Dipole vs Yagi - Can these two antennas compete?

VIDEO:

I'm Peter G3OJV from Waters & Stanton. Over the years I've had plenty of conversations with hams wondering whether it's worth upgrading a simple dipole to a Yagi. In this article I'll explain the real differences — impedance, gain, directivity, noise behaviour, radiation angle — and the practical costs and compromises you should expect. My aim is to help you decide whether to keep that low-cost dipole or invest in a beam.

Why the dipole is still so popular

The half-wave dipole is the foundation of many antennas. It's simple, cheap (especially in wire form), effective and easy to erect between two trees or on simple supports.

1. Impedance and matching:

A centre-fed half-wave dipole has a feedpoint impedance around 70 ohms in free space, but that value changes with height above ground and can drop to roughly 55–60 ohms. That makes it a reasonable match to 50 ohm coax — typical VSWR figures are around 1.2:1, a small and manageable mismatch.

2. Radiation pattern:

The dipole radiates broadside to the wire in both directions. If your dipole runs north–south, you get good radiation east–west — often a useful pattern for European stations.

3. Angle of radiation:

A dipole mounted at typical heights has a useful takeoff/receive angle for long-distance (DX) work. For example on 20 m a half-wave above ground (≈10 m / 33 ft) the peak takeoff angle is around 32°; as you raise the antenna the peak angle falls (see the dedicated section on angles below).

4. Practical install:

Very little hardware required: a length of wire, feedline and a simple common-mode choke (10–12 turns of coax on a ferrite core) can tame feedline currents and give you a functioning, low-cost HF antenna.

What a Yagi (beam) gives you

A Yagi is fundamentally a dipole with parasitic elements added. The big differences are directionality, forward gain and improved front-to-back rejection.

• Directionality:

A Yagi radiates predominantly in one direction. You lose the bidirectional broadside coverage of a dipole but gain the ability to focus energy (and reception) where you need it.

• Gain and front-to-back:

Add one parasitic element (typically a director) and you can see as much as ~5 dB of forward gain and up to ~15 dB front-to-back when properly spaced and tuned. A practical, home-built two-element Yagi typically yields about 4 dB across the band as a rule of thumb.

• Three-element Yagi:

Add both a director and a reflector and a correctly constructed three-element beam can give around 8 dB forward gain and front-to-back ratios in excess of 20 dB — roughly 1.5 S-points improvement over a dipole when transmitting and receiving.

• Impedance and matching:

Parasitic elements change the feedpoint impedance significantly. A two-element arrangement can drop the feed impedance to roughly 20 ohms, so a matching system is required. Gamma matches, delta matches or other matching networks are commonly used — get the matching wrong and you’ll lose some of the expected gain.

• Low-noise claims:

You may see Yagis marketed as “low-noise” antennas. That simply refers to directionality: they suppress signals (and noise) from the rear and sides. They won't magically remove local noise sources in all directions; they help where the noise comes from directions other than the beam heading.

Angle of radiation — dipole vs Yagi

One common myth is that a Yagi gives a lower takeoff angle than a dipole. In reality the peak radiation angle (takeoff/receive angle) of a horizontal antenna depends primarily on its height above ground, not on whether it’s a dipole or a Yagi. At the same height the dipole and the Yagi have essentially the same takeoff angles; what changes is the amplitude (gain) in that direction.

Based on classic field tests (not just modelling), representative peak takeoff angles for horizontal antennas on 20 m are:

1. Half-wave above ground (~10 m / 33 ft): peak ≈ 32°
2. 3/4 wavelength above ground: peak ≈ 20°
3. 1 wavelength above ground (~20 m / 65 ft): peak ≈ 15°
4. 2 wavelengths above ground (~40 m / 120–130 ft): peak ≈ 10°

So, putting a Yagi at the same height as a dipole doesn’t give you a lower angle — it only concentrates more energy at that existing angle. For many DX paths you don’t need ultra-low angles anyway; mid-range takeoff angles often work just fine thanks to how signals interact with the ionosphere.

Practical considerations and costs

1. Installation:

A dipole is easy — string it between two supports. A Yagi usually needs a rotator and a mast or tower to get it up and keep it stable. If you erect a beam on a flimsy mast you’ll have reliability problems in wind.

2. Tower and rotator:

Expect to spend on a decent rotator to avoid stripped gears and failures. A reasonably robust rotator can be a few hundred pounds/dollars — this is not the place to cut corners.

3. Wind loading:

Beams catch the wind more than a simple wire dipole. Guys, stronger supports or a proper tower are typically required.

4. Running more power instead:

If you weigh the cost of a tower and Yagi against running more power on a dipole, remember that the effective radiated power of an 8 dB gain beam (three-element) with 100 W is roughly equivalent to about 400–500 W into a dipole. Increasing transmit power can partially compensate for lack of antenna gain, but you’ll miss front-to-back improvement and receive gain benefits.

Practical tips

Summary

To sum up the comparison:

1. A dipole is cheap, simple, a decent match to 50Ω coax and radiates equally in two directions. It’s only modestly behind a Yagi in many practical circumstances.
2. A Yagi gives directionality, forward gain (typically 4–8 dB for 2– and 3-element designs) and much better front-to-back rejection, but requires matching, a strong support structure and a rotator.
3. Angles of radiation are determined by height above ground — a Yagi does not inherently give a lower takeoff angle than a dipole at the same height.

If you can afford the hardware and have the space and permissions, a Yagi is a joyful upgrade — turning the beam and hearing stations lift is great fun. If not, a properly installed dipole with a good feed choke will still get you many DX contacts and is a perfectly respectable HF antenna. Either way, enjoy your ham radio and make the most of what you can practically put up.

73, Peter G3OJV

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