📡 Yagi Antenna: The Complete Guide for Radio Amateurs
From theory to practice, everything you need to know about the most popular directional antenna
The Yagi-Uda is the radio amateur's directional antenna par excellence. From HF to UHF, it offers high gain, straightforward construction and remarkable performance. This guide takes you from the fundamental theory to practical recommendations for choosing, building or buying your Yagi.
📚 History and principle of the Yagi antenna
The Yagi-Uda antenna was invented in 1926 by Japanese professor Shintaro Uda of Tohoku Imperial University, then popularised internationally by his colleague Hidetsugu Yagi, who published the work in English. Although the correct name is “Yagi-Uda”, common usage has settled on “Yagi”.
The fundamental principle relies on the electromagnetic interaction between several parallel conducting elements. Only one element is connected to the transmission line (the active or driven element), while the other elements act as parasitic elements: they pick up the radiated energy and re-radiate it with a controlled phase shift, creating constructive interference in a preferred direction.
🔧 Anatomy of a Yagi antenna
A Yagi antenna consists of three types of elements arranged in parallel on a support called the boom:
Driven Element
This is the only element connected to the coaxial cable. It is usually a dipole (about λ/2), which may be straight or folded (folded dipole). It converts the electrical signal into a radio wave (and vice versa on receive).
Reflector
Placed behind the driven element, it is slightly longer (about 5% longer than the driven element). It reflects energy forwards, improving gain and the front-to-back ratio. A Yagi usually has only one reflector.
Directors
Placed in front of the driven element, they are progressively shorter (about 5% shorter). Each additional director increases the gain and narrows the radiation lobe. There can be anything from 1 to more than 20.
Boom (Support)
The horizontal bar that supports all the elements. It can be made of aluminium, fibreglass or even wood. Its cross-section (round or square) and diameter slightly influence the element dimensions.
Figure 1: Diagram of a 3-element Yagi antenna (reflector + driven + director)
📊 Key parameters of a Yagi antenna
To choose or design a Yagi antenna properly, you need to understand its fundamental parameters:
Gain (dBi / dBd)
Gain measures the antenna's ability to concentrate energy in one direction. It is expressed in dBi (relative to an isotropic antenna) or in dBd (relative to a dipole). The relationship is simple:
Gain increases with the number of elements, but logarithmically: the first directors add a lot, the following ones less and less.
| Number of elements | Typical gain (dBd) | Typical gain (dBi) | Boom length |
|---|---|---|---|
| 2 (reflector + driven) | 3-4 dBd | 5.1-6.1 dBi | ≈ 0.15-0.20λ |
| 3 | 5-6 dBd | 7.1-8.1 dBi | ≈ 0.30-0.40λ |
| 5 | 7-9 dBd | 9.1-11.1 dBi | ≈ 0.80-1.2λ |
| 7 | 9-11 dBd | 11.1-13.1 dBi | ≈ 1.5-2.0λ |
| 10+ | 11-14 dBd | 13.1-16.1 dBi | ≈ 2.5-4.0λ |
Front-to-back ratio (F/B)
The front-to-back (F/B) ratio indicates the difference in dB between radiation to the front and to the rear. A good F/B (> 20 dB) lets you reject unwanted signals coming from behind, which is very useful on VHF/UHF to avoid interference.
Impedance and SWR
The feed-point impedance of a Yagi varies with the design. A straight dipole gives about 20-30 Ω, which requires a matching system (balun, gamma match, hairpin match) to reach the standard 50 Ω of coaxial cable. A folded dipole gives a higher impedance (~200-300 Ω), which is brought down to 50 Ω with a 4:1 balun.
Bandwidth
The bandwidth of a Yagi is the range of frequencies over which the SWR remains acceptable. Yagis with few elements generally have a wider bandwidth. Long Yagis (many elements) have higher gain but narrower bandwidth, which is an important consideration on wide HF bands such as 10 metres.
Beamwidth
The opening angle (or beamwidth) at -3 dB defines the width of the main beam. The higher the gain, the narrower the angle. For DX contacts a narrow beam is desirable; for local use a wider angle is preferable.
