Vertical Antennas
The vertical antenna is the workhorse of mobile and portable ham radio, and a favorite of HF operators who want an omnidirectional, low-angle radiation pattern for DX work. Unlike the dipole which needs to be strung horizontally between two supports, a vertical stands straight up from the ground — simpler to install, needing only one support, and omnidirectional in the horizontal plane. Understanding how verticals work, what the ground system does, and when to choose a vertical over a dipole are key skills for any ham operator.
The quarter-wave vertical uses the ground (or a radial system) as an electrical mirror. The reflected image of the vertical element below ground creates the lower half of an effective half-wave dipole.
View LargerThe Monopole and the Image Principle
A vertical antenna above a flat conducting ground plane is technically called a monopole — it has only one pole (the vertical element), unlike the two-pole structure of a dipole. However, the conductive ground plane serves as an electrical mirror, creating a virtual image of the antenna below the ground surface.
Think of looking at a vertical stick standing on a mirror. You see the real stick above the mirror and a perfect reflection below it. Together, the real stick and its mirror image look like a full-length vertical stick passing through the mirror surface. Electrically, the quarter-wave monopole above a perfect ground plane behaves identically to a half-wave dipole in free space — except that all of the radiation occurs above the ground plane (not below it, since the ground blocks that direction). This means the quarter-wave vertical radiates all of the same power that a half-wave dipole would radiate, but into only the upper half-space. The result is a theoretically perfect omnidirectional pattern in the horizontal plane with no radiation downward into the ground.
This image principle is not just a mathematical trick — it is a physical reality. Return currents from the antenna really do flow through the ground (or radial system) back to the transmitter. The ground is literally the other half of the antenna circuit. If the ground is lossy, those return currents encounter resistance and some of the power is converted to heat rather than radiated. This is why the ground system is so critically important for vertical antennas — it completes the antenna circuit and its quality directly determines efficiency.
Quarter-Wave Vertical Length Formula
The same end-effect and velocity-factor corrections that shorten the half-wave dipole also apply to the quarter-wave vertical. The free-space quarter-wavelength would be λ/4 = 246/fMHz feet or 75/fMHz meters. After the ~5% correction for end effects:
Length (feet) = 234 / fMHz
Length (meters) = 71.3 / fMHz
The constant 234 (feet) or 71.3 (meters) is exactly half the dipole constant (468/2 = 234; 143/2 = 71.5), as expected — the vertical is a quarter-wave element, which is half of the half-wave dipole. Cut the vertical slightly longer than the formula suggests and trim to resonance, just as with the dipole.
Length = 234 / 7.150 = 32.7 feet = 9.97 meters
The 40-meter vertical is about 33 feet tall. This is a practical length for a mast or telescoping fiberglass pole. Each radial should also be a quarter wavelength — 32.7 feet. Use 4–8 radials as a minimum; 16 or more for good performance. More details on radial length and number in the Ground System section.
Quarter-Wave Vertical Calculator
Quarter-Wave Vertical Length Calculator
Calculate the vertical element length and suggested radial length. Formula: 234/f(MHz) in feet, 71.3/f(MHz) in meters.
| Band | Frequency (MHz) | Element length (feet) | Element length (meters) |
|---|---|---|---|
| 160 m | 1.900 | 123.2 | 37.5 |
| 80 m | 3.700 | 63.2 | 19.3 |
| 40 m | 7.150 | 32.7 | 9.97 |
| 20 m | 14.150 | 16.5 | 5.04 |
| 15 m | 21.150 | 11.1 | 3.37 |
| 10 m | 28.500 | 8.21 | 2.50 |
| 6 m | 51.000 | 4.59 | 1.40 |
| 2 m | 146.000 | 1.60 | 0.488 |
Feedpoint Impedance: Why ~36 Ohms?
The feedpoint impedance of a quarter-wave vertical over a perfect ground plane is approximately 36.5 ohms, resistive at resonance. This is exactly half the impedance of a half-wave dipole (73/2 = 36.5 ohms). The factor of two comes directly from the image principle: the monopole has exactly half the total resistance (both radiation and loss) of the equivalent half-wave dipole, because the ground plane provides the return path at zero resistance in the ideal case.
In reality, the ground plane is never perfect — it has finite resistance, creating losses that add to the feedpoint resistance. A vertical over a poor ground (few radials, high-resistance soil) might show a feedpoint resistance of 50–80 ohms or more, with the extra resistance being loss resistance. Increasing the radial count reduces this loss resistance and brings the feedpoint resistance back toward the theoretical 36.5 ohms. This is a useful diagnostic: a quarter-wave vertical that measures 50 ohms at resonance probably has significant ground loss; one that measures 37–40 ohms has a much better ground system.
