Are you looking to boost your signal on the 70-centimeter band? Do you want to hit that distant repeater or perhaps even try your hand at satellite communication? Look no further! The 3-Element Yagi antenna for 70cm UHF Band is a fantastic project for any radio amateur looking for a reliable, high-gain directional antenna that’s surprisingly straightforward to build.
Yagi-Uda antenna (often just called a “Yagi”) is a directional antenna that uses multiple passive elements alongside a single driven element to achieve significant gain and directivity. This means your signal goes where you want it to go, rather than scattering in all directions, making it perfect for targeting specific stations or repeaters.
This particular design is a finely tuned beast for the UHF (Ultra High Frequency) band, specifically optimized for the popular 430-440 MHzsegment used by amateur radio operators.
Let’s break down its key components:
- The Reflector (334 mm): This is the longest element, placed at the back of the antenna. Its job is to reflect radio waves, pushing them forward towards your intended direction.
- The Driven Element (292 mm tall, 25 mm wide): This is the heart of the antenna – a folded dipole. It’s where your coaxial cable connects, and it’s responsible for radiating and receiving the signal. The folded dipole design often provides a better impedance match (50 Ohms in this case) and wider bandwidth compared to a simple dipole.
- The Director (300 mm): The shortest element, placed in front of the driven element. The director helps to focus the radiated energy, sharpening the beam and increasing the antenna’s gain in the forward direction.
The Magic in the Spacing
The performance of a Yagi isn’t just about the element lengths; it’s also about the precise spacing between them. The design specifies:
- 103 mm between the Reflector and the Driven Element.
- 172 mm between the Driven Element and the Director.
These dimensions are critical for achieving optimal gain, front-to-back ratio, and impedance matching.
3-Element Yagi antenna – Radiation Characteristics
In practical installations, a 3-element Yagi antenna of this type typically provides:
- Forward gain of approximately 4–6 dBi
- Good front-to-back ratio
- Narrow beamwidth compared to omnidirectional antennas
- Horizontal polarization, as drawn
The compact spacing also helps maintain pattern stability in confined installations such as rooftops, balconies, or attic mounting.
The gain can be defined as a ratio of the signal transmitted in the “maximum” direction to that of a standard or reference antenna. This may sometimes be called the “forward gain”
3-Element Yagi antenna – Construction Considerations
Aluminum or copper rods or tubing may be used for all elements, keeping diameters consistent to preserve symmetry. The boom should be non-conductive or the elements must be insulated from it to avoid detuning.
The feedline should exit the folded dipole at right angles for a short distance to reduce common-mode currents. Final tuning is best done with an antenna analyzer or NanoVNA, trimming the director slightly if needed for best forward gain.
Related Posts
- Stacked 5/8-wave VHF Antenna for 146 MHz (December 26, 2025)
- Simple High-Gain collinear antenna using coaxial cable (December 19, 2025)
- Dual-Band RW4HFN Antenna for 145/430 MHz bands (December 6, 2025)
- A Broadband Butterfly Antenna for VHF and UHF (December 3, 2025)
- ZED Dipole Antenna – A Simple and Smart Design for VHF/UHF (November 13, 2025)