📐 Sizing formulas
The dimensions of a Yagi antenna are directly related to the wavelength (λ) of the operating frequency. Here are the fundamental formulas:
Reflector ≈ 0.495 × λ Driven element ≈ 0.473 × λ Director 1 ≈ 0.440 × λ Director 2 ≈ 0.435 × λ Director 3 ≈ 0.430 × λ
Reflector-driven spacing ≈ 0.20 × λ Driven-director spacing ≈ 0.15 × λ Spacing between directors ≈ 0.20-0.30 × λ
Examples of calculated dimensions
| Band | Centre frequency | λ | Reflector | Driven | Director 1 |
|---|---|---|---|---|---|
| 10 m | 28.5 MHz | 10.53 m | 5.21 m | 4.98 m | 4.63 m |
| 6 m | 50.15 MHz | 5.98 m | 2.96 m | 2.83 m | 2.63 m |
| 2 m | 145.0 MHz | 2.07 m | 1.02 m | 0.98 m | 0.91 m |
| 70 cm | 435.0 MHz | 0.69 m | 34.1 cm | 32.6 cm | 30.3 cm |
| 23 cm | 1296.0 MHz | 23.1 cm | 11.5 cm | 10.9 cm | 10.2 cm |
📻 Types of Yagi antenna
Monoband Yagi
A monoband Yagi is optimised for a single frequency band. It offers the best performance in terms of gain, F/B ratio and bandwidth. It is the ideal choice if you operate mainly on one specific band.
Multiband Yagi (tribander)
Tribanders typically cover the 20 m, 15 m and 10 m bands (14, 21 and 28 MHz). They use elements fitted with traps (trapped elements) or interlaced elements. The trade-off is slightly lower bandwidth and gain than a monoband antenna, but with the advantage of putting up just one antenna.
Log-periodic Yagi (LPDA)
Although technically different from a pure Yagi, the LPDA (Log-Periodic Dipole Array) is often compared with it. It covers a very wide frequency range with moderate, constant gain. Ideal for operators who want to cover all the HF bands with a single antenna.
Crossed Yagi (X-Yagi)
Used mainly for satellite communications and EME (Earth-Moon-Earth) operation, the crossed Yagi combines two perpendicular Yagis to generate circular polarisation, essential to compensate for the Faraday rotation of signals passing through the ionosphere.
Wideband Yagi (OWA)
OWA (Optimized Wideband Array) designs use specially calculated element spacing and dimensions to provide a direct 50 Ω impedance across the whole band, with no matching system needed. An excellent choice for the VHF/UHF bands.
🔨 Building your own Yagi antenna
Building a Yagi antenna is a rewarding project within reach of any radio amateur. Here are the steps and tips for a successful build.
Materials required
- Elements: 6061-T6 aluminium tube or rod, 6-12 mm diameter (VHF) or 12-25 mm (HF)
- Boom: Square or round aluminium tube, 20-30 mm section (VHF) or 40-50 mm (HF)
- Insulators: Polyethylene, HDPE or Delrin blocks to insulate the driven element from the boom
- Connector: SO-239 or N connector (recommended on UHF) mounted at the feed point
- Hardware: Stainless steel bolts and nuts (A2/A4), mounting clamps, washers
- Coaxial cable: RG-213 (HF) or Aircom/Ecoflex (VHF/UHF) with 50 Ω impedance
- Balun or matching system: Gamma match, hairpin match or balun depending on the design
Construction steps
- Choose a proven design: don't start from scratch! Use a published design (DK7ZB, G0KSC, WA5VJB) or one simulated with NEC software. Note the exact dimensions for your element diameter.
- Cut the elements: cut the aluminium tubes to the exact dimensions. Deburr the ends. Add 1-2 mm of margin that you can trim during tuning.
- Prepare the boom: mark the position of each element precisely on the boom. Drill the mounting holes, checking that the elements will be properly perpendicular.
- Mount the parasitic elements: fit the reflector and the directors. These elements may be in electrical contact with the boom if it is conductive (this is part of the NEC calculation).
- Mount the driven element: install the driven element with its insulator. Fit the coaxial connector and the matching system (gamma match, hairpin, etc.).
