Physics
Antenna Beamwidth
Quick fact
The world's largest radio telescope, FAST in China, has a beamwidth so narrow that it could detect a cellphone signal on the Moon.
Why this is interesting
Point a flashlight at a wall—the spot it makes has a certain width. Now imagine doing the same with a radio wave: that spreading is called beamwidth. But why does it matter whether the beam is wide or narrow?
Read the full explanation
Understanding Antenna Beamwidth
An antenna doesn't radiate equally in all directions. Instead, it focuses energy into a main lobe—the primary direction of transmission. Beamwidth is the angle across that main lobe where the signal power drops to half (or -3 dB) of its peak. Think of a car's high beams vs. fog lights: high beams have a narrow beamwidth for long-distance visibility, while fog lights spread wide to illuminate nearby areas. Similarly, a satellite dish uses a narrow beamwidth to target a specific satellite, while a Wi-Fi router uses a wider beamwidth to cover a room.
A deeper explanation
Beamwidth is intimately linked to directivity: a narrow beamwidth means energy is concentrated in a small angular region, giving higher directivity and gain. This is a direct consequence of diffraction and the antenna's aperture size—larger apertures produce narrower beams. In practice, beamwidth determines resolution in radar (a narrow beam can distinguish two closely spaced targets) and coverage in communications (a wider beam covers more area but with less power per unit area). The trade-off is that narrow beams require precise pointing, so tracking mechanisms are often needed. Understanding beamwidth allows engineers to balance these factors for applications like cellular base stations, where sector antennas have specific beamwidths to divide coverage areas.