Yagi-Uda Antenna
Understanding Yagi-Uda Antennas
The Yagi-Uda antenna is one of the most successful antenna designs ever created. Its combination of simplicity, moderate gain, and directivity makes it ideal for applications requiring a compact directional antenna from VHF through UHF frequencies.
Yagi Elements
- Driven element: Fed by the transmission line. Resonant at the operating frequency (lambda/2).
- Reflector: Behind the driven element, ~5% longer. Reflects energy forward.
- Directors: In front, ~5% shorter. Guide energy forward. More directors = more gain and narrower beam.
Yagi Performance
| Elements | Gain | Beamwidth | F/B Ratio |
|---|---|---|---|
| 3 (1R+1D+1DR) | 7-8 dBi | 70 deg | 15 dB |
| 5 | 10-11 dBi | 50 deg | 20 dB |
| 10 | 13-14 dBi | 35 deg | 20 dB |
| 15+ | 15-16 dBi | 25 deg | 20 dB |
Frequently Asked Questions
What is a Yagi antenna?
A Yagi is a directional antenna with a driven element (dipole), a reflector behind, and one or more directors in front. Parasitic elements create a directional beam. 6-15 dBi gain depending on the number of elements. Used for TV, amateur radio, and point-to-point links.
How many elements should a Yagi have?
More elements = more gain but also longer antenna and narrower bandwidth. 3-5 elements: compact, moderate gain (7-11 dBi), reasonable bandwidth. 10-15 elements: high gain (13-16 dBi) but long and narrowband. Choose based on required gain and size constraints.
What is the bandwidth of a Yagi?
A standard Yagi has 3-10% bandwidth (VSWR < 2.0). Long Yagis with many directors are narrower. Wideband Yagi designs with log-periodic feeding achieve wider bandwidth but sacrifice some gain. Yagis are generally narrowband antennas.