- Tune the antenna: with an antenna analyser (NanoVNA, RigExpert), measure the SWR and adjust the length of the driven element and the matching system to obtain minimum SWR on the desired frequency.
- Weatherproof: protect all connections with self-amalgamating tape and/or silicone sealant. Apply contact grease to the aluminium fixings to prevent galvanic corrosion.
Recommended simulation software
| Software | Platform | Price | Description |
|---|---|---|---|
| MMANA-GAL | Windows | Free | Excellent for getting started, intuitive interface, built-in optimiser |
| 4nec2 | Windows | Free | Based on NEC-2, very powerful, 3D pattern visualisation |
| EZNEC | Windows | Paid (~89 USD) | The reference for radio amateurs, accurate, excellent documentation |
| EZNEC Demo | Windows | Free | Limited to 20 segments, sufficient for simple Yagis |
| YagiCAD | Windows | Free | Yagi-specific, fast calculation, design library |
| xnec2c | Linux | Free | NEC-2 port for Linux, GTK interface, real-time visualisation |
⚡ Impedance matching systems
The feed-point impedance of a Yagi antenna is rarely 50 Ω. Here are the main methods for matching it:
Gamma Match
A parallel conductor connected to the boom and to a point on the driven element via a variable capacitor. A robust, adjustable solution, very popular on commercial HF Yagis. It can match impedances of 15-30 Ω to 50 Ω.
Hairpin Match (Beta Match)
A U-shaped short-circuit (hairpin) connected across the terminals of the split dipole. Simple, effective and with no moving parts. Used on many modern commercial Yagis (Cushcraft, M2).
4:1 Balun + Folded Dipole
The folded dipole offers an impedance of about 200-300 Ω, brought down to 50 Ω by a 4:1 balun. Wide bandwidth and excellent balance. Popular on VHF/UHF.
75 Ω quarter-wave (DK7ZB)
A length of coaxial cable λ/4 long acts as an impedance transformer: Z_in = Z_cable² / Z_load. The DK7ZB method designs the Yagi for about 28 Ω and matches it to 50 Ω with a quarter-wave section made of two 75 Ω cables in parallel (37.5 Ω): 37.5² / 28 ≈ 50 Ω. An elegant, lossless solution for VHF Yagis.
🏗️ Installation and setting up
Mounting height
The height of a Yagi antenna above ground directly influences its take-off angle (radiation angle). For DX (long distance), a low angle is what you want:
| Height (in λ) | Main take-off angle | Recommended use |
|---|---|---|
| 0.25λ (quarter-wave) | ~45° | Regional communications / NVIS |
| 0.5λ (half-wave) | ~30° | General use, good compromise |
| 1.0λ (one wavelength) | ~15° | Long-distance DX |
| 1.5λ or more | ~10° or less | Optimum DX, contesting |
The antenna rotator
To make full use of a Yagi's directivity, a rotator is essential. It lets you point the antenna in the desired direction.
