Glossary term
Yagi-Uda Antenna
A directional antenna using one driven element and parasitic reflector and director elements.
Definition
deviceA Yagi-Uda antenna is a directional antenna made from a driven element, a reflector, and one or more parasitic director elements.
The driven element is connected to the feed line, while nearby parasitic elements reradiate energy with phase relationships that shape the radiation pattern. Yagi-Uda antennas are widely used where moderate to high gain, directional reception or transmission, and relatively simple construction are needed.
A Yagi-Uda antenna uses mutual coupling between a driven element and parasitic elements to create a directional radiation pattern. The reflector is usually slightly longer than resonance and sits behind the driven element. Directors are usually slightly shorter and sit in front of it. Their spacing and length control forward gain, front-to-back ratio, impedance, bandwidth, sidelobes, and mechanical size.
The antenna does not amplify power by itself. It concentrates radiation in a preferred direction, increasing gain in that direction while reducing radiation elsewhere. This improves link margin when the antenna is aimed correctly, but it also makes alignment, polarization, and mounting more important.
Engineering use
Yagi-Uda antennas are used for television reception, amateur radio, point-to-point links, telemetry, direction finding, wildlife tracking, and some measurement setups. They are attractive because they can be lightweight, inexpensive, and mechanically simple compared with phased arrays or reflector antennas.
Design depends on operating frequency, element diameter, boom geometry, feed arrangement, matching network, polarization, ground proximity, wind loading, corrosion, and installation environment. A narrowband design may achieve good gain but poor tolerance to frequency shift, manufacturing variation, icing, or nearby metal structures.
Common mistakes
A common mistake is selecting a Yagi only by advertised gain. Bandwidth, impedance match, front-to-back ratio, side lobes, polarization, connector loss, cable loss, mast interaction, and aiming accuracy can dominate field performance. Another mistake is assuming free-space simulations match rooftop, vehicle, or tower installations. A strong antenna review states frequency band, gain, beamwidth, polarization, standing-wave ratio, feed impedance, element dimensions, mounting environment, wind load, and measured pattern or acceptance test.