.
Elevated systems suit portables, rocky or sandy ground, roofs, and balconies — no digging, no destroyed lawn. Buried systems suit permanent backyard sites with grass to spare, and multiband verticals specifically, because buried radials are non-resonant and inherently broadband.
Three common mistakes
Mistake 1: one ground rod used as a radial. A ground rod serves electrical safety and DC bonding. As an RF ground for a vertical it is nearly useless — high impedance, no low-resistance return path. The ARRL Antenna Book puts it bluntly: driven ground rods are satisfactory for safety and lightning protection but of little value as an RF ground. If your vertical’s SWR will not come down and its impedance reads high and erratic, count your radials before you blame the antenna.
Mistake 2: short radials padded out with more of them. Buried radials should not go below about one eighth of a wavelength. The classic data point: a quarter-wave vertical with 16 radials of one eighth wavelength runs near 50 percent efficiency. Short radials can be compensated for with quantity, but only with a lot of it.
Mistake 3: no common-mode choke at the feedpoint. Even with a perfect radial field, common-mode current finds the second path — the outside of your coax. The feedline becomes an unplanned radial, carrying return current and importing household noise into the receiver. A 1:1 current balun or choke at the feedpoint is standard practice on every vertical installation, elevated systems especially.
Feedpoint impedance and matching
With a competent ground system, a quarter-wave vertical returns to its theoretical 36 ohms or so. The gap to 50 ohms is small and can be closed three ways:
- Slope the elevated radials down about 45 degrees, and the impedance climbs toward 50 ohms naturally
- Add a simple L-network at the feedpoint
- Use a quarter-wave impedance transformer
Note the diagnostic value: a vertical measuring 37 to 40 ohms at resonance has a healthy ground system, while one reading 50 to 80 ohms is telling you, in plain numbers, that ground loss is significant.
Practical summary
- Elevated where possible: 4 quarter-wave radials, lightly trimmed, drooped 45 degrees, plus a choke — the best return on copper in the hobby
- Buried where necessary: start at 16 radials, aim for 32, never shorter than one eighth wavelength
- Multiband verticals: buried radials, because they are broadband and need no tuning
- Every installation: a common-mode choke at the feedpoint
- Never rely on a ground rod: it protects the shack, not your signal
One more point in the vertical’s favor. On 80 and 160 meters, getting a horizontal dipole to half a wavelength means 40 m of altitude — beyond almost everyone. Low-angle radiation, meanwhile, is precisely what long-distance contacts demand. That is why, on the low bands, a vertical with a serious ground system regularly outperforms a dipole that never got high enough to matter.
References
- Al Christman, KB8I, “Elevated Vertical Antenna Systems,” QST, August 1988, pp. 35-42
- G. H. Brown, “Ground Systems as a Factor in Antenna Efficiency,” Proceedings of the IRE, June 1937
- The ARRL Antenna Book (ARRL), Chapter 6: “Low-Frequency Antennas” (current edition)
- Terry Graves, K7FE, “Antennas and Antenna Myths,” ARRL presentation (2009)
- Ham Radio Base, “Build a 40 Meter Vertical Antenna” (accessed 2026)
- 73QRZ, “Antenna Calculator” (accessed 2026)