| Model | Torque | Use | Guide price |
|---|---|---|---|
| Yaesu G-450C | 450 kg·cm | Light VHF/UHF Yagis, small HF | ~CHF 450 |
| Yaesu G-650C | 650 kg·cm | Medium tribanders | ~CHF 550 |
| Yaesu G-1000DXC | 1000 kg·cm | Tribanders, VHF stacks | ~CHF 750 |
| Yaesu G-2800DXC | 2800 kg·cm | Large HF Yagis, arrays | ~CHF 1,500 |
| Prosistel D | Variable | Made in Italy, very robust | ~CHF 800-2,000 |
Coaxial cabling
The choice of coaxial cable is critical, especially on VHF/UHF where losses are significant:
| Cable | Loss at 145 MHz (/100 m) | Loss at 435 MHz (/100 m) | Use |
|---|---|---|---|
| RG-58 | 15.5 dB | 28.5 dB | Short runs only (<5 m) |
| RG-213 | 7.8 dB | 14.5 dB | HF, VHF short distances |
| Aircell 7 | 5.9 dB | 10.8 dB | VHF/UHF, good compromise |
| Ecoflex 10 | 3.6 dB | 6.5 dB | VHF/UHF, excellent choice |
| Ecoflex 15 | 2.4 dB | 4.3 dB | Long runs, contesting |
| Aircom Plus | 3.2 dB | 5.8 dB | VHF/UHF, very high performance |
🛒 Recommended commercial models
Here is a selection of popular, proven commercial Yagi antennas available in Europe:
HF Yagis (tribanders and monobanders)
| Model | Bands | Elements | Gain | Boom | Guide price |
|---|---|---|---|---|---|
| Mosley TA-33-M | 20/15/10 m | 3 | 8 dBi | 3.7 m | ~CHF 600 |
| Cushcraft A3S | 20/15/10 m | 3 | 8 dBi | 4.3 m | ~CHF 650 |
| Hy-Gain TH-3MK4 | 20/15/10 m | 3 | 8.5 dBi | 4.3 m | ~CHF 800 |
| Optibeam OB9-5 | 20/17/15/12/10 m | 9 (5 bands) | 9-11 dBi | 6.2 m | ~CHF 2,500 |
| SteppIR DB18E | 20-6 m (continuous) | 3 | 7-10 dBi | 5.5 m | ~CHF 3,000 |
VHF Yagis (2 metres: 144 MHz)
| Model | Elements | Gain | Boom | Guide price |
|---|---|---|---|---|
| DK7ZB 5 el. 28Ω | 5 | 9.2 dBd | 2.55 m | DIY (~CHF 50) |
| Tonna 20809 | 9 | 13.0 dBd | 3.10 m | ~CHF 120 |
| Wimo X-Quad 2m | 2×8 | 11.6 dBd | 3.70 m | ~CHF 250 |
| InnovAntennas LFA 8 | 8 | 12.0 dBd | 4.00 m | ~CHF 350 |
| FlexaYagi FA144-10 | 10 | 13.5 dBd | 5.65 m | ~CHF 200 |
UHF Yagis (70 cm: 432 MHz)
| Model | Elements | Gain | Boom | Guide price |
|---|---|---|---|---|
| DK7ZB 9 el. 28Ω | 9 | 12.0 dBd | 1.50 m | DIY (~CHF 30) |
| Tonna 20919 | 19 | 16.0 dBd | 2.80 m | ~CHF 110 |
| Diamond A430S10 | 10 | 13.1 dBd | 1.86 m | ~CHF 100 |
| M2 436CP30 | 30 | 17.5 dBd | 5.50 m | ~CHF 500 |
🎯 Practical applications
DX HF
A tribander on a tower is the classic set-up for DX on 20/15/10 m. With 3 elements at 15 m height, the whole world is within reach.
Contesting
In contests, gain and directivity make the difference. Contest stations often use stacks of Yagis (2 or 4 antennas stacked) to maximise the signal.
Satellite & EME
Crossed VHF/UHF Yagis are ideal for satellite operation (ISS, QO-100) and for Earth-Moon-Earth contacts using long, high-gain Yagis.
VHF/UHF DX
On VHF, a horizontal Yagi lets you take advantage of tropospheric propagation, aircraft and meteor scatter, and sporadic-E openings.
APRS & Packet
A small 3-element Yagi is perfect for a directional APRS gateway station (iGate) on 144.800 MHz, with better range than an omnidirectional antenna.
Portable & SOTA
Light, demountable Yagis (3-5 elements on 2 m) are very popular for SOTA activations. Easy to carry in the mountains, they provide worthwhile gain.
🏔️ Portable Yagi: SOTA and mountain activations
SOTA (Summits On The Air) activations are very popular in Switzerland, with its many listed summits. A light VHF Yagi is an excellent choice for these activities.
Criteria for a portable Yagi
Light weight
Under 1 kg for the complete Yagi. Go for thin aluminium elements (6 mm) or telescopic rods. The boom can be fibreglass or light aluminium tube.
Demountable / Foldable
The antenna must fit in a rucksack. Screw-in or push-fit elements go together in a few minutes. Some models use steel measuring tape (tape measure Yagi).
Robust
In the mountains the wind can be violent. Choose a compact 3-5 element Yagi rather than a long, fragile one. Simplicity is king.
