Directional Antenna
Understanding Directional Antennas
Directional antennas trade coverage breadth for focused power in a specific direction. Higher directivity means more gain in the forward direction but narrower beamwidth. The choice between directional and omnidirectional depends on the application: point-to-point links use directional; broadcast uses omnidirectional.
Types of Directional Antennas
- Yagi-Uda: 7-17 dBi. VHF/UHF. TV reception, amateur radio.
- Horn antenna: 10-25 dBi. Microwave. Feeds for reflectors, standard gain reference.
- Parabolic dish: 25-60+ dBi. Microwave/mmWave. Satellite, radar, point-to-point.
- Patch antenna: 5-9 dBi per element. Microwave. Arrays for 5G, radar, satellite.
- Log-periodic: 6-10 dBi. Wideband. EMC testing, broadband monitoring.
G = eta x D
Directivity from beamwidth:
D = 41,253 / (theta_E x theta_H) (approximate)
Example: 10-degree E, 15-degree H:
D = 41,253 / (10 x 15) = 275 = 24.4 dBi
With eta = 0.65: G = 22.3 dBi
Frequently Asked Questions
What is a directional antenna?
A directional antenna focuses radiation in a preferred direction, providing higher gain in that direction and less gain elsewhere. Examples include Yagi, horn, patch, and parabolic dish antennas. They are used when maximum signal is needed in one direction.
When should I use a directional antenna?
Use a directional antenna for point-to-point links, satellite communication, radar, and any application where you know the direction of the desired signal. Use omnidirectional when you need 360-degree coverage or do not know the signal direction.
What determines the gain of a directional antenna?
Gain depends on the antenna's physical aperture relative to wavelength. Larger aperture (relative to wavelength) produces narrower beamwidth and higher gain. Gain = 4 pi x effective aperture / wavelength^2.