Directional Antennas — Yagis, Quads, and Log-Periodics
Why Go Directional?
A dipole radiates equally in two directions (broadside). If the station you want to work is in a specific direction, that means half your power is going the wrong way. A directional antenna focuses your power (and receiving sensitivity) where you need it.
The Yagi-Uda Antenna
The most popular directional antenna for amateur radio. It works like this:
- Reflector (behind): Slightly longer than λ/2 — pushes energy forward
- Driven element (middle): About λ/2 — the only element connected to the feedline
- Directors (in front): Slightly shorter than λ/2 — pull energy forward
| Elements | Gain (dBd) | Front-to-back | Practical note |
|---|---|---|---|
| 2 | ~5 | ~10 dB | Compact, good starter beam |
| 3 | ~7 | ~15 dB | Most popular for 20m/15m/10m |
| 5 | ~9 | ~20 dB | Serious DX contesting |
Quad Antenna
Uses full-wavelength square or diamond loops instead of straight elements. For the same boom length, a quad has slightly more gain than a Yagi and wider bandwidth. But it's physically larger and harder to build.
Log-Periodic Dipole Array (LPDA)
The "broadband" directional antenna. Unlike a Yagi (which is designed for one band), an LPDA works across a wide range of frequencies — for example, one antenna covering all of 14–30 MHz.
The trade-off: lower gain than a Yagi on any single frequency. An LPDA gives maybe 5 dBd where a 3-element Yagi gives 7 dBd, but the LPDA covers many bands without switching.