The 36.5-ohm impedance of a vertical over a perfect ground plane is actually quite close to 50 ohms — the SWR into 50-ohm coax is 50/36.5 = 1.37:1. This is even better than the 1.46:1 SWR of a dipole. In practice, with real ground systems that add some loss resistance, the feedpoint resistance often rises to 40–50 ohms, making a direct 50-ohm coaxial connection a very reasonable match — no additional transformer is needed in many installations. This is another practical advantage of the vertical over the dipole for direct coax feed.
Radiation Pattern: The DX Advantage
The radiation pattern of the quarter-wave vertical over a good ground plane has two distinctive features that make it valuable for specific applications:
Omnidirectional in azimuth: The vertical radiates equally in all compass directions. This is ideal for mobile operation (you don't know which direction you'll be pointing), for repeaters (which need to serve in all directions), and for any situation where you cannot or don't want to point an antenna in a specific direction.
Low-angle elevation pattern: The elevation pattern of a vertical over a good ground plane has its maximum radiation at or near the horizon (0–5 degrees elevation angle), rather than at higher angles. This is ideal for long-distance (DX) contacts, because DX signals arrive and depart at very low angles. A horizontal dipole at low height (under one half-wavelength) has most of its radiation going straight up — poor for DX. A vertical can outperform a low horizontal dipole for DX, even though the vertical has no more gain.
This low-angle advantage makes verticals particularly popular for HF DX operation and for contesting. Many competitive DX stations use verticals or vertical arrays for 160 and 80 meters, where the impractical height needed for a horizontal dipole to produce low-angle radiation makes the vertical the only practical choice for low-angle performance.
Elevation pattern comparison: the quarter-wave vertical radiates at lower angles than a horizontal dipole at low heights, making it better for DX contacts. At great heights, the horizontal dipole regains the advantage.
View LargerThe Ground System: Radials Are Everything
No part of a vertical antenna system is more important, or more often neglected, than the ground system. The ground system provides the return path for RF current from the antenna. Without a good ground system, those return currents flow through lossy soil, heating it rather than producing radiation. The result is a dramatic reduction in antenna efficiency.
A ground rod by itself is almost useless as an RF ground for a vertical antenna. A single 8-foot ground rod provides excellent protection against lightning and presents a safe earth ground for AC power safety purposes, but its RF resistance is typically hundreds of ohms — far too high to serve as the return path for antenna current. The metal object is simply too small at radio frequencies to collect return current from a wide enough area of soil.
Radials are the solution. Radials are wires laid on or buried just below the surface of the soil, extending outward from the base of the vertical element in all directions. Each radial serves as a low-resistance conductor for the RF return current from the antenna, collecting that current from the soil below the antenna and returning it efficiently to the feedpoint. The more radials you have, and the longer they are, the lower the total ground resistance and the higher the antenna efficiency.
Radials can be buried or laid on the surface. Buried radials are protected from lawn mowers and foot traffic and look clean. Surface radials are easier to install and work equally well electrically — the RF return current flows in the first few inches of soil, so buried or surface radials in direct contact with the soil are both effective. Burying radials 2–4 inches deep is the most common approach.
Radial length matters, but not as much as you might think. A radial that is a quarter-wave long is the traditional recommendation, but even radials of 0.1 wavelength (40% of the quarter-wave length) provide significant benefit. The diminishing returns on length mean that using more shorter radials is often more practical than fewer long ones. Some studies suggest that 16 radials of any length greater than 0.1 wavelength approach the performance of 120 quarter-wave radials remarkably well.
How Many Radials?
The relationship between radial count and antenna efficiency has been studied extensively. The following table summarizes approximate results for a quarter-wave vertical on a typical medium-conductivity soil:
| Radial count (quarter-wave radials) | Approx. ground loss resistance (Ω) | Approx. antenna efficiency | Notes |
|---|---|---|---|
| 0 (ground rod only) | 200–500+ | 5–15% | Very poor; most power lost in ground |
| 4 | 40–60 | 38–48% | Significant improvement; still major loss |
| 8 | 20–30 | 55–65% | Usable; noticeable improvement over 4 |
| 16 | 10–15 | 71–78% | Good performance; major gains diminishing |
| 32 | 5–8 | 82–88% | Excellent; suitable for serious DX work |
| 64 | 2–4 | 90–94% | Near-professional; high cost/effort |
| 120 (broadcast standard) | 1–2 | 95–98% | Broadcast tower standard; rarely done by amateurs |
The improvement from 0 to 4 radials is enormous — potentially 5–10 dB. The improvement from 4 to 16 radials is still significant — 2–4 dB. The improvement from 16 to 32 is 1–2 dB. Beyond 32 radials, returns diminish but further improvement is still measurable. The practical recommendation for serious HF vertical operation is at least 16 radials, with 32 or more if you are willing to put in the work. Even 4 radials beat a ground rod dramatically.
