Yagi Antennas Explained: How They Work, How Many Elements You Need and How to Size One

The Yagi antenna is one of the most recognisable shapes in radio: a single boom with a row of metal elements running across it. It has been around since the 1920s, and it is still the first choice whenever a link needs to reach further in one direction without adding transmitter power. This guide explains how a Yagi works, what changes as you add elements, how to work out approximate element lengths, and how to pick the right model from the Renair Yagi range.

What Is a Yagi Antenna?

A Yagi antenna, properly called a Yagi-Uda antenna after its Japanese inventors Hidetsugu Yagi and Shintaro Uda, is a directional antenna built from a row of parallel elements on a common boom. Only one of those elements is connected to the feeder cable. The rest are parasitic: they are not driven directly, but they pick up and re-radiate energy in a way that pushes the signal forwards.

The result is an antenna that concentrates energy into a beam. Instead of spreading the signal evenly in every direction, as an omnidirectional antenna does, a Yagi focuses it towards the station you want to reach and listens more carefully in that same direction.

The Three Types of Element

• Reflector. The longest element, sitting behind the driven element. It reflects energy forwards and reduces signal off the back of the antenna.
• Driven element. The only element connected to the feeder. It is usually a dipole or folded dipole cut to roughly half a wavelength.
• Directors. Slightly shorter elements in front of the driven element. Each one adds a little more gain and narrows the beam.

A 2-element Yagi has a reflector and a driven element. Everything from 3 elements upwards adds directors. Element count is simply the total of all three types.

How Element Count Changes Gain and Beamwidth

Adding directors increases forward gain, but each extra element adds less than the one before. It also narrows the beam, which is the trade-off that matters most when choosing a model. Typical figures for VHF Yagis are:

• 2 elements: around 5 to 6 dBd, with a broad beam of roughly 70 degrees horizontally
• 3 to 4 elements: around 7 to 8 dBd
• 6 elements: around 9 to 10 dBd
• 8 elements: around 10 to 11 dBd, with a beam narrowing to 35 to 40 degrees
• 12 elements (UHF): higher again, with a tight beam suited to long fixed links

Every 3 dB of gain doubles the effective radiated power in the direction the antenna is pointing. That is why a modest upgrade from a 3-element to a 6-element Yagi can make a marginal path workable. The narrower beam is an advantage for point-to-point links and repeater receive antennas, where the far end does not move. It becomes a disadvantage if you need to cover a wide arc from one site.

A Simple Yagi Sizing Guide

Element lengths are set by wavelength. To find the wavelength in metres, divide 300 by the frequency in MHz. As a rule of thumb, the reflector is about half a wavelength long, the driven element about 0.475 wavelengths and the first director about 0.44 wavelengths. Reflector to driven element spacing is typically around 0.2 wavelengths.

Approximate element lengths at common UK frequencies:

• 150 MHz (wavelength 2.00 m): reflector 1.00 m, driven element 0.95 m, first director 0.88 m
• 160 MHz (wavelength 1.88 m): reflector 0.94 m, driven element 0.89 m, first director 0.83 m
• 170 MHz (wavelength 1.76 m): reflector 0.88 m, driven element 0.84 m, first director 0.78 m
• 410 MHz (wavelength 0.73 m): reflector 0.37 m, driven element 0.35 m, first director 0.32 m
• 450 MHz (wavelength 0.67 m): reflector 0.33 m, driven element 0.32 m, first director 0.29 m
• 470 MHz (wavelength 0.64 m): reflector 0.32 m, driven element 0.30 m, first director 0.28 m

These figures are a starting point for understanding why VHF Yagis are so much larger than UHF ones, not a build specification. Real designs are optimised for element diameter, boom material, spacing and the match to 50 ohm feeder. A commercially tuned Yagi will outperform a home-built one cut from a calculator, and it comes with a known VSWR and gain figure you can design a link budget around.

Matching the Yagi to Your Frequency

A Yagi is tuned to a band, and it falls off quickly outside it. A model optimised for 160 MHz will not perform well at 130 MHz. Before ordering, confirm your transmit and receive frequencies and check them against the antenna's stated range. Broadband designs that cover a whole sub-band, such as 146 to 174 MHz, are the practical choice for general PMR and marine work. Narrowband designs give slightly better performance within a tighter window and suit dedicated repeater sites.

Polarisation, Mounting and Wind Load

Most UK land mobile, PMR and marine systems use vertical polarisation, so a Yagi serving those networks should be mounted with its elements vertical. Mixing polarisation between the two ends of a link can cost 20 dB or more, which wipes out the gain you paid for.

Yagis present a meaningful wind load, especially long-boom VHF models. Use stainless steel clamps rated for your mast diameter, keep the mounting structure within its rated load and allow clearance from other antennas on the same mast. For more on this, see our guide to wind loading for rooftop Yagis.

Where Yagis Earn Their Place

• Point-to-point links between two fixed sites, such as a depot and a hilltop repeater
• Repeater receive antennas pointed at a known coverage area
• Telemetry and SCADA links where a remote outstation talks to a single base
• Direction finding, where a narrow beam helps locate a transmitter
• Fringe reception at sites on the edge of coverage

If you need to cover a full 360 degrees from one site, an omnidirectional base station antenna is usually the better fit. Our base station antenna buying guide covers the options.

Choosing a Yagi From the Renair Range

• The 3 ELEMENT YAGI - UHF is a compact starting point for short UHF links where a wider beam is useful.
• The 6 ELEMENT YAGI - VHF balances gain and beamwidth for general VHF base and repeater use.
• The 8 ELEMENT YAGI - VHF provides high directional gain for point-to-point links, repeater feeds and direction finding.
• The 12 ELEMENT YAGI - UHF is built for long, fixed UHF paths where every decibel counts.

Not sure which element count you need? Send us your frequency, path length and site details and we will recommend a model: renair.co.uk/contact-us.

Frequently Asked Questions

What is the difference between a Yagi and a Yagi-Uda antenna?

There is no difference. Yagi-Uda is the full name, crediting both inventors. Yagi is the common short form used across the industry.

Does a Yagi antenna increase power?

No. A Yagi does not add power. It concentrates the power you already have into one direction, which increases the effective radiated power towards the far station and improves reception from that direction.

Can I use a Yagi calculator to build my own antenna?

A calculator gives you approximate element lengths and spacings, which is useful for understanding a design. For a commercial or safety-critical link, a factory-tuned Yagi with a published gain and VSWR figure is the more reliable choice.

Should my Yagi be mounted horizontally or vertically?

Match the polarisation used by the rest of the network. Most UK PMR, marine and land mobile systems are vertically polarised, so the elements should be vertical.

Related products

• 3 ELEMENT YAGI - UHF
• 6 ELEMENT YAGI - VHF
• 8 ELEMENT YAGI - VHF
• 12 ELEMENT YAGI - UHF

Related reading

• Omnidirectional vs Directional Antennas: How to Choose the Right One
• Selecting a VHF Yagi Antenna: A Practical Guide
• Wind Loading and Mechanical Considerations for Rooftop Yagis
• Antenna Polarisation Explained