Adequate performance
3 elements = ~5.5 dBd of gain, perfectly adequate from a summit. The altitude more than makes up for the lack of gain compared with a larger Yagi.
🇨🇭 Swiss context: Yagi antennas and regulations
In Switzerland, installing outdoor antennas is subject to several regulations that you should be aware of:
OFCOM regulations
OFCOM (Swiss Federal Office of Communications) issues amateur radio licences (HB9 and HB3). The maximum permitted power is 1000 W PEP for HB9 (CEPT) licences, which is more than enough to make full use of a Yagi. HB3 (novice) licences are limited to 100 W.
Planning permission
Installing a tower and directional antennas generally requires municipal planning permission. The criteria vary from one municipality to another, but the following points are usually examined:
- Mast height: often limited to 6-10 m in residential areas
- Visual integration: municipalities may impose colours or maximum heights
- Heritage protection: additional restrictions in historic or protected areas
- ONIR standards: the Ordinance on Protection against Non-Ionising Radiation (ORNI/ONIR) sets limit values
- Neighbours' rights: neighbours can lodge objections during the public consultation period
SOTA summits in Switzerland
Switzerland is a paradise for SOTA activations, with more than 1,300 listed summits in the HB/HB0 associations. Portable 2 m and 70 cm Yagis are widely used on these activations, allowing contacts across the whole of Switzerland and neighbouring countries from Alpine ridges and peaks.
Local clubs and resources
| Resource | Description | Link |
|---|---|---|
| HB9V | Radio Amateurs of Canton Vaud, activities, mutual help | hb9v.ch |
| USKA | National association, defending members' rights, legal assistance with antennas | uska.ch |
| OFCOM | Federal regulator, licences, exams, regulations | bakom.admin.ch |
| SOTA HB | Directory of Swiss summits for portable activations | sotadata.org.uk |
| Phonicom | Swiss amateur radio shop, antennas, cables, accessories | phonicom.ch |
❓ Frequently asked questions
How many elements for my first Yagi?
To get started, a 3-element Yagi (1 reflector + 1 driven + 1 director) is ideal. It offers around 5-6 dBd of gain, a good F/B ratio and simple construction. That is enough for a clear improvement over an omnidirectional antenna.
Horizontal or vertical Yagi?
On HF, polarisation is generally horizontal. On VHF/UHF, local FM operation uses vertical polarisation, while DX, SSB and satellites use horizontal. Match the polarisation of your Yagi to your main mode of operation.
Does a Yagi need a balun?
A choke balun (1:1) is always recommended at the feed point to prevent common-mode current on the coaxial cable, which would distort the radiation pattern and cause interference in the shack. The impedance matching system (gamma match, hairpin, etc.) is a separate question.
Can I use a Yagi without a rotator?
Yes! On VHF/UHF you can point your Yagi in a fixed direction (for example towards a distant repeater or a geographical area of interest). It still performs far better than an omnidirectional antenna in that direction. On HF, a tilting mast lets you turn it by hand.
What effect does a metal boom have on the elements?
A metal boom running through the elements (centre mounting) electrically shortens the elements by a few millimetres. Simulation software (EZNEC, MMANA) includes this correction. If you mount the elements insulated from the boom, no correction is needed.
📋 Checklist before you start
- Define your goal: HF DX? Local VHF? Satellite? SOTA? The choice of band and number of elements depends directly on it.
- Assess the constraints: available space, permitted height, budget, municipal regulations, landlord's consent (if you rent).
- Choose: build or buy: DIY is very rewarding and economical on VHF/UHF. On HF, commercial antennas offer superior mechanical robustness.
- Size the mast and rotator: calculate the wind load (area × pressure) and choose a rotator suited to the torque required.
- Invest in good coaxial cable: don't skimp on cable, especially on VHF/UHF. Cable losses cancel out the antenna's gain.
- Get an antenna analyser: a NanoVNA (from CHF 30) lets you tune your antenna precisely and diagnose problems.
- Install, measure, adjust: mount the antenna at its final height before the final tuning. The ground and surroundings influence the parameters.
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