Gain, directivity and radiation patterns
Antennas do not create power — they concentrate it. Understanding how is the key to reading every spec sheet.
Radiation patterns
A radiation pattern plots how strongly an antenna radiates in each direction. An omnidirectional vertical radiates evenly around the horizon; a dipole shows a two-lobed ‘figure-eight’; a beam concentrates energy into a single main lobe.
Directivity and gain
Directivity is how much an antenna focuses energy compared with a theoretical isotropic radiator. Gain is directivity minus losses, and is quoted in:
- dBi — relative to an isotropic source
- dBd — relative to a dipole (add 2.15 to get dBi)
The trade-off
More gain always means a narrower beam. A Yagi trades omnidirectional coverage for ~7–15 dBi forward; a parabolic dish can reach 40+ dBi but with a beam so narrow it must be aimed precisely. Pick the gain that matches how well you can point the antenna at the other station.