Elevated Radials
Instead of buried radials, you can use elevated radials — horizontal wires attached to the base of the antenna at some height above ground. Elevated radials completely avoid contact with the soil, so they avoid soil resistance entirely. In theory, even 2–4 elevated quarter-wave radials can achieve very low ground resistance, approaching the performance of an extensive buried radial system.
Elevated radials do change the feedpoint impedance. When radials are drooped at an angle below horizontal, the feedpoint impedance increases toward 50 ohms — a better match to coaxial cable. The optimal droop angle (typically 30–45 degrees below horizontal) can give an impedance very close to 50 ohms, eliminating the need for a matching network. The AH-4 (Icom auto-tuner style) antennas and many commercial VHF/UHF ground plane antennas use this technique.
Elevated radials are particularly practical for VHF and UHF vertical antennas, where the required length is small and the antenna can be mounted on a mast with short radials extending from the mast at a convenient height. Many commercial 2-meter ground plane antennas use 4 quarter-wave elevated radials at 45 degrees below horizontal, achieving close to 50-ohm match and excellent efficiency.
Common Vertical Antenna Types
| Type | Description | Feedpoint Z | Best use |
|---|---|---|---|
| Quarter-wave vertical | Single element, quarter wavelength, fed at base | ~36 Ω (perfect ground); 40–50 Ω (real ground) | Single-band HF; mobile; VHF/UHF |
| 5/8-wave vertical | Longer element (5/8λ) with base loading or direct feed | ~50 Ω with matching network | Mobile VHF/UHF; slightly lower radiation angle than quarter-wave |
| Half-wave vertical | Full half-wave element fed at base (voltage feed) or center | Very high at base (voltage max); 73 Ω at center | Requires matching transformer at base; no ground plane needed |
| Trap vertical | Single element with LC traps for multi-band operation | Variable per band; 50 Ω with design | Multi-band HF; compact; some efficiency loss at traps |
| Shunt-fed tower | Tower fed by a shunt wire connected partway up | 50 Ω with correct shunt placement | Using existing tower as antenna element on LF/HF |
- A quarter-wave vertical uses the ground as an electrical mirror. The image below ground completes the antenna to an effective half-wave dipole.
- Length (feet) = 234/f(MHz); length (meters) = 71.3/f(MHz). Half the dipole formula.
- Feedpoint impedance ≈ 36 ohms over a perfect ground; rises with ground loss. SWR into 50-ohm coax is 1.37:1 with good ground system.
- The vertical pattern is omnidirectional in azimuth and radiates at low elevation angles — ideal for DX and mobile operation.
- The ground system (radials) is critical — going from a ground rod to 16+ radials can add 5–10 dB of effective radiated power.
- Elevated radials avoid soil entirely and can match the performance of many buried radials with just 2–4 wires.
Frequently Asked Questions
Is a vertical antenna better than a dipole for HF?
It depends on the situation. For DX work, a vertical with a good ground system often outperforms a dipole at low height because the vertical has a lower-angle radiation pattern. For distances where high-angle radiation is needed (NVIS contacts within 300 miles), a horizontal dipole often wins. For contest operating where you want to work in all directions without rotating an antenna, the vertical's omnidirectional pattern is an advantage. For locations where you cannot put up a horizontal antenna, the vertical is the only practical choice. Neither is universally "better" — they suit different situations.
Can I use a single copper ground rod instead of radials?
For lightning protection and safety grounding, yes — a ground rod is essential. But for RF performance, a ground rod provides almost no benefit. Its RF impedance is typically hundreds of ohms because the rod's surface area is far too small to collect return current from a significant area of soil. Always add radials for any vertical antenna installation. Even 2–4 radials radically outperform a ground rod. The RF ground and the safety ground are separate concerns, and a ground rod satisfies the safety concern but not the RF performance concern.
My 40-meter vertical shows 70 ohms feedpoint resistance at resonance. Is it broken?
Not broken, but it has significant ground losses. A well-designed quarter-wave vertical over a good ground system shows 37–45 ohms at resonance. 70 ohms means roughly 30–35 ohms of loss resistance is present — that is the resistance of lossy return paths through the soil. The immediate fix is to add more radials, or to switch to elevated radials. Adding 8 more buried radials will likely drop the resistance by 20–30 ohms and dramatically improve both efficiency and SWR. A feedpoint resistance of 70 ohms means roughly half your transmitter power is being dissipated as heat in the ground.
Test Your Knowledge
Answer the questions below to check your understanding. Every answer can be found in